1. Instructor: Yuntian Zhu
MSE 791: Mechanical Properties of Nanostructured Materials Module 3: Fundamental Physics and Materials Design
Instructor: Yuntian Zhu
Office: 308 RBII
Ph:
Lecture 2
Twin morphologies in fcc metals: growth twins and deformation twins
Text book,
Office hour, by appointment
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2. Twin formation by stacking mistakes during growth
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3. Twin formation by the slip of partial dislocations (deformation twins)
HW: How about –b1, -b2, - b3
One partial is needed on each slip plane to produce a twin
Twin is generated by any or a mixture of b1, b2 and b3
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4. What does an fcc twin look like at atomic scale?
A twin can be observed along 3 <110> directions on the coherent twin boundary. They should look crystal graphically identical
HW: show that the angle between two close packed planes are 70.53°
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5. What does an fcc growth twin NORMALLY look like at low magnification?
Straight, clean twin coherent boundaries
Straight incoherent boundaries
No macoscopic strain in the grains
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6. What does an fcc deformation twin look like at low magnification (examples)?
Coherent twin boundaries may still look straight, not not always
Image looks less clean (often messy)
Macroscopic strain is usually produced, but may not be easily seen at low magnification
Newczas
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7. Homework (due in 1 week) Lecture 2: 1,
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