Microstructural influences on the Dynamic Response of Tungsten Heavy Alloys

Abstract

The influence of tungsten content, swaging, and grain size on the dynamic behavior of commercially available tungsten-nickel-iron (W-Ni-Fe) alloys has been examined using the compression Kolsky bar. The observed flow stresses increase with increasing tungsten content and with degree of swaging but are essentially independent of grain size for these compressive deformations. Further, the flow stresses sustained by these materials have a distinct dependence on strain rate, in that the flow stress increases by at least 20 pct over a range from 10^-4 s^-1 to 7 × 10³ s^-1. The rate sensitivity itself increases with increasing tungsten content. The rate sensitivity of the alloy with the highest tungsten content (97 pct W) appears to be essentially the same as that of pure polycrystalline tungsten. In addition to showing greater strain hardening, the unswaged alloy also shows a much higher rate dependence than the swaged alloys, with the flow stress almost doubling when the rate of deformation increases from quasistatic to 5 X 10³ s^-1. The rate-hardening mechanism within the composite appears to be essentially that as- sociated with the tungsten grains; however, the matrix contribution is significant in the case of an unswaged alloy.