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 1
Introduction, fcc, bcc and hcp crystal structures, partial and full dislocations in fcc metals
Text book,
Office hour, by appointment
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2. Policies and Procedures see the Syllabus for more details
Attendance
Attendance expected (0.2% penalty for missing a quiz)
All HW are due in 1 week. 75% of the credit for late HW
Reading (textbook) Material: “Deformation Twinning in Nanocrystalline Materials,”Prog. Mater. Sci . 57, 1-62 (2012).
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3. Grading Homework 9% Test 1 30% Test 2 30% Final 30% No grade markup
Ask students to think about it, and ask questions
No grade markup
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4. Teaching style Active student participation in class
A dice will be rolled to determine who participates
0.2% will be deducted if you are not present in the class to answer a quiz;
0.2% will be given if you give the right answer
0.2% will be given to a volunteer who gives the right answer
No credit will be given or deducted if you give a wrong answer.
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5. Strength and ductility of materials
A material can be strong or ductile, but rarely both at the same time
Good ductility is desired to prevent catastrophic failure
Nano-Ti
Nano-Cu
Youssef, Scattergood, Murty, Horton, Koch, APL,
87, (2005)
Valiev, Alexander, Zhu & Lowe, J. Mater. Res., 17 (2002) 5. Our work

6. Only a few nanostructured materials show good ductility
The yielding strength is normalized by the yield strength of a material’s coarse-grained counterpart
Nanostructured materials have much higher strength than their coarse-grained counterparts
Koch, Scripta Mater. 49 (2003) 657
Zhu & Liao, Nature Mat., 3 (2004) 351.
Issue: How do we obtain high ductility in nanostructured materials?

7. fcc, bcc and hcp structures
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8. Dislocations
Screw Dislocation
Cartepilar
Dislocation cartoon
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9. Burgers Vector
Decide on the sense (vector) of dislocation line (arbitrary)
Use “right-hand screw” to draw the Burgers circuit around the dislocation line
Draw a Burgers circuit with equal length on each side; b = vector from the starting point to ending point (see (a))
Or: Draw a closed Burgers circuit and then the circuit in a perfect crystal, b = vector from the ending point to starting point in the perfect crystal circuit (see (b))
Quiz: What is the sense of the dislocation in (a) and (b)?
(a) (b)
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10. The Burgers Vectors are conserved
Each dislocation line can only have 1 Burger vector
At a dislocation node where several dislocations meet, the sum of Burgers vectors of dislocations going to the node equals the sum of Burgers vectors of dislocations going out from the node
A dislocation line cannot end inside a perfect crystal
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11. Dislocations in fcc metals
Define slip planes, full dislocations, and partial dislocations
Definition of the Thompson tetrahedron
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12. Thompson Tetrahedron
Determine the Burgers vector of AB, BC and CD and partial dislocations on ABC plane
Define stair-rod dislocation
Show some dislocation reactions using the Thompson tetrahedron.
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13. Homework (due in 1 week) Lecture 1: #10 & 13
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