Effect of W Addition on Compressive Strength of Nb-10Mo-10Ti-18Si-Base In-Situ Composites

摘要

Niobium solid solutioniobium 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 percent 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 1870K 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_pSi_3 silicide, while primary Nb solid solution appeared as a result of substituting W for Nb. The microstrocture 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 percent yield strength (#sigma#_(0.2)) and the specific 0.2 percent yield strength (#sigma#_(0.2s) (#sigma#_(0.2) divided by the density) at 1670 K increased markedly with increasing W content. The directionally solidified samples showed higher #sigma#_(0.2) and #sigma#_(0.2s) than the are-cast samples. Even at 1770 K, the directionally solidified sample with 15 mol percent W showed #sigma#_(0.2) of about 650MPa.