Classes and Properties: Semiconductors Distinguishing features
Made primarily from metalloids
Regular arrangement of atoms (crystals, but not, e.g., solar cell amorphous Si)
Extremely controlled chemical purity
Adjustable conductivity of electricity
Opaque to visible light
Some have good plasticity, but others are fairly brittle
Some have an electrical response to light
Semiconductors define the Digitial Revolution and Information Age.
Starting with extremely pure crystalline form, their electrical conductions can be controlled by impurity doping (and defect).
The result is a tiny electrical switching called a "transistor". Transistors (at present) can be packed to about 1 billion in the size of a Lincoln Penny.
Classes and Properties: Semiconductors Elements occurring in semiconductors 19
Classes and Properties: Semiconductors Applications and Examples
Electrical components (transistors, diodes, etc.)
Light-emitting diodes (LEDs)
Flat panel displays
Microelectromechanical devices (MEMS)
Examples: Si, Ge, GaAs, and InSb
Classes and Properties: Composites Distinguishing features
Composed of two or more different materials (e.g., metal/ceramic, polymer/polymer, etc.)
Properties depend on amount and distribution of each type of material.
Collective properties more desirable than possible with any individual material.
Applications and Examples
Sports equipment (golf club shafts, tennis rackets, bicycle frames)
"Smart" materials (sensing and responding)
Fiberglass (glass fibers in a polymer)
Space shuttle heat shields (interwoven ceramic fibers)
Paints (ceramic particles in latex)
Tank armor (ceramic particles in metal)
Materials Science From the polymers in the chair you’re sitting on, the metal ball-point pen you’re using, and the concrete that made the building you live or work in to the materials that make up streets and highways and the car you drive, plane you using. All these items are products of materials science and technology. Briefly defined, materials science is the study of “stuff.” Materials science is the study of solid matter.
Material Science The discipline of investigating the relationships that exist between the structures and properties of materials and its performance.
What is Materials Science and Engineering ? Processing -> Structure -> Properties -> Performance
Processing Texturing, Temperature, Time, Transformations Properties characterization Physical behavior Response to environment Crystal structure Defects Microstructure
Materials Science and Engineering Core, including the end-user Source: Materials science and engineering—forging stronger links to users, NRC 1999
It all about the raw materials and how they are processed
That is why we call it materials ENGINEERING
Minor differencesin Raw materials or processing parameters can meanmajor changes in the performanceof the final material or product
(d) 30mm (c) (b) (a) 4mm 30mm 30mm Properties depend on Structure (strength or hardness) 6 00 5 00 4 00 Hardness (BHN) 3 00 2 00 100 0.01 0.1 1 10 100 1000 Cooling Rate (ºC/s) And: Processing can change structure! (see above structure vs Cooling Rate)
Another Example: Rolling of Steel
At h1, L1
At h2, L2
Structure determines Properties but Processing determines Structure!
Multiple Length Scales Critical in Engineering In Askeland and Phule’s book, from J. Allison and W. Donlon (Ford Motor Company) 31
Properties of Materials
An alternative to major classes, you may divide materials into classification according to properties.
One goal of materials engineering is to select materials with suitable properties for a given application, so it’s a sensible approach.
Just as for classes of materials, there is some overlap among the properties, so the divisions are not always clearly defined
Mechanical properties A. Elasticity and stiffness (recoverable stress vs. strain) B. Plasticity (non-recoverable stress vs. strain) C. Strength D. Brittleness or Toughness E. Fatigue 32
Properties of Materials Electrical properties A. Electrical conductivity and resistivity Dielectric properties A. Polarizability B. Capacitance C. Ferroelectric properties D. Piezoelectric properties E. Pyroelectric properties Magnetic properties A. Paramagnetic properties B. Diamagnetic properties C. Ferromagnetic properties 33
Properties of Materials Optical properties A. Refractive index B. Absorption, reflection, and transmission C. Birefringence (double refraction) Corrosion properties Deteriorative properties Biological properties A. Toxicity B. bio-compatibility 34
400 300 (W/m-K) 200 Thermal Conductivity 100 0 0 10 20 30 40 Composition (wt% Zinc) 100mm THERMAL Properties • Space Shuttle Tiles: --Silica fiber insulation offers low heat conduction. • Thermal Conductivity of Copper: --It decreases when you add zinc! Adapted from Fig. 19.4W, Callister 6e. (Courtesy of Lockheed Aerospace Ceramics Systems, Sunnyvale, CA) (Note: "W" denotes fig. is on CD-ROM.) Adapted from Fig. 19.4, Callister 7e. (Fig. 19.4 is adapted from Metals Handbook: Properties and Selection: Nonferrous alloys and Pure Metals, Vol. 2, 9th ed., H. Baker, (Managing Editor), American Society for Metals, 1979, p. 315.)
