Mechanical behaviors and microstructure evolution of Ni-W medium heavy alloy at various strain rates under uniaxial tension

In this study, a novel medium-heavy alloy (MHA) of 56Ni-38 W-5Co-1Ta was prepared using conventional casting and forging methods. This novel Ni-W alloy exhibits a unique combination of medium density, high strength and ductility under quasi-static loading conditions. In this study, the dynamic mechanical behaviors and deformation mechanisms of this novel Ni-W alloy were systematically investigated. The Ni-W alloy exhibited that yield strength increase form -1.6 GPa (1 x 10-3 s- 1) to -2.0 GPa (3 x 103 s-1) owing to the formation and accumulation of nano-sized deformation twinning at dynamic loading condition. Although twin boundaries are attributed to their higher strength owing to the Hall-Petch effect, nano-sized cracks also prefer to nucleate at twin boundaries because of the strong interaction between dislocations and twins. This strong interaction introduces local stress concentration and crack nucleation at deformed zone and finally lead to the decreasing of uniform elongation form -0.31 (1 x 10-3 s-1) to -0.18 (1-3 x 103 s-1). The major deformation mechanism exhibited a clear transition from dislocation slip to deformation twinning in the Ni-W alloys under dynamic loading. Our results provide a comprehensive picture of how the deformation modes govern the mechanical behavior and failure of Ni-W MHA at high strain rates.