Abstract
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.
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