Diffusion bonding is a solid-state welding technique that joins materials together through atomic diffusion without melting. It involves applying high pressure and moderate heat to join carefully cleaned and mated surfaces. Diffusion occurs in two stages - initial metal-to-metal contact formation followed by atomic diffusion and grain growth across the interface to form a complete bond. Various factors like temperature, pressure, time and surface preparation influence the diffusion rate. Common diffusion bonding methods include gas pressure bonding, vacuum fusion bonding and eutectic bonding. Diffusion bonding finds applications in the fabrication of components for industries like aerospace, nuclear and others.
Electron Beam Welding is a fusion welding process in which a beam of high-velocity electrons is applied to the material to be joined. The work-piece melt as the kinetic energy of the electrons is transformed into heat upon impact. The EBW process is well-positioned to provide industries with highest quality welds and machine designs that have proven to be adaptable to specific welding tasks and production environments.
Electron Beam Welding is a fusion welding process in which a beam of high-velocity electrons is applied to the material to be joined. The work-piece melt as the kinetic energy of the electrons is transformed into heat upon impact. The EBW process is well-positioned to provide industries with highest quality welds and machine designs that have proven to be adaptable to specific welding tasks and production environments.
Recrystallization is the process in which deformed grains of the crystal structure are replaced by a new set of stress-free grains that nucleate and grow until all the original grains have been consumed. The process is accomplished by heating the material to temperatures above that of crystallization.
This Presentation covers the basic concepts of Hot cracks and cold cracks in welding. For more information, please refer the books mentioned in the references slide.... Thank you
Presentation on Carburizing (Heat Treatment Process).
Presented To,
Engr. Ubaid-ur-Rehman Ghouri, Department of Industrial & Manufacturing Engineering, UET Lahore (RCET Campus).
Presented By,
Muhammad Zeeshan
Zahid Mehmood
Ali Iqbal
Muhammad Waqas
What is laser beam hardening (LBH)? Advantages, Disadvantages
Applications, What is laser peening? Difference between laser beam hardening (LBH) and electron beam hardening (EBH)
Welding process
Arc Welding
Resistance Welding
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Other Fusion Welding Processes
Solid State Welding
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Recrystallization is the process in which deformed grains of the crystal structure are replaced by a new set of stress-free grains that nucleate and grow until all the original grains have been consumed. The process is accomplished by heating the material to temperatures above that of crystallization.
This Presentation covers the basic concepts of Hot cracks and cold cracks in welding. For more information, please refer the books mentioned in the references slide.... Thank you
Presentation on Carburizing (Heat Treatment Process).
Presented To,
Engr. Ubaid-ur-Rehman Ghouri, Department of Industrial & Manufacturing Engineering, UET Lahore (RCET Campus).
Presented By,
Muhammad Zeeshan
Zahid Mehmood
Ali Iqbal
Muhammad Waqas
What is laser beam hardening (LBH)? Advantages, Disadvantages
Applications, What is laser peening? Difference between laser beam hardening (LBH) and electron beam hardening (EBH)
Welding process
Arc Welding
Resistance Welding
Oxy fuel Gas Welding
Other Fusion Welding Processes
Solid State Welding
Weld Quality
Weld ability
Design Considerations in Welding
Permeability of concrete, chemical attack, acid attack, efflorescence, Corrosion in concrete. Thermal conductivity, thermal diffusivity, specific heat. Alkali Aggregate Reaction
B.Sc. (Engineering)
Department of Mechanical Engineering
Khulna University of Engineering & Technology
Course - Manufacturing Process
Topic - Welding, Brazing & Soldering
Duplex 2209 Weld Overlay by ESSC ProcessIJERA Editor
In the modern world of industrialization the wear is eating metal assets worth millions of dollars per year. The wear is in the form of corrosion, erosion, abrasion etc. which occur in the process industries like oil & gas, refineries, cement plants, steel plants, shipping and offshore working structures. The equipments like pressure vessels, heat exchangers, hydro processing reactors which very often work at elevated temperatures face corrosion in the internal diameter. Duplex 2209 weld overlay on ferrous material is developed for high corrosion resistance properties and having high productivity by Electroslag strip cladding process due to its less dilution ~10% as compared to SMAW , GTAW or FCAW process. Because of Low Dilution ~10% undiluted chemistry can be achieved with single layer as compared to other weld overlay processes. The facility was developed inhouse to carry out weld overlay by ESSC and Testing.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
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Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
2. Definition
Diffusion bonding is a solid-state welding
technique, wherein coalescence of the faying
surfaces is produced by the application of
pressure and temperature to carefully cleaned
and mated metal surfaces so that they actually
grow together by atomic diffusion.
