Effect Of Co, Cr, W, Mo And C On Microstructure And Mechanical Properties Of FGH4097 PM Superalloy

In this paper, several nickel based powder metallurgy (PM) superalloys FGH4097 with different compositions of alloy elements like Co, Cr, Mo, W and C are prepared by PREP+HIP+HT route. By means of thermodynamic calculation, physicochemical phase analysis, SEM, FEG-SEM, EDS, EPMA and TEM, the effects of Co, Cr, Mo, W and C on microstructure and mechanical properties of FGH4097 are investigated. After long-term aging treatment, five selected superalloys are tested to investigate the effects of Co, Cr, Mo, W and C contents on the stability of microstructure and mechanical properties at elevated temperature. The main purpose of this paper is to enhance the yield strength of FGH4097 by modifying the contents of Co, Cr, Mo, W and C without seriously decreasing its phase stability and other mechanical properties, such as crack propagation resistance and plasticity.The results show that Co, Cr, Mo and W increase the lattice parameter of y matrix and the absolute value of γ/γ’ misfit, enhancing solution strengthening effect and coherent strain strengthening effect, however, excessive Co, Cr, Mo and W decrease plasticity, and facilitate the precipitation of topological close-packed phases like μ phase, decreasing phase stability at elevated temperature. Carbon accelerates the formation of MC type carbide in grain by reacting with partial refractory elements, which improves the plasticity and suppresses the precipitation of μ phase at some level, proper carbon addition improves plasticity and fatigue performance.Taking comprehensive factors, such as mechanical properties and phase stability, into consideration, FGH4097 has the highest strength, acceptable phase stability and mechanical properties as the mass fractions of Co, Cr, Mo, W and C are 16.50%, 10.00%,4.20%,5.90%, and 0.04%(or 0.06%) respectively in this paper.