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This paper's aim is to present the gear micropitting performance of two industrial gear oils: a standard mineral lubricant (CM) containing a special micropitting additive package and a biodegradable ester with low toxicity additivation.

Gear micropitting tests were performed on the FZG machine, using type C gears made of case carburized steel. Lubricant samples were collected during the tests for analyzing the wear particles generated during operation. Post‐test analysis included the visual inspection of the teeth flanks and the assessment of the micropitting area, the mass loss of the gear, the ferrometric analysis of the lubricant samples and the surface roughness measurement of the teeth flanks, below and above the pitch line.

The micropitting performance of the two lubricants was very similar, confirming the advantage of using the ester lubricant (CE) as an industrial gear oil, now that it is an environmentally friendly product.

The tests were only performed on carburizing steel and refer to the tested lubricants.

The study confirms the appropriateness of biodegradable ester oil to industrial gear applications, allowing the replacement of environmentally harmful gear lubricants. It shows that the micropitting protection conferred is similar to that exhibited by highly additivated CMs.

The paper shows the applicability of biodegradable CEs to gear lubrication, mainly where it concerns micropitting protection, and shows its potential advantages, together with the biodegradability.

The purpose of this paper is to get a better understanding of roughness evolution and micropitting initiation on the tooth flank, as well as the evolution of surface topography during the test load stages in a modified DGMK short micropitting test procedure.

A modified DGMK short micropitting test procedure was performed, using an increased number of surface observations (three times more) in order to understand the evolution of the surface during each load stage performed. Each of these surface observations consists in the evaluation of surface roughness, surface topography, visual inspection and also weigh measurements as well as lubricant analysis.

This work showed that the larger modifications on surface took place in the beginning of tests, especially during load stage K3 (lowest load, considered as running‐in) and on the first period of load stage K6, that is, during the first 200,000 cycles of the test. The 3D roughness parameters (St and Sv), obtained from the surface topographies, gave a more precise indication about surface roughness evolution and micropitting generation than the 2D parameters, especially in what concerns to inferring the depth of micropits and the reduction of roughness. Tooth flank topography allows to identify local changes on the surface and the appearance of first micropits.

This work was performed with gears holding a high surface roughness and with a ester‐based lubricant. It was interesting to see the differences observed for surface evolution, for other base oils and also for gears with lower roughness.

The main implication of this work is the understanding that major changes in the surface took place in the first cycles, indicating that the running‐in procedure could be very important for the surface fatigue life. This work also showed that micropitting depends on local contact conditions. Depending on the roughness of the counter surface, micropitting can appear on the bottom of the deep valleys and/or do not appear on the tip of the roughness peaks. The surface topography, and implicitly 3D roughness parameters, is very useful for the observation of surface evolution.

This paper shows in detail the evolution of the tooth surface during a micropitting test. The micropits generation and evolution and also surface wear evolution are presented.

This study aims to investigate the influence of surface roughness and viscosity on micropitting and their influence sequence.

Specimens were made of carburized and quenched 18CrNiMo7-6, and different surface roughness was obtained by grinding and shot peening. Tests were carried out on a rolling-sliding tribometer, with different viscosity lubricants and a heavy load under a boundary lubrication condition. The laser confocal microscope was used to measure the aspects, surface roughness, profiles in the contacted region and micropitting damage percentage. A factorial experiment was designed, and the range analysis was applied to find the sequence of influence of surface roughness and viscosity.

The result shows that surface roughness has a more noticeable influence since the change of viscosity cannot generate sufficient wear loss to suppress micropitting.

The influence sequence of two factors on micropitting was investigated and the reason for the distribution was analyzed.

This paper reviews the performance features of a new generation of industrial gear oils, developed for both mineral and synthetic base oils. These new products were designed to provide the highest levels of protection against the relatively new wear mechanism called micropitting. However, great stress was placed on providing these new products with balanced performance capabilities, so that they will perform with high reliability in the wide variety of conditions to which modern industrial gear oils are exposed. Performance areas such as filterability, foam control, corrosion protection, water separation, oxidation control and bearing protection were of particular concern. This paper compares the overall performance of these new technologies with conventional commercial products and it describes the extensive rig and field‐testing used to confirm their performance. It also reviews the phenomenon of gear micropitting and optimum methods for its assessment.

The purpose of this paper is to study a new liquid-phase assisted texture treatment method to improve the tribological properties of 304 stainless steel.

