Microstructure and elevated temperature properties of a refractory TaNbHfZrTi alloy

Abstract

Compression properties of a refractory multi-component alloy, Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀, were determined in the temperature range of 296–1473 K and strain rate range of 10⁻¹–10⁻⁵ s⁻¹. The properties were correlated with the microstructure developed during compression testing. The alloy was produced by vacuum arc melting, and it was hot isostatically pressed (HIPd) and homogenized at 1473 K for 24 h prior to testing. It had a single-phase body-centered cubic structure with the lattice parameter a = 340.4 pm. The grain size was in the range of 100–200 μm. During compression at a strain rate of έ = 10⁻³ s⁻¹, the alloy had the yield strength of 929 MPa at 296 K, 790 MPa at 673 K, 675 MPa at 873 K, 535 MPa at 1073 K, 295 MPa at 1273 K and 92 MPa at 1473 K. Continuous strain hardening and good ductility (ε ≥ 50%) were observed in the temperature range from 296 to 873 K. Deformation at T = 1073 K and έ ≥ 10⁻³ s⁻¹ was accompanied by intergranular cracking and cavitation, which was explained by insufficient dislocation and diffusion mobility to accommodate grain boundary sliding activated at this temperature. The intergranular cracking and cavitation disappeared with an increase in the deformation temperature to 1273 and 1473 K or a decrease in the strain rate to ~10⁻⁵ s⁻¹. At these high temperatures and/or low-strain rates the alloy deformed homogeneously and showed steady-state flow at a nearly constant flow stress. Partial dynamic recrystallization, leading to formation of fine equiaxed grains near grain boundaries, was observed in the specimens deformed at 1073 and 1273 K and completed dynamic recrystallization was observed at 1473 K.