单晶过渡液相扩散焊接头单晶化机理

Mechanism of single crystallization of transient liquid phase diffusion bonded single crystal superalloy joint

为了探明单晶高温合金TLP扩散焊接头单晶化机理,采用扫描电镜(SEM)、背散射电子(BES)和背散射衍射(EBSD)分析接头微观组织.结果表明,接头内形成贯穿型晶界和等轴晶粒是接头无法实现单晶化的主要原因.在实际焊接过程中,应严格控制试样加工、中间层添加、装配、焊接等工序.在等温凝固阶段,液相依附于固态单晶基体以平面晶的方式外延生长,直至液相消失,界面上形成具有一致晶体取向的一块单晶,随着保温时间的延长,固态均匀化过程充分进行,冷却后将形成单晶化的接头.

Microstructure of transient liquid phase( TLP)diffusion bonded N5 single crystal superalloy joint had been investigated using scanning electron microscopy( SEM),backscattered electron( BES) and electron back scattering diffraction( EBSD) for understanding mechanism of single crystallization of joint. The results showed that formation of transjoint grain boundary and equiaxed grain in joint resulted in non single-crystallization joint. During bonding, those should be controlled carefully for machining of specimens,accession of interlayer,fitting, bonding and so on. During isothermal solidification process,liquid commenced to solidification by the flat crystal growing epitaxially from the unmelt single crystal base metal until liquid disappeared. Common single crystal grain with uniform crystal orientation at the interface was formed. Sufficient homogenization process was carried out with increasing welding time.After cooling of joint,single crystallization of joint would be obtained.