材料科學(xué)基礎(chǔ)英文版課件_(12)(已修改)
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【正文】 Chapter 5 Imperfections in Solids Lecturer: Shenhua SONG Outline ? Point defects 1. Point defects in metals 2. Point defects in ceramics ? Linear defects Dislocations ? Plane defects External surfaces Grain boundaries Twin boundaries Stacking faults Phase boundaries ? Volume defects Pores, cracks, inclusions, and second phases Point Defects – Point Defects in Metals (1) 1. Vacancies and Interstitials (selfinterstitials) ? Thermal equilibrium vacancies and interstitials ? Quenchinginduced nonequilibrium vacancies and interstitials ? Irradiationinduced nonequilibrium vacancies and interrstitials ? Deformationinduced nonequilibrium vacancies Frenkel pair: vacancy + interstitial Schottky defect: moving an atom to the surface produces a vacancy Point Defects – Point Defects in Metals (2) Formation – leading to an increase of internal energy – free energy increase (?G = ?H T?S, H=U+PV, U? H ? G ?) Formation – leading to an increase of entropy (randomness) –free energy decrease At a given temperature, there must be a concentration of point defects at which the free energy of the system has a minimum value. Why there is a thermal equilibrium concentrat
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