W元素在新型镍基粉末高温合金中的强化作用

Strengthening Effect of W Element in New Nickel-based Powder Metallurgy Superalloys

通过真空感应熔炼(VIM)棒料+电极感应熔炼氩气雾化(EIGA)制粉+热等静压(HIP)成形+热处理(HT)工艺制备三种W含量(质量分数4.1%、6.1%和8.1%)的新型镍基粉末高温合金实验锭坯。以此锭坯为对象,结合金属材料相图计算及材料性能模拟软件JMatPro 6.5计算,利用SEM、EBSD和XRD分析W含量对热处理态锭坯显微组织(如晶粒尺寸、退火孪晶、γ′强化相及错配度)的影响,测试分析不同温度下合金的拉伸性能,通过经验公式量化分析各强化机制对合金室温屈服强度的贡献情况。结果表明,随着W含量增加,γ基体层错能明显降低,热处理态退火孪晶界Σ3数量增多;W促使晶内一次γ′强化相由立方状加速粗化为固态枝晶状,对γ′总量和二次、三次γ′的影响不大;W进入γ基体产生晶格畸变的程度大于γ′强化相,使得γ′/γ错配度呈下降趋势;W有助于提高室温和650~800℃拉伸强度,但略微降低塑性;W主要起固溶强化、γ/γ′共格应变强化和晶界强化作用,其中固溶强化贡献相对最低,固溶强化时以强化γ基体为主,γ基体固溶强化和γ/γ′共格应变强化效果随W含量增加而减弱,W含量为6.1%时晶界强化效果最大;固溶强化、γ/γ′共格应变强化和晶界强化贡献值总和不足室温屈服强度实测值的50%,合金以γ′相沉淀强化为主,测试值和计算值较为吻合。

Three experimental high-strength Ni-based PM superalloy ingots with different W contents(4.1wt%,6.1wt%,and 8.1wt%)were prepared by the process of vacuum induction melting(VIM)+electrode induction melting gas atomization(EIGA)+hot isostatic pressing(HIP)+heat treatment(HT).Combined with the software JMatPro 6.5 and SEM,EBSD,and XRD,the effects of W content on the grain size,annealing twin boundaries,theγ′phase and the lattice mismatch were analyzed,and the effect of W content on the tensile properties at different temperatures were also calculated and studied.The results indicated that the stacking fault energy of theγmatrix decreased significantly with the increase of W content,resulting in the increase ofΣ3 annealing twin boundaries;W transformed the shape of primaryγ′from cuboid to solid state dendrite,but had little impact on the total amount ofγ′phase and secondary and tertiaryγ′phases;the degree of lattice distortion caused by W enteringγphase is greater than that ofγ′phase,resulting in a decrease of theγ′/γlattice mismatch;W contributed to improving the tensile strength at room temperature and 650—800℃,but slightly reduced the ductility.W had better strength above 750℃,and it was widely added in the fourth generation PM superalloys.W mainly played the role of solid solution strengthening,γ/γ′coherent strain strengthening,and grain boundary strengthening.Among them,the contribution of solid solution strengthening was relatively low and W mainly strengthened theγmatrix.The effect ofγmatrix solution strengthening andγ/γ′coherent strain strengthening decreased with the increase of W content,and the grain boundary strengthening effect was the largest when W content was 6.1%.The total contribution of solid solution strengthening,γ/γ′coherent strain strengthening and grain boundary strengthening was less than 50%of the measured yield strength at room temperature,which indicated that the alloy was mainly strengthened by theγ′phase.