Mechanical and thermal properties of identified zones at a Ti-based bulk metallic glass weld spot jointed by friction stir spot welding (FSSW)

The weld spot of (Ti41Zr25Be28Fe6)(93)Cu-7 bulk metallic glass is characterized after friction stir spot welding. The mechanical and thermal properties of different zones of the weld spot are studied using X-ray diffraction, Vickers micro hardness, nanoindentation and differential scanning calorimetry. Base metal (BM), stir zone under the tool shoulder and around the tool tip (SSZ), stir zone under the tool tip (TSZ) and thermos-mechanically affected zone (TMAZ); have been identified in the weld spot. The TMAZ reveals the minimum hardness, while the TSZ presents the lowest elastic modulus and the greatest thermal stability. The highest hardness and elastic modulus and also the less thermal stability are observed in the SSZ. Analysis of the pop-in marks on the P - h curves verifies the formation of tensile stress in the TSZ, creation of the excess free volume in the TMAZ and the formation of nanocrystals in the SSZ during welding.