Microstructure and room temperature mechanical properties of hot-pressed Nb–Si–Ti–Fe alloys

Bulk alloys were fabricated by uniaxial hot pressing from ball milled Nb-Si–Ti–Fe powder mixtures with the fixed Si content (16 at.%) and various compositions of Ti and Fe, and the effects of Ti and/or Fe on the ball milling, microstructure and room temperature mechanical properties of the materials were investigated. It was revealed that the Ti addition inhibited the ball milling process with the same milling parameters. For the hot-pressed alloys, Nb4FeSi phase was detected in the alloys containing Fe, and Fe mainly dissolved into niobium silicides from the result of elemental mapping. The solubility of Si in Nbss was enhanced by the addition of Ti, and Nb3Si expected was not observed in the Ti-bearing alloys that may be due to the lower Ti content in the reaction zone between the particles. The Ti-added alloys hot pressed from a shorter time showed the coarser microstructure with Nbss in the shape of narrow strip distributed in river pattern, while near-equiaxed macrostructure was obtained in the Nb–Si–Fe alloys. The improvement in both room temperature fracture toughness and flexural strength was achieved in Ti-added alloys. The toughening and strengthening mechanisms were discussed from the ductile-phase toughening of crack bridging and solid solution strengthening, respectively.