Plasma-melt-gas-atomization of High Temperature Intermetallic Compound (Nb3Al)

Rapidly solidified niobium aluminides (Nb sub 3 Al) have been studied to understand their suitability as structural materials for ultra-high temperature applications. A new gas atomization process combined with plasma-skull-melting without any refractory, refractory metal, and ceramic, has been developed to produce ultra-clean powders. In this process, named plasma-melt-gas-atomization (PMGA), a pouring nozzle for molten metal stream is made of water-cooled Cu with a bottom hole. Rapidly solidified powders of Nb sub 3 Al have been successfully obtained. Mean diameter of the powders is approx 100 mu m, and oxygen content is 300 ppm. PMGA'ed powders of Nb--22 at.% Al mostly consists of supersaturated solid solution of Al in Nb (bcc), although cast ingot of same composition wholly consists of ordered A15. Because microstructure of powder is identical to melt-spun ribbon, solidification rate of PMGA can be considered very high.