This study investigates the effect of laser volume energy density (VED) on the properties of AISI 420 stainless steel and TiN/AISI 420 composite manufactured by selective laser melting (SLM). The composite contained 1 wt.% TiN and the average diameters of AISI 420 and TiN powders were 45 µm and 1 µm, respectively. The powder for SLMing the TiN/AISI 420 composite was prepared using a novel two-stage mixing scheme. The morphology, mechanical, and corrosion properties of the specimens were analyzed, and their correlations with microstructures were investigated. The results showed that the surface roughness of both SLM samples decreases with increasing VED, while relative densities greater than 99% were achieved at VEDs higher than 160 J/mm³. The SLM AISI 420 specimen fabricated at a VED of 205 J/mm³ exhibited the highest density of 7.7 g/cm³, tensile strength (UTS) of 1270 MPa, and elongation of 3.86%. The SLM TiN/AISI 420 specimen at a VED of 285 J/mm³ had a density of 7.67 g/cm³, UTS of 1482 MPa, and elongation of 2.72%. The microstructure of the SLM TiN/AISI 420 composite displayed a ring-like micro-grain structure consisting of retained austenite on the grain boundary and martensite in the grain. The TiN particles strengthened the mechanical properties of the composite by accumulating along the grain boundary. The mean hardnesses of the SLM AISI 420 and TiN/AISI 420 specimens were 635 and 735 HV, respectively, which exceeded previously reported results. The SLM TiN/AISI 420 composite exhibited excellent corrosion resistance in both 3.5 wt.% NaCl and 6 wt.% FeCl₃ solutions, with a resulting corrosion rate as low as 11 µm/year.

Enhancing the mechanical properties and surface finish of components fabricated via Fused Deposition Modeling (FDM) is essential to ensuring structural integrity and reliability in engineering applications. This study proposes an optimization methodology to identify the optimal FDM process parameters for polylactic acid (PLA) material that simultaneously improve mechanical performance and surface quality. The effects of three key FDM parameters—layer height, infill density, and nozzle temperature—on the tensile strength and surface roughness of printed samples were systematically investigated. Using the Taguchi method combined with Grey Relational Analysis (GRA), the optimal settings were determined to be a 0.15 mm layer height, 70% infill density, and a nozzle temperature of 210 °C. Under these conditions, the fabricated samples achieved a tensile strength of 37.12 MPa and a surface roughness of 5.23 µm, demonstrating significant improvements in both strength and surface finish. By integrating rigorous experimentation with robust statistical analysis, the proposed framework contributes to advancing additive manufacturing practices and provides a reliable approach for enhancing the quality of PLA-based FDM components.