Yonosuke Murayama and Shuji Hanada
Institute for Materials Research, Tohoku University, Sendai, Japan
The effect of concentration ratio of niobium to aluminium on stress-strain curves and deformation microstructures of Nb3Al at high temperatures was examined. Specimens prepared by hot isostatically pressing (HIP) Nb-Al alloy powders under 200 mesh size contain Nb3Al over 95% in volume. The samples with four compositions which were from the phase boundary between Nb3Al and Nb solid solution to that between Nb3Al and Nb2Al were prepared. Compression tests were carried out above 1273 K at 1.67{×}10-4 s-1.
Yield stress increases with increasing concentration of aluminium at 1473 K. This composition dependence becomes indistinct with increasing compression temperature. The width of dissociated a/2 <{100}>{001} dislocations in Nb3Al show a composition dependence. The dissociated width increases with increasing concentration of aluminium at 1473 K. Fine dynamically recrystallized grains constituting the so-called `necklace structure' and a large deformation softening in the stress-strain curve were observed in the sample with widely dissociated dislocations. However, the composition dependence becomes indistinct with increasing compression temperature, because the size of grains resulting from dynamical recrystallization is large and then an amount of deformation softening decreases suddenly.
(Received May 17, 1996)
Nb3Al, powder metallurgy, dissociated dislocation, dynamic recrystallization, composition dependence
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