Precipitation at Tungsten/Tungsten Interfaces in Tungsten–Nickel–Iron Heavy Alloys

Abstract

A study of precipitation at the tungsten grain boundaries in the tungsten–nickel–iron ternary alloy system has been undertaken. Scanning and transmission electron microscopy techniques have been used to study the effect of various post-sintering heat treatments on the precipitation reaction. Grain boundary precipitates with a crystal structure and lattice parameter the same as the matrix binder phase (fcc, α0 = 0·360 nm) have been shown to form at the tungsten grain boundaries during heat treatment in the 800–1300°C temperature range. A mechanism for the formation of these precipitates is proposed. It has also been found that the tungsten grain boundary precipitates consistently behave in a ductile manner upon tungsten/tungsten interfacial failure. This may give an opportunity for an improvement in ductility of the inherently brittle tungsten grain boundaries in these alloys. PM/0338