Correlation of Ta/W Compositional Ratios with the High Temperature Properties of Ni-Cr-Al-Ta-W(-Co) Single Crystal Superalloys

Abstract

The optimum Ta/W compositional ratio was searched for in Ni-10/11 mol % Cr-12/14 mol% Al -Ta-W( -5mol% Co) alloys in order to get an excellent combination of creep-rupture, phase stability and hot-corrosion resistance in a Na₂SO₄-NaCl salt. Solidification and precipitation temperatures were also examined as a function of the Ta/W ratio. The γ' solvus temperature and the creep-rupture life were found to increase with increasing Ta/W ratio up to 1.0. However, when the ratio exceeded 1.0, the creep-rupture life reversely decreased probably due to the increase in the residual amount of the eutectic γ' phase in alloys. On the other hand, hot-corrosion resistance increased monotonously with the Ta/W ratio. From the present study it was concluded that the Ta/W compositional ratio of 0.5 to 1.0 was most suitable for balancing the high temperature properties in this alloy system.