Understanding the microstructure and mechanical performance of heat-treated Inconel 625/TiC composite produced by laser powder bed fusion

This work aims to develop and characterize Inconel 625 (IN625) reinforced with 1 wt% of sub-micrometric TiC particles processed by the Laser Powder Bed Fusion (LPBF) process. The effect of TiC particles on the IN625 alloy was investigated in the as-built and two heat-treated conditions. A volumetric energy density of 99 J/mm3 could produce bulk IN625 and IN625/TiC samples with residual porosity less than 0.15%. The as-built IN625 and IN625/TiC showed columnar grains along the building direction and sub-micrometric dendritic architectures. The as-built IN625/TiC presented higher hardness, tensile strength, and similar elongation at failure with respect to the as-built IN625 alloy. These mechanical properties are mainly attributed to the reinforcement effect of the TiC particles predominantly located along the grain boundaries, melt pool contours, and interdendritic areas. After heat treatments at 980 ◦C and 1150 ◦C, the IN625 alloy and IN625/TiC composite presented different microstructure stability and mechanical properties evolution, revealing greater hardness and tensile strength for the composite. In particular, when heat-treated, the IN625 was subjected to a remarkable dendritic dissolution at 980 ◦C and recrystallization at 1150 ◦C. Conversely, the IN625/TiC revealed a limited dendritic dissolution at 980 ◦C and the inhibition of recrystallization at 1150 ◦C. Overall, the pinning effect of the TiC particles was effective in providing less microstructure and mechanical properties variations under heat treatments. The current work describes the effect of adding TiC particles on the microstructure stabilization and mechanical properties evolution of additively processed LPBFed IN625 alloy in as-built and heat-treated conditions.