Microstructure and tensile behavior of small scale resistance spot welding of sandwich bulk metallic glasses

In this work, a small-scale resistance spot welding method was utilized to join two dissimilar Zr-based bulk metallic glasses and to fabricate the sandwich-laminated metallic glass plates. The laminates exhibit an almost fully amorphous structure without undesirable crystallization. Elemental line scanning across the joint interface shows a uniform distribution of the main elements, demonstrating favorable metallurgical bond in the laminate. The resultant tensile strength of the welded laminate is comparable to that of the parent metallic glasses. The fractured surface of the laminate exhibits extensive multiple failure planes, suggesting that the fracture instability was mediated by a crack branching mechanism over across the joint interface. Such a crack branching mechanism results in a stepwise fracture behavior which is contrastingly different from the conventional single primary shear band dominated catastrophic fracture in monolithic metallic glasses under tension. The unique stepwise fracture behavior endows the sandwiched metallic glass laminates with an excessive strain energy absorption through the joint interface than monolithic metallic glasses. Our results demonstrate that small-scale resistance spot welding is a promising approach to scaling up metallic glasses and to fabricating metallic glass laminates with desirable mechanical performance for structural applications.