In recent years, the Ti-6Al-4V alloy fabricated using additive manufacturing (AM) has garnered significant attention as a metallic biomaterial due to its high potential in medical applications, particularly in body implants. However, challenges such as the corrosion and tribocorrosion behavior of this alloy in the body environment remain critical issues, as these factors can lead to the release of harmful ions and pose a risk to patient health. In AM methods, particularly in powder bed fusion (PBF) techniques, manufacturing parameters and the specimen's orientation relative to the build direction play a decisive role in the final properties of the implants. Accordingly, this study aimed to eva‎luate the role of manufacturing parameters and build orientation on the microstructure, hardness, corrosion, and tribocorrosion of the Ti-6Al-4V alloy fabricated by electron beam melting (EBM). In this regard, Ti-6Al-4V samples fabricated under two different operational conditions—one based on Arcam's standard manufacturing parameters and the other with selected parameters. Variations in current and build speed were applied to precisely assess the impact of these parameters on the final performance of the implants. Additionally, the effects of spatial orientation relative to the build direction was examined as one of the key factors influencing the properties of AM-fabricated samples. The results of this study showed that all samples consisted of a dual-phase α/β structure, and changes in manufacturing parameters had no significant effect on the microstructure. It was also found that in the XY planes, which are perpendicular to the build direction, higher cooling rates resulted in more elongated and columnar grain growth, while the YZ planes, which are parallel to the build direction, exhibited smaller grains with layer-by-layer growth. Electrochemical tests in phosphate-buffered saline (PBS) and hydrogen peroxide (H₂O₂) solutions, conducted to simulate inflammatory conditions at a temperature of 37°C, revealed that although the corrosion resistance of the samples varied depending on the manufacturing parameters and spatial orientation, all samples exhibited appropriate corrosion behavior for use in body implants by forming a passive oxide layer. However, the XY planes demonstrated higher corrosion resistance compared to the YZ planes, likely due to differences in cooling rates and manufacturing parameters. The findings indicated that not only manufacturing parameters but also spatial orientation relative to the build direction can influence tribocorrosion behavior, as tribocorrosion tests under open-circuit potential conditions showed that XY planes exhibited a reduced potential drop due to their more noble electrochemical behavior. Finally, after 14 days of immersion in SBF solution at 37°C, all implants demonstrated favorable bioactive behavior. Overall, this study indicated that manufacturing parameters and spatial orientation relative to the build direction can affect the final performance of Ti-6Al-4V implants fabricated by EBM. The findings indicated that the sample produced with Arcam's standard parameters in the XY plane exhibited the best performance in terms of corrosion resistance and tribocorrosion.

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رحمت اله عمادي , عباس بهرامي