The effect of trace elements on the creep behaviour of an NiCr-base alloy

This paper describes the results of an investigation of the effect of trace elements on the creep and stress rupture performance at 850°C of the high-chromium alloy IN939 which is used for blades and nozzle guide vanes in land-based gas turbines. The results showed that both Pb and Bi had a seriously detrimental effect on creep performance which was independent of the ductility of the base alloy. The presence of impurity caused increased amounts of grain boundary cavities which resulted in premature failure, and in this respect the results were consistent with those obtained for other alloys of this type. However, the creep resistance was reduced in the material doped with Pb and with Bi and this behaviour had not been observed in previous work on similar alloys. The results have been analysed in the context of recent developments in the understanding of mechanisms of creep deformation and fracture.