The process does not involve macroscopic
deformation or relative motion of the parts. The
process can join either like or dissimilar metals
with or without the use of another material
between.
2
3. Theory of diffusion Welding
3
Diffusion welding process involves two steps:
Any surface to be diffusion welded is never
extremely smooth. It has a number of peak points
and valleys. Moreover, this surface may have,
(i) An oxidized layer
(ii) Oil, grease, dirt etc.,
(iii) Absorbed gas, moisture.
4. 4
The first stage is to achieve intimate metal to metal
contact between the two pieces to be diffusion
welded. This is done by the application of pressure
that deforms the substrate roughness and disrupts
and disperses the above mentioned surface layers
and contaminants.
The pressure applied in diffusion welded ranges from
350 to 700 kg/cm2.
The second stage involves diffusion and grain
growth to complete the weld and ultimately eliminate
the interface formed in the previous stage. The
second stage induces complete metallic bonding
across the area of contact.
In order to increase diffusion rate, moderate heating
temperatures are used.
6. Diffusion Bonding Process
a
b
c
d
e
a) Initial 'point' contact
b) Yielding and creep leading to
reduced voids
c) Final yielding and creep (some
voids left)
d) Continued vacancy diffusion,
leaving few small voids
e) Bonding is complete
6
7. Diffusion Bonded Methods
7
1. Gas pressure boding
2. Vacuum fusion bonding
3. Eutectic bonding
Gas pressure boding:
Parts to be joined are placed together in intimate
contact and then heated to around 815 0C. During
heating, an inert gas pressure is built up over all
the surfaces of the parts to be welded.
Non ferrous metals are joined with the help of gas
pressure bonding method.
8. 8
Vacuum fusion bonding:
Parts to be joined are pressed together
mechanically or hydraulically. A hydraulic pres used
for diffusion welding resembles that employed in
forging and is equipped to pressurize from three
directions.
Heating is carried out the same way as in gas
pressure bonding.
Process is carried out in vacuum chamber.
Since, pressure higher than those in gas pressure
bonding can be applied in this process, vacuum
fusion boding is used for steel and its alloys.
For diffusion bonding of steel, the temperature and
pressure required are approximately 1150 0C and
700 kg/cm2 respectively.
9. 9
Eutectic fusion bonding:
It is a low temperature diffusion welding process.
A thin plate of some other material is kept between
the pieces to be joined.
As the pieces are heated to a elevated temperature,
the filler material diffuses and forms an eutectic
compound with the parent metals.
10. Diffusion bonding parameters
10
Main diffusion bonding parameters are
1. Pressure
2. Temperature
3. Time
Others parameters are
4. Surface preparation
5. Metallurgical factors
6. Use of interlayer
11. 11
Pressure:
It assures consistency of bond formation.
The initial deformation phase of bond formation is
directly affected by the intensity of pressure applied.
For any given time temperature value, increased
pressure invariably results in better joints.
However, increased pressures require costlier
equipment.
12. 12
Temperature:
It serves the important function of increasing the surface
energy.
Temperature affects
(i) Plasticity,
(ii) Diffusivity
(iii) Oxide solubility
(iv) Allotropic transformation
(v) Recrystallization
Temperature must be controlled to promote or avoid
these factors as desired.
Generally, increasing temperature shortens diffusion
welding cycle and improves the economics of the
process.
Diffusion welding temperature usually ranges from 0.55
13. 13
Time:
Time is a dependent process parameter.
An increase in temperature shortens the time
required to complete the diffusion welding.
