Effect of Strain Rate on the High-Temperature Deformation Behavior of Nb₃Al Hipped from Prealloyed Powder

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The effect of strain rate on stress-strain curves and deformation microstructures of Nb₃Al at high temperatures was examined. Specimens prepared by hot isostatically pressing (HIP) Nb–Al alloy powder under 200 mesh size contain Nb₃Al over 90% in volume. The concentration of aluminum in Nb₃Al, measured by an electron probe micro analyzer (EPMA), is determined to be 23.4 mol%. Compression tests were carried out above 1273 K at four initial strain rates, 1.68×10⁻² s⁻¹, 1.67×10⁻³ s⁻¹, 1.67×10⁻⁴ s⁻¹ and 3.34×10⁻⁵ s⁻¹. Yield stress increases with increasing the initial strain rate and with decreasing compression temperature. In this experiment, stress-strain curves except for samples compressed at the initial strain rate of 3.34×10⁻⁵ s⁻¹ at 1673 K and 1773 K, and 1.67×10⁻⁴ s⁻¹ at 1773 K show a distinct peak stress followed by deformation softening. This peak stress is regarded to be caused by dynamic recrystallization, because the samples compressed at 1473 K show the typical necklace structure. Nb₃Al can deform plastically to a large strain by dynamic recrystallization accompanied by grain boundary sliding. The dynamically recrystallized grain size increases and the peak stress on stress strain curves becomes indistinct with decreasing the initial strain rate and with increasing compression temperature.