The document discusses various types of defects that can occur in crystalline materials, including point defects like vacancies and self-interstitials, and linear defects like dislocations. It explains that all crystals contain vacancies which increase with temperature according to an exponential relationship. Dislocations are line defects characterized by their Burgers vector, and can be either edge, screw, or mixed configurations. Interfacial defects like grain boundaries separate regions with different crystal orientations. These defects influence many material properties.
This document discusses various types of defects that can occur in crystalline solids. It defines point defects as defects involving a few extra or missing atoms located at or near a single lattice point. The main types of point defects discussed are vacancies, where an atom is missing from its site; interstitials, where atoms occupy spaces between normal lattice sites; and substitutions, where one atom replaces another. It also describes Frenkel defects, where an atom moves from its normal site to an interstitial site, and Schottky defects, which involve vacancies of oppositely charged ions in ionic crystals to maintain neutral charge. These defects influence properties like ion transport and electrochemical reactions in solids.
The document discusses crystal structures and defects. The key points are:
- A crystal is a solid with a regularly repeating pattern of atoms or molecules extending in three dimensions, known as the unit cell.
- Point defects occur when atoms or ions are misplaced or replaced at a single point in the crystal structure. Non-stoichiometric defects occur when the crystal does not have the proper ratio of elements.
- Common point defects include vacancies, when an atom is missing from its normal site, and interstitials, when an atom occupies a space between normal lattice sites.
This document provides an overview of crystal structures and bonding in materials. It discusses topics such as the differences between crystalline and amorphous solids, unit cells, lattice structures, metallic crystal structures like body centered cubic and face centered cubic, atomic packing factors, and anisotropic vs isotropic materials. The key concepts covered include how crystal structures are composed of a periodic arrangement of points in a lattice, with atoms attached at each lattice point, and how properties can differ based on crystal structure and orientation.
The document summarizes key concepts related to crystal structure:
Crystalline materials have atoms or molecules arranged in a regular, orderly 3D pattern which gives them high strength, while non-crystalline materials have a random arrangement and lower strength. A crystal structure is a regular repetition of this 3D pattern defined by a unit cell and space lattice. Common crystal structures include simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed. Crystal defects such as point defects, dislocations, grain boundaries, and voids are also discussed.
There are several types of imperfections or defects that can occur in crystal structures including point defects, line defects, interfacial defects, and bulk defects. Point defects include vacancies and interstitials which occur naturally in all crystals. Line defects are imperfections where rows of atoms have a differing structure, such as dislocations. Interfacial defects include grain boundaries and twin boundaries. The number and type of defects can be controlled and affect material properties, both positively and negatively.
This document provides an overview of high entropy alloys (HEAs). It discusses how HEAs were discovered in 1996 and research interest increased after 2004 papers by Yeh and Cantor. Key points include: HEAs have 5+ principal elements each between 5-35% concentration; entropy effect stabilizes solid solution phase; criteria for HEAs include parameters like entropy of mixing and valence electron concentration; four core effects are lattice distortion, sluggish diffusion, cocktail effect, and formation of solid solution phase. Examples of HEA applications discussed are coatings, bulk metallic glass, and refractory and carbide/cermet materials. The conclusion emphasizes that computational modeling of HEA properties could help address misconceptions about these materials.
This document discusses quantum dots, which are semiconductors on the nanometer scale that obey the principle of quantum confinement. The energy band gap of quantum dots determines the wavelength of light they can absorb and emit, and this wavelength depends on the size of the dot. Solutions containing quantum dots of different sizes appear different colors because the particles absorb and emit light within the visible spectrum. Potential applications of quantum dots include improving solar cells, use in televisions, and medical imaging.
E = g lk+ 2
+ − − +
r m 0 m 0 4 ε 0 h ( ε 0 2 e 0 m 0
8 em hm πεr 2 2ε ) m m hm
Brus, L. E. J. Phys. Chem. 1986, 90, 2555
Semiconductor quantum dots are nanocrystals made of semiconductor materials such as CdSe, ZnSe, ZnS, and ZnO. They exhibit size-dependent optical and electronic properties due to
This document discusses various types of defects that can occur in crystalline solids. It defines point defects as defects involving a few extra or missing atoms located at or near a single lattice point. The main types of point defects discussed are vacancies, where an atom is missing from its site; interstitials, where atoms occupy spaces between normal lattice sites; and substitutions, where one atom replaces another. It also describes Frenkel defects, where an atom moves from its normal site to an interstitial site, and Schottky defects, which involve vacancies of oppositely charged ions in ionic crystals to maintain neutral charge. These defects influence properties like ion transport and electrochemical reactions in solids.
The document discusses crystal structures and defects. The key points are:
- A crystal is a solid with a regularly repeating pattern of atoms or molecules extending in three dimensions, known as the unit cell.
- Point defects occur when atoms or ions are misplaced or replaced at a single point in the crystal structure. Non-stoichiometric defects occur when the crystal does not have the proper ratio of elements.
- Common point defects include vacancies, when an atom is missing from its normal site, and interstitials, when an atom occupies a space between normal lattice sites.
This document provides an overview of crystal structures and bonding in materials. It discusses topics such as the differences between crystalline and amorphous solids, unit cells, lattice structures, metallic crystal structures like body centered cubic and face centered cubic, atomic packing factors, and anisotropic vs isotropic materials. The key concepts covered include how crystal structures are composed of a periodic arrangement of points in a lattice, with atoms attached at each lattice point, and how properties can differ based on crystal structure and orientation.
The document summarizes key concepts related to crystal structure:
Crystalline materials have atoms or molecules arranged in a regular, orderly 3D pattern which gives them high strength, while non-crystalline materials have a random arrangement and lower strength. A crystal structure is a regular repetition of this 3D pattern defined by a unit cell and space lattice. Common crystal structures include simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed. Crystal defects such as point defects, dislocations, grain boundaries, and voids are also discussed.
There are several types of imperfections or defects that can occur in crystal structures including point defects, line defects, interfacial defects, and bulk defects. Point defects include vacancies and interstitials which occur naturally in all crystals. Line defects are imperfections where rows of atoms have a differing structure, such as dislocations. Interfacial defects include grain boundaries and twin boundaries. The number and type of defects can be controlled and affect material properties, both positively and negatively.
This document provides an overview of high entropy alloys (HEAs). It discusses how HEAs were discovered in 1996 and research interest increased after 2004 papers by Yeh and Cantor. Key points include: HEAs have 5+ principal elements each between 5-35% concentration; entropy effect stabilizes solid solution phase; criteria for HEAs include parameters like entropy of mixing and valence electron concentration; four core effects are lattice distortion, sluggish diffusion, cocktail effect, and formation of solid solution phase. Examples of HEA applications discussed are coatings, bulk metallic glass, and refractory and carbide/cermet materials. The conclusion emphasizes that computational modeling of HEA properties could help address misconceptions about these materials.
This document discusses quantum dots, which are semiconductors on the nanometer scale that obey the principle of quantum confinement. The energy band gap of quantum dots determines the wavelength of light they can absorb and emit, and this wavelength depends on the size of the dot. Solutions containing quantum dots of different sizes appear different colors because the particles absorb and emit light within the visible spectrum. Potential applications of quantum dots include improving solar cells, use in televisions, and medical imaging.
