Pulverization by hydrogenation is applicable to powder fabrication for refractory intermetallic alloys. Hydrogen absorption of various Nb-Al alloys containing 0-28 mol% Al was investigated using bulk specimens in a Sieverts-type apparatus at test temperatures of 313-373 K under hydrogen pressure of 0-3.4 MPa. The lattice parameter of Nb solid solution (Nbss) was determined precisely as a function of Al concentration. It was found that (1) the lattice parameter of Nbss is linearly reduced with increasing Al content, and (2) hydrogen absorption of Nbss is also remarkably reduced by Al addition. The atomic radius of Al in Nbss is determined to be 139.2 pm. Large hydrogen absorption more than 0.5 mass% H is observed only for pure Nb and Nb3Al-based two-phase alloys. However, pulverization and the large hydrogen absorption at a constant pressure (plateau) take place only in the latter alloys. This plateau does not stand for equilibrium hydride formation, but for rapid absorption through increased surface area by pulverization. These aspects are discussed in connection with hydrogen diffusivity.
ASJC Scopus subject areas