Time required for diffusion welding varies from a few
minutes to several hours.
14. 14
Surface preparation:
Better prepared and cleaned surfaces lower the
minute the minimum diffusion welding temperature
or pressure.
Surface to be diffusion bonded are
(i) Machined, ground or abraded so that they are
sufficiently smooth to ensure that the interfaces can
be passed to proper contact without excessive
deformation.
(ii) Cleaned of chemically combined films, oxides
etc.
(iii) Cleaned of gaseous, aqueous or organic surface
films.
15. 15
Metallurgical factors:
1. Allotropic transformation:
Hardenable steels undergo allotropic
transformation and involve volume change during
diffusion welding. This may affect dimensional
stability of the welded component.
2. Recrystallization:
Many cold worked metals tend to recrystallize
during diffusion welding. This may be good for
certain materials but undesirable for others, e.g.,
refractory metals.
3. Surface oxides:
Beryllium, aluminium, chromium, etc., form
tenacious surface oxides. They and alloys
containing them are, therefore, more difficult to
weld than those which form less stable oxide films
16. 16
Use of interlayers:
It differing from base metals being joined is growing
in diffusion welding. An interlayer is a lower strength
intermediate or one containing a diffusive element.
An interlayer solves alloying compatibility problems
when joining dissimilar metals. Also, it being soft,
confines deformation to itself and thus minimizes
distortion of work pieces when pressed to contact.
Interlayers may, however, give rise to decreased
strength or stability.
The most common interlayer materials used at this
time are titanium, nickel and silver.
17. Materials diffusion bonded
17
Many similar and dissimilar metals have been joined
by diffusion welding, but most applications of this
process have been with
Titanium alloys,
Zirconium Alloys and
Nickel base alloys.
18. Advantages of diffusion bonding
18
a) Welded having essentially the same physical,
chemical and mechanical properties as the base
metal can be produced.
b) Heat treating operations can be incorporated
during the bonding cycle.
c) Continuous, leak tight welds can be formed.
d) The process is well suited for welding dissimilar
metals and ceramics.
e) Numerous welds can be made simultaneously.
f) Weldability is largely independent of material
thickness.
19. Limitations of diffusion bonding
19
i. A major difficulty is the removal of oxide and the
contaminating layers present on practically all metals
exposed to natural or industrial environment.
ii. Opposing surfaces must be mated in size to within a
few angstroms of each other in order to achieve a
satisfactory metal bond.
iii. Diffusion welding requires a relatively long, time
consuming thermal cycle.
iv. With dissimilar materials, difficulties due to time /
temperature / pressure requirements are frequently
encountered.
v. Diffusion welding is not classified as a mass
production process.
20. Application of Diffusion bonding
20
1. Fabrication of reactor components in atomic
energy industries.
2. Fabrication of honeycomb, rocket engines,
helicopter rotor hub, turbine components, etc., in
aerospace missile and rocketry industries.
3. Two controversial aerospace vehicles have brought
diffusion bonding into the light e.g., B-1 bomber
and space shuttle.
4. Fabrication of composite materials.
21. Diffusion
Many reactions and processes that are
important in the treatment of materials rely on
the transfer of mass either within a specific
solid (ordinarily on a microscopic level) or
from a liquid, a gas, or another solid phase.
This is necessarily accomplished by diffusion,
the phenomenon of material transport by
atomic motion.
The phenomenon of diffusion may be
demonstrated with the use of a diffusion
couple, which is formed by joining bars of two
different metals together so that there is
intimate contact between the two faces.
21
22. 22
(a) A copper–nickel diffusion couple
before a high-temperature heat
treatment.
(b) Schematic representations of
Cu (red circles) and Ni (blue
circles) atom locations within the
diffusion couple.
(c) Concentrations of copper and
nickel as a
function of position across the
couple.
23. 23
(a)A copper–nickel diffusion
couple after a high-
temperature heat treatment,
showing the alloyed diffusion
zone.
(b) Schematic representations
of Cu (red circles) and Ni
(blue circles) atom locations
within the couple.
(c) Concentrations of copper
and nickel as a function of
position across the couple.
