材料加工原理2012-05-21_PMP-PT_Answer First.pptxVIP

Principles of Materials ProcessingPart III-金属材料热处理原理Heat Treatment Principles of MetalsANSWER FIRST – QUIZ/Game Lecturer: Ke Chen 2012-05-20 What are the energy terms associated to the resistance to the martensitic transformation? Resistance: Aγ (or, 界面能Sσ) and V△Gs (or, 应变能Vε) , plus: Energy increase for overcoming shear resistance to transform crystal structure Energy increase due to the defects (dislocations or twins) in martensite Energy increase due to plastic deformation in surrounding austenite 2 Describe all the carbon diffusions associated in the pearlite growth based on the following figure. 3 What is the effect of carbon content on the austenitization rate? Higher  more interphase interfaces  higher nucleation rate Higher  shorter diffusion distance Higher  higher diffusion coefficients of Fe and C BUT, increased amount of remaining cementite requires longer heat treatment time to reach homogeneity 4 What are the heterogeneous nucleation sites? Homogeneous sites Vacancies Dislocations Stacking faults Grain boundaries and interphase boundaries Free surfaces 5 The key characteristics of martensitic transformation? Shear and diffusionless 6 What is the effect of tensile stress on the Ms? And why? 7 8 Why there are two plateaus? Segregation of C to dislocations  Cottrell atmosphere Normal quenching  Cottrell atmosphere formed to strengthen austenite Cooling very fast  Formation of Cottrell atmosphere inhibited  lower the strength of austenite  Ms increased Explain how fcc transformed into bct in martensitic transformation. 9 Explain why dislocation can assist nucleation. 10 11 Describe the microstructural hierarchy of lath martensite. 12 List all the types of martensite, in the order of their corresponding transformation temperature. 13 The formation process for austenitization 14 Austenite nucleation Nuclei growth Dissolution of remaining Fe3C Homogenization of austenite What is the most favorite site for austenite nucleation and why? Most f