Current status of ductile tungsten alloy development by mechanical alloying

There were considerable differences in ductility and recrystallization temperatures among fine-grained, carbide-dispersed tungsten alloys developed so far by mechanical alloying, followed by sintering and hot working. The differences are attributable mainly to three microstructural factors giving detrimental effects on the ductility and recrystallization temperature; (1) precipitation of the brittle W₂C phase, (2) heterogeneity in grain size and particle distributions and (3) loss of carbon which is a constituent of transition metal carbides. Therefore, a process to eliminate these factors is presented. The improved process was applied to fabricate tungsten alloys, and microstructural observation and three-point bending tests were performed on the alloys. It is demonstrated that the developed alloys have microstructures almost free from the three factors; the developed alloys exhibited no ductility before fracture in the as-HIPed state, but showed appreciable ductility in the as-forged state, indicating importance of plastic working to improve the ductility of the alloys.