Joining mechanism of bulk metallic glasses in their supercooled liquid region

Bulk metallic glasses (BMGs) are promising engineering materials due to their high strength, high fracture toughness and excellent corrosion resistance. However, the wide application of BMGs has been limited by the casting sample size. Joining of BMGs in their supercooled liquid region (SCLR) has shown the possibility to get rid of the casting size limitation. In this work, the physical mechanism of joining BMGs in their supercooled liquid region is systematically investigated. Specifically, the effects of joining temperature and time on the joint strength are studied by experiments, and the effects of joint strain and bonding morphologies are simulated by finite element analysis. It is observed that the joint strength is solely determined by the area fraction of the bonded regions, and the bonded regions increase with the joining temperature and joining time but are almost independent of the bonding morphologies. Based on the experiments and simulations, three microscopic processes that are oxide deforming and cracking, pristine BMGs flowing to contact and forming metallic bonds are identified to optimize the joint performance. By correlating the joining conditions with the three responsible microscopic processes, BMGs can be joined with predictable performance. Our work provides the fundamental physical processes for joining of BMGs in their SCLR, which could offer solution to the size limitation in application of BMGs.