E = g lk+ 2
+ − − +
r m 0 m 0 4 ε 0 h ( ε 0 2 e 0 m 0
8 em hm πεr 2 2ε ) m m hm
Brus, L. E. J. Phys. Chem. 1986, 90, 2555
Semiconductor quantum dots are nanocrystals made of semiconductor materials such as CdSe, ZnSe, ZnS, and ZnO. They exhibit size-dependent optical and electronic properties due to
This document discusses the atomic arrangement and properties of crystalline solids such as metals. It begins by describing the long-range order in crystalline solids compared to the short-range order in amorphous solids. It then discusses various crystal structures including cubic, hexagonal, and body-centered cubic. It provides examples of calculating properties like atomic packing factor and theoretical density based on crystal structure. Finally, it discusses using X-ray diffraction to determine crystal structure by measuring spacing between crystal planes.
There are three main types of point defects in crystals: vacancies, interstitials, and impurities. Line defects include dislocations, which can be edge or screw dislocations. Planar defects involve discontinuities across a plane, such as grain boundaries between differently oriented crystal grains or twin boundaries between mirrored crystal structures. Volume defects create internal surfaces through the absence of atoms in voids.
Quantum dots are semiconductor nanocrystals that exhibit size-dependent optical and electrical properties due to quantum confinement effects. Their bandgap increases as size decreases, causing emitted light to shift to higher energies (blueshift). They are fabricated using lithography, colloidal synthesis, or epitaxy. Potential applications include use in QLED displays for televisions and phones (offering higher brightness and efficiency than OLEDs), solar cells, medical imaging to detect diseases, and programmable matter that can change properties in response to electron manipulation.
This document discusses different types of defects in solids. There are two main types of defects - point defects and line defects. Point defects include vacancy defects, where lattice sites are vacant, and interstitial defects, where particles occupy interstitial positions. Point defects in stoichiometric crystals include Schottky defects and Frenkel defects. Non-stoichiometric crystals can have metal excess defects with anionic vacancies or excess cations at interstitial sites, or metal deficient defects with cation vacancies or extra anions at interstitial sites. Impurity defects occur when impurity ions are present at lattice sites or interstitial sites.
This document provides an overview of dislocations in face-centered cubic (FCC) metals. It discusses several types of dislocations that can occur in FCC metals including perfect dislocations with 1/2<110> Burgers vectors, Shockley partial dislocations formed by splitting a perfect dislocation, and Frank partial dislocations formed by inserting or removing a close-packed plane. The document also describes how Shockley partial dislocations can cross-slip between planes, the formation of Lomer-Cottrell locks at intersections of partial dislocations, and the nucleation of stacking fault tetrahedra in low stacking fault energy metals.
This document discusses solid state physics and crystal structures. It begins by defining solid state physics as explaining the properties of solid materials by analyzing the interactions between atomic nuclei and electrons. It then discusses different types of solids including single crystals, polycrystalline materials, and amorphous solids. Single crystals have long-range periodic atomic order, while polycrystalline materials are made of many small crystals joined together and amorphous solids lack long-range order. The document goes on to describe crystal structures including crystal lattices, unit cells, and common crystal systems such as cubic, hexagonal, and orthorhombic. It provides examples of crystal structures including sodium chloride and its cubic lattice structure.
The document discusses different types of crystal structures including simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC). It defines key terms like unit cell, lattice points, coordination number, and atomic packing factor. SC has a coordination number of 6 and atomic packing factor of 52%. BCC has a coordination number of 8 and packing factor of 68%. FCC has a coordination number of 12 and packing factor of 74%.
This document discusses and compares two techniques for growing single crystal silicon: the Bridgman technique and the Czochralski (CZ) technique. It states that while the Bridgman technique is simpler, involving a quartz ampoule, boat, heater and temperature profile, crystals grown with this method contain many dislocations. The CZ technique is more complex but can produce higher quality crystals. It involves controlling a furnace, crystal pulling rate, ambient conditions and system. The document concludes that the CZ technique is preferable for growing single crystal silicon due to producing crystals with fewer defects.
This document discusses line defects called dislocations in crystal structures. It describes two main types of dislocations: edge dislocations, which involve an extra half-plane of atoms, and screw dislocations, where lattice planes spiral around the dislocation line. The direction and magnitude of the slip caused by a dislocation is represented by the Burgers vector. For edge dislocations, the Burgers vector is perpendicular to the dislocation line, while for screw dislocations it is parallel to the line. Dislocations influence many material properties.
Density of States (DOS) in Nanotechnology by Manu ShreshthaManu Shreshtha
1. The document discusses density of states (DOS), which describes the number of accessible quantum states at each energy level in a system. It explains how electrons populate energy bands based on DOS and the Fermi distribution function.
2. Calculation of DOS for a semiconductor is shown, and applications like quantization in low-dimensional structures and photonic crystals are described. Impurity bands formed by dopants are also discussed.
3. In summary, the document provides an overview of density of states, how it is calculated, and its applications in areas like quantization effects and photonic crystals.
[1] Crystal defects are irregularities in the structure of a crystal that arise from imperfect packing of atoms. There are several types of crystal defects including point defects, line defects, surface defects, and volume defects.
[2] Point defects are zero-dimensional and include vacancies, interstitial defects, Schottky defects, and Frenkel defects. Line defects are one-dimensional and include edge and screw dislocations. Surface defects are two-dimensional and include grain boundaries, twin boundaries, and stacking faults. Volume defects are three-dimensional voids or non-crystalline regions within the crystal structure.
This document discusses different types of defects that can occur in crystalline materials. There are two main types of defects - point defects and line defects. Point defects include vacancy defects, where lattice sites are vacant, and interstitial defects, where atoms occupy interstitial positions between lattice sites. Vacancy and interstitial defects can both occur as Schottky or Frenkel defects in stoichiometric compounds. Non-stoichiometric compounds can exhibit metal excess or metal deficient defects due to anionic/cationic vacancies or interstitial atoms. Impurity defects also arise from the presence of impurity ions in the crystal lattice or interstitial sites. These various defects impact the macroscopic properties of materials and some
Defects exist in all solids and can affect material properties. Point defects include vacancies and interstitials. Line defects are dislocations. Area defects are interfaces like grain boundaries. Defects can be controlled by temperature and processing. They may improve properties through mechanisms like solid solution strengthening or may degrade properties if they cause cracking. Engineering materials are designed and processed to achieve the optimal defect structure for the required application.
The document discusses various microstructural transformations in steel alloys as a function of temperature and time. It introduces time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams as tools to predict microstructures resulting from different heat treatments. TTT diagrams apply to isothermal heat treatments where temperature is held constant, while CCT diagrams apply to continuous cooling processes. The document outlines various microstructures including pearlite, bainite, martensite, and spheroidite and how they form on these diagrams. It also discusses how alloying elements can shift the transformation curves and impact critical cooling rates required to form martensite.
Introduction to Mechanical Metallurgy (Our course project)Rishabh Gupta
The document summarizes key concepts in materials science and engineering. It discusses:
1. The importance of selecting high quality materials for better product design and performance.
2. The four main components in materials science - processing, structure, properties, and performance - and how they interrelate.
3. The main classes of materials - metals, ceramics, polymers, composites, semiconductors, and elastomers - and some of their key characteristics.
4. Crystal structures of metals and how they are classified based on atomic packing efficiency. Factors that determine a material's density are also covered.
