Influence of TiC and TiN Ceramic Reinforcements on the Microstructure, Thermal Expansion Behavior, and Tensile Properties of Invar 36 Manufactured by Laser Powder Bed Fusion

Invar, an Fe–Ni alloy with an exceptionally low coefficient of thermal expansion (CTE), is widely used in precision engineering applications but is limited by its poor mechanical strength. Improving its strength through particle reinforcement without compromising its low CTE remains a major challenge. This study investigates the effect of titanium carbide (TiC) and titanium nitride (TiN) on the microstructure, tensile behavior, and thermal stability of Invar fabricated via laser powder bed fusion (LPBF). Invar was blended with 10 wt% of TiC and TiN to produce reinforced composites. Microstructural analysis showed that TiC refinement increased high‐angle grain boundaries, contributing to enhanced dislocation density. Tensile testing revealed that TiC and TiN reinforcements increased ultimate tensile strength (UTS) to 745 and 591 MPa, respectively, compared to 430 MPa for unreinforced Invar, albeit with reduced ductility. Thermal expansion analysis indicated that TiC retained Invar's low CTE, with only a ~35% increase compared to LPBF Invar, while TiN exhibited a ~139% increase. These findings highlight that TiC is an effective reinforcement for strengthening Invar while preserving its thermal stability, making it a promising candidate for applications requiring dimensional precision and higher load‐bearing capacity.