Digital representation of the wear behaviour of Ti-6Al-4V and Ti-6Al-7Nb biomaterial alloys: A fractal analysis of the worn surface

Currently, Ti-6Al-4V alloy is one of the most used materials in biomedical devices, namely in orthopedic prothesis, thanks to its outstanding properties. However, its composition contains vanadium ions, considered toxic to the human body. Since the 1980s, there has been a growing effort to replace this alloy with less toxic alternatives. A promising candidate is the Ti-6Al-7Nb alloy. There are relatively few studies on the surface properties of this alloy, on the other hand, the knowledge of its tribological performance is of great importance for the use of this alloy in biomedical applications. Digital tribology has great potential in a quantitative inspection of wear in materials engineering. Methodologies of surface inspection, such as fractal description, can explain the relationship between microstructural, tribological parameters, and surface roughness. In this work, the inspection of the fractal behavior of worn surfaces of both Ti-6Al-4V and Ti-6Al-7Nb samples was carried out. Tribological tests were performed in a block-on-disk tribometer, using AISI 1045 steel as antagonist material, under different conditions. The fractal values were correlated to tribological parameters and the evolution of morphological aspects along the surface. Elevation maps of the sliding surfaces were built from pictures obtained from optical microscopy (OM). The "Extended depth from focus", (EDF) reconstruction method, allowed the ordering of stacks of images to conduct a quantitative investigation of the behavior of surfaces.