The document discusses different types of crystalline defects including point defects, line defects, planar defects, and volume defects. Point defects involve a single atom change and include vacancies, interstitials, and impurities. Line defects are discontinuities in the crystal structure and include edge and screw dislocations. Planar defects are discontinuities across a plane, such as grain boundaries between differently oriented crystal grains, tilt boundaries of misaligned grains, and twin boundaries where crystals are mirror images. Volume defects are voids that form internal surfaces in the crystal.
This document discusses different types of crystal defects. It begins by defining an ideal crystal and explaining that real crystals contain defects due to deviations from a completely ordered atomic arrangement. Crystal defects are classified as point defects, line defects, planar defects, or bulk defects depending on their geometry. Point defects, which occur around a single atom, are further divided into vacancy defects, interstitial defects, Schottky defects, and Frenkel defects. Line defects include edge dislocations and screw dislocations. Planar defects involve grain boundaries and stacking faults, while bulk defects are voids, cracks, or impurity inclusions. The document provides examples and descriptions of each type of defect.
Grain size measurement according to astm standardsJMB
This document discusses three standard ASTM methods for measuring grain size: the comparison method, planimetric/Jeffries' method, and intercept method. The comparison method involves comparing a grain structure to graded images or overlays at 10x magnification, with a repeatability of ±1 grain size number. The planimetric method counts grains within a known area at higher magnifications from 100-500x, achieving ±0.25 grain size units precision. The intercept method counts the number of grains intercepted by a test line, allowing measurement of elongated grains faster than the planimetric method at the same precision of ±0.5 grain size units.
Crystal defects refer to any deviations from the regular geometric arrangement of atoms in a crystal structure. No crystal is truly perfect, as defects are always present due to imperfect packing during crystal formation and thermal vibrations. Common types of defects include vacancies where atomic sites are missing, interstitial defects where extra atoms occupy interstitial spaces, Schottky defects where an anion-cation pair is missing, and Frenkel defects where a cation shifts from its regular site to an interstitial site. Line defects called dislocations are also common, where the crystal structure is distorted along a line, and include edge dislocations from extra atomic planes and screw dislocations from spiral displacements of atoms. Defects significantly
The document is a lecture on materials science and crystallography given by Hari Prasad. It begins by outlining the learning objectives which include differences between crystalline and non-crystalline structures, crystal systems, atomic packing factors, and unit cells. It then defines key concepts such as space lattices, unit cells, crystal systems, coordination number, and lattice parameters. Examples are provided of different crystal structures including simple cubic, body centered cubic, face centered cubic, and hexagonal close packed. Miller indices and how to determine plane intercepts are also discussed.
Teks ini membahas tentang cacat kristal dan dislokasi pada bahan padat. Dijelaskan berbagai jenis cacat kristal seperti cacat titik, cacat bidang, dan cacat ruang. Dislokasi didefinisikan sebagai pergeseran atom-atom akibat tegangan mekanik yang dapat menyebabkan deformasi plastis pada logam."
This document discusses the atomic arrangement and properties of crystalline solids such as metals. It begins by describing the long-range order in crystalline solids compared to the short-range order in amorphous solids. It then discusses various crystal structures including cubic, hexagonal, and body-centered cubic. It provides examples of calculating properties like atomic packing factor and theoretical density based on crystal structure. Finally, it discusses using X-ray diffraction to determine crystal structure by measuring spacing between crystal planes.
There are three main types of point defects in crystals: vacancies, interstitials, and impurities. Line defects include dislocations, which can be edge or screw dislocations. Planar defects involve discontinuities across a plane, such as grain boundaries between differently oriented crystal grains or twin boundaries between mirrored crystal structures. Volume defects create internal surfaces through the absence of atoms in voids.
Quantum dots are semiconductor nanocrystals that exhibit size-dependent optical and electrical properties due to quantum confinement effects. Their bandgap increases as size decreases, causing emitted light to shift to higher energies (blueshift). They are fabricated using lithography, colloidal synthesis, or epitaxy. Potential applications include use in QLED displays for televisions and phones (offering higher brightness and efficiency than OLEDs), solar cells, medical imaging to detect diseases, and programmable matter that can change properties in response to electron manipulation.
This document discusses different types of defects in solids. There are two main types of defects - point defects and line defects. Point defects include vacancy defects, where lattice sites are vacant, and interstitial defects, where particles occupy interstitial positions. Point defects in stoichiometric crystals include Schottky defects and Frenkel defects. Non-stoichiometric crystals can have metal excess defects with anionic vacancies or excess cations at interstitial sites, or metal deficient defects with cation vacancies or extra anions at interstitial sites. Impurity defects occur when impurity ions are present at lattice sites or interstitial sites.
This document provides an overview of dislocations in face-centered cubic (FCC) metals. It discusses several types of dislocations that can occur in FCC metals including perfect dislocations with 1/2<110> Burgers vectors, Shockley partial dislocations formed by splitting a perfect dislocation, and Frank partial dislocations formed by inserting or removing a close-packed plane. The document also describes how Shockley partial dislocations can cross-slip between planes, the formation of Lomer-Cottrell locks at intersections of partial dislocations, and the nucleation of stacking fault tetrahedra in low stacking fault energy metals.
This document discusses solid state physics and crystal structures. It begins by defining solid state physics as explaining the properties of solid materials by analyzing the interactions between atomic nuclei and electrons. It then discusses different types of solids including single crystals, polycrystalline materials, and amorphous solids. Single crystals have long-range periodic atomic order, while polycrystalline materials are made of many small crystals joined together and amorphous solids lack long-range order. The document goes on to describe crystal structures including crystal lattices, unit cells, and common crystal systems such as cubic, hexagonal, and orthorhombic. It provides examples of crystal structures including sodium chloride and its cubic lattice structure.
The document discusses different types of crystal structures including simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC). It defines key terms like unit cell, lattice points, coordination number, and atomic packing factor. SC has a coordination number of 6 and atomic packing factor of 52%. BCC has a coordination number of 8 and packing factor of 68%. FCC has a coordination number of 12 and packing factor of 74%.
This document discusses and compares two techniques for growing single crystal silicon: the Bridgman technique and the Czochralski (CZ) technique. It states that while the Bridgman technique is simpler, involving a quartz ampoule, boat, heater and temperature profile, crystals grown with this method contain many dislocations. The CZ technique is more complex but can produce higher quality crystals. It involves controlling a furnace, crystal pulling rate, ambient conditions and system. The document concludes that the CZ technique is preferable for growing single crystal silicon due to producing crystals with fewer defects.
This document discusses line defects called dislocations in crystal structures. It describes two main types of dislocations: edge dislocations, which involve an extra half-plane of atoms, and screw dislocations, where lattice planes spiral around the dislocation line. The direction and magnitude of the slip caused by a dislocation is represented by the Burgers vector. For edge dislocations, the Burgers vector is perpendicular to the dislocation line, while for screw dislocations it is parallel to the line. Dislocations influence many material properties.
Density of States (DOS) in Nanotechnology by Manu ShreshthaManu Shreshtha
1. The document discusses density of states (DOS), which describes the number of accessible quantum states at each energy level in a system. It explains how electrons populate energy bands based on DOS and the Fermi distribution function.
2. Calculation of DOS for a semiconductor is shown, and applications like quantization in low-dimensional structures and photonic crystals are described. Impurity bands formed by dopants are also discussed.
3. In summary, the document provides an overview of density of states, how it is calculated, and its applications in areas like quantization effects and photonic crystals.
