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h

SUMM RY

3.40 Oct 5t LECTURE

10/07/09/ 7/ 9

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•

 DISLOCATION INTERACTIONS

plastically deform materials

•▫ 

Forests of Dislocations 

x Hall - Petch Relationship

▫ Precipitates

▫ Schematic of a Dislocation

Pile up at a Grain Boundary

Mechanical Metallurgy, Dieter G., 3rd Edition http://en.wikipedia.org/wiki/File:Dislocation_pileup.png 

Courtesy of Markus Buehler. Used with permission.

 ┴  ┴

 ┴ ┴

d

2nd source

http://en.wikipedia.org/wiki/File:Dislocation_pileup.pnghttp://en.wikipedia.org/wiki/File:Dislocation_pileup.png

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•

OROWAN LOOPING 

OROWAN LOOPING 

obstacles:

• Dislocation density hasunits of 1/Area

• Ageing Treatment

▫ 

Precipitation Hardening▫  eg. Al – Cu alloys

▫   verage ng

Microstructure of an aged Al – 4 % Cualloy showing CuAl2 precipitates

Fig. 1204.03.18 in Jacobs, M. H. "1204 Precipitation Hardening."

 Introduction to Aluminium Metallurgy. TALAT, 1999.

http://aluminium.matter.org.uk/

http://www.eaa.net/eaa/education/talat/lectures/1204.pdfhttp://aluminium.matter.org.uk/http://aluminium.matter.org.uk/http://www.eaa.net/eaa/education/talat/lectures/1204.pdf

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 • Orowan’s Equation:

1010 1011 1012 1013 1014 10150.1

1

10

100

1000

Dislocation density, ρ (m-2)

   R  e  s  o   l  v  e   d  s   h  e  a  r  s   t

  r  e  s  s .

   M   P  a

Schematic of a Stress Strain Cur ve

Heavily Cold Worked Steel

Microstructure

http://en.wikipedia.org/wiki/File:Work_HArd.png

Microstructures, George Langford, MIT

Courtesy of George Langford. Used with permission.Figure by MIT OpenCourseWare.

http://en.wikipedia.org/wiki/File:Work_HArd.pnghttp://en.wikipedia.org/wiki/File:Work_HArd.png

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•

WORK HARDENING 

WORK HARDENING 

• Holloman Power LawHardening

• –Exponent

• –Coefficient Values of n and K for certain selected

me a s

Handbook of Workability and Process design, Dieter GE

Table removed due to copyright restrictions.

Please see Table 9 in "Design for Deformation Processes."

Ch. 11 in Dieter, George Ellwood, Howard A. Kuhn, and

S. L. Semiatin. Handbook of Workability and Process Design.

Materials Park, OH: ASM International, 2003.

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• Sta es in a sin le cr stal 

▫ 

Stage I : Single Slip▫  Stage II : Work Hardening Stage

▫  Stage III : Saturation of Work Hardening

http://www.doitpoms.ac.uk/tlplib/slip/slip_in_ccp.php  Courtesy of DoITPoMS, University of Cambridge. Used with permission.

http://www.doitpoms.ac.uk/tlplib/slip/slip_in_ccp.phphttp://www.doitpoms.ac.uk/tlplib/slip/slip_in_ccp.php

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•

▫ 

Elastic Anisotropyx Local stress state is

complicated 

▫ 

 Accommodation of Plasticity

satisfied 

x Nucleates “Geometrically

Necessary Dislocations” toremove the incompatibility Removal of Shape

Incompatibilities duringx  deformation

 

Mechanical Metallurgy, Dieter G., 3rd Edition

deformation

Image removed due to copyright restrictions.Please see Fig. 4.23c in Courtney, Thomas.

 Mechanical Behavior of Materials. Long Grove,

IL: Waveland Press, 2005.

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QUESTIONS ? 

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