[en] Highlights: • Joining of a Ti-based strong glass former using friction stir spot welding process was studied. • Effects of welding parameters on the fracture load and fractured surfaces were analyzed. • Different zones in the weld spot were characterized and stir zone, TMAZ and base metal were identified. • Nano crystal/BMG's composite formation in the stir zone under the tool shoulder was the reason for higher fracture load. • Stir zone under the tool tip and the TMAZ had similar hardness and shear bands pattern with different structural reasons. In this study, TiZrFeBeCu bulk metallic glass plates have been welded together by using the friction stir spot welding method. The effects of processing parameters on the microstructure and mechanical properties of the joints have been studied. It has been found that the plunge depth has a crucial effect on the fracture mode and fracture strength of the joint. Both tool rotation speed and holding time significantly influence the tensile/shear fracture load and the fracture toughness. The correlation between fracture surface and the fracture toughness have been analyzed. The results revealed that there exist three regions in the spot welding of bulk metallic glass plates: stirring zone, thermo mechanically affected zone and base metal. It shows that stirring zone under the tool shoulder and around the tool tip possesses different structures and micro-hardness from that beneath the tool tip. The thermo mechanically affected zone and the stirring zone under the tool tip have similar hardness and structure. Stress relief annealing was used to clarify the reason for the hardness difference at different regions. Changes in the hardness in different areas of the welding spot can be correlated with the shear bands pattern and plastic zone size around the Vickers indents.

[en] Highlights: • A strategy for designing ductile metallic glass composites by forming nanocrystals in the high-entropy alloy particles during deformation was proposed. • The ex situ high-entropy alloy particle toughened Zr-based metallic glass composites were prepared by spark plasma sintering. • By adding CoCrFeNiAl high-entropy alloy particles, the Zr-based metallic glass composites exhibit enhanced strength-ductility synergy. • The toughening mechanisms were discussed in accordance with experiments and modeling. In this work, we prepared equiatomic AlCoCrFeNi high-entropy alloy (HEA)-particle-toughened, Zr-based metallic glass composites by spark plasma sintering. By adding HEA particles as the second phase, the strength and plasticity of the Zr-based metallic glass composites improved concomitantly. After fracture, high-density dislocations and nanocrystals were formed in the HEA particles due to local severe plastic deformation, which consumed massive strain energy to enable the resistance to crack formation. Substantial lattice distortion imparted a remarkable work-hardening capacity to the HEAs and enhanced crack-tip dislocation trapping, and thus led to an extreme refinement of the grain size. Finite-element analyses indicated that the strain hardening behavior of HEA particles reduced the magnitude of strain localization, promoted generation of multiple shear bands, and stabilized shear band propagation. We attribute the enhanced strength-ductility synergy in the current composites to high-density dislocations and nanocrystal formation in the HEA particles, and stable propagation of multiple shear bands.