[1] Crystal defects are irregularities in the structure of a crystal that arise from imperfect packing of atoms. There are several types of crystal defects including point defects, line defects, surface defects, and volume defects.
[2] Point defects are zero-dimensional and include vacancies, interstitial defects, Schottky defects, and Frenkel defects. Line defects are one-dimensional and include edge and screw dislocations. Surface defects are two-dimensional and include grain boundaries, twin boundaries, and stacking faults. Volume defects are three-dimensional voids or non-crystalline regions within the crystal structure.
This document discusses different types of defects that can occur in crystalline materials. There are two main types of defects - point defects and line defects. Point defects include vacancy defects, where lattice sites are vacant, and interstitial defects, where atoms occupy interstitial positions between lattice sites. Vacancy and interstitial defects can both occur as Schottky or Frenkel defects in stoichiometric compounds. Non-stoichiometric compounds can exhibit metal excess or metal deficient defects due to anionic/cationic vacancies or interstitial atoms. Impurity defects also arise from the presence of impurity ions in the crystal lattice or interstitial sites. These various defects impact the macroscopic properties of materials and some
Defects exist in all solids and can affect material properties. Point defects include vacancies and interstitials. Line defects are dislocations. Area defects are interfaces like grain boundaries. Defects can be controlled by temperature and processing. They may improve properties through mechanisms like solid solution strengthening or may degrade properties if they cause cracking. Engineering materials are designed and processed to achieve the optimal defect structure for the required application.
The document discusses various microstructural transformations in steel alloys as a function of temperature and time. It introduces time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams as tools to predict microstructures resulting from different heat treatments. TTT diagrams apply to isothermal heat treatments where temperature is held constant, while CCT diagrams apply to continuous cooling processes. The document outlines various microstructures including pearlite, bainite, martensite, and spheroidite and how they form on these diagrams. It also discusses how alloying elements can shift the transformation curves and impact critical cooling rates required to form martensite.
Introduction to Mechanical Metallurgy (Our course project)Rishabh Gupta
The document summarizes key concepts in materials science and engineering. It discusses:
1. The importance of selecting high quality materials for better product design and performance.
2. The four main components in materials science - processing, structure, properties, and performance - and how they interrelate.
3. The main classes of materials - metals, ceramics, polymers, composites, semiconductors, and elastomers - and some of their key characteristics.
4. Crystal structures of metals and how they are classified based on atomic packing efficiency. Factors that determine a material's density are also covered.
The document discusses different types of crystalline defects including point defects, line defects, planar defects, and volume defects. Point defects involve a single atom change and include vacancies, interstitials, and impurities. Line defects are discontinuities in the crystal structure and include edge and screw dislocations. Planar defects are discontinuities across a plane, such as grain boundaries between differently oriented crystal grains, tilt boundaries of misaligned grains, and twin boundaries where crystals are mirror images. Volume defects are voids that form internal surfaces in the crystal.
This document discusses different types of crystal defects. It begins by defining an ideal crystal and explaining that real crystals contain defects due to deviations from a completely ordered atomic arrangement. Crystal defects are classified as point defects, line defects, planar defects, or bulk defects depending on their geometry. Point defects, which occur around a single atom, are further divided into vacancy defects, interstitial defects, Schottky defects, and Frenkel defects. Line defects include edge dislocations and screw dislocations. Planar defects involve grain boundaries and stacking faults, while bulk defects are voids, cracks, or impurity inclusions. The document provides examples and descriptions of each type of defect.
Grain size measurement according to astm standardsJMB
This document discusses three standard ASTM methods for measuring grain size: the comparison method, planimetric/Jeffries' method, and intercept method. The comparison method involves comparing a grain structure to graded images or overlays at 10x magnification, with a repeatability of ±1 grain size number. The planimetric method counts grains within a known area at higher magnifications from 100-500x, achieving ±0.25 grain size units precision. The intercept method counts the number of grains intercepted by a test line, allowing measurement of elongated grains faster than the planimetric method at the same precision of ±0.5 grain size units.
Crystal defects refer to any deviations from the regular geometric arrangement of atoms in a crystal structure. No crystal is truly perfect, as defects are always present due to imperfect packing during crystal formation and thermal vibrations. Common types of defects include vacancies where atomic sites are missing, interstitial defects where extra atoms occupy interstitial spaces, Schottky defects where an anion-cation pair is missing, and Frenkel defects where a cation shifts from its regular site to an interstitial site. Line defects called dislocations are also common, where the crystal structure is distorted along a line, and include edge dislocations from extra atomic planes and screw dislocations from spiral displacements of atoms. Defects significantly
The document is a lecture on materials science and crystallography given by Hari Prasad. It begins by outlining the learning objectives which include differences between crystalline and non-crystalline structures, crystal systems, atomic packing factors, and unit cells. It then defines key concepts such as space lattices, unit cells, crystal systems, coordination number, and lattice parameters. Examples are provided of different crystal structures including simple cubic, body centered cubic, face centered cubic, and hexagonal close packed. Miller indices and how to determine plane intercepts are also discussed.
Teks ini membahas tentang cacat kristal dan dislokasi pada bahan padat. Dijelaskan berbagai jenis cacat kristal seperti cacat titik, cacat bidang, dan cacat ruang. Dislokasi didefinisikan sebagai pergeseran atom-atom akibat tegangan mekanik yang dapat menyebabkan deformasi plastis pada logam."
The document discusses various phenomena related to yielding and plastic deformation in metals including:
1) Yield phenomenon and twinning that occurs in iron containing small amounts of carbon and nitrogen at different temperatures.
2) Blue brittleness that occurs due to strain aging during plastic deformation within a specific temperature range.
3) Lüders bands that form due to localized plastic deformation caused by dynamic strain aging of interstitial atoms pinning dislocations.
4) The Bauschinger effect where yield strength decreases when the direction of applied stress is reversed due to back stresses and annihilation of dislocations.
This document discusses giant magnetoresistance and its applications. It begins with a history of magnetoresistance discovery in 1857. It then covers ferro magnetic materials, spintronics concepts like spin dependent conduction. It describes giant magnetoresistance using schematics of magnetic multilayers and the first evidence of GMR. Applications discussed include spin valves used in hard drive read heads, MRAM for data storage, and spin transistors. Future areas of research mentioned are magnetic switching transistors, next-gen low power MRAM, and integrating spintronics with semiconductors.
Dokumen tersebut membahas tentang K3 dalam pekerjaan konstruksi. Terdapat penjelasan mengenai latar belakang, dasar hukum, kecelakaan kerja, sebab-sebab kecelakaan, dan langkah-langkah K3 yang perlu diterapkan dalam berbagai aktivitas konstruksi seperti penggalian, pondasi, beton, baja, dan sarana bangunan. Dokumen ini juga membahas tentang kewajiban melaporkan proyek konstruksi dan akte pengaw
The process of transformation of a substance from liquid to solid state in which the crystal lattice forms and crystals appear.
•Volume shrinkage or volume contraction
Dokumen tersebut membahas latar belakang permasalahan keselamatan dan kesehatan kerja pada sektor konstruksi, yang meliputi data kecelakaan konstruksi dan penyebabnya serta karakteristik kegiatan proyek konstruksi. Dokumen juga menjelaskan dasar hukum dan peraturan terkait K3 di bidang konstruksi.
