Microstructure characteristics and a deformation mechanism of fine-grained tungsten heavy alloy under high strain rate compression

The dynamic behavior of fine-grained 93W–4.9Ni–2.1Fe–0.03Y (wt.%) alloy with an average grain size of ∼6 μm was investigated under the strain rates of 1.2 × 103, 1.5 × 103, 1.8 × 103 and 1.9 × 103 s−1. Microstructures in the tested specimens were characterized by optical microscopy and transmission electron microscopy. The results show that the fine-grained alloy exhibit low rate-sensitivity and strain hardening. The slope of the elastic deformation stage corresponding to the stress–strain curve of 1.9 × 103 s−1 is much smaller than those of the other curves due to slight premature instability. In addition, adiabatic shear bands (ASBs) were formed in the specimen with the strain rate of 1.9 × 103 s−1. Numerous dislocations and some twins in the W and γ-(Ni, Fe) could be observed in the ASB, indicating that no sharp temperature increase occurred in the specimen, and the adiabatic shear failure is probably independent of the significant thermal softening effect during high strain rate compression. The significant thermal softening independence of the adiabatic shear failure in the alloy is mainly attributed to the contributions stemming from the grain refinement and second-phase particles of yttrium.

Research highlights▶ The paper revealed the microstructure characteristics of fine-grained tungsten heavy alloys (WHAs) after high-strain-rate loading in detail by TEM and HRTEM. ▶ Authors correlated the phenomenon that adiabatic shear banding occurred in fine-grained WHAs under lower high-strain-rate loading with the microstructure, and proposed an innovate standpoint that adiabatic shear banding can be triggered in the condition of insignificant thermal softening effect. ▶ Adiabatic shear banding in fine-grained WHAs can be attributed to grain refinement and containing yttrium second-phase particles, which greatly reduce the required critical shear strain for adiabatic shear localization.