Hydrogen pulverization is expected to be used as a method for producing powder with high quality and low cost. In this study, hydrogen pulverization is investigated using a Nb-16mol%Al alloy, which is composed of Nb solid solution (Nbss) and Nb3Al, in terms of volume fraction of Nbss and Nb3Al and fracture toughness. The volume fractions were controlled through heat treatments of 1473, 1773 and 1873 K for 86·4 ks in vacuum. Before hydrogenation, the microstructures were observed by a scanning electron microscope (SEM). The volume fractions were evaluated by analyzing the SEM images. An equation is proposed to evaluate Nbss solvus using volume fraction ratio of Nbss/Nb3Al by taking atomic volume change into account. In addition, electron probe micro analysis (EPMA) was carried out to determine phase equilibrium compositions. Thus, we propose phase boundaries of Nbss and Nb3Al in the Nb-Al phase diagram. Vickers hardness tests were conducted and fracture toughness was estimated from length of a crack introduced by indenter. With rising heat treatment temperature, hardness decreases and fracture toughness increases, partially because volume fraction of Nbss increases with rising temperature. After surface treatment, hydrogenation was carried out and pressure-composition-isotherm (PCT) curves were measured under hydrogen pressure from 0 to 3·4 MPa at 313 K. By analyzing the distribution of powder sizes after hydrogen pulverization, it is found that the powder size becomes large with rising heat treatment temperature. It is concluded that powder size can be easily controlled by changing volume fraction of constituent phases, microstructure and fracture toughness through heat treatments.
ASJC Scopus subject areas
- 化学 (全般)