脉冲TIG焊接工艺参数对高温镍基合金焊缝组织的调控研究

Study on Controlling of Welding Seam Microstructure about Nickel-based High-temperature Alloy by Pulse TIG Welding Process

镍基合金因其热导率小,焊接过程中接头在高温停留时间长,导致焊缝晶粒具有粗大倾向。为合理调控焊缝晶粒,本文利用脉冲钨极惰性气体保护焊（Pulse tungsten inert gas,PTIG）参数可调程度高、热输入相对较小的优点,采用优化之后的焊接参数对镍基合金Inocnel690平板进行堆焊试验。焊后采用光学显微镜和扫描电镜对焊缝的微观组织和析出相进行表征分析。结果发现不同的PTIG工艺参数对焊缝形貌和晶粒大小调控效果显著,且在合理的参数范围内,焊缝晶粒随着脉冲峰值电流、占空比和脉冲频率的增加有明显细化效果;而增大基值电流则不利于焊缝组织的细化。通过扫描电子显微镜（Scanning electron microscope,SEM）和能谱仪（Energy dispersive spectroscopy,EDS）分析,奥氏体晶界上的析出相为M23C6(Cr23C6)型碳化物,呈现连续分布;奥氏体晶内的析出相为典型颗粒状MC（NbC,TiC）型碳化物,弥散分布在枝晶间隙中,且在占空比较大的时候,MC型碳化物有长大成片状的趋势。

Owing to the small thermal conductivity of nickel-based alloys,the residence time of the joint in the welding process became long,which leads to a coarse tendency about the weld grains.In order to control the size of weld grains,the PTIG welding parameters are optimized and performed the bead-on-plate welding of Inocnel690,using PTIG welding method with adjustable parameters has the advantages of high heat input level is relatively small.The microstructure and precipitation phase of the weld are characterized by energy dispersive spectroscopy（EDS）and scanning electron microscope（SEM）after welding.The results show that the effect of PTIG of different process parameters on the weld morphology and grain size is significant.When the parameters is in a reasonable range,weld grain becomes smaller with the increasing of peak current,duty ratio and pulse frequency.The precipitates is M23C6(Cr23C6)type carbides distributed in succession on the austenite grain boundary.The precipitated particle in austenite grain is granular MC（Nb C,Ti C）carbide,dispersed in the dendrite gap.And when the duty cycle is relatively large,the MC type carbide grows into lamellar trend.