1. Solidification occurs when a liquid metal cools and transforms into a solid below its melting point, through the process of nucleation and crystal growth.
2. During nucleation, small clusters of atoms (nuclei) form in the undercooled liquid, which must reach a critical size to become stable crystals.
3. Once stable nuclei form, the crystals grow through addition of atoms from the liquid until they impinge on neighboring crystals. Cooling curves can be used to study phase changes during solidification of pure metals and alloys.
This document discusses the process of solidification in castings. It covers topics including the introduction to solidification, concepts of solidification in castings, solidification of pure metals and alloys, nucleation and growth. Specifically, it describes how solidification begins with the formation of nuclei near the mold walls and progresses through dendritic growth until the entire melt is crystallized. It also discusses solidification curves and phase diagrams for pure metals and alloys.
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The document discusses various types of imperfections that can exist in solid materials, including point defects like vacancies and interstitial atoms, and linear defects like dislocations. It explains that point defects involve missing or extra atoms in the crystal lattice, while linear defects involve distortions or disruptions in the regular ordering of atoms along lines. The document provides examples of how these defects influence important material properties and can be classified based on factors like the dimensionality and nature of the atomic irregularity.
Defects are common in real crystals and influence their properties. Point defects include vacancies, interstitials, and impurities. Line defects are dislocations like edge and screw dislocations. The type and amount of defects can be controlled to alter electrical, thermal, and mechanical properties in beneficial ways like improving semiconductor performance or alloy strength. Defects are characterized by their geometry and the Burgers vector, which describes the crystal distortion caused by a dislocation.
The document discusses crystal defects and their significance. It begins with an introduction to crystals and crystal defects. There are four main types of crystal defects discussed: point defects, line defects, surface defects, and volume defects. Point defects include vacancies, interstitials, and impurities. Line defects are dislocations like edge and screw dislocations. Surface defects include grain boundaries, twin boundaries, and stacking faults. Volume defects occur on a larger scale and include voids, porosity, and precipitates. In conclusion, the presence discusses how crystal defects can impact properties and significance like improving semiconductor performance or lowering melting points.
This document discusses defects in crystals. It begins by introducing the three main types of defects: point defects, line defects, and surface defects. Point defects include vacancies, interstitials, and substitutions. Line defects are dislocations like edge and screw dislocations. The document then explains why defects are important as they influence many material properties. It provides details on different point defects, dislocation concepts like Burgers vector and slip systems, and how dislocation interactions influence hardness. Examples are also provided to calculate vacancy concentration and to predict solid solubility based on Hume-Rothery rules.
This document discusses various types of crystal defects including point defects, line defects, and planar defects. It defines point defects as zero-dimensional defects involving a single atom change, such as vacancies, interstitials, and impurities. Line defects are described as one-dimensional dislocations, including edge and screw dislocations. Planar defects are two-dimensional grain boundaries that separate crystalline regions with different orientations within a polycrystalline solid. The document explores how these defects influence material properties.
This document discusses various types of crystal defects including point defects, line defects, and planar defects. It defines point defects as zero-dimensional defects involving a single atom change, such as vacancies, interstitials, and impurities. Line defects are described as one-dimensional dislocations, including edge and screw dislocations. Planar defects are two-dimensional grain boundaries that separate crystalline regions with different orientations within a polycrystalline solid. The document explores how these defects influence material properties.
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1. There are three main types of crystal imperfections - point defects, line defects, and interfacial defects. Point defects involve atoms being missing or in irregular positions in the lattice. Line defects are groups of atoms in irregular positions known as dislocations. Interfacial defects are boundaries separating regions with different crystal structures.
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3. Dislocations are line defects that allow plastic deformation to occur when they move in response to stress. Their motion produces slip between crystal planes
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The document discusses various types of bonding and intermolecular forces found in solid state materials, including covalent bonding, metallic bonding, ionic bonding, hydrogen bonding, and van der Waals forces. It also describes different types of crystal defects such as point defects, line defects, stoichiometric defects, impurity defects, and non-stoichiometric defects. Finally, it covers topics like semiconductors, ferromagnetism, and the magnetic properties associated with orbiting and spinning electrons.
This document discusses various types of crystal imperfections or defects. It describes point defects like vacancies, interstitials, and substitutions that involve missing or extra atoms at atomic sites. Line defects called dislocations are also covered, including edge dislocations formed by the insertion of an extra half plane of atoms, and screw dislocations where there is a spiral distortion of crystal planes. These defects influence material properties, for example increasing strength. Dislocations also enable plastic deformation through slip along crystal planes.
This document discusses various types of imperfections that can occur in solid materials, including crystalline defects. It begins by noting that real materials have irregularities in their crystal structure compared to the assumed perfect order in previous lectures. Defects are then classified as either point defects (e.g. vacancies, interstitials), line defects (dislocations), or planar defects (e.g. grain boundaries, twins, stacking faults). The document goes on to describe various defect types in more detail and how defects influence material properties. It also discusses grain structure formation during solidification and examines defects using microscopy techniques.
This document discusses various types of defects that can occur in crystalline solids, including point defects, line defects (dislocations), two-dimensional defects (surfaces and interfaces), and volume defects. It focuses on point defects such as vacancies, interstitials, and solute/impurity atoms. Intrinsic point defects include vacancies and interstitials, while extrinsic defects are caused by solute/impurity atoms. These defects can have significant effects on properties like electrical conductivity in semiconductors and mechanical strength in structural alloys.
undamentals of Crystal Structure: BCC, FCC and HCP Structures, coordination number and atomic packing factors, crystal imperfections -point line and surface imperfections. Atomic Diffusion: Phenomenon, Fick’s laws of diffusion, factors affecting diffusion.
This document discusses ceramics and their properties. It begins by defining ceramics as inorganic materials processed at high temperatures that have non-metallic properties. Ceramics have great durability in terms of chemical, mechanical, and thermal properties. They are resistant to acids/alkalis, oxidation, and abrasion. Ceramics can also withstand high temperatures. The document then discusses different types of ceramics and defects in ceramics like point defects that influence material properties. Diffusion, an important phenomenon in ceramics, occurs through vacancy, interstitial, or interstitialcy mechanisms and is governed by factors like activation energy and stoichiometry.
Crystal imperfections are broadly classified into four categories: point defects, line defects, planar/surface defects, and volume defects. Point defects include vacancies, interstitials, and impurities which lower the crystal's energy and make it more stable. Line defects are dislocations which are line discontinuities in the crystal structure. Planar defects include grain boundaries, tilt boundaries, and twin boundaries which separate regions of different crystal orientation. Volume defects such as stacking faults disrupt the ordered stacking of close-packed crystal planes. Defects can be either desirable by improving material properties, or undesirable if they reduce properties.
This document discusses different states of matter and properties of liquids and solids. It defines key terms like phases, intermolecular forces, and boiling point. It describes different types of solids like ionic, molecular, metallic and network solids. It also discusses properties of liquids like surface tension, capillary action, and viscosity.
