Effect of Coating and Low Viscosity Oils on Piston Ring Friction under Mixed Regime of Lubrication through Analytical Modelling

This paper presents the impact of coating topography in piston ring-liner conjunction under mixed regime of lubrication using low viscosity oils. The study provides a time efficient analytical model including mixed-hydrodynamics regime of lubrication under different contact conditions. The method modified the expressions of the contact load and area of Greenwood-Tripp model in order to capture the real asperities interaction into contact. The model represents the tribological behavior of a thin top ring at Top Dead Centre, where boundary and mixed conditions are predominant. Electroplated CrN and PVD TiN coated rings were studied to predict the ring friction. The results are compared with an uncoated steel ring. The CrN coating shows slighter coefficient of friction, due to the coating morphology and roughness parameters. The TiN coating presents thicker lubricant films and higher coefficient of friction because the surface topography is quite rough with high peaks. This can be explained because of the major contribution of the roughness parameter and asperity slope in the boundary friction prediction.

Wear of the PG-CP4 coating applied by plasma to 40H13 steel and subjected to laser treatment

This paper discusses the wear of PG-CP4 powder coating deposited by plasma on 40H13 steel and treated by laser. A multi-factor model was established that relates the absolute wear of the PG-CP4 coating to independent factors of the laser processing process and allows you to reduce the coating wear. The longitudinal feed Spr of the laser beam and distance L from the protective glass of the laser head to the processed surface have the greatest and approximately equal influence on the absolute wear of the coating, and the radiation power W -a minimum influence. The research of 40H13 steel coated (the first option) and uncoated steel (the second option), showed that of all the samples that provide reliable adhesion of the coating to the substrate and the greatest reduction in absolute wear (from 80 to 22 micrometers, by 72.5 %) was achieved in the first case at the mode: W = 3 kW, Spr = 10 mm/s and L = 60 mm. The results of the research are recommended for use in enterprises that implement the processes of plasma and laser processing of materials, as well as in design organizations that develop modern technological laser systems.

Tribocatalytically-activated formation of protective friction and wear reducing carbon coatings from alkane environment

Minimizing the wear of the surfaces exposed to mechanical shear stresses is a critical challenge for maximizing the lifespan of rotary mechanical parts. In this study, we have discovered the anti-wear capability of a series of metal nitride-copper nanocomposite coatings tested in a liquid hydrocarbon environment. The results indicate substantial reduction of the wear in comparison to the uncoated steel substrate. Analysis of the wear tracks indicates the formation of carbon-based protective films directly at the sliding interface during the tribological tests. Raman spectroscopy mapping of the wear track suggests the amorphous carbon (a-C) nature of the formed tribofilm. Further analysis of the tribocatalytic activity of the best coating candidate, MoN-Cu, as a function of load (0.25–1 N) and temperature (25 °C and 50 °C) was performed in three alkane solutions, decane, dodecane, and hexadecane. Results indicated that elevated temperature and high contact pressure lead to different tribological characteristics of the coating tested in different environments. The elemental energy dispersive x-ray spectroscopy analysis and Raman analysis revealed formation of the amorphous carbon film that facilitates easy shearing at the contact interface thus enabling more stable friction behavior and lower wear of the tribocatalytic coating. These findings provide new insights into the tribocatalysis mechanism that enables the formation of zero-wear coatings.

Dual-frequency ultrasonic cleaning with diluted phosphoric acid solution for removing oxide scale of uncoated steel sheets in hot stamping

Dual-frequency ultrasonic cleaning with a diluted phosphoric acid solution was developed to remove oxide scales on surfaces of hot-stamped parts from uncoated steel sheets, and conventional shot blasting processes are omitted. The removal of the oxide scale by ultrasonic cleaning is accelerated by the phosphoric acid solution and the dual frequency. The removing time for the phosphoric acid solution was shorter than that for a hydrochloric acid solution, and rust appearing for leaving after cleaning was prevented by generating an iron phosphate layer. In dual-frequency ultrasonic cleaning with the diluted phosphoric acid solution, the oxide scale was dissolved, and then the oxide scales were exfoliated from the thin scale and high-pressure portions. The removing time decreased with decreasing pH and oxide scale thickness and with increasing solution temperature. The surface roughness and distortion of an ultrasonic-cleaned hot-stamped part were smaller than those for shot blasting, and the weldability and paintability were similar. The oxide scale of a hot-stamped part having a nonuniform distribution of oxide scale thickness was successfully removed by dual-frequency ultrasonic cleaning with the diluted phosphoric acid solution.

Tribocatalytically-activated carbon-based tribofilm formation for wear reduction in alkane environment

Minimizing the wear of the surfaces exposed to mechanical shear stresses is an ideal solution to maximizing the lifespan of rotary mechanical parts. In this study, we have discovered the anti-wear capability of a series of metal nitride-copper nanocomposite coatings tested in a liquid hydrocarbon environment. The results indicate substantial reduction of the wear in comparison to the uncoated steel substrate. Analysis of the wear tracks indicates the formation of carbon-based protective films directly at the sliding interface during the tribological tests. Raman spectroscopy mapping of the wear track suggests the amorphous carbon (a-C) nature of the formed film. Further analysis of the tribocatalytic activity activation as a function of load (0.25-1 N) and temperature (25°C, and 50°C) was performed in three alkane solutions, decane, dodecane, and hexadecane. Results indicated that elevated temperature and high contact pressure result in more stable friction behavior of the coating. The elemental energy dispersive x-ray spectroscopy analysis and Raman analyses reveal how a-C film facilities easy shearing at the contact interface thus enabling more stable friction and lower wear at higher loads and elevated temperature. These results provide new insights into the tribocatalysis mechanism that enables the formation of zero-wear coatings.

Low velocity oxy fuel spraying of hydroxyapatite coating on a multifunctional UNS S31254 austenitic stainless steel

Artificial material such as stainless steel (SS) is widely used for orthopaedic applications owing to its superior properties, ease of fabrication and lower cost. However, in the body environment, stainless steel can leach toxic elements such as nickel and chromium. To prevent this, a hydroxyapatite (HAp) coating having chemical characteristics very similar to the human bone was deposited on a medical-grade UNS S31254 austenitic stainless steel by a Low-velocity oxy-fuel spray gun (LVOF). The coating was characterised by using a field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscope (FTIR). The adhesion strength, microhardness and corrosion behaviour were studied using the Tensometre, Vickers microhardness tester and potentiodynamic polarisation with electrochemical impedance spectroscope. The bacterial adhesion and bioactivity of the coating were also evaluated. The LVOF sprayed HAp coating has shown better corrosion resistance, higher bioactivity and higher hardness than the uncoated steel. The presence of tricalcium phosphate, octa-calcium phosphate (OCP) and tetra-calcium phosphate (TTCP) was found in the coating. LVOF sprayed HAp coating is also found suitable in lowering the bacterial adhesion on the steel substrate.

Modelo de baixo custo para aprendizagem de consistências à palpação no exame físico geral veterinário

Palpation is a method that is part of the physical examination in veterinary routine, in which there are different types of consistency, such as hard, firm, soft, smooth, fluctuating and crackling. The aim of this study was the confection of a teaching model for consistencies palpation. It was used low cost and easily acquisition materials, as latex balloons filled by different materials (plaster, silicone, water, stones and flour) and uncoated steel wool. The filled balloons and steel wool were placed on a MDF board and covered with fabric. The model was validated by 29 veterinary doctors, including professors and residents. The model was evaluated positively by the majority of professionals.