Surface topography control in CoCrMo alloy additive manufacturing through laser powder bed fusion process

Laser powder bed fusion (LPBF) enables precise fabrication of CoCrMo alloy components for biomedical applications; however, achieving optimal surface properties for orthopedic implants remains challenging. Surface engineering plays a pivotal role in enhancing both biological and tribological responses, particularly in improving the adhesion of bioactive coatings. This study integrates LPBFed surface optimization with atmospheric plasma-sprayed (APS) hydroxyapatite (HAp) coatings to enhance interfacial bonding strength. LPBF process parameters were systematically optimized to tailor surface roughness, followed by APS deposition of HAp coatings on the optimized CoCrMo substrates. In this study, LPBF process parameters were varied to fabricate CoCrMo samples, and specimens were evaluated based on microhardness (320–375 ± 12 HV 0.5 ), porosity (<1.1%), relative density (~98.9%), and surface roughness (R a : 3–13 μm). Based on these criteria, three representative samples were selected for in-depth microstructural and mechanical characterization. Microstructural analysis revealed a dual-phase γ-FCC + ε-HCP (~14.4 vol%) matrix with cellular substructures, columnar grains, and oxide inclusions. Transmission electron microscopy (TEM) analysis revealed nano-sized chromium-rich oxides (~50 nm) and (Co, Mo, W) 2 Si Laves phases along grain boundaries, which act as dislocation barriers and contribute to enhanced strength, strain hardening, and microstructural stability. The optimized LPBFed CoCrMo alloy exhibited a yield strength of ~800 ± 15 MPa and elongation of 8 ± 0.5%, attributed to the refined cellular structure, planar defects, and solid-solution strengthening. Following HAp deposition via APS, adhesion strength measurements revealed significantly enhanced interfacial bonding (~45 MPa) in a sample with optimized surface morphology. Scanning electron microscope observations confirmed reduced tensile cracking and improved coating cohesion. Nanoindentation further demonstrated superior hardness and elastic modulus, indicating dense and mechanically stable coatings. These results confirm that LPBF combined with parameter optimization and surface engineering can significantly improve the mechanical integrity and adhesion strength of bioactive coatings for advanced orthopedic implants.