Remelting-induced enhancement of mechanical properties in SS316L/IN625 functionally graded materials produced by selective laser melting

Purpose This study aims to enhance the mechanical performance and structural integrity of SS316L/IN625 functionally graded materials (FGMs) fabricated via selective laser melting (SLM). Building on the development of a custom multi-powder SLM platform, the research investigates how layer-wise re-melting influences densification, interfacial bonding and overall mechanical reliability in multi-material additive manufacturing. Design/methodology/approach A custom-built SLM platform capable of depositing six discrete compositional gradients from SS316L to IN625 was used. Each deposited layer underwent in-situ laser re-melting under optimized parameters to promote defect healing and compositional homogeneity. The fabricated FGMs were characterized through optical and scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). Mechanical behavior was evaluated through hardness mapping and tensile, compression and shear tests to establish quantitative process–structure–property relationships. Findings Layer-wise re-melting markedly improved densification and metallurgical bonding, reducing lack-of-fusion porosity and producing smoother melt-pool boundaries and more continuous columnar growth at interfaces. XRD confirmed partial carbide dissolution and solute retention within the γ matrix, while EDS showed a controlled, near-linear compositional gradient. Surface roughness decreased by 16%, and hardness increased consistently across the graded regions. Mechanically, re-melting enhanced ultimate tensile strength (+8.7%), total elongation (+22.7%), ultimate shear strength (+16.2%) and compressive proof stress (+5.1%) relative to non-remelted samples, demonstrating concurrent gains in both strength and ductility. Originality/value This work introduces a robust fabrication strategy that integrates multi-powder deposition with in-situ layer-wise re-melting to achieve superior microstructural continuity and mechanical performance in metal FGMs. The findings provide a validated framework for tailoring graded metallic components with improved density, bonding integrity and surface quality – offering practical advantages for aerospace, marine and high-temperature applications.