EFFECT OF STRAIN AND TEMPERATURE IN A SUPERPLASTIC NI-MODIFIED TI-6AL-4V ALLOY

Ni modified Ti-6A1-4V alloy has been investigated under uniaxial test conditions at different temperatures 1023 ∽ 1103 K and at strain rates in the range of 5 × 10-5 to 5 × 10-3 s-1. The maximum elongation (about 422%) was found to occur at 1088 K and a strain rate of 2.0 × 10-4 s-1. There was evidence of strain hardening or strain softening. Strain hardening occurred at comparatively elevated temperatures and lower strain rates, whereas, the opposite was true for strain softening. There was apparently a dynamic balance between the strain hardening and softening phenomena, when the specimens were deformed at intermediate strain rate (2.0 × 10-4 s-1) and in the temperature range of 1023 to 1088 K. The strain rate sensitivity values at different temperatures and strain rates were also evaluated. It was found that the temperature for maximum ductility did not coincide with that was obtained for optimum strain rate sensitivity. © 1990, The Japan Institute of Metals. All rights reserved.