Mumbai University_Mechanical Enginnering_SEM III_ Material technology_Module 1.2
Lattice Imperfections:
Definition, classification and significance of Imperfections Point defects: vacancy, interstitial and impurity atom defects, Their formation and effects, Dislocation - Edge and screw dislocations Burger’s vector, Motion of dislocations and their significance, Surface defects - Grain boundary, sub-angle grain boundary and stacking faults, their significance, Generation of dislocation, Frank Reed source, conditions of multiplication and significance
Phase refers to any physically distinct structure within a material. There are several types of phases including solid, liquid, and gas for pure elements. Alloys can also have multiple solid phases that differ in crystal structure. When other elements are added to a pure material intentionally as alloying elements, they are accommodated through solid solution, compound formation, or phase separation into distinct structures. Solid solutions are classified as substitutional, where atoms replace ones in the host lattice, or interstitial, where small atoms fill spaces within the host lattice. Compounds form new crystal structures distinct from the components. Hume-Rothery rules outline factors that influence solid solution formation such as atomic size, valence, and electronegativity differences between
There are several types of defects that can arise in solids, including point defects like vacancies and interstitials, line defects like dislocations, and area defects like grain boundaries. The number and type of defects can be controlled through processing parameters and affect the material properties. While some defects are undesirable, others can play important roles like enabling plastic deformation through dislocation motion. Advanced microscopy techniques allow direct imaging of these defect structures at atomic scales.
1. The document discusses the constitution of alloys and phase diagrams. It describes different types of solid solutions like substitutional and interstitial solutions and classifies phase diagrams as unary, binary, and ternary.
2. The iron-iron carbide equilibrium diagram is examined in detail. It identifies the various phases involved like ferrite, austenite, and cementite. Critical temperatures like A1, A2, A3 are defined.
3. The microstructure and properties of steels and cast irons are determined by their position in the iron-carbon phase diagram and the phases present at room temperature. Hypoeutectoid steels contain ferrite and pearlite while hyp
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1.
Part 1: Material Science
Crystal Geometry
Crystal Structure and Defects
Bonds in Solids
Electron Theory of Metals
Diffusion in Solids
Contents
2.
3.
All crystalline materials on an atomic scale
contain large numbers of various defects or
imperfections. .
Many of the properties of materials are
profoundly sensitive to deviations from
crystalline perfection;
the influence is not always adverse,
often specific characteristics are deliberately
fashioned by the introduction of controlled
amounts or numbers of particular defects.
4.
By “crystalline defect” is meant a lattice irregularity
having one or more of its dimensions on the order of
an atomic diameter.
Classification of crystalline imperfections is frequently
made according to geometry or dimensionality of the
defect.
Several different imperfections are
point defects (those associated with one or two atomic
positions),
linear (or one-dimensional) defects,
interfacial defects, or boundaries (two-dimensional).
Impurities in solids may exist as point defects.
5.
The simplest of the point defects is a vacancy, or
vacant lattice site,
one normally occupied from which an atom is
missing.
All crystalline solids contain vacancies and, in fact, it
is not possible to create such a material that is free of
these defects.
Point Defects: VACANCIES
6.
The necessity of the existence of vacancies is
explained using principles of thermodynamics;
in essence, the presence of vacancies increases the
entropy (i.e., the randomness) of the crystal.
Point Defects: VACANCIES
7.
The equilibrium number of vacancies for a
given quantity of material depends on and
increases with temperature according to
N is the total number of atomic sites,
Qv is the energy required for the formation of a vacancy,
T is the absolute temperature in Kelvins,
k is the gas or Boltzmann’s constant = 1.38✕10-23 J/atom-K,
or 8.62✕10-5eV/atom-K, depending on the units of Qv.
Point Defects: VACANCIES
8.
For most metals, the fraction of vacancies Nv/N just
below the melting temperature is on the order of 10-4;
that is, one lattice site out of 10,000 will be empty.
A number of other material parameters have an
similar exponential dependence on temperature.
Point Defects: VACANCIES
9.
A self-interstitial is an atom from the crystal that is
crowded into an interstitial site,
a small void space that under ordinary circumstances
is not occupied.
Point Defects: SELF-INTERSTITIALS
10.
In metals, a self-interstitial introduces relatively large
distortions in the surrounding lattice because the
atom is substantially larger than the interstitial
position in which it is situated.
Consequently, the formation of this defect is not
highly probable, and it exists in very small
concentrations, which are significantly lower than for
vacancies.
Point Defects: SELF-INTERSTITIALS
11. 3
• Vacancies:
-vacant atomic sites in a structure.
Vacancy
distortion
of planes
• Self-Interstitials:
-"extra" atoms positioned between atomic sites.
self-
interstitialdistortion
of planes
POINT DEFECTS
15. 7
• Low energy electron
microscope view of
a (110) surface of NiAl.
• Increasing T causes
surface island of
atoms to grow.
• Why? The equil. vacancy
conc. increases via atom
motion from the crystal
to the surface, where
they join the island.
Island grows/shrinks to maintain
equil. vancancy conc. in the bulk.
Reprinted with permission from Nature (K.F.
McCarty, J.A. Nobel, and N.C. Bartelt, "Vacancies in
Solids and the Stability of Surface Morphology",
Nature, Vol. 412, pp. 622-625 (2001). Image is
5.75 mm by 5.75 mm.) Copyright (2001) Macmillan
Publishers, Ltd.
OBSERVING EQUIL. VACANCY CONC.
Click on image to animate
16. 8
• Frenkel Defect
--a cation is out of place.
• Shottky Defect
--a paired set of cation and anion vacancies.
Shottky
Defect:
Frenkel
Defect
• Equilibrium concentration of defects ~ e
QD /kT
Adapted from Fig. 13.20,
Callister 5e. (Fig. 13.20 is from
W.G. Moffatt, G.W. Pearsall,
and J. Wulff, The Structure and
Properties of Materials, Vol. 1,
Structure, John Wiley and
Sons, Inc., p. 78.) See Fig.
12.21, Callister 6e.
DEFECTS IN CERAMIC STRUCTURES
17. 9
Two outcomes if impurity (B) added to host (A):
• Solid solution of B in A (i.e., random dist. of point defects)
• Solid solution of B in A plus particles of a new
phase (usually for a larger amount of B)
OR
Substitutional alloy
(e.g., Cu in Ni)
Interstitial alloy
(e.g., C in Fe)
Second phase particle
--different composition
--often different structure.
POINT DEFECTS IN
ALLOYS
18.
A pure metal consisting of only one type of atom
just isn’t possible;
impurity or foreign atoms will always be present, and
some will exist as crystalline point defects.
In fact, even with relatively sophisticated
techniques, it is difficult to refine metals to a
purity in excess of 99.9999%.
At this level, on the order of 1022 to 1023 impurity
atoms will be present in one cubic meter of material.
IMPURITIES IN SOLIDS
19.
Most familiar metals are not highly pure; rather, they
are alloys,
in which impurity atoms have been added
intentionally to impart specific characteristics to the
material.
Ordinarily, alloying is used in metals to improve
mechanical strength and corrosion resistance.
IMPURITIES IN SOLIDS
20.
For example, sterling silver is a 92.5% silver 7.5%
copper alloy.
In normal ambient environments, pure silver is highly
corrosion resistant, but also very soft.
Alloying with copper significantly enhances the
mechanical strength without depreciating the
corrosion resistance appreciably.
IMPURITIES IN SOLIDS
21.
The addition of impurity atoms to a metal will result
in the formation of a solid solution and/or a new
second phase, depending on the kinds of impurity,
their concentrations, and the temperature of the
alloy.
IMPURITIES IN SOLIDS
22. Several terms relating to impurities and solid
solutions: solute and solvent.
“Solvent” represents the element or compound that is
present in the greatest amount;
on occasion, they are also called host atoms.
