摘要
利用JmaPro热力学计算结合光学显微镜、扫描电镜、电子探针等方法研究了高镍铌耐蚀合金945A的析出相类型、铸态组织特征及元素偏析行为.结果表明:945A合金非平衡凝固过程中,液相中依次会析出MC型碳化物、M2O3型氧化物、7基体、MN型氮化物、Laves相及η相.电渣锭铸态组织为典型的凝固组织,衬度差异明显,枝晶间大块析出相附近有针状相富集.合金元素偏析严重,Cr、Fe、Al元素偏聚于枝晶干,负偏析程度kCr＞KFe＞KAl,Nb、Mo、Ti元素在枝晶间富集,正偏析程度kNb＞KMo＞KT1.由于Ni、Nb、Ti在大块析出相附近偏聚,促使了针状η-Ni3(Ti,Nb)的析出,而Nb、Mo、Ti在枝晶间的偏聚,导致凝固末期MgO.Al2O3+(Ti,Nb)N、(Nb,Ti)(C,N)+M23C6非金属夹杂多分布于此.
Abstract
By employing JmaPro thermodynamic calculations in conjunction with optical microscopy,scanning e-lectron microscopy,and electron probe microanalysis,the types of precipitated phases,characteristics of the as-cast microstructure,and element segregation behaviors of corrosion resistant alloy 945A with high level of nick-el and niobium were investigated.The results indicate that during the non-equilibrium solidification process of the 945A alloy,M2O3-type oxides,MC-type carbides,γ matrix,MN-type nitrides,Laves phase and η phase were sequentially precipitated in the liquid phase.The as-cast microstructure of the electroslag ingot exhibited a typical solidified structure with significant contrast differences,and there was an enrichment of needle-shaped phases near the large precipitated phases in the interdendritic regions.Severe element segregation was observed in the alloy,with Cr,Fe,and Al elements segregating towards the dendrite core,and the degree of negative segregation follows the order:KCr＞KFe＞KAl.Nb,Mo.Ti elements were enriched in the interdendritic re-gions,and the degree of positive segregation was KNb＞KMo＞KTi.Due to the segregation of Ni,Nb,and Ti near the large precipitated phases,the precipitation of needle-shaped η-Ni3(Ti,Nb)was facilitated.The segre-gation of Nb,Mo,and Ti in the interdendritic regions at the end of solidification led to the distribution of non-metallic inclusions such as MgO.Al2O3+(Ti,Nb)N,(Nb,Ti)(C,N)+M23C6.
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