MCG 2360 Lecture Notes - Lecture 9: Solid Solution, Nitriding, Interstitial Defect

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Diffusion is atom movement/migration in materials (solids, liquids, gases). It"s important in: heat treatment (phase transformation from solid to solid) solidification (liquid to solid) surface hardening of steel (carburising, nitriding, carbo-nitriding) corrosion and oxidation coatings (galvanising, electroplating, anodising) Impurity diffusion (inter-diffusion) in solid material with more than 1 type of element (alloy) Self-diffusion random movement of atoms in chemically pure materials. Point defects (vacancy) must be present in a crystal for diffusion to occur atomic diffusion is in a way the migration of these defects vacancy diffusion (substitutional diffusion) Rate of vacancy diffusion depends on: concentration of vacancies (@ of vacancies increases as temperature increases) activation energy for atom migration eg. nickel in copper alloy interstitial diffusion. Migration of an interstitial atom to an adjacent vacant interstitial site occurs in interstitial solid solutions. Rate of interstitial diffusion depends on: concentration of interstitial atoms eg. carbon in iron (steel)

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