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

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.