"相变-扩散钎焊(T/DB)"新工艺及其接头界面形貌

为减小相变超塑性扩散连接的循环次数,提出了一种新型焊接工艺"相变-液相扩散焊(T/DB)",即在待焊母材间预先放入液相扩散焊用的中间层,然后按传统相变超塑性扩散连接工艺施焊,但要求温度循环的峰值温度须同时大于母材的相变点与中间层的熔点.试验以低碳钢为母材,以镍基非晶箔带(BNi2)为中间层,进行了低碳钢的相变-扩散钎焊(循环3次)与液相扩散焊接(1200℃×3 min)的对比试验.结果表明相变-液相扩散焊所需温度循环次数少,接头无界面空洞,其接合线呈非平面状;而液相扩散焊接头的接合线较平直.分析认为,界面的起伏是母材的适度溶解与超塑性流变共同作用的结果;非平面状界面有利于增大金属-金属接触面积及扩散通道的面积,为获得合格接头做出了相应贡献.

New Bonding Process of Transformation/Diffusion Brazing and the Interfacial Morphology in Its Joints

To reduce the numbers of thermal cycles in traditional transformation superplastic diffusion bonding(TSDB),a new welding process of transformation/diffusion brazing (T/DB) was proposed.The T/DB process combines TSDB with diffusion brazing (or transient liquid phase brazing),namely which require to insert a interlayer for transient liquid phase (TLP)brazing before joining,and to heat/cool in cycling like TSDB process.But the maximum temperatwre must be higher than the transformation one of base metal and the liquidus of interlayer.Some low carbon steel joints previously inserted amorphous foil BNi2 were produced using the new process and transient liquid phase brazing respectively.The experiment results show that there are no voids along the interface,and the bond line morphology in transformation/diffusion brazed joint is non-planar,while which in TLP brazed joint is normally planar.It is suggested that the formation of the non-planar bond line are due to the combined efects of suitable dissolution (to inhibit) and superplastic deformation (to accelarate) of base metal,and the non-planar bond line are advantageous to increasing areas for diffusion paths and metal-metal contact,so it also contributes to mechanical properties of joints.