This work aimed to investigate the effect of the burnishing surface treatment on the tribocorrosion resistance related to Ti6Al4V specimens, in the framework of the head-neck tribo-pair characterising a total hip replacement. The experimental procedure carried out started by choosing the specimens referred to different burnishing conditions together with specimens not treated or treated only with the turning process. Then, tribocorrosion experiments with fixed load and two frequencies were conducted through a reciprocating tribometer equipped with a potentiostat able to measure the electrochemical corrosion potential and current associated to the synergistic wear phenomenon analysed together with the coefficient of friction. Furthermore, optical topographical acquisitions were performed before and after the experiments. The results showed that the non-burnished specimens exhibited unexpected oscillations of the coefficient of friction approximately in the middle of the rubbing phase and the same happens for the cell potential; the wear volume was measured after the tribocorrosion test. This allowed to estimate the wear factor related to all the analysed configurations, showing a greater mean value in correspondence of greater sliding frequencies in the non-burnished cases, while the opposite happens in the burnished cases. Finally, the burnished sample at the lower burnishing force resulted to have the noblest corrosion potential, while the non-burnished samples exhibited the lowest corrosion current density.
Aiming to solve the problem of the gear lubrication of unmanned aerial vehicles (UVAs), a grease mixed Thermal-elastohydrodynamic lubrication (TEHL) model is established, and the lubrication state of the gearbox of oil-powered heavy-duty UAVs is numerically analyzed. In this study, grease is regarded as a non-Newtonian fluid whose properties change nonlinearly with respect to pressure, temperature, and other conditions. The complex meshing state of a spiral bevel gear tooth surface is analyzed using the loaded tooth contact analysis (LTCA) method, and three points on the tooth surface are selected as samples to describe the lubrication state of the entire tooth surface. The thickness of grease film and the temperature rise of the tooth surface are studied in detail, considering the natural roughness of the tooth surface and influence of different greases. The results show that the established model agrees with results from the literature. The dangerous point of tooth surface lubrication is at the meshing midpoint. Under cruise conditions, the lubricating grease viscosity significantly influences the temperature rise of the tooth surface.
Copper-based functionally gradient composite material is developed using powder metallurgy processing technique, as a potential wind turbine brake pad material. The developed composite has a gradient composition of Cu, CeO2, Al2O3, Fe, and C-g to enable joint strength at the interface (brake calliper) and wear resistance at the contact surface (brake disc). The article presents a comprehensive analysis on the microstructure, microhardness, and tribological performance of the developed composite. The wear mechanism is deduced through surface morphology, elemental composition, and phase composition analysis using field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and X-ray photoelectron spectroscope. A maximum hardness of 198.2 HV was obtained at the contact surface. Experimental values from tribology tests show that a decreasing trend was obtained with a wear rate of 2.013 x 10(-7) g N-m(-1) and a friction coefficient was 0.215.
The tribological characteristics of stir cast Al-15%Si-10%Zn matrix with 15%ZrO2 reinforced composite were investigated. The microstructure of the Al-15Si alloy consisted of coarse primary Si and acicular eutectic Si phases randomly distributed in the Al dendrites. The Al-15%Si-10%Zn/ZrO2 composite showed spherical Si with a size between 25 and 75 & mu;m; fragmented eutectic Si phase and uniform dispersion of ZrO2 particles in the matrix. The wear test was conducted using in a pin-on-disc method at different loads and sliding velocities. It was found reduced coefficient of friction, significant increase in the hardness and wear resistance of the composite compared to the matrix alloy. High wear resistance in the composite due to the effect of solid lubrication provided by Zn, and good fracture toughness and wear resistance by the reinforced ZrO2 particles. The predominant oxidative and abrasive wear were identified as the mechanisms leading to material failure through plastic deformation and delamination.
The machinability studies for the Inconel 718 alloy with the coated cemented carbide cutting tool having 0.4 and 1.2 mm nose radius, varying cutting speeds (65, 81, 95 and 106 m/min) with a constant feed rate of (0.15 mm/rev) and a depth of cut (0.2 mm) were conducted. The cutting force decreases with the increase in cutting speed due to the thermal softening of the work surface at a high temperature. With the increase in nose radius a decrease in the cutting force is observed due to the increase in the cutting edge of the tool. The formation of residual stress has a profound effect on the change in the tool morphology during the machining of the alloy. Furthermore, the chip analysis in terms of chip morphology is carried out in detail. The detailed tool fracture studies are conducted and are explained for the various machining processes.
