Chapter 5 Diffusion University of Tennessee（第五章扩散田纳西大学）.pdf

Introduction To Materials Science FOR ENGINEERS, Ch. 5 Diffusion MSE 201 Callister Chapter 5 1 University of Tennessee, Dept. of Materials Science and Engineering Introduction To Materials Science FOR ENGINEERS, Ch. 5 Goals: Diffusion - how do atoms move through solids? • Fundamental concepts and language • Diffusion mechanisms – Vacancy diffusion – Interstitial diffusion – Impurities • Diffusion equations – Fick’s first law – Fick’s second law • Factors that influence diffusion – Diffusing species – Host solid – Temperature – Microstructure 2 University of Tennessee, Dept. of Materials Science and Engineering Introduction To Materials Science FOR ENGINEERS, Ch. 5 What is diffusion? Diffusion is material transport by atomic motion. Inhomogeneous materials can become homogeneous by diffusion. For an active diffusion to occur, the temperature should be high enough to overcome energy barriers to atomic motion. 3 University of Tennessee, Dept. of Materials Science and Engineering Introduction To Materials Science FOR ENGINEERS, Ch. 5 Atomic Vibrations • Heat causes atoms to vibrate • Vibration amplitude increases with temperature • Melting occurs when vibrations are sufficient to rupture bonds • Vibrational frequency ~ 1013 Hz • Average atomic / electronic energy due to thermal excitation is of order kT [with a distributio