Fracture toughness of W heavy metal alloys

Abstract

Heavy metal W alloys containing from 90–97% W constitute a particularly interesting family of brittle-ductile coarse two-phase composites which combine high density, high strength and relatively high ductility in spite of their high W content. Valid toughness values are almost non-existent in the literature for this technologically important family of alloys. The scarcity of such data is surprising because in those applications where heavy metal alloys are used toughness requirements are of essential importance. This paper presents measurements of K IC and J IC values for several heavy alloys showing the effect of composition, structural size and prior plastic strain. The results are discussed on the basis of fractographic observations and, for low-toughness alloys, rationalized in terms of the bridging of the advancing crack tip by ductile ligaments of the f.c.c. phase surrounding the globular W grains of the alloys. Such a toughening mechanism is akin to that found in hard metals and ceramic metal composites.