“Solute” is used to denote an element or compound
present in a minor concentration.
IMPURITIES IN SOLIDS
23.
A solid solution forms when, as the solute atoms are
added to the host material, the crystal structure is
maintained, and no new structures are formed.
A solid solution is compositionally homogeneous;
the impurity atoms are randomly and uniformly
dispersed within the solid.
Solid Solutions
24.
Impurity point defects are found in solid solutions,
of which there are two types: substitutional and
interstitial.
For the substitutional type, solute or impurity atoms
replace or substitute for the host atoms.
Solid Solutions
26.
Several features of the solute and solvent atoms
that determine the degree to which the former
dissolves in the latter:
1. Atomic size factor.
2. Crystal structure.
3. Electronegativity.
4. Valences.
Solid Solutions
27.
1. Atomic size factor.
When the difference in atomic radii between the two
atom types is < ±15%, appreciable quantities of a
solute may be accommodated in this type of solid
solution
Otherwise the solute atoms will create substantial
lattice distortions and a new phase will form.
Solid Solutions
28.
2. Crystal structure.
For appreciable solid solubility the crystal structures
for metals of both atom types must be the same.
Solid Solutions
29.
3. Electronegativity.
The more electropositive one element and the more
electronegative the other, the greater is the likelihood
that they will form an inter-metallic compound
instead of a substitutional solid solution.
beda Compound dan Solution => Text Book
Solid Solutions
30.
4. Valences.
a metal will have more of a tendency to dissolve
another metal of higher valence than one of a lower
valence. -> Solvent
Solid Solutions
31. Example: substitutional solid solution of Cu-Ni.
They are completely soluble in one another at all
proportions.
the atomic radii: Cu = 0.128 and Ni = 0.125 nm,
both have the FCC crystal structure,
their electronegativities are 1.9 and 1.8
the most common valences are Cu =+1, Ni =+2.
Solid Solutions
32.
For interstitial solid solutions, impurity
atoms fill the voids or interstices among the
host atoms (see Figure).
For metallic materials that have relatively
high atomic packing factors, these interstitial
positions are relatively small.
Consequently, the atomic diameter of an
interstitial impurity must be substantially smaller
than that of the host atoms.
Solid Solutions
33.
Normally, the maximum allowable concentration of
interstitial impurity atoms is low (less than 10%).
Even very small impurity atoms are ordinarily larger
than the interstitial sites, and as a consequence they
introduce some lattice strains on the adjacent host
atoms.
Solid Solutions
34.
Carbon forms an interstitial solid solution when
added to iron;
the maximum concentration of carbon is about 2%.
The atomic radius of the C 0.071 nm << Fe 0.124 nm.
Solid solutions are also possible for ceramic
materials.
Solid Solutions
35.
36.
37.
A dislocation is a linear or one-dimensional defect
around which some of the atoms are misaligned.
(see Figure 4.3):
an extra portion of a plane of atoms, or half-plane, the
edge of which terminates within the crystal.
DISLOCATIONS—LINEAR DEFECTS
39.
a linear defect that centers around the line that is
defined along the end of the extra half-plane of
atoms.
sometimes termed the dislocation line.
For the Figure 4.3 is perpendicular to the plane of the
page.
Edge Dislocation
40.
Within the region around the dislocation line
there is some localized lattice distortion.
The atoms above the dislocation line in Figure 4.3
are squeezed together,
those below are pulled apart;
this is reflected in the slight curvature for the
vertical planes of atoms as they bend around this
extra half-plane.
The magnitude of this distortion decreases
with distance away from the dislocation line;
at positions far removed, the crystal lattice is
virtually perfect.
Edge Dislocation
41.
Sometimes represented by the symbol ⊥
also indicates the position of the dislocation line.
May also be formed by an extra half-plane of atoms
that is included in the bottom portion of the crystal;
its designation is a ⊤.
Edge Dislocation
42.
formed by a shear stress that is applied to produce
the distortion shown in Figure 4.4a:
the upper front region of the crystal is shifted one atomic
distance to the right relative to the bottom portion.
Screw Dislocation
43.
The atomic distortion associated with a screw
dislocation is also linear and along a
dislocation line, line AB in Figure 4.4b.
The screw dislocation derives its name from
the spiral or helical path or ramp that is
traced around the dislocation line by the
atomic planes of atoms.
Sometimes the symbol ↻ is used to designate
a screw dislocation.
Screw Dislocation
46.
Most dislocations found in crystalline materials are
probably neither pure edge nor pure screw, but
exhibit components of both types; these are termed
mixed dislocations.
Mixed Dislocations
50.
The magnitude and direction of the lattice distortion
associated with a dislocation is expressed in terms of
a Burgers vector, denoted by a b.
Burgers vectors are indicated in Figures 4.3 and 4.4 for
edge and screw dislocations, respectively.
Burgers vector
51.
The nature of a dislocation is defined by the relative
orientations of dislocation line and Burgers vector.
For an edge, they are perpendicular
For a screw, they are parallel
They are neither perpendicular nor parallel for a
mixed dislocation.
Burgers vector
52.
Even though a dislocation changes direction
and nature within a crystal (e.g., from edge to
mixed to screw), the Burgers vector will be
the same at all points along its line.
For example, all positions of the curved dislocation in
Figure 4.5 will have the Burgers vector shown.
For metallic materials, the Burgers vector for
a dislocation will point in a close-packed
crystallographic direction and will be of
magnitude equal to the inter-atomic spacing.
Burgers vector
53.
Virtually all crystalline materials contain
some dislocations that were introduced
during solidification,
during plastic deformation,
as a consequence of thermal stresses that result
from rapid cooling.
Dislocations are involved in the plastic
deformation of crystalline materials, both
metals and ceramics.
They have also been observed in polymeric
materials.
54.
Interfacial defects are boundaries that have two
dimensions and normally separate regions of the
materials that have different crystal structures
and/or crystallographic orientations.
INTERFACIAL
DEFECTS
56.
One of the most obvious boundaries is the
external surface, along which the crystal
structure terminates.
Surface atoms are not bonded to the
maximum number of nearest neighbors,
therefore are in a higher energy state than the
atoms at interior positions.
The bonds of these surface atoms that are not
satisfied give rise to a surface energy, expressed
in units of energy per unit area (J/m2 or
erg/cm2).
INTERFACIAL DEFECTS:
External Surfaces
57.
To reduce surface energy, materials tend to
minimize, if at all possible, the total surface area.
For example, liquids assume a shape having a
minimum area—the droplets become spherical.
Of course, this is not possible with solids, which are
mechanically rigid.
INTERFACIAL DEFECTS:
External Surfaces
58.
as the boundary separating two small grains or
crystals having different crystallographic
orientations in polycrystalline materials.
A grain boundary is represented schematically from
an atomic perspective in Figure 4.7.
Within the boundary region, which is probably
just several atom distances wide, there is some
atomic mismatch in a transition from the
crystalline orientation of one grain to that of an
adjacent one.
INTERFACIAL DEFECTS:
Grain Boundaries
60.
Various degrees of crystallographic misalignment
between adjacent grains are possible (Figure 4.7).
When this orientation mismatch is slight, on the
order of a few degrees, then the term small- (or low- )
angle grain boundary is used.
These boundaries can be described in terms of
dislocation arrays.
INTERFACIAL DEFECTS:
Grain Boundaries
61.
