Synergistic Effect Of Elements And Optimization Of Composition For Ni-based Superalloys

Nickel-based single crystal superalloys usually contain up to more than ten elements,and the interaction between the elements is very complex.Based on the idea of integrating the experiment and computation,the correlation between the synergistic effect of multi-chemical elements and physical properties of materials was studied by using atom probe tomography(APT),scanning transmission electron microscopy(STEM),and first-principles calculation and so on.The program of the low-rhenium alloy composition optimization and the corresponding heat treatment process were designed.The results of APT show that the addition of alloying elements affects the partitioning coefficient of W,Re,Mo,and Cr in the ?+?? phase,while the influence of partitioning coefficient of Ta,Ru,and Co is negligible.In particular,the addition of Ru and Co reduces the partitioning coefficient of the Re.Using first-principles density-functional calculations,we investigated the partitioning coefficient and diffusion rate of 3d(Ti~Ni),4d(Zr~Pd),and 5d(Hf~Pt)transition metal solutes.For ternary model Ni-based single crystal superalloys,the 3d solutes(except Ti)partition to the matrix phase,whereas 4d and 5d solutes(except Ru,Rh,and Ir)prefer ?? precipitates.The existing atom probe tomography results are consistent with the calculation results.We performed first-principles calculations to investigate the diffusion rate of alloying elements(3d,4d,5d).To minimize the coarsening rate,we screened alloying elements that both have a low diffusion rate in the ? matrix and partition to the ?' phase.These alloying elements(Pd,Pt,Ta,W,and Re)will suppress the coarsening behavior of the precipitates and are expected to contribute to the stability of precipitates at elevated temperature.Furthermore,the synergistic effect influenced solute diffusion in the Ni–X–Y systems(X,Y: Al,Ti,Nb,Ta,Cr,Co,Mo,W,Re,Ru)was investigated.Adding alloying elements(except Co and Cr)could decrease diffusion because it produces a complicated local atomic environment and a strong interatomic bonding of X–Y pairs,increasing the diffusion barrier of the solutes.By performing experiments with high-temperature thermal exposure,we verified that adding Ta,W,Re,and Ru to superalloys significantly reduced the solute diffusivities and slowed ?? coarsening;in contrast,adding Co increased the diffusivities of other elements and promoted ?? coarsening.The experimental data agree well with the results of first-principles calculations.Combined the research on the accumulation of multi-component alloys with the computer aided design,the alloys with low-rhenium and low-cost were designed.After the fine standard heat treatment process,the creep rupture life of optimized Ni-based single crystal superalloys at 1100?/137 MPa is greater than 300 hours.