The Development and Characterization of a High Performance Experimental Single Crystal Superalloy

Abstract

A titanium-free single crystal alloy designated MXON is shown to possess a substantially higher creep strength at high temperatures than that of the currently available conventional single crystals. A further investigation of the role of cobalt showed that the absence of this element improves the overall creep resistance of the alloy. The degree of chemical homogeneity achieved through the solutioning durations affects the subsequent stability of the alloy during high temperature creep. Small amounts of a tungsten-rich p phase (0.3%) were found to precipitate if sufficient chemical homogeneity is not achieved prior to the tests. Increasing the cobalt level beyond 5% facilitates the formation of this phase even at intermediate temperatures. The precipitation of the i-~ phase, which lowers the creep resistance of the alloy, can be avoided by longer solutioning durations prior to the creep tests. The alloy containing 7.5% cobalt shows an anomalously high primary creep due to inhomogeneous ~111~<112~ slip. The high cycle fatigue strength is not affected by the 1-1 phase. The MXON alloy has excellent corrosion resistance due to the development of a stable oxide layer.