EME 201 Materials Science Diffusion.

Slides:



Advertisements
Similar presentations
Lecture on DIFFUSION IN SOLIDS. Applications of Diffusion in Solids
Advertisements

Lecture 3.
Chapter 6 Diffusion in Solids.
Chapter ISSUES TO ADDRESS... How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for.
Chapter ISSUES TO ADDRESS... How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for.
Diffusion Movement of atoms in a material Thermal Energy = Atom Movement Eliminates concentration differences Important for material processing (heat treating,
CHAPTER 6: DIFFUSION IN SOLIDS
Chapter 1: Introduction and Basic Concepts
Dislocations – Linear Defects –Two-dimensional or line defect –Line around which atoms are misaligned – related to slip Edge dislocation: –extra half-plane.
CHAPTER 5: DIFFUSION IN SOLIDS
CHAPTER 5 Diffusion 5-1.
Thermally Activated Processes and Diffusion in Solids
Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad.
Materials Science and Engineering --- MY2100 Chapters 1 and 2 Metals and Metal Structures Key Concepts  Major Engineering Alloy Systems  The Design Process.
Chapter 5 Diffusion Skip Sec. 5-7, 5-8 and Homework No. 6 Problems 4-17, 4-19, 4-32, 4-47, 4-48, 5-9, 5-15, 5- 23, 5-26, 5-60.
ENS 205 Materials Science I Chapter 5: Diffusion
DIFFUSION IN SOLIDS  FICK’S LAWS  KIRKENDALL EFFECT  ATOMIC MECHANISMS Diffusion in Solids P.G. Shewmon McGraw-Hill, New York (1963)
1 Diffusion Diffusion: Atom and Ion Movements in Materials Applications of Diffusion  Nitriding - Carburization for Surface Hardening of Steels  p-n.
 Density is the amount of matter there is in a certain amount of space.  Density = Mass / Volume  Unit is g / cm 3  Frank has a paper clip. It has.
Introduction To Materials Science, Chapter 5, Diffusion University of Virginia, Dept. of Materials Science and Engineering 1 Diffusion  how atoms move.
Relative Energy Levels of Defects Information was extracted from: Porter and Easterling, Phase Transformations in Metals and Alloys, 2nd Edition, CRC Press,
Chapter 8 Metallic Bonding
Introduction Material transport by atomic motion Diffusion couple:
IMPERFECTIONS IN SOLIDS
CHAPTER 5 Diffusion 5-1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Atomic Diffusion in Solids Diffusion.
CHE 333 CLASS 20 DIFFUSION.
ISSUES TO ADDRESS... How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases?
1 ISSUES TO ADDRESS... How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple.
1 CHAPTER 7 Structure and Properties of Materials Defects and Properties : Point Defects and Diffusion.
ISSUES TO ADDRESS... How does diffusion occur? Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases?
Chapter 1 Diffusion in Solids. Diffusion - Introduction A phenomenon of material transport by atomic migration The mass transfer in macroscopic level.
Lecture 17: Diffusion PHYS 430/603 material Laszlo Takacs UMBC Department of Physics.
Material science & Metallurgy L D College of Engineering Mechanical Engineering 1.
MIT Microstructural Evolution in Materials 6: Substitutional Diffusion Juejun (JJ) Hu
KS4 Chemistry Metallic Bonding.
Introduction to Materials Science and Engineering
CHAPTER 5: DIFFUSION IN SOLIDS
DIFFUSION IN SOLIDS ISSUES TO ADDRESS... • How does diffusion occur?
Chapter 1: Introduction and Basic Concepts
Diffusion Thermally activated process
5 Atom and Ion Movements in Materials
Dislocation Interactions
Imperfections in the Atomic and Ionic Arrangements
Chapter 5: Diffusion ISSUES TO ADDRESS... • How does diffusion occur?
Dislocations and Strengthening
Chapter 6 Diffusion.
EME 201 Materials Science INTRODUCTION.
Chapter 5 Metals.
Ionic vs Molecular
Diffusion how atoms move in solids
Point Defects in Crystalline Solids
"War is a matter of vital importance to the State;
Atom and Ion Movements in Materials
Chapter 5: Diffusion in Solids
11/22/ /22/2018 HOT MATERIALS © 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or.
Effects of Elevated Temperatures on Structural Steel
MIT Microstructural Evolution in Materials 6: Substitutional Diffusion
SOLID STATE CHMISTRY By: Dr. Aamarpali
Rate Process and Diffusion
Mechanical Properties of Metals
Atomic Structure and Interatomic Bonding
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon.
CHAPTER 5: DIFFUSION IN SOLIDS
TOPIC 2: Diffusion in Solids
Rate Process and Diffusion
PDT 153 Materials Structure And Properties
ELECTRICAL PROPERTIES
Diffusion Chapter 5 9/4/2019 9:52 AM9/4/2019 9:52 AM
Diffusion.
Presentation transcript:

