Superplastic deformation in W–0.5 wt.% TiC with approximately 0.1 μm grain size

Abstract In order to reveal the occurrence of superplasticity in ultra-fine grained W–TiC, W–0.5 wt.% TiC consolidates were fabricated utilizing mechanical alloying (MA) in purified H2 (W–0.5TiC–H2) or Ar (W–0.5TiC–Ar) and hot isostatic pressing. The W–0.5TiC–H2 and W–0.5TiC–Ar feature equiaxed ultra-fine grains with average diameters of 150 and 70 nm, respectively, and W–0.5TiC–Ar contains a high density of nano-sized Ar bubbles. Tensile tests were conducted at 1673–1973 K (0.45–0.54Tm, Tm: melting point of W) at initial strain rates from 5 × 10−5 to 5 × 10−3 s−1. It is found that W–0.5TiC–H2 exhibits a large strain rate sensitivity of flow stress, m, of 0.5–0.6, which is a feature of superplastic materials, whereas W–0.5TiC–Ar exhibits a smaller m value of approximately 0.2. This suggests that the Ar bubbles cause an adverse effect on superplastic deformation. The activation energy for deformation is 300 kJ mol−1 for W–0.5TiC–H2 and 570 kJ mol−1 for W–0.5TiC–Ar, corresponding to those for grain boundary diffusion and lattice diffusion in W, respectively. Each deformation controlling mechanism is discussed.