Research On High Temperature Fatigue Life Models Of Powder Metallurgy

Compared with conventional cast and wrought superalloys, powder metallurgy (P/M) superalloys have many advantages such as homogeneous organization, superfine grain, high yield strength and high fatigue and creep resistance. P/M turbine disks are worldwide adopted in most advanced aeroengines. At the last of 1970's, China started the research on P/M superalloys and turbine disks. At present, P/M superalloys FGH95 has been worked out and applied to a turboshaft engine disks. To satisfy the safety, reliability and durability of the P/M components, research on creep-fatigue life prediction of the P/M superalloys have been done in this paper. The evolution of creep-fatigue life prediction models is reviewed. Then, the previous studies on creep-fatigue life prediction of P/M superalloys are surveyed. A new method of estimating the parameters in B-P model is presented. The computational results indicate that the accuracy and efficiency of the new method are improved. Research on the creep-fatigue life prediction models of P/M superalloys is implemented relatively deeply. The parameters estimating methods and material test schemes of SRP and TS-SRP are presented. The computer programs for parameters estimating and life prediction of the two methods are developed. Both the methods are evaluated for Rene 95, a nickel-base superalloy for turbine disks. Results indicate that SRP is not able to predict the creep-fatigue life of Rene 95, while TS-SRP improves the life prediction accuracy of Rene 95. Based on the character of high strength, low ductility alloy that the inelastic strainranges are small and difficult to determine, a modification of SRP is presented, and then a total strain version of the modified SRP is formulated. The two new methods are evaluated and verified using the test data of Rene 95. Results indicate that the prediction accuracy is improved. The new methods are expected being applied to the creep-fatigue life prediction of FGH95. The work of this paper will lay a foundation for the creep-fatigue life prediction of P/M turbine disks.