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 H, (W-0.5TiC-H-2) or Ar (W-0.5TiC-Ar) and hot isostatic pressing. The W-0.5TiC-H-2 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 (0.45-0.54T(m), T-m: melting point of W) at initial strain rates from 5 x 10(-5) to 5 x 10(-3) s(-1). It is found that W-0.5TiC-H-2 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-H-2 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. (c) 2007 Elsevier B.V. All rights reserved.