镍基合金焊丝GTAW熔敷金属凝固偏析行为

Investigation on the solidification segregation behavior of GTAW nickel alloy deposited metal

关键词:  镍基合金  凝固结晶  偏析

Key words:  nickel alloy  solidification  segregation

摘要:

采用OM，SEM，EDS，EPMA等分析手段对试制的镍基合金焊丝GTAW熔敷金属开展了凝固偏析行为研究.结果表明，熔敷金属中主要包括γ相、（Nb，Ti） C碳化物、Laves相等，金相组织主要为柱状晶，在枝晶间存在宽度约为5~10 μm的偏析区域；按照Scheil公式对EPMA分析结果进行了偏析系数计算，估算的Nb，Mo，Ni，Cr，Fe偏析系数分别为k_Nb=0.23，k_Mo=0.68，k_Ni=1.07，k_Cr=1.05，k_Fe=1.23，在结晶过程中Nb，Mo更倾向于分配在残余液相，Nb的偏析倾向最大，Mo次之，Fe更倾向于分配在固相中，Ni，Cr基本为固液平均分配.文中试验用镍基合金焊丝GTAW熔敷金属凝固结晶路径为L→L+γ→L+γ+MC→L+γ+MC+Laves相→γ+MC+Laves相.

Abstract:

The solidification segregation behavior of deposited metal with nickel alloy wires by GTAW was investigated by Optical Microscope (OM), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and Electron probe X-ray microanalyser (EPMA), etc. Results indicated that microstructure was composed of γ phase, MC carbides, Laves phases in the deposited metal. The metallurgical structure was columnar crystals with segregation zone of 5~10 μm in width. The segregation coefficients of primary elements were calculated with EPMA results according to Scheil formula, k_Nb=0.23, k_Mo=0.68, k_Ni=1.07, k_Cr=1.05, k_Fe=1.23. During solidification, Nb and Mo tended to segregate in the liquid phase, while Fe prefers to distribute into solid phase, Ni and Cr did not show significant distributions differences between liquids and solids. The reaction sequence of deposited metal with experimental nickel alloy wires during solidification was L→L+γ→L+γ+MC→L+γ+MC+Laves→γ+MC+Laves.