Influence of additive manufacturing process parameters on Ti6Al4V surface properties and performances

This study investigates the effect of additive manufacturing process parameters on the surface characteristics and performances of titanium Ti6Al4V, used for orthopedic implants. Parts were manufactured by selective laser melting, using a variety of volumetric energy densities, ranging from 58 to 152 J/mm3. Through a rigorous optimization of process parameters coupled with optical examinations of porosity distribution and morphology, a volumetric energy density of 58 J/mm3 was identified as an optimal manufacturing condition that resulted in extremely high densities of 99.8% in Ti6Al4V titanium alloy. X-ray diffraction measurements revealed the development of anisotropic residual stress states, characterized by elevated tensile stresses oriented along the build direction. Phase analysis results indicate a predominant martensitic acicular alpha ' structure, resulting from the rapid heating and cooling kinetics intrinsic to additive manufacturing, with a minor residual prior-beta phase. Optical examinations reveal a microstructural transition from equiaxed prior-beta grains to a columnar structure correlated with an increase in scanning speed (decrease in volume energy density). Corrosion tests were performed in Ringer's solution at 37 degrees C to simulate physiological conditions. It has been established that the presence of elongated pores combined with high tensile residual stresses can significantly compromise the corrosion resistance of additively manufactured parts. Minimizing porosity, through optimized SLM process parameters, significantly improved corrosion resistance. This resulted in a continuous and dense passive film, reducing the corrosion rate by 72%, from 22 to 6 mu m/year. These findings enable prosthesis manufacturers to enhance additively manufactured implant performances, extending their longevity.