Effect of W Addition on Compressive Strength of Nb–10Mo–10Ti–18Si-Base <I>In-Situ</I> Composites

Abstract

Niobium solid solution/niobium silicides in-situ composites are expected to have applications in the future as high-temperature structural materials. To improve the high temperature strength further, we tried to add tungsten to Nb–10Mo–10Ti–18Si eutectic alloy by replacing Nb with 0, 5, 10 and 15 mol%W. The samples were prepared by arc casting and some of them were directionally solidified by the floating zone melting technique at a growth rate of 15 mm/h. After annealing at 1870 K for 100 h, the microstructure, Vickers hardness and high-temperature compressive strength were examined. The samples without W consisted of eutectic Nb solid solution and (Nb, Mo, Ti)5Si3 silicide, while primary Nb solid solution appeared as a result of substituting W for Nb. The microstructure of directionally solidified samples was coarse and oriented in the direction of growth, but they did not show the typical microstructure often observed in the case of directionally solidified materials. The Vickers hardness increased with increasing W content. The 0.2% yield strength (σ0.2) and the specific 0.2% yield strength (σ0.2S) (σ0.2 divided by the density) at 1670 K increased markedly with increasing W content. The directionally solidified samples showed higher σ0.2 and σ0.2S than the arc-cast samples. Even at 1770 K, the directionally solidified sample with 15 mol% W showed σ0.2 of about 650 MPa.