Insights into the microstructure, property, and metallurgy mechanism of 93WNiFe/steel diffusion bonding joint utilizing a NiFeW solid solution interlayer

Abstract

93WNiFe alloy and 30CrMnSiA steel was diffusion bonded successfully with NiFeW solid solution (NiFeWss) interlayer prepared on the surface of the former by using in-situ reduction technology. The microstructure, property, and metallurgy mechanism of the joint was investigated by experiments and molecular dynamic simulations. The results indicate that, the microstructure of the joint using NiFeWSS interlayer with ideal purity (100%) and suitable average thickness (∼100 μm) is W/ (NiFeWSS matrix + tiny W particle) diffusion layer /steel, without any interfacial intermetallic compound. The thermal expansion coefficient of (NiFeWSS matrix + tiny particle W) diffusion layer is between that of W substrate and steel substrate, which is beneficial to release the residual thermal stress. At the optimized technology parameters, which are bonding pressure of 50 MPa, bonding temperature of 1020 °C and holding time of 60 min, the tensile strength of the joint reaches 289 MPa. The formation mechanism of diffusion layer can be elaborated that, at the bonding temperature, although W particles in W substrate do not provide any element into NiFeWss interlayer, the mutual diffusion behaviors between steel substrate and NiFeWss interlayer, especially element Ni (diffusion coefficient of 5.29 × 10−9 m2/s) and element Fe (diffusion coefficient of 2.75 × 10−9 m2/s), are significantly. The mutual diffusion phenomenon results in the composition deviation of interlayer (diffusion layer), which exceeds the solid solubility of element W in NiFeWss at room temperature. Therefore, as temperature decreases, the excessive element W will be precipitated as tiny W particles, leading to the formation of (NiFeWSS matrix + tiny particle W) diffusion layer.