Strength and thermal conductivity enhancement by solute substitution during laser powder bed fusion of NiWCo/Cu dissimilar alloy joint

Abstract

Joints between Ni-based superalloys and copper, where the latter functions as a heat sink for high temperature applications, have poor structural integrity owing to the development of thermally induced strains and formation of brittle intermetallic compounds (IMCs) at their interfaces. In this study, a NiWCo/Cu joint based on a solute substitution strategy is fabricated using laser powder bed fusion (LPBF). Microstructural analysis reveals that the NiWCo/Cu interface has a hierarchical microstructure that consists of sub-micron W particles embedded within a chemically heterogeneous Ni-Cu rich matrix. Mechanical tests indicate that the dissimilar alloy assembly deforms in the Cu portion, with a good combination of yield strength and elongation to failure. Transient thermal conductivity (κ) investigations indicate that it also has excellent heat dissipation characteristics that reduce the peak temperature in the NiWCo portion by ∼50 °C, compared to that in pristine NiWCo. These characteristics are attributed to the unique microstructural features of the interface which develop due to a thermodynamically driven solute substitution reaction at the NiWCo/Cu interface. Multi-phase simulations and phase equilibrium analysis are employed to explain the microstructural evolution. Contributions of the microstructural features to yield strength and the thermal resistance of the interface are quantitatively estimated. Finally, a critical appraisal of the solute-substitution strategy for enhancing the service temperature of high temperature components is provided.