Microstructure evolution and strength–conductivity trade-off in L-PBF fabricated Fe–10Cu alloy under hot isostatic pressing

Abstract

Laser powder bed fusion (L-PBF) enables the formation of supersaturated solid solutions in immiscible alloy systems such as Fe–Cu under rapid solidification conditions. However, the resulting non-equilibrium microstructures inherently involve a trade-off between mechanical strength and thermal conductivity. In this study, Fe–10Cu alloy fabricated by L-PBF was subjected to hot isostatic pressing (HIP) at 100 MPa and 570-1170 °C, and diffusion-controlled phase evolution and corresponding process-microstructure-property relationships were systematically investigated. X-ray diffraction and electron microscopy analyses revealed that progressive Cu precipitation and grain growth occurred with increasing HIP temperature, indicating diffusion-mediated Cu redistribution and pore closure of the initially supersaturated non-equilibrium microstructure. The as-built and HIP-treated (570 °C) conditions exhibited high tensile strengths of 851.8 and 901.1 MPa, respectively, owing to solid-solution strengthening, grain refinement strengthening, and precipitation hardening. In contrast, high-temperature HIP treatments (970-1170 °C) promoted Cu coarsening and grain growth, resulting as reduction of tensile strength to 399.1 and 328.4 MPa, respectively, while thermal conductivity increased up to 80.3 W/m·K. The inverse correlation between strength and thermal conductivity is consistent with the competing microstructural requirements of Hall-Petch strengthening and solid-solution strengthening versus reduced electron scattering associated with solute depletion and grain coarsening. These findings suggest that the strength–conductivity balance in Fe–Cu immiscible alloys is governed by the degree of non-equilibrium supersaturation and the extent of diffusion-mediated Cu redistribution and pore closure during HIP. These results establishe a HIP-temperature-dependent strength–thermal conductivity property map for L-PBF Fe–10Cu alloys, enabling property-space navigation through diffusion-mediated Cu redistribution and microstructural evolution.