Role of Rhenium on Solidification, Microstructure, and Mechanical Properties of Standard Alloy 718

The effect of Rhenium (Re) additions to Standard Alloy 718 on solidification, microstructure, and mechanical properties represented by hardness was studied. Re has a very high strain hardening rate, which is about 3.5 times than that of W or Mo. Re retards γ″ and γ′ coarsening, and also forms clusters within the γ matrix. In addition, Re does not from carbides. However, the microstructure of Re-containing Alloy 718 has a higher volume fraction of δ phase than the standard alloy. Electron microprobe analysis and transmission electron microscopy observations were used to identify the precipitation of hard γ″ and γ′ phases as well as δ phase. Re elevates phase transformation temperatures of γ matrix, eutectic γ/NbC, and eutectic γ/Ni2Nb. The volume fractions of γ dendrites, NbC and Ni2Nb phases, are increased with Re content in Alloy 718. Enhancement of hardness was also evident in the vicinity of a Re-cluster.