Thermoplastic bonding of TC4 and 316L stainless steel with a Ti-based bulk metallic glass as the filler metal

Dissimilar TC4 titanium alloy and 316L stainless steel were successfully joined utilizing thermoplastic bonding (TPB) with a Ti-based bulk metallic glass (BMG) as the filler. Good physical pre-bonding and metallurgical bonding were successively achieved through superplastic flowing in the superliquid region and solid-sate atomic diffusion and reaction. The experimental results indicated that the superplastic flow of BMG in the superliquid region greatly promoted void shrinkage in the interfaces. Hence, a compact contacting was obtained at temperature much lower than the melting point of the filler metal, which is beneficial to the atomic diffusion between the filler metal and base metals as temperature increased. After holding for some time below the melting point of the filler metal, three different reaction layers derived from the atomic diffusion and reaction between the base metal and filler metal were formed in the interfacial regions. A series of irregular bulky and small plate-shaped fine phases were formed and uniformly distributed in the interfacial regions and intermediate region. The shearing tests showed that a high strength of 225 MPa was obtained after diffusing at 695 °C for 60min. The fracture surface of the joint shifted from the 316L interface to then central crystallization layer as temperature increased.