Morphology and phase constituents of mechanically alloyed Nb-Ti-Si based ultrahigh temperature alloy powders

Preparation of high-quality powder blends is the first step for hot-press sintering of Nb-Ti-Si based ultrahigh temperature alloys. In the present work, powder blends of Nb-22Ti-15Si-6Cr-4Hf-3Al-1.5B-0.06Y (at.%) were prepared by ball milling the elemental powder mixtures. The morphology and phase constituents of the powder blends were analyzed by XRD, SEM and EDS techniques. The mechanical alloying process, including diffusion, phase formation and powder deformation was revealed. The results show that supersaturated Nbss (Nb solid solution) formed during the milling process, the deformation of the powders became more serious and thus more crystal defects appeared in the powders with the prolonging of milling time at different rotating speeds. The powder size firstly increased and then decreased, and the size distribution of powders became more uniform with the increase in milling time. A small quantity of nanometer scaled spheroidal particles formed after ball milling for a certain time. It was found that the alloying process was faster upon a higher rotating speed ball milling, but with a lower powder yield.