Fe+3%Si Fe Magnetization Magnetic Field MAGNETIC Properties • Magnetic Permeability vs. Composition: --Adding 3 atomic % Si makes Fe a better recording medium! • Magnetic Storage: --Recording medium is magnetized by recording head. Adapted from C.R. Barrett, W.D. Nix, and A.S. Tetelman, The Principles of Engineering Materials, Fig. 1-7(a), p. 9, Electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey. Fig. 20.23, Callister 7e. (Fig. 20.23 is from J.U. Lemke, MRS Bulletin, Vol. XV, No. 3, p. 31, 1990.)
-8 “as-is” 10 “held at 160ºC for 1 hr before testing” crack speed (m/s) -10 10 Alloy 7178 tested in saturated aqueous NaCl solution at 23ºC increasing load 4mm --material: 7150-T651 Al "alloy" (Zn,Cu,Mg,Zr) Adapted from Fig. 11.26, Callister 7e. (Fig. 11.26 provided courtesy of G.H. Narayanan and A.G. Miller, Boeing Commercial Airplane Company.) DETERIORATIVE Properties • Heat treatment: slows crack speed in salt water! • Stress & Saltwater... --causes cracks! Adapted from Fig. 11.20(b), R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials" (4th ed.), p. 505, John Wiley and Sons, 1996. (Original source: Markus O. Speidel, Brown Boveri Co.) Adapted from chapter-opening photograph, Chapter 17, Callister 7e. (from Marine Corrosion, Causes, and Prevention, John Wiley and Sons, Inc., 1975.)
Electrical: Resistivity of Copper Increase resistivity of Cu
by adding impurities
by mechanical deformation
Fig. 19.8 Callister Resistivity 10-8 Ohms-m scattering of e- by microstructure scattering of e- impurities scattering of e- by phonons T (0C) 38
low from ceramic oxide (structure and conduction properties)
changes due to alloying in metals (even though same structure)
Silica (SiO2) fibres in space shuttle tiles Fig. 23.18 Callister 40
bcc Fe Fig. 6.14 Callister - 200 C - 100 C Stress (MPa) + 25 C Strain Deterioration and Failure e.g., Stress, corrosive environments, embrittlement, incorrect structures from improper alloying or heat treatments, … USS Esso Manhattan 3/29/43 Fractured at entrance to NY harbor http://www.uh.edu/liberty/photos/liberty_summary.html 41
The COMET: first jet passenger plane - 1954 In 1949, the COMET aircraft was a newly designed, modern jet aircraft for passenger travel. It had bright cabins due to large, square windows at most seats. It was composed of light-weight aluminum. In early 1950's, the planes began falling out of the sky. These tragedies changed the way aircraft were designed and the materials that were used. The square windows were a "stress concentrator" and the aluminum alloys used were not "strong"enough to withstand the stresses. Until then, material selection for mechanical design was not really considered in designs. 43
Concorde Jetliner - August, 2000 A Concorde aircraft, one of the most reliable aircraft of our time, was taking off from Paris Airport when it burst into flames and crashed killing all on board. Amazingly, the pilot knowingly steered the plane toward a less populated point to avoid increased loss of life. Only three people on the ground were killed. Investigations determined that a jet that took-off ahead of Concorde had a fatigue-induced loss of a metallic component of the aircraft, which was left on runway. During take-off, the Concorde struck the component and catapulted it into the wing containing filled fuel tanks. From video, the tragedy was caused from the spewing fuel catching fire from nearby engine exhaust flames and damaging flight control. 44
World Trade Center Collapse CNN Tubularconstructed building. Well designed and strong. Strong but not from buckling. Supports lost at crash site, and the floor supported inner and outer tubular structures. Heat from burning fuel adds to loss of structural support from softening of steel (strength vs. T, stress-strain behavior). Building “pancakes” due to enormous buckling loads. See estimate by Tom Mackie in MIE 45
Alloying and Diffusion: Advances and Failures
Alloying can lead to new or enhanced properties, e.g. Li, Zr added to Al (advanced precipitation hardened 767 aircraft skin).
It can also be a problem, e.g. Ga is a fast diffuser at Al grain boundaries and make Al catastrophically brittle(noplastic behaviorvs.strain).
Need to know T vs. c phase diagrams for what alloying does.
Need to know T-T-T (temp - time - transition) diagrams to know treatment.
T vs c for Ga-In Bringing an plane out of the sky! When Ga (in liquid state) is alloyed to Al it diffusesrapidly alonggrain boundaries(more volume) making bonds weaker and limiting plastic response. liquid Liquid at R.T. All these are concepts we will tackle. T.J. Anderson and I. Ansara, J. Phase Equilibria, 12(1), 64-72 (1991). 46