Chapter 5 -
Chapter 5 -2
ISSUES TO ADDRESS...
• What types of defects arise in solids?
• Can the number and type of defects be varied
• How do defects affect material properties?
• Are defects undesirable?
IMPERFECTIONS IN SOLIDS
•Reading: pp128 –136, 140-147
Chapter 5 -3
•Solidification- result of casting of molten material
•Nuclei grow to form crystals –grain structure
•Start with a molten material –all liquid
Imperfections in Solids
•Crystals grow until they meet each other
Adapted from Fig. 5.19 (b), Callister & Rethwisch 3e.
Issues to address: what types of defects arise in solids, can the number and type of defects be varied and controlled, how do defects affect material properties, are defects undesirable, reading: pp128 136, 140-147. Imperfections in solids: solidification- result of casting of molten material. 2 steps: nuclei form, nuclei grow to form crystals grain structure, start with a molten material all liquid nuclei liquid crystals growing grain structure. 5. 19 (b), callister & rethwisch 3e: crystals grow until they meet each other. There is no such thing as a perfect crystal. Many of the important properties of materials are due to the presence of imperfections. Types of imperfections: vacancy atoms, interstitial atoms, substitutional atoms, dislocations, grain boundaries, cracks, pores. Vacant atomic sites in a structure. distortion of planes: self-interstitials: extra atoms positioned between atomic sites. distortion of planes. Equilibrium concentration: point defects: equilibrium concentration varies with temperature! Boltzmann"s constant (1. 38 x 10-23 j/atom-k) (8. 62 x 10-5 ev/atom-k)