Surface topography in machining Ti alloys for biomedical applications: correlative microscopy approach for qualitative and quantitative analysis

V-free Ti-6Al-7Nb alloy may be an interesting candidate as a substitute to the traditional Ti-6Al-4V alloy on the development of biomedical components. The inspection of surface integrity through digital microscopy techniques shows strong potential for comparative analysis and optimization of manufacturing processes. This work deals with the comparative analysis of turned surfaces of dual-phase (α+β) titanium alloys: Ti-6Al-4V and Ti-6Al-7Nb, under different cutting conditions. Digital image processing and analysis technique has been used to evaluate the volume fraction of phases and their distribution. An innovative methodology for digitizing the surface topography was applied, based on the association of modern microscopy techniques with digital image processing-correlative microscopy. The global outcomes show that Ti-6Al-4V samples presented better homogeneity, with a mean β volume fraction of about 17%, compared to 11% of Ti-6Al-7Nb samples. The combination of higher feed rate and lower velocity produce rougher topography for both alloys, while the topographic formation obtained by the combination of lower feed rate and higher velocity seems smoother. In addition, Ti-6Al-4V alloy presents rougher topography in comparison topography of Ti-6Al-7Nb, under all conditions, probably due to the different phase distribution. The correlative microscopy allowed a correspondence between the cutting conditions and the microstructural properties of both Ti-6Al-4V and Ti-6Al-7Nb alloys, through the analysis of the machined surface.