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 gamma '' and gamma' coarsening, and also forms clusters within the gamma matrix. In addition, Re does not from carbides. However, the microstructure of Re-containing Alloy 718 has a higher volume fraction of delta phase than the standard alloy. Electron microprobe analysis and transmission electron microscopy observations were used to identify the precipitation of hard gamma '' and gamma' phases as well as d phase. Re elevates phase transformation temperatures of gamma matrix, eutectic gamma/NbC, and eutectic gamma/Ni2Nb. The volume fractions of gamma 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.