N5单晶过渡液相扩散焊接头微观组织研究

Investigation of Microstructure of Transient Liquid Phase Diffusion Bonded N5 Single Crystal Superalloy Joint

为了提高N5单晶高温合金过渡液相(TLP)扩散焊接头的力学性能,采用扫描电镜(SEM)和能谱分析仪(EDS)研究接头微观组织,以及TLP扩散焊过程中基体组织的变化。结果表明,接头由连接区和基体区所组成,未发现明显的扩散区特征。连接区由等温凝固区和快速凝固区组成。快速凝固区主要是由接头中心的硼化物、γ和γ'相的三元共晶,及靠近等温凝固区的γ和γ'相二元共晶组成。快速凝固区可以通过延长保温时间的方法予以消除。TLP扩散焊过程对基体组织有重要影响。随着焊接温度升高、焊接时间延长,基体内的γ'相尺寸增加。

Microstructure of transient liquid phase （TLP） diffusion bonded N5 single crystal superalloy joint and parent material during TLP diffusion bonding is investigated by using scanning electron microscopy （SEM） and energy-dispersive spectrum （EDS） for improving mechanical propertiy of joint. The results show that the joint contains bonding zone and parent material zone. The diffusion zone is not obviously observed. The bonding zone contains isothermal solidification zone and rapid solidification zone. Metallographic examination reveals that rapid solidification zone contains two different structures, which is ternary eutectic of borides, y, and 7＇ phase developing in the center of joint, binary eutectic of y and y＇ phase appearing close to isothermal solidification zone. Rapid solidification zone could be absented by increasing welding time. Effect of TLP diffusion bonding on the microstructure of the parent material is very important. The y＇ phase size in the parent material increases with welding temperature and welding time increasing.