Small scale resistance spot welding of Cu47Ti34Zr11Ni8 (Vitreloy 101) bulk metallic glass

The resistance spot welding of Vitreloy 101 (Cu₄₇Ti₃₄Zr₁₁Ni₈) metallic glass ribbons was studied by mechanical testing, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Material was expelled along the weld interface and around the electrode contact points on the alloy surface. There were no significant changes in composition between the melted and native alloy although minor (∼8%) crystallization was observed in DSC data. Failure during peel and tensile-shear tests of the welds was observed to occur at the periphery of the weld (pullout failure), where slower melting and cooling occurred away from the heat sink effects of the welding electrodes. Measurements of lap welds indicated a maximum shear strength of 810 ± 77 MPa, about 75% of the predicted shear strength of the monolithic alloy. Embrittlement and crystallization around the weld likely contributed to failure. A finite element analysis (FEA) model was developed to explore the temperature–time relation inside the metallic glass during and following welding and it confirmed the main features observed experimentally. The model indicated rapid melting as temperatures reached ∼2000 K followed by cooling of the center of the weld nugget at rates up to ∼48,000 K s⁻¹, greatly exceeding the critical cooling rate for this material of 250 K s⁻¹. A torus of material around the weld nugget remained molten for longer and cooled more slowly than the center of the weld nugget.