Three groups of textured type (KY, KJ and YJ) were prepared on 304 stainless steel surface using laser circular and cross scanning method in air and liquid assisted condition. The surface morphology and element content of test samples were measured with scanning electron microscope, energy spectrum. Then, the tribological test was carried out using MWF-500 reciprocating friction and wear testing machine under dry and oil lubrication condition.

The experimental results showed that the textured surface of laser processing in air was obviously blackened, and the oxygen content was increased from 16.9% to 24%. These cases did not occur on liquid-assisted laser textured surface, which induced a better wettability and surface texture processing quality. For friction test, the friction coefficient of cross-scanning textured surface prepared in assisted liquid (YJ) was the smallest. It is reduced by 55% in oil lubrication case compared to the original surface (YS). The cross-scanning textured surface prepared in air (KJ) was a little worse in friction coefficient and a little better in wear quantity than the cross-scanning textured surface prepared in assisted liquid (YJ). It is indicated that the laser processing surface with assisted liquid has obvious advantages in surface texture quality and interfacial tribological property. The main reason is that the assisted liquid plays a role in cooling and protecting action of the machined surface. The bubbles, generated at the solid–liquid interface because of the laser heat effect, scatter the laser beam and carry out the processed melt meanwhile. The lubricating medium is easier to penetrate and store in the contact interfaces because of the higher surface textured performance and wettability.

The main contribution of this work is in providing a new surface texture processing method that has a better surface micropits quality and interfacial tribology regulation ability.

The aim of this work is the study the tribological behaviour and tribocorrosion resistance of newly developed multilayer PVD coatings Cr/CrN and CrN/ZrCN applied on nitrided F1272 steel for gear applications.

Tribological characterization has been completed by several tribological tests performed under ball‐on‐disc configuration, extreme pressure tests to determine the maximum load before the films failure and rolling‐sliding tests under line‐contact conditions (35‐40 per cent of sliding). The response of the different coatings to sodium chloride aggressive environment has been simulated by accelerated tribocorrosion tests, combining simultaneously chemical and mechanical factors. The synergistic effect of wear on corrosion behaviour and vice versa, has been studied in order to compare the protective properties of the different PVD coatings developed.

Cr/CrN PVD coating improves wear in almost a 90 per cent compared to the nitrided substrate, presenting a similar behaviour to this one under extreme pressure conditions. CrN/ZrCN coating also improved substrate wear and especially good behaviour for this coating was observed under extreme pressure conditions. Cr/CrN coating strongly decreases micropitting and scuffing effect when it is tested under rolling‐sliding configuration. Under micro‐pitting conditions, coating protects the substrate and reduces the fatigue of uncoated discs. When adhesive wear (scuffing) is studied also Cr/CrN improves notable the nitrided steel performance. Under simultaneously corrosion‐wear conditions, Cr/CrN coating registered the lowest material loss because in this case only corrosion effect contributed to the coated surface degradation being the mechanical contribution inappreciable.

New multilayer coatings with improved wear performance and tribocorrosion resistance have been developed and comprehensively characterized. These coatings can be used in advanced gears for corrosive environmental conditions as well as with biodegradable lubricants.

Boundary layers, which develop during manufacturing and operation, can protect tooth flanks from metal-to-metal contacts. The characteristics of boundary layers and the running behavior of gears are determined by the preconditioning processes (manufacturing and run-in). This paper aims to analyze the influence of the grinding process parameters and the grinding oil on the characteristics of boundary layers.

Sets of test parts and test gear sets with different grinding process variants and different metalworking fluids were manufactured to investigate the mechanisms of action of thermomechanical and chemical surface preconditioning during grinding. The test parts were analyzed with regard to their boundary layer by metallography and chemistry and regarding their running behavior on test rigs lubricated with transmission oil.

In the tests, reproducible differences in gear strength regarding low-cycle fatigue and micropitting were determined for the test parts ground with different thermomechanical energy inputs and with different metalworking fluids. As the test results could not be sufficiently explained on the basis of conventionally tolerated component properties such as roughness, hardness and residual stresses, a model was discussed which combines the mechanisms of action of the formation of the manufacturing-induced boundary layer with the running behavior of the parts.

By combining both measurement and test results, possible correlations between manufacturing and operation are investigated to establish a more sustainable and economical design of gears.

The purpose of this study is to investigate the microstructure of fretting wear behavior in 6061-T6 aluminum alloy. The fretting wear of blind riveted lap joints of 6061-T6 aluminum alloy plates, which are widely used in