Effect of growth rate on microstructure and mechanical properties in a directionally solidified Nb-silicide base alloy

The ingots with the composition of Nb–22Ti–16Si–7Cr–3Al–3Ta–2Hf–0.1Ho (at.%) have been successfully fabricated by using directional solidification, and the microstructure and mechanical properties of the resulted ingots were investigated as a function of growth rate. It is found that with the increase of growth rate the microstructure becomes finer, which can be characterized by the decreased average cell size, intercellular boundary width and interphase spacing. However, in the meanwhile more discontinuous Nb-silicides columns appear at high growth rate, and this will counteract the improvement of yield strength from the refined microstructure. In addition, the refinement of Nbss plates with increasing growth rate is unfavorable to the enhancement of fracture toughness.