Mechanisms of reactive element Y on the purification of K4169 superalloy during vacuum induction melting

The effects of rare earth element Y on the purification of K4169 superalloy during vacuum induction melting were investigated at different superheating temperatures. The corresponding interaction mechanisms were also clarified. Results showed that the addition of Y remarkably promoted the purification effect on the K4169 melt. The contents of O and S in the K4169 as-cast alloy ingots after purification were 3–4 and 8–10 ppm, respectively. The degrees of deoxidation and desulfurization increased to 50% and 57%, respectively, upon the addition of 0.1 wt% Y. The yttrium-rich phase that precipitated at the grain boundary blocked the diffusion of C and the accumulation of S, thereby contributing to the purification of the alloy.

Effect of Zr addition on precipitates in K4169 superalloy

In order to investigate the effect of Zr addition on the precipitations of K4169 superalloy,a manual electric arc furnace was used to prepare the superalloy with different Zr addition from 0.03wt.% to 0.07wt%.After standard heat treatment and long-time aging,the microstructures of the alloys were observed using XRD,SEM and TEM.The results show that Zr not only inhibits the precipitation of Laves phase at the grain boundary,but also significantly promotes the precipitation of earlobe-like γ' and γ″ phases.After long time aging at 680℃ for 500 h,the γ″ phase grows up obviously and forms a γ'/γ'' clad microstructure when the Zr addition is 0.03 wt.%.A large number of fine orbed γ' particles precipitate in the grains and some γ″ phase transforms to disk-like δ phase when the Zr addition increases to 0.05wt.%.The nano-polycrystalline γ' phase precipitates in the grains and there is a little δ phase when the Zr addition is 0.07wt.%.As the Zr addition increases,the amount of Laves phase at the grain boundary decreases at first,and then increases and forms flaky morphology.