Instructor: Yuntian Zhu · 2020. 4. 13. · Department of Materials Science and Engineering 1 NC...
Transcript of Instructor: Yuntian Zhu · 2020. 4. 13. · Department of Materials Science and Engineering 1 NC...
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NC State UniversityDepartment of Materials Science and Engineering 1
MSE 360: Phase Transformation and Diffusion
Instructor: Yuntian ZhuOffice: 308 RBIIPh: 513-0559
Lecture 19
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Martensitic formation
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http://.blogspot.com//martensite-formation_08.hmetallu2010/04rgyfordummiestml
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Diffusionless Transformation (Martensitic transformation)
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High c% Medium c% Low c%Plate Martensite Lathe martensiteTwin Dislocation
Morphology of Martensites
p.384
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Plate (Lenticular) Martensite
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Lathe Martensite
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Characteristics of martensite
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• Surface tilting• Surface continuous• Coherent with the matrix• Grow very fast (near the
speed of sound)• Military transformation• Accompanied by a volume
expansion• Supersaturated solution• Metastable
Habit plane is the interface plane of the α’/γHabit plane is not distorted
p.385
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Thermodynamics and kinetics of martensitic transforamtion
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ΔGγ→ #α = ΔH γ→ #α T0 −MS
T0
p.386
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Effect of alloy elements
• Increased hardenability• Mechanisms
• Austenite stabilizer– Ni, Mn, Cu
• Ferrite stabilizer– Cr, Mo, Si
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Home Work
• Reading assignment (to be quizzed at the next lecture): Ch. 6.2, 6.3
• HW: none
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