Phase stability and fundamental properties of Nb-Al binary system

Phase stability and mechanical properties of Nb-Al binary system have been investigated. Utilizing mainly X-ray diffraction and microstructure analyses, phase stability of Nb-Al system has been studied and binary phase diagram has been proposed. It was found that the Nb3Al intermetallic compound having A15-type structure was the stable single phase in the range of about 20.6 to 23.0 at.% Al. The composition range is narrower than ever reported and does not contain stoichiometry composition of A15-type structure Nb-25 at.% Al. The mechanical properties of alloys in the Nb-Al system also have been examined. By means of hardness tests at room temperature, the composition of ductile-brittle transition (DBT) of Nb-Al system was found to be Nb-16 at.% Al. By increasing Al content from 16 to 25 at.% Al, the value of microhardness showed a precipitous increase up to 1,100 Hv. Strength of Nb-19.4 at.% Al alloy at high temperatures was examined by compression test. Nb-19.4 at.% Al alloy exhibit plastic deformation above 1,473 K. By eliminating microvoids and inhomogeneity through HIP (hot isostatic pressing) treatment, peak stress at 1,873 K was increased from 49.0 to 94.4 MPa