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Kinetics and Mechanisms of Creep in Hot Isostatically Pressed Niobium Carbide

Published online by Cambridge University Press:  28 February 2011

Robert D. Nixon
Affiliation:
North Carolina State University, Materials Engineering, Box 7901, Raleigh, NC 27695-7901; Metals and Ceramics Division, Oak Ridge National Laboratories, Oak Ridge, TN 37830.
Robert F Davis
Affiliation:
North Carolina State University, Materials Engineering, Box 7901, Raleigh, NC 27695-7901; Metals and Ceramics Division, Oak Ridge National Laboratories, Oak Ridge, TN 37830.
James Bentley
Affiliation:
North Carolina State University, Materials Engineering, Box 7901, Raleigh, NC 27695-7901; Metals and Ceramics Division, Oak Ridge National Laboratories, Oak Ridge, TN 37830.
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Abstract

Constant compressive stress creep experiments in the temperature and stress ranges of 1730K - 2100K and 16 MN/m2 - 70 MN/m2 on HIPed NbC0.74 have revealed stress exponents of 2.0 under stress levels of 16–54 MN/m2 at all temperatures investigated and 3.2 under stress levels of 54–70 MN/m2 at 1830K. The activation energy of steady state creep is approximately 230 kJ/mol in the temperature range of 1730K - 1930K under 48–54 MN/m and 470 kJ/mol in the temperature range of 1900K - 2100K under 64 MN/m2. TEM of the annealed but uncrept material reveals grown-in dislocation subboundaries. At 1730K and under 34–54 MN/m2, these subboundaries become single dislocations and dipoles. At 1830K and under 54–70 MN/m the subboundaries evolve into simple tilt boundaries which are occasionally knitted, indicating more glide activity at higher stresses. At 1930K and under 34–54 MN/m , hexagonal subboundaries form, but are not as well defined as in the annealed material. At 2100K and under 16–30 MN/m2, the subboundaries are well-defined hexagonal networks which become polygonized under higher stresses on 64 MN/m2. The experimental and TEM results indicate that at low temperatures (below 0.5 Tm = 2073K) and at all stresses, creep occurs by dislocation glide which is accompanied by subgrain and high angle boundary interaction. At high temperature (above 0.5 Tm), strain occurs by glide and subboundary movement; recovery occurs by climb in the subboundary.

Type
Research Article
Copyright
Copyright © Materials Research Society 1986

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