From as-cast to heat treated X-40 superalloy: Effect of cooling rate after partial solution treatment on microstructural evolutions and mechanical properties

Abstract

Abstract This research study aims at investigating the influence of partial solution treatment and the subsequent cooling strategy on the microstructure and mechanical properties of an as-cast Co–Cr–W superalloy. Three different cooling scenarios were employed to explore the effect of cooling rate on the carbide reprecipitation potential from the \solid solution formed during the heat treatment. The partial dissolution/breakdown of the continuous network of the Cr-rich M7C3 carbides during the partial solution treatment cycle along with their transformation to M23C6 carbides and formation of secondary carbides during the cooling stage were taken into account to discuss the obtained hardness values, and high-temperature creep results. Regardless of the applied cooling rate, the secondary carbides were formed during the cooling stage, and the heat-treated samples showed almost the same microstructure and mechanical properties, which eliminates the need for the aging cycle. This can alleviate the concerns associated with the heat treatment of the large-size X-40 industrial components since the gradient in the cooling rate after the heat treatment cycle would not lead to non-uniform parts. From the hardness and creep viewpoints, all of the samples could meet the minimum requirements of the X-40 superalloy. Mechanical properties suggest that the applied partial solution treatment cycle can be considered as a suitable candidate for high-temperature applications of X-40 superalloy.