Newtonian Viscous Flow and Superplasticity in Fine Grained Metallic Alloys

Abstract

Superplasticity in crystalline solids is an area of expanding scientific and technical interest Superplastic materials are characterized by a high value of the strain-rate-sensitivity exponent, m. kinds of superplasticity have been identified: fine structure superplasticity (FSS) and internal stress superplasticity (ISS). In the case of FSS materials, a strain-rate-sensitivity exponent equal to about 0.5 is usually found and these materials deform principally by a grain-boundary-sliding (g.b.s.) mechanisms accommodated by slip, involving dislocation climb. It is shown, however, that FSS materials can be appropriately alloyed to achieve a value of m equal to one, i.e. ideal Newtonian-viscous flow. This occurs in fine grained Class I solid solution alloys where the deformation process is g.b.s. accommodated solute-drag- controlled slip. The reason why Newtonian-viscous flow is achieved is because no pile stress is generated as in g.b.s. accommodated by dislocation climb.

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Document Details

Document Type
Technical Report
Publication Date
Jan 31, 1993
Accession Number
ADA276325

Entities

People

  • Eric Taleff
  • Oleg D. Sherby
  • Shih-chung Cheng

Organizations

  • Stanford University

Tags

Communities of Interest

  • Advanced Electronics
  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Aluminum Alloys
  • Carbon Steels
  • Ceramic Matrix Composites
  • Chemistry
  • Composite Materials
  • Creep
  • Engineering
  • Iron
  • Materials
  • Materials Processing
  • Materials Science
  • Mechanical Properties
  • Metal Matrix Composites
  • Metallurgy
  • Powders
  • Silicon Carbide
  • Solid Solutions

Readers

  • Fluid Dynamics.
  • Powder metallurgy of Titanium alloys.