EME 201 Materials Science Diffusion

Stability of Atoms and Ions Atoms or ions in their actual positions in the crystal structures are not at rest. Instead, atoms or ions will have thermal energies and will move. For example, an atom can move from its actual crystal structure to fill a space close to it. An atom can pass from one interstitial site to another at the same time. Atoms or ions can cross a grain boundary. The ability of atoms and ions to move rises as the temperature or thermal energy that atoms and ions possess increases. The diffusion process can be exlained with the help of the diffusion couple, that is created by joining pieces of two different metals together.

Mechanisms for Diffusion This pair is heated for a long time at a high temperature and then cooled to room temperature. Chemical analysis brings to light that pure copper and nickel are separated by an alloyed region. The concentration of both metals varies depending on the position of both materials. This result indicates that the copper atoms migrate into nickel and the nickel atoms are dispersed into the copper. The process at which atoms of a metal diffuse into another metal is called interdiffusion. The high-low concentration regions have a net transport of atoms. In void or vacancy containing materials, atoms move or skip from one lattice position to another.

Mechanisms for Diffusion Figure 1. Nickel and copper diffusion pair before and after heat treatment

Mechanisms for Diffusion There is a net atom motion from high concentration to low concentration regions within the alloy structure. There are two basic mechanisms by which atoms or ions can move or diffuse. Figure 2. Diffusion process of vacancy and interstitial atom

Mechanisms for Diffusion Vacancy type of diffusion mechanism: In diffusion involving self-propagation and substitution atoms, an atom is separated from the lattice space to fill a near void (thus creating a new void or vacancy in the original lattice position). When the diffusion process continues, there is a countercurrent flow of atoms and vacancy, called vacancy type of diffusion. As the temperature increases, the number of vacancy increases also. When a small foreign or interstitial atom or ion is present in the crystal structure, the atom or ion passes from one interstitial region to another. There is no need for vacancy type of diffusion mechanism.

Mechanisms for Diffusion Vacancy type of diffusion mechanism: In part, interstitial diffusion is much easier than vacancy type of diffusion because there are far more interstitial sites than voids or vacancy sites. In addition, relatively small interstitial atoms can be propagated more rapidly. For many ceramic type of material possessing ionic bonds, the structure can be regarded as close packing of anions with cations in interstitial sites. In this type of materials, smaller cations move faster than larger anions. The rate at which atoms or ions move or diffuse within a material can be measured by the flux (J ).

Rate of Diffusion (Fick’s First Law) The diffusion flux can be defined as the number of atoms or ions passing through a plane of unit area per unit time. Fick’s first law is used to explain the net flux of atoms or ions: J = -D(dc/dx) Where -J = the flux -D = the diffusivity or diffusion coefficient (cm2/s) -dc/dx = the concentration gradient (atoms/cm3.cm) Several factors will determine the flux of atoms during the diffusion process.

Rate of Diffusion (Fick’s First Law) Concentration Gradient : The concentration gradient (dc/dx) illustrates how the composition of the substance changes with the diffusion distance The concentration gradient (dc/dx) can be established when two materials of different composition are in contact or when unstable structures are produced in a material being treated. The flux (J) at a certain temperature is fixed only if the concentration gradient is constant. However, in many practical situations, these compositions change as the atoms redistribute, and so the flux changes. In general, we find that the flux is initially high and gradually decreases when the concentration gradient is reduced by diffusion.

REFERENCES William D. Callister, ‘Materials Science and Engineering: An Introduction’, Seventh edition, John Wiley & Sons, Inc., U.S.A. Brian S. Mitchell, ‘AN INTRODUCTION TO MATERIALS ENGINEERING AND SCIENCE FOR CHEMICAL AND MATERIALS ENGINEERS’, John Wiley & Sons, Inc., U.S.A, 2004. J. W. Martin, ‘Materials for Engineering’, Third Edition, WOODHEAD PUBLISHING LIMITED, Cambridge, England. Donald R. Askeland & Pradeep P. Fulay, ‘Essentials of Materials Science and Engineering’, Second Edition, Cengage Learning, Toronto, Canada. G. S. Brady, H. R. Clauser, J. A. Vaccari, ‘Materials Handbook’, Fifteenth Edition, McGraw-Hill Handbooks.