Processing and physical metallurgy of tungsten-nickel aluminide composites

Environmental concern over the use of depleted uranium (DU) for high strain applications has focused interest on tungsten alloys as cleaner alternatives. Tungsten heavy alloys exhibit similar low strain rate properties as DU, but show a 10% lower performance than DU at high strain rates. The performance difference is attributed to adiabatic shearing resulting in localized deformation in DU while tungsten alloys exhibit bulk deformation. Therefore, the premise of the study was to induce adiabatic shear in a tungsten composite using Ni{dollar}sb3{dollar}Al as the matrix, making use of its anomalous thermal behavior. Nickel aluminide exhibits a positive strengthening effect with increasing temperature up to a critical temperature, approximately 700{dollar}spcirc{dollar}C. Upon obtaining this critical temperature, Ni{dollar}sb3{dollar}Al softens quickly. This event replicates the {dollar}beta{dollar} to {dollar}gamma{dollar} transformation in DU, which is believed to be the mechanism by which DU adiabatic shears. This study developed tungsten alloys, where the matrix was either fully or partially Ni{dollar}sb3{dollar}Al. Major emphasis was placed on the effects of processing on the retention of the L1{dollar}sb2{dollar} structure in XFe-(1-X)Ni{dollar}sb3{dollar}Al system and fabrication of the components with good low strain properties. The effects of W alloying on Ni{dollar}sb3{dollar}Al properties were two-fold: W increased the matrix hardness by 55 VHN/at.% W, and the critical temperature for softening was reduced by over 100 K. Addition of Fe to the matrix resulted in improved tensile strength due to a reduction in the matrix solubility for W and the formation of order/disorder phases within the matrix. High strain rate testing shows improved performance as compared to 93W alloys equivalent performance as 97W alloys.