Effects of atmosphere temperature and composition on densification of nickel-tungsten-manganese alloys

Because of the excellent mechanical, physical and chemical properties, bulk metallic glass (BMG) materials have shown profound potential in a wide range of engineering applications. To prevent catastrophic failure of monolithic BMG at very small strains, metal fibres or ceramic particles are normally used to reinforce the material and improve the ductility. Mechanical properties of Zr-based BMG reinforced with 80% Tungsten fibres by volume were experimentally investigated in the present study at room temperature and elevated temperature up to 873 K. The quasi-static and dynamic compressive deformation and fracture behaviour were investigated by means of INSTRON, MTS testing machines and split Hopkinson pressure bar (SHPB), respectively. The failure patterns and mechanical properties of cylindrical specimens with different aspect (length to diameter) ratios under quasi-static compression were studied. It was found that the failure of BMG composite material was resulted from the combination of BMG shear failure, fibres’ axial splitting and fibre-matrix debonding. Results of quasi-static tests at different temperatures revealed that the yield strength decreased with temperature, and the strain hardening behaviour was replaced with strain softening after the yield stress when the temperature was elevated. Results from SHPB tests at room temperature showed approximately 30% higher strengths compared to the quasi-static counterpart, but the specimens were found partially losing the deformability and fail at smaller strains. The dynamic strengths were also found to decrease with the increase of temperature. An empirical relation to describe the change of yield strength due to temperature elevation was proposed based on the test data. The mechanism of self-sharpening behaviour of penetrator made of BMG composites was explained based on the material behaviour at high strain rate and high temperature.