The objective of this paper is to show the dependence relationship between the crystallographic orientations upon brittle-to-ductile transition during diamond turning of monocrystalline silicon. Cutting tests were performed using a −5° rake angle round nose diamond tool at different machining scales. At the micrometre level, the feedrate was kept constant at 2.5micrometres per revolution (µm/r), and the depth of cut was varied from 1 to 5 µm. At the submicrometre level, the depth of cut was kept constant at 500 nm and the feedrate varied from 5 to 10 µm/r. At the micrometre level, the uncut shoulder generated with an interrupted cutting test procedure provided a quantitative measurement of the ductile-to-brittle transition. Results show that the critical chip thickness in silicon for ductile material removal reaches a maximum of 285 nm in the [100] direction and a minimum of 115 nm in the [110] direction, when the depth of cut was 5 µm. It was found that when a submicrometre depth of cut was applied, microcracks were revealed in the [110] direction, which is the softer direction in silicon. Micro Raman spectroscopy was used to estimate surface residual stress after machining. Compressive residual stress in the range 142 MPa and smooth damage free surface finish was probed in the [100] direction for a depth of cut of 5 µm, whereas residual stresses in the range 350 MPa and brittle damage was probed in the [110] direction for a depth of cut of 500 nm.

Raman scattering technique was used to investigate the structural phase transformations and multiple phase generation of silicon induced by cyclic microindentations. Indentation cycles were performed on three different samples: monocrystalline, amorphous film, and on partially amorphous silicon generated by single point diamond turning. The results indicated that the formation of some pressure induced structural phases may be dependent upon the initial structural state of the materials surface: Several different structural phases were only observed in crystalline and partially amorphous Si after microindentation cycles. For completely amorphous Si, no phase formation was evidenced even after several cyclic indentations.

The Ti-6Al-4V alloy is widely used in orthopedic and dental implants due to its excellent mechanical, corrosion, and biological properties. However, it exhibits several limitations that can compromise its performance in clinical applications. Notably, the alloy suffers from a high coefficient of friction, which can lead to increased wear and reduced longevity of implants under relative movement conditions. Additionally, Ti-6Al-4V shows susceptibility to localized corrosion in physiological environments, particularly in the presence of bodily fluids that may result in the formation of pitting. These challenges underscore the need for surface modifications that can enhance the alloy’s tribological performance, thereby improving its overall efficacy and durability as a biomaterial in medical settings. In this context, the manuscript presents applied and innovative research that assesses the impact of implementing nanostructured Nb₂O₅ coatings through the reactive sputtering technique on the wear performance of Ti-6Al-4V alloy under both air and artificial saliva (AS) solution conditions using a Pin-on-Disk apparatus. The nanostructured Nb₂O₅ coating demonstrated the ability to reduce the wear rate and volume by up to 88% without inducing any modifications to the R_a and R_t of Ti-6Al-4V, a feature that is desirable for applications in implantable devices. The reduction in wear can be attributed to the shift from adhesive wear mechanisms on uncoated surfaces to abrasive mechanisms on coated surfaces. This research highlights the strategic advantage of utilizing Brazil’s abundant niobium resources to advance biomaterial technology and facilitate applications that benefit public health.