ME 370/570 Materials Science and Engineering-I Chapter...
Transcript of ME 370/570 Materials Science and Engineering-I Chapter...
1Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
ME 370/570Materials Science and Engineering-I
Chapter VII
• Instructor: Dr. R. Srinivasan• Mechanical and Materials
Engineering Dept.
2Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Plastic Deformation• Plastic deformation in metals has been
observed to occur on specific crystallographic planes and along specific crystallographic directions
• These planes and directions are typically close-packed planes and close-packed directions– Planes with a high density of atoms– Directions along which atoms touch each other
3Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
From “Principles of Materials Science and Engineering,” 3rd Edition, by W.F. Smith McGraw-Hill, 1996
4Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
From “Principles of Materials Science and Engineering,” 3rd Edition, by W.F. Smith McGraw-Hill, 1996
5Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
• Deformation by slip occurs at a stress level much lower than is predicted by theoretical analysis of bonds breaking and reforming after planes slide over each other.
• Dislocations help explain why.• The entire plane does not slide, only parts of
the planes near dislocations do.– Inch-worm analogy– Ripple in a rug analogy
6Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
7Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
8Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Movie “Dislocations” showing “Ripple in a Rug” analogy
9Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
10Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
11Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
12Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
For Ti, Mg, Zr, (c/a) < ideal (1.633). Therefore, there are additional planes with a high density of atomsPrism plane: and Pyramidal plane: { }0110 { }1110
13Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
When you have a large number of slip systems, the one with the highest resolved shear stress is the one on which plastic deformation (movement of dislocations) occurs.
Resolved shear force =
Area of plane =
Resolved shear stress =
Schmid Factor
λcosF
φcosA
λφτ coscosAF
R =
λφ coscos=m
14Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
In polycrystalline metals, each grain is oriented differently, and the active slip sytem(s) may be different. When loaded, each grain deforms its own way.However, for the solid to remain as one piece, each grain must also be able to accommodate the deformation of its neighbors at the grain boundary.This requires multiple slip systems to be available at the grain boundary. Theoretically, at least 5.FCC and BCC crystals have more than 5, but HCP crystals do not.Polycrystalline HCP may be brittle.
15Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Equiaxed Elongated
Rolling direction
16Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
17Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
• Slip– Orientation of crystal above and
below slip plane is the same– Displacement of atoms is multiples
of the burger’s vector– Large strain is possible
• Twinning– Crystal is reoriented– Mirror image about twin plane– Displacement increases as you go
away from the twin plane– Displacement of atoms may be
fractions of atomic spacing– Strain magnitude is small– Occurs when slip is not possible– Reorientation may activate other
slip systems
18Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Strengthening Mechanisms
• Grain boundary strengthening• Solid solution strengthening• Cold working
19Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
20Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
)2/1(0
−+= kdy σσ
21Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
• Pure metals are always weaker than alloys.• Solute atoms cause a distortion of the lattice.• Dislocations also cause distortion of the lattice.• Solute atoms and dislocations try to position
themselves to minimize distortion• Free movement of dislocations becomes difficult
22Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
23Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Increased dislocation density results in:•Increased strength•Decreased ductility
( ) 100%0
0 ×−
=AAACW d
Cold Working
Deformation at low temperatures results in Work hardening or Strain hardening
24Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
25Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
Annealing of a cold worked metal
Recovery, Recrytallization and Grain Growth
26Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
27Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
28Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
29Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
30Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
31Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University
32Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley
This material is for educational used only within Wright State University