DEDp and LPBF additive manufacturing of a TiC-reinforced case-hardened steel matrix composite

Iron-Based Metal Matrix Composites (IMMCs) exhibit high specific stiffness as well as excellent wear and thermal resistance. These properties make IMMCs suited for structural components subjected to friction such as gears, bushes and bearings. However, ensuring homogeneous dispersion of the reinforcements and reliable interfacial anchoring is still challenging (Chen S. 2025). Achieving a homogeneous composite powder composition at the LPBF melt pool scale also remains complex. DEDp offers greater flexibility in processing powders, but the larger melt pool combined with the need for coarser powders can result in unmolten particles. In the current work a 16NCD13 + 3.2 wt% TiC IMMC has been manufactured with both LPBF and DEDp. TiC promotes high hardness, low density, and excellent metallurgical compatibility with steels. The 16NCD13 matrix, a low-alloy case-hardening steel containing chromium and molybdenum, promotes the precipitation of mixed secondary carbides, thereby enhancing high-temperature mechanical strength (Chengru L. 2023). Two powder processing routes were considered: (1) for DEDp, a premixed composite powder blend with 15-35 µm TiC particles was optimized to allow suitable powder projection and ensure proper TiC dilution in melt-pool, (2) for LPBF, 16NCD13 powders were grafted with nanosized TiC particles. Good density, crack-free microstructures with a uniform distribution of TiC reinforcements were obtained using both the LPBF and DEDp processes. The addition of carbide increased the hardness from 350 HV (pure 16NCD13) to approximately 600 HV. However, the resulting microstructures are different: (1) DEDp forms large dendritic cells (~ 8um) composed of tempered martensite with micrometric titanium-rich precipitates. Lower layers consist of tempered martensite due to thermal cycling, resulting in lower hardness values. (2) LPBF leads to fine grains (~ 200nm) and homogeneously distributed nanometric precipitates. Austenitization followed by water quench were applied to both microstructures.