Microstructural Influences on the Ductility of Tungsten Alloys

Abstract : The ductility of tungsten-nickel-iron alloys is determined as a function of composition for Ni/Fe ratios of 7:3 and 1:1, and for tungsten compositions in the range 87.5 to 97.5 weight percent. Quantitative metallographic methods are used to estimate phase volume fractions, interphase interface areas, contiguity, contributions of different fracture paths to rupture as well as the types of crack nuclei and their size. Nucleation of fracture was predominantly by tungsten-tungsten interface fracture, however the alloy was quite resistant to crack propagation and rupture occurred at a stress level where a cascade of individual fractures occurred. The generally higher ductility of 7:3 Ni/Fe ratio alloys compared to 1:1 ratio Ni/Fe alloys is at least partly due to lower tungsten-tungsten interface area per unit volume in the former.