EFFECT OF SILICON ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF YTTRIUM MODIFIED Ni_3Al BASE ALLOY IC6

The effect of different amounts of silicon on the microstructure of the yttrium modified Ni3Al base alloy IC6 was studied with transmission electron microscope (TEM). The chemical compositions of phases formed due to the presence of silicon and yttrium were analyzed with energy dispersive spectrum(EDS) technique of electron probe microstructural analysis (EPMA). The results showed that a bulk shape phase rich in Mo and Si was formed in the alloys with addition of 0.10-0.20wt%Si and 0.12wt%Y, and that a needle like phase named Y-NiMo was precipitated in the interdendritic area in the alloy with addition of 0.30wt%Si and 0.12wt%Y besides the formation of the bulk shape phase mentioned above. The stress rupture properties under 1100℃/80MPa and the thermal fatigue properties at 1100℃ were improved by adding 0. 12wt%Y but decreased by adding 0.10-0.30wt%Si and 0.12wt%Y. The addition of 0. 10-0.20wt%Si and 0.12wt%Y has no obvious influence on the tensile properties of alloy IC6 at room temperature (R. T.), 760, and 900℃, respectively.