The processing and properties of heavily cold worked directionally solidified Ni-W eutectic alloys

Abstract

Certain two phase metallic alloys display impressive strengths following extensive deformation processing. Provided an appropriate phase morphology and/or texture is developed initially, somewhat surprising combinations of metals (e.g., copper-chromium) can be so processed. Thus this scheme offers the possibility for developing high strength metal matrix composites at a comparatively low price. In the work described, we consider another material combination—the Ni-W directionally solidified eutectic—as a candidate for this interesting class of material. This alloy can be cold worked to true deformation strains of four. The tensile strengths of alloys so deformed are impressive (2470 MPa), but so are those of the cold worked nickel-tungsten solid solution which is a component of the eutectic. Based on the work-hardening behavior of tungsten and on a recently advanced model which qualitatively explains the strengths of heavily cold worked two phase metals, it is argued that further deformation processing of these alloys would lead to substantially higher strengths. Estimates on the fracture toughness of the cold worked eutectic are made from tensile properties. Estimated toughnesses are remarkably high and point to the possibility that this process can produce high strength-high toughness metallic materials to a degree not possiblevia conventional processing.