Effect of silicon on microstructure and stress rupture properties at 1100°C of yttrium modified Ni-Al-Mo-B alloy IC6

The effect of adding 0.10–0.30 wt%Si on microstructure of the yttrium modified alloy IC6 was examined by scanning electron microscope (SEM), energy dispersive spectrum(EDS) technique of electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results show that two bulk shape phases, Mo1.24Ni0.76 and Mo6(Ni0.75Si0.25)7 are formed in the interdendritic area in the alloy with addition of 0.10–0.20 Siwt% and 0.12 wt%Y, and that a needle like phase named Y-NiMo precipitates in the interdendritic area in the alloy with addition of 0.30 wt% silicon and 0.12 wt% yttrium besides the formation of the bulk shape phases mentioned above. The stress rupture properties under 1100°C/80 MPa were improved by adding 0.12 wt%Y but decreased by adding 0.10–1.30 wt%Si and 0.12 wt%Y.