Avaliação do efeito combinado de tratamento superficial à laser e passivação no limite de fadiga em flexão da liga comercial Ti-6Al-4V ELI

Abstract

Laser irradiation is a widely used technology for the surface modification of titanium alloy implants, enabling their identification and traceability. This process locally heats the alloy surface, generating a dark oxide layer. Subsequent passivation with nitric acid is commonly applied to reduce reactivity and enhance corrosion resistance. However, the combination of these treatments represents a significant challenge in the industry due to the variety of parameters affecting surface topography and microstructure. In this context, the objective of this project was to evaluate the combined effect of a surface treatment using Nd:YAG laser irradiation and nitric acid passivation on the fatigue limit of Ti-6Al-4V ELI alloy. The four-point bending fatigue tests was employed, applying the fatigue limit value at 1 million cycles defined according to ASTM F382:17 standard. Scanning electron microscopy (SEM) was used to characterize the irradiated and fractured surfaces to establish a correlation between surface modification and fatigue limit. The results showed that the fatigue limit of 615 MPa for the polished and passivated condition was maintained compared to the polished condition. After irradiation, a 58,5% reduction in the fatigue limit was observed, reaching 255 MPa. Finally, passivation after irradiation resulted in a 47,1% increase compared to the irradiated condition, reaching 375 MPa. The increase in fatigue limit from 255 to 375 MPa after passivation can be attributed to the reduction in surface roughness (Ra and Rz), reducing stress concentration and delaying crack propagation. The significance of these results lies in the optimization of surface treatments for titanium implants, aiming to improve their durability and performance in biomedical applications.