特集 金属間化合物の粉末冶金と諸持性 脆い金属間化合物の延性化に関する研究

Abstract

Several kinds of brittle intermetallics have been reported to be ductilized on the basis of fundamental studies on mechanical properties in relation to chemistry of a grain boundary, composition dependence of phase stability, environmental embrittlement, etc. Most of those intermetallics possess fee-, bcc- or hcp-derivative ordered crystal structure and their Peierls stress is relatively low at ambient temperatures. However, many intermetallics having superior properties possess more complicated crystal structure and consequently high Peierls stress. It seems difficult to ductilize these monolithic intermetallics by alloying with a small amount of elements or suppression of environmental embrittlement. A promising process is 'toughening' by distribution of a ductile phase. Refractory intermetallic Nb3Al is shown to have very high strength at elevated temperatures because of high flow stress of an a dislocation consisting of two a/2 partial dislocations and a complex stacking fault. Finely distributed Nb solid solution particles in Nb3Al lead to ductility improvement.Nb3(Al, Sn) superconducting thin wires with a high critical current density(Jc) can be fabricated by heavy deformation and diffusion annealing of Nb/Sn-Al composites prepared by the infiltration process. It is suggested that the interface between Nb3Al and Nb2Al acts as an effective pinning site, thereby increasing Jc.