不同冷速作用下K424镍基高温合金相变及组织形成规律

Phase Transformation and Microstructure Formation of K424 Superalloy with Different Cooling Rate

使用差示扫描量热仪,研究了不同冷却速率作用下K424镍基高温合金的相变过程。使用光学显微镜(OM)、扫描电镜(SEM)及能谱分析仪(EDS)对K424合金二次枝晶间距及成分偏析随冷速的变化规律进行了分析。结果表明,提高冷却速率使合金二次枝晶间距及碳化物的尺寸减小。枝晶组织的细化及相变速率的加快,导致空间上残余液相的分散分布及时间上初生相的不充分生长,从而减弱了枝晶间Ti,Nb等正偏析元素的富集,降低了碳化物的析出温度及转变程度,甚至可抑制其二次析出。

Phase transformation processes of K424 superalloy with different cooling rates were investigated by differential scanning calo- rimetry. The variations of secondary dendrite spacing and concentration segregation as the function of cooling rate were analyzed by u- sing OM, SEM and EDS. The results indicate that both the length of secondary dendrite spacing and the size of carbides reduce with the increasing of cooling rate. The refinement of dendrite structure and the acceleration of phase transformation rate result in the disper- sive distribution of residual liquid phase and insufficient growth of primary phase, which weakens the richness of solute Ti and Nb ele- ments in inter-dendrite region. Consequently, both the temperature and the transformation of carbides are suppressed, even with the absence of second formation.