Comparative Study on the Cleanliness and Mechanical Properties of a Cast and Wrought Ni-Based Superalloy GH4738 Prepared with Revert Addition

Superalloy recycling is recognized as an economic and strategic necessity, but very little quantitative information is available regarding the criterion for operating, including the recycling procedure, the percentage of revert for usage, the content of impurities and the final confidence level of the properties. In this work, we provide a comparative study on the cleanliness, microstructure and mechanical properties of a cast and wrought Ni-based superalloy GH4738 prepared with different recycled revert additions. Results demonstrated that the content of impurities and count as well as size of non-metallic inclusions increased significantly with the revert addition. No apparent effects on secondary carbides and γ′ precipitation was observed, but the count as well as size of MC carbides increased sharply and exhibited characteristics of grain boundary aggregation. Tensile testing revealed that revert addition takes little effect on the room and 760 °C ultimate or yield strength but drastically deteriorates the tensile ductility. A mixture of intergranular and transgranular fracture modes occurred regardless of revert content, but intergranular failure gradually dominates. In addition, the stress fracture test at 730 °C/550MP showed that revert addition induces rapid decrease in stress rupture life and ductility, and this can be attributed to the contamination of impurities and inclusions, as well as the grain boundary aggregation of MC carbides.