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# Review! - Review Session(Exam#2 MATSE 259 Review...

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Review Session (Exam #2) MATSE 259 Review Session (Exam #2) Slide 1

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Exam #2 Wednesday, October 13 6:30 PM to 7:45 PM 158 Willard (Last Names A through H) 160 Willard (Last Names I through Q 160 Willard (Last Names I through Q) 162 Willard (Last Names R through Z) MATSE 259 Review Session (Exam #2) Slide 2
Topics Covered by Exam Diffusion Strengthening Mechanisms Failure Mechanisms-Fracture Failure Mechanisms-Fatigue Failure Mechanisms-Creep Failure Mechanisms Creep Readings Callister, Materials Science and Engineering: An Introduction MATSE 259 Review Session (Exam #2) Slide 3 Chapter 5 Chapter 7 Chapter 8

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Diffusion MATSE 259 Review Session (Exam #2) Slide 4
Important Terminology Interdiffusion Vacancy Diffusion Self-Diffusion Interstitial Diffusion Steady-State Diffusion (Fick’s First Law) Non-Steady State Diffusion (Fick’s Second Law) Carburization MATSE 259 Review Session (Exam #2) Slide 5

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In steady state diffusion, diffusion flux does not change with time. Steady State Diffusion Gaseous Diffusion through a Metal Plate MATSE 259 Review Session (Exam #2) Slide 6 B A B A x x C C = Δ Δ = x C gradient ion Concentrat
Fick’s First Law dC D J = D = Diffusion coefficient (m 2 /sec) dx dC Negative sign indicates that the direction of diffusion is down the concentration gradient from a high to a low concentration. dx = concentration gradient MATSE 259 Review Session (Exam #2) Slide 7 For steady state diffusion, the concentration gradient is the driving force.

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Non-Steady State Diffusion Diffusion flux and the concentration gradient at a point in a solid vary with time, with a net accumulation or depletion of diffusing species resulting. Example: Ni coating Cu x MATSE 259 Review Session (Exam #2) Slide 8
C C Fick’s Second Law Under non-steady state conditions, Fick’s first law is not applicable: = x D x t 2 C D C (Fick’s second law) 2 x t = Solutions to this expression (both position and time) are possible only when physically meaningful boundary conditions are specified MATSE 259 Review Session (Exam #2) Slide 9 only when physically meaningful boundary conditions are specified.

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Solution for a Semi-Infinite Solid with a Constant Surface Concentration Source of diffusing species is a gas phase and the partial pressure is held constant. 1. For t = 0, C = C 0 at 0 x 2. For t > 0, C = C s at x = 0 (constant surface concentration) 3. C = C 0 at x = Boundary Conditions : = Dt x erf C C C C s x 2 1 0 0 MATSE 259 Review Session (Exam #2) Slide 10
Effect of Changes in Temperature on the Diffusion Coefficient Diffusion Coefficient for Mg in Al at 550ºC : D (T) = D o e -Q/RT ( ) + × = K 273 550 K - J/mo 314 8 J/mol 131000 exp / m 10 2 . 1 2 4 s D MATSE 259 Review Session (Exam #2) Slide 11 ( )( ) J/mol .

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## This note was uploaded on 11/10/2010 for the course MATSE 259 taught by Professor Muhlstein,christo during the Spring '07 term at Penn State.

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Review! - Review Session(Exam#2 MATSE 259 Review...

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