Question

1. What are point defects? Please explain the relationship between point defects and materials strength and ductility. (10 pts) 2. What are dislocations? Please explain the relationship between dislocation and materials strength and ductility (10 pts) 3. What are grain and grain boundary? Please explain the relationship between grain size/grain boundary and materials strength and ductility. (10 pts) 4. What is the solid solution and what factors affect solubility? (5 pts) 5. What is the stacking fault? (5 pts) 6. What is a unit dislocation? What is a partial dislocation? What is an extended dislocation? (10 pts) 7. The actual strength of a metallic material is tens of times smaller than its theoretical strength because of dislocation. However, the strength of the same material can be significantly increased through dislocation strengthening. Why does dislocation appear to behave in an opposite way? (10 pts) 8. Please use the characteristics of chemical bonding, crystal structures and dislocations to explain why metallic materials are strong and ductile and why ionic and covalent materials are strong but brittle? (20 pts)

Answer 1

1. Point defects : occurs when an atom is missing or is in different place than normal lattice structure. It can be : vacancies, interstitial defect or substitutional defects.

Point defects hinders the dislocation motion so, materials strength increases. It promotes ductile behavior of materials.