Properties and Selection of Engineering Materials

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Smithells Metals Reference Book, Butterworth and
Heinemann, 1992
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Adhesion between metals 1 lowest 4 highest
Smithells Metals Reference Book, Butterworth and
Heinemann, 1992
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Surface hardening methods

• Surface work-hardening
• Surface heat-treatment
• Surface chemical modification
• Coating

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SAE specification of sheet metal
31.1 Texture in materials
r is to do with texture
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• Texture
• Non-isotropic (anisotropic) microstructure, with
  preferred orientation
• Result of texture
• Anisotropic properties

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Texture of cold-drawn PET sheet
I.M. Ward, Mechanical Properties of Solid Polymers
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Cold worked sheet metal with texture.
Sheet texture ? different plastic properties
along l, w, t.
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• Plastic necking strain ratio r ?w/?t
• Greater r, greater resistance to thinning in
  metal forming.

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Example Sheet steel specification by GM.
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31.2 The grain structure of crystals
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Simulated atomic structure of grains
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Grain and grain boundary in Champaign, IL.
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• Grain Each grain is a single crystal.
• Grain boundary where the grains meet.
• Grain size the average diameter of the grains.
• Grain size ranges from 0.01?m to 104 mm.

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• Non-textured the grains are randomly orientated.
• Texture preferred orientation of the grains.
• Grain size and texture have important effects on
  properties.

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31.3 Effect of grain-size on properties

• Decreasing grain-size
• Advantage greater yield strength, ductility,
  resistance to fracture, resistance to quench
  cracking
• Disadvantage poorer creep resistance, greater
  electrical resistance, poorer optical properties

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Fracture along grain boundary
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31.4 Formation of Grains in Solidification.
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31.5 Grain growth
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• Grain-size increases with time at high
  temperatures, such as during processing or
  service
• Atoms in smaller grains are under a larger
  pressure than those in large grains.
• Atoms will migrate from small grain to large
  grains, leading to growth of large grains and
  elimination of small grains
• Grain growth is to be avoided in most cases.

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Refinement of grain-size in an Al alloy by boride
without boride with boride