Investigation on hybrid bonding of tungsten/steel with in-situ formed composites interlayer

Hybrid bonding between steel and W using 88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures sandwiched between Ni and Cu foils was carried out in vacuum for 60 min at 1120 ℃ with a pressure of 5 MPa. The assembly sequence of bonding specimens was steel/Ni/Cu/88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures/Cu/Ni/Cu/W. The microstructures and composition distribution of the joint were studied by SEM and EDS. Joint properties were evaluated by shear experiment tests, and the fracture characteristics of the shear samples for the joints were also determined by SEM. The results showed that the joints comprised steel/Ni/composites/Cu-Ni/W, wherein the composites interlayer consisting of tungsten heavy alloy and irregular Ni agglomerate in-situ formed by the combined sintering of 88(97W-2.7Cu-0.3Ni)−12Ni powder mixtures. The hybrid bonding mechanisms of the interfaces in the joint include solid-phase diffusion bonding and transient liquid phase diffusion bonding. An additional hot-dip experiment found that obvious solid-liquid interface diffusion and Ni segregation occurred under the bonding conditions, and a large number of W atoms diffused into the Cu-Ni liquid phase. In the Cu-Ni alloy layer, the content of element W is more than 4.22% (at.%). The average shear strength of W/steel joints was 263 ± 7 MPa and all the shear samples were fractured in the W near the bonding interface.