Effect of bonding process on the microstructures and strength of W/steel joints with a W-Cu-Ni interlayer

Abstract

Bonding between W and steel using a 90W-9Cu-1Ni powder mixtures/Ni multi-interlayer was carried out in vacuum for 60 min at 1120 °C with a bonding pressure of 20 MPa and a bonding pressure of 5 MPa assisted with presetting Co powder on the surface of W. The microstructures, composition distribution, and fracture characteristics of the joint were studied by SEM, EDS. Joint properties were evaluated by shear experiments tests. The results showed that the joints comprised W/W-Cu-Ni composites/Ni/steel. The W-Cu-Ni composites with a homogeneous and dense microstructure formed by liquid phase sintering of 90W-9Cu-1Ni powder mixtures prepared by high energy ball mill method. Under the bonding pressure of 20 MPa, a bonding line with a width of about 0.5 μm and high element tungsten content formed between W-Cu-Ni composites and W, which resulted in high shear strength (275 ± 12 MPa) of the W/steel joints and failure during testing was always located at W near the W-Cu-Ni composites/W interface. For the bonding process of bonding pressure of 5 MPa assisted with presetting Co powder on the surface of W，μ-(Co, Ni)7W6 intermetallic compounds layers were formed in W-Cu-Ni composites and W, which atomic ratio of Co to Ni is 2 to 1. The average shear strength of W/steel joints bonded by this bonding process was 242 ± 9 MPa and all joints were fractured in the Ni layer near the W-Cu-Ni composites/Ni interface.