Fine-grained two phase alloys (in-situ composite) consisting of A15-type Nb3Al and bcc Nb solid solution (Nbss) were synthesized via powder processing and their tensile deformation behavior was investigated in vacuum at high temperatures at 1473 and 1573 K at various strain rates from 1.6×10-3 to 3.1×10-5s-1. Nb3Al/Nbss in-situ composites with an average grain size of about 1 μm for both phases were prepared by mechanical alloying (MA) elemental Nb and Al powders in an Ar atmosphere and consolidating the mechanically alloyed powders with cold isostatic press (CIP) and hot isostatic press (HIP) followed by heat treatment. X-ray diffraction analysis indicated the existence of a small amount of Nb2C, which would be formed by a reaction of powders with methanol, in addition to Nb3Al and Nbss. A stress peak in the stress-strain curve becomes more pronounced at an initial stage of deformation with decreasing temperature and increasing strain rate. Steady state deformation is observed at higher temperatures and lower strain rates. Flow stress of the fine-grained samples in this study is always much lower than that of large-grained samples reported elsewhere if it is compared at the same strain rate and deformation temperature. By plotting logarithmic peak stress against logarithmic strain rate, strain rate sensitivity m is evaluated to be 0.49 at 1473 and 1573K. The samples exhibit small elongation of less than 35%. Scanning electron microscopy on fractured sufaces revealed that cavities tend to form at interfaces between matrix and fine Nb2C particles with sizes of less than 1 μm. A specimen prepared by consolidating MA powder without a process control agent, which contains no Nb2C particle, exhibits about 60% elongation at 1573K and 1.6×10-4 s-1.
|ジャーナル||Materials Science Forum|
|出版ステータス||Published - 1997 1月 1|
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