One simple small angle grain boundary is formed
when edge dislocations are aligned in the manner of
Figure 4.8.
This type is called a tilt boundary; the angle of
misorientation, Θ, is also indicated in the figure.
When the angle of misorientation is parallel to
the boundary, a twist boundary results, which can
be described by an array of screw dislocations.
INTERFACIAL DEFECTS:
Grain Boundaries
62.
63.
The atoms are bonded less regularly along a grain
boundary (e.g., bond angles are longer), and
consequently, there is an interfacial or grain
boundary energy similar to the surface energy
described above.
The magnitude of this energy is a function of the
degree of misorientation, being larger for high-angle
boundaries.
INTERFACIAL DEFECTS:
Grain Boundaries
64.
Grain boundaries are more chemically reactive than
the grains themselves as a consequence of this
boundary energy.
Impurity atoms often preferentially segregate along
these boundaries because of their higher energy state.
INTERFACIAL DEFECTS:
Grain Boundaries
65.
The total interfacial energy is lower in large or
coarse-grained materials than in fine-grained ones,
since there is less total boundary area in the former.
Grains grow at elevated temperatures to reduce the
total boundary energy.
INTERFACIAL DEFECTS:
Grain Boundaries
66.
In spite of the disordered arrangement of atoms and
lack of regular bonding along grain boundaries,
a polycrystalline material is still very strong; cohesive
forces within and across the boundary are present.
The density of a polycrystalline specimen is virtually
identical to that of a single crystal of the same
material.
INTERFACIAL DEFECTS:
Grain Boundaries
67.
A twin boundary is a special type of grain boundary
across which there is a specific mirror lattice
symmetry;
that is, atoms on one side of the boundary are located
in mirror-image positions of the atoms on the other
side (Figure 4.9).
The region of material between these boundaries is
appropriately termed a twin.
INTERFACIAL DEFECTS:
Twin Boundaries
69.
Twins result from atomic displacements that are
produced
from applied mechanical shear forces (mechanical
twins),
and also during annealing heat treatments following
deformation (annealing twins).
INTERFACIAL DEFECTS:
Twin Boundaries
70.
Twinning occurs on a definite crystallographic plane
and in a specific direction, both of which depend on
the crystal structure.
Annealing twins are typically found in metals that
have the FCC crystal structure,
Mechanical twins are observed in BCC and HCP
metals.
INTERFACIAL DEFECTS:
Twin Boundaries
71.
Other possible interfacial defects include
stacking faults,
phase boundaries,
ferromagnetic domain walls.
Stacking faults are found in FCC metals when there
is an interruption in the ABCABCABC . . . stacking
sequence of close-packed planes.
Miscellaneous Interfacial
Defects
72.
Phase boundaries exist in multiphase materials
across which there is a sudden change in physical
and/or chemical characteristics.
For ferromagnetic and ferrimagnetic materials, the
boundary that separates regions having different
directions of magnetization is termed a domain wall.
Miscellaneous Interfacial
Defects
73.
Associated with each of the defects is an interfacial
energy,
the magnitude of which depends on boundary type,
and which will vary from material to material.
Normally, the interfacial energy will be greatest for
external surfaces and least for domain walls.
Miscellaneous Interfacial
Defects
74.
The surface energy of a single crystal depends on
crystallographic orientation.
Does this surface energy increase or decrease with an
increase in planar density. Why?
Interfacial Defects
75.
76.
77.
Other defects exist in all solid materials that are
much larger:
pores, cracks, foreign inclusions, and other phases.
They are normally introduced during processing and
fabrication steps.
BULK OR VOLUME
DEFECTS
78.
Every atom in a solid material is vibrating
very rapidly about its lattice position within
the crystal.
These atomic vibrations may be thought of
as imperfections or defects.
At any instant of time not all atoms vibrate at
the same frequency and amplitude, nor with
the same energy.
At a given temperature there will exist a
distribution of energies for the constituent
atoms about an average energy.
ATOMIC VIBRATIONS
79.
Over time the vibrational energy of any
specific atom will also vary in a random
manner.
With rising temperature, this average energy
increases,
in fact, the temperature of a solid is really just a
measure of the average vibrational activity of
atoms and molecules.
At room temperature, a typical vibrational
frequency is on the order of 1013 vibrations
per second, whereas the amplitude is a few
thousandths of a nanometer.
ATOMIC VIBRATIONS
80.
Many properties and processes in solids are
manifestations of this vibrational atomic motion.
For example, melting occurs when the vibrations are
vigorous enough to rupture large numbers of atomic
bonds.
ATOMIC VIBRATIONS
84.
Transmission Electron Microscopy (TEM)
a specimen to be examined must be prepared in the
form of a very thin foil;
Magnifications approaching 1,000,000✕ are possible
with transmission electron microscopy,
which is frequently utilized in the study of dislocations.
Electron Microscopy
85.
A more recent and extremely useful investigative
tool.
The surface of a specimen to be examined is scanned
with an electron beam, and the reflected (or back-
scattered) beam of electrons is collected, then
displayed on a video monitor.
Scanning Electron
Microscopy (SEM)
86.
The surface may or may not be polished and
etched, but it must be electrically conductive;
a very thin metallic surface coating must be
applied to nonconductive materials.
Magnifications ranging from 10 to in excess
of 50,000 times are possible, as are also very
great depths of field.
Accessory equipment permits qualitative and
semiquantitative analysis of the elemental
composition of very localized surface areas.
Scanning Electron
Microscopy (SEM)
87.
It differs from the optical and electron microscopes.
neither light nor electrons is used to form an image.
the microscope generates a topographical map, on an
atomic scale, that is a representation of surface
features and characteristics of the specimen being
examined.
Scanning Probe
Microscopy (SPM)
88.
Some of the features :
Examination on the nanometer scale is possible
magnifications as high as 109 are possible;
Three-dimensional magnified images are
generated that provide topographical information
about features of interest.
may be operated in a variety of environments
(e.g., vacuum, air, liquid); thus, a particular
specimen may be examined in its most suitable
environment.
Scanning Probe
Microscopy (SPM)
92.
Grain size number is used extensively in the
specification of steels.
The grain size may be estimated by using
an intercept method.
ASTM method
GRAIN SIZE
DETERMINATION
93.
Intercept method
Straight lines all the same length are drawn through
several photomicrographs that show the grain
structure.
The grains intersected by each line segment are
counted;
The line length is then divided by an average of the
number of grains intersected, taken over all the line
segments.
The average grain diameter is found by dividing this
result by the linear magnification of the
photomicrographs.
94.
The American Society for Testing and Materials
(ASTM) method.
Prepared properly the specimen to reveal the grain
structure; photograph at a magnification of 100✕.
Compare with the chart provided by ASTM.
Express the grain size as the grain size number of the
chart that most nearly matches the grains in the
micrograph.
95.
The rationale:
Let n represent the grain size number, and N the
average number of grains per square inch at a
magnification of 100✕.
These two parameters are related to each other
through the expression
96.
97.
98.
Part 2: Material Properties
Mechanical Properties
Thermal Properties
Electrical and Magnetic Properties
Superconductivity
99.
Part 3: Material Engineering
Alloy Systems
Phase Diagrams and Phase Transformations
Heat Treatment
Deformation of Materials
Corrosion
Organic Materials:
Polymers and Elastomers
Wood
Composites
Nano structured Materials