Abstract

Laser powder bed fusion (LPBF) enables the fabrication of complex CoCrMo alloy implants but introduces detrimental residual stresses that compromise their structural integrity and tribological performance. While heat treatment (HT) is a common stress-relief strategy, its specific impact on the bio-tribological behavior under physiologically relevant conditions remains unclear. Hence, this study elucidates the effect of HT (550°C, 675°C, 800°C, and 1100°C) on the microstructural evolution, stress relief, and bio-tribological properties of LPBF-fabricated CoCrMo. The microstructural analysis confirmed progressive stress relaxation, with recrystallization and extensive M23C6 carbide/Cr2O3 oxide formation dominating at 1100°C. The 1100°C HT reduced the main body (plates) wear by 25% and 50% under dry conditions and synovial fluid lubrication, respectively. The counter-body (balls) wear was reduced by 40 and 60%, respectively, demonstrating a synergistic protective effect crucial for the longevity of biomedical implant systems. Raman spectroscopy revealed that the superior performance at 1100°C is governed by the formation of a multifunctional tribo-layer, comprising lubricious Co3O4, graphitic carbon (dry) and a stable oxide-phosphate film (lubricated). Our findings demonstrate that HT at 1100°C provides an optimal combination of complete stress relief, extreme hardness, and protective surface chemistry, establishing it as an excellent approach to enhance the longevity and reliability of biomedical implants.