24. Inter diffusion
This result indicates that copper atoms have migrated or diffused into
the nickel, and that nickel has diffused into copper. This process,
whereby atoms of one metal diffuse into another, is termed inter
diffusion, or impurity diffusion.
Initially
After some time
24
25. Self-Diffusion
Inter diffusion may be discerned from a macroscopic
perspective by changes in concentration that occur over
time, as in the example for the Cu–Ni diffusion couple.
There is a net drift or transport of atoms from high to low
concentration regions. Diffusion also occurs for pure
metals, but all atoms exchanging positions are of the same
type; this is termed self-diffusion.specific atom movement
A
B
C
D
After some time
A
B
C
D
25
26. Diffusion Mechanisms
From an atomic perspective, diffusion is just the
stepwise migration of atoms from lattice site to lattice
site. In fact, the atoms in solid materials are in constant
motion, rapidly changing positions. For an atom to make
such a move, two conditions must be met:
(1) there must be an empty adjacent site,
(2) the atom must have sufficient energy to break bonds
with its neighbour atoms and then cause some lattice
distortion during the displacement.
This energy is vibrational in nature. At a specific
temperature some small fraction of the total number of
atoms is capable of diffusive motion, by virtue of the
magnitudes of their vibrational energies.
This fraction increases with rising temperature. Several
different models for this atomic motion have been
26
27. Vacancy Diffusion
27
One mechanism involves the interchange of an
atom from a normal lattice position to an adjacent
vacant lattice site or vacancy. This mechanism is
aptly termed vacancy diffusion.
Of course, this process necessitates the presence of
vacancies, and the extent to which vacancy diffusion
can occur is a function of the number of these
defects that are present; significant concentrations
of vacancies may exist in metals at elevated
temperatures.
Because diffusing atoms and vacancies exchange
positions, the diffusion of atoms in one direction
corresponds to the motion of vacancies in the
opposite direction. Both self-diffusion and inter
diffusion occur by this mechanism; for the latter, the
29. Interstitial diffusion
The second type of diffusion involves atoms that
migrate from an interstitial position to a neighbouring
one that is empty. This mechanism is found for inter
diffusion of impurities such as hydrogen, carbon,
nitrogen, and oxygen, which have atoms that are
small enough to fit into the interstitial positions.
Host or substitutional impurity atoms rarely form
interstitials and do not normally diffuse via this
mechanism. This phenomenon is appropriately
termed interstitial diffusion.
In most metal alloys, interstitial diffusion occurs
much more rapidly than diffusion by the vacancy
mode, because the interstitial atoms are smaller and
thus more mobile.
Furthermore, there are more empty interstitial29
32. Steady State Diffusion
32
Diffusion is a time-dependent process that is, in a
macroscopic sense, the quantity of an element that
is transported within another is a function of time.
Often it is necessary to know how fast diffusion
occurs, or the rate of mass transfer. This rate is
frequently expressed as a diffusion flux (J), defined
as the mass M diffusing through and perpendicular
to a unit cross-sectional area of solid per unit of time.
In mathematical form, this may be represented as
At
M
J
33. 33
In differential form, this expression becomes
If the diffusion flux does not change with time, a
steady-state condition exists. One common example
of steady-state diffusion is the diffusion of atoms of a
gas through a plate of metal for which the
concentrations (or pressures) of the diffusing
species on both surfaces of the plate are held
constant. When concentration C is plotted versus
position within the solid x, the resulting curve is
termed the concentration profile. The slope at a
particular point on this curve is the concentration
gradient.
dt
dM
A
J
1
concentration gradient
dx
dC
34. For diffusion problems, it is sometimes convenient to express concentration
in terms of mass of diffusing species per unit volume of solid (kg/m3 or
g/cm3).
Steady State Diffusion Across A Thin
Plate
BA
BA
xx
CC
x
C
dx
dC
34
35. 35
The mathematics of steady-state diffusion in a single
(x) direction is relatively simple, in that the flux is
proportional to the concentration gradient through
the expression
The constant of proportionality D is called the
diffusion coefficient, which is expressed in square
meters per second. The negative sign in this
expression indicates that the direction of diffusion is
down the concentration gradient, from a high to a
low concentration. Above equation is called Fick’s
first law.
Sometimes the term driving force is used in the
context of what compels a reaction to occur. For
diffusion reactions, several such forces are possible;
dx
dC
DJ
36. Non Steady State Diffusion
36
Most practical diffusion situations are non steady
state ones. That is, the diffusion flux and the
concentration gradient at some particular point in a
solid vary with time, with a net accumulation or
depletion of the diffusing species resulting. Under
conditions of non steady state, use of Steady state
equation is no longer convenient; instead, the partial
differential equation known as Fick’s second law.
If the diffusion coefficient is independent of
composition, above equation simplifies to
x
c
D
xt
c
2
2
x
c
D
t
c
37. Calculate Activated Diffusion
Room temperature (kBT = 0.026 eV)
Typical activation energy Em (~ 1 eV/atom) (like Qv)
Therefore, a large fluctuation in energy is needed for
a jump.
Probability of a fluctuation or frequency of jump, Rj
0 exp m
j
B
E
R R
k T
R0 = attempt frequency proportional to
vibration frequency
37
38. 1. Probability of finding a vacancy in an adjacent lattice
site:
2. Probability of thermal fluctuation
Calculate Activated Diffusion
The diffusion coefficient = Multiply
0 exp m
j
B
E
R R
k T
.exp v
B
Q
P Const
k T
.exp expm V
B B
E Q
D Const
k T k T
0 exp d
B
Q
D D
k T
38
39. Diffusion and Temperature
Diffusion coefficient increases with increasing T.
Activation energy - energy required to produce the movement of 1
mole of atoms by diffusion.
0 0exp expd dQ Q
D D D
RT kT
D0 - Temperature-independent (m2/s)
Qd - The activation energy (J/mol or eV/atom)
R - The gas constant (8.31 J/mol-K)
or
kB - Boltzmann constant ( 8.6210-5 eV/atom-K)
T - Absolute temperature (K)
39
40. Diffusion – Temperature Dependence
0
1
ln ln dQ
D D
R T
or 0
1
log log
2.3
dQ
D D
R T
The above equation has represented as straight
line equation
40
41. The diffusing species, host material and temperature
influence the diffusion coefficient.
Diffusion of different species
41
42. Factors that Influence Diffusion
Diffusing Species:
The magnitude of the diffusion coefficient D is indicative
of the rate at which atoms diffuse. Coefficients, both self-
and inter diffusion, for several metallic systems are listed
in Table 5.2.
The diffusing species as well as the host material
influence the diffusion coefficient. For example, there is a
significant difference in magnitude between self-diffusion
and carbon inter diffusion in iron at 500 0C, the D value
being greater for the carbon inter diffusion (3 X 10-21 vs.
2.4 X 10-12 m2/s).
This comparison also provides a contrast between rates
of diffusion via vacancy and interstitial modes as
discussed earlier. Self-diffusion occurs by a vacancy
mechanism, whereas carbon diffusion in iron is
42
43. 43
Temperature:
Temperature has a most profound influence on the
coefficients and diffusion rates. For example, for the
self-diffusion of Fe in -Fe, the diffusion coefficient
increases approximately six orders of magnitude (3
X 10-21 vs. 1.8 X 10-15 m2/s) in rising temperature
from 500 0C to 900 0C (Table 5.2). The temperature
dependence of the diffusion coefficients is
0 0exp expd dQ Q
D D D
RT kT
45. 45
The activation energy may be thought of as that
energy required to produce the diffusive motion of
one mole of atoms. A large activation energy results
in a relatively small diffusion coefficient. Table 5.2
also contains a listing of D0 and Qd values for
several diffusion systems. Taking natural logarithms
of above equation yields
Or
Because D0, Qd and R are all constants, above
equation takes on the form of an equation of a
straight line:
where y and x are analogous, respectively, to the
variables log D and 1/T.
0
1
ln ln dQ
D D
R T
0
1
log log
2.3
dQ
D D
R T
cmxy