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The Strain Rate Sensitivity of Polycrystalline and Single Crystal NiAl

  • Tsang-Sheau Lee (a1), Wei-Pirn Hon (a1), Sy-Cherng Yang (a1), Shu-En Hsu (a1), Stephen Chin (a2) and Donald L. Anton (a2)...

Abstract

The compressive and tensile strain rate sensitivities of polycrystalline and single crystal NiAl have beem evaluated at 877°C which is well above the static DBTT. Samples were prepared to specific grain sizes by hot press consolidation of appropriate powder sizes and minimizing post-consolidation thermal exposures. NiAl single crystals were grown in the near [100] orientation using a modified Bridgeman technique. The use of high oxygen content powders to fabricate polycrystalline NiAl with very fine grain sizes resulted in increased strengths but did not debit ductility. The yield and tensile strength of polycrystalline NiAl as a function of grain size generally follows a Hall-Petch type relationship. A tensile strain rate effect was found at strain rates of 1 to 10−4 sec−1. The strain rate sensitivity exponent, m, in the equation σ = Cε m is in the range 0.10 to 0.13. The highest strain rate (1 sec−1) resulted in significantly higher strengths and little or no observed tensile ductility. Cleavage-type transgranular fractures were found on samples tested at the highest strain rate (1 sec−1) and ductile fractures were found on samples tested at the lower strain rates (10−1 and 10−4 sec−1). Compression testing at strain rates of 10−5 to 10−3 sec−1 also indicated an effect of strain rate on strength.

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The Strain Rate Sensitivity of Polycrystalline and Single Crystal NiAl

  • Tsang-Sheau Lee (a1), Wei-Pirn Hon (a1), Sy-Cherng Yang (a1), Shu-En Hsu (a1), Stephen Chin (a2) and Donald L. Anton (a2)...

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