On the Effect of Super-Solidus Heat Treatment on the Microstructure and Creep Properties of a Third-Generation Single Crystal Ni-Based Superalloy

A Super-Solidus Hot Isostatic Pressing, SSHIP, heat treatment has been developed and applied to the third-generation Ni-based single crystal superalloy CMSX-4 Plus. The aim of this new type of heat treatment is to significantly reduce the solution heat treatment time and improve the mechanical properties compared to those resulting from subjecting the single crystal to conventional heat treatment routes. The partial melting of the regions with the lowest solidus temperatures during SSHIP results in the acceleration of the diffusional processes, while the control of the cooling rate after SSHIP results in the optimum precipitation of the fine gamma/gamma' microstructure. This innovative type of heat treatment, which can significantly reduce the economic penalties associated with lengthy high-temperature solution treatments while having a positive effect on the final mechanical properties, could be applied to other complex single crystal Ni-based superalloys containing large amounts of refractory elements (like rhenium, tungsten and tantalum), showing strong dendritic segregation and/or a large volume fraction of eutectics in the as-cast state.