Thermoplastic bonding (TPB) of TiAl- and Ni-based alloys with Zr-Al-Ni-Cu bulk metallic glass

Highlights: • A new strategy called "Thermoplastic Bonding (TPB)" was developed and applied to join hard-to-weld dissimilar materials. • TPB is a "solid brazing" technology. It can obtain a liquidus brazing effect by atomic diffusion below melting point. • The phases of the joint were very fine and the tension tests show that the maximum tension strength was as high as 415 MPa. -- Abstract: The joining of dissimilar materials such as TiAl- and Ni-based alloys has always been a challenging work due to the larger differences in properties. In this work, a new strategy called thermoplastic bonding (TPB) was proposed and successfully applied in joining of the two alloys. Through utilizing superplastic flow of bulk metallic glasses (BMGs), a good mechanical bonding with no cracks between the base metals and filler was achieved, and after holding a time at a higher temperature lower than the melting point of the filler, the alloys were metallurgical bonded through atomic diffusion. The results showed that the phases in the joint bonded by TPB were very fine (approximately 300 nm) and uniformly distributed at the grain boundaries due to the low temperature and concomitant sluggish diffusion effect, while a series of directional intermetallics detrimental to the joint strength formed in the joint bonded by vacuum brazing. Tension tests showed that the strength of the TPB bonded joint was as high as 415 MPa, while that of the vacuum brazed joint was only approximately 315 MPa. These results verified that this new joining method can obtain a liquidus bonding effect equivalent to that obtained by a solid diffusion method.