Intermediate-temperature creep behaviors of an equiatomic VNbMoTaW refractory high-entropy alloy

Abstract

As one of refractory high-entropy alloys (RHEAs), VNbMoTaW is considered to be a promising candidate for elevated-temperature application. However, its creep behavior is rarely reported. In the present work, the compressive creep behaviors of an equiatomic VNbMoTaW RHEA with a grain size of 138 ± 36 μm were well studied over an intermediate temperature range (973–1173 K) and under high applied stress (130–520 MPa). The stress exponent of the alloy is found to remain stable (∼1) at relatively low temperatures (973–1073 K), whereas a stress-dependent transition behavior occurs at high temperatures (1123–1173 K), i.e., the stress exponent of the alloy changes from ∼1 in the low stress region (130–390 MPa) to ∼ 4 in the high stress region (390–520 MPa). Meanwhile, the creep activation energy increases from 139 to 156 kJ mol−1 at low temperatures to 307–373 kJ mol−1 at high temperatures. The low stress exponent and low activation energy at low temperatures suggest that the creep is controlled by dislocation pipe diffusion. The low stress exponent and relatively high activation energy in the high-temperature low-stress region suggest that the creep is controlled by lattice diffusion. In the high-temperature high-stress region, the prevalent dislocations detected by the post-mortem microstructural observation, the high stress exponent, and high activation energy suggest that the creep deformation is controlled by a lattice diffusion mediated dislocation climb process. These findings provide a fundamental understanding of the creep behavior and deformation mechanism of VNbMoTaW, which can be applied to design advanced creep-resistant RHEAs.

Keywords

• VNbMoTaW
• Refractory high-entropy alloy
• Creep behaviors
• Stress-dependent transition behavior
• Lattice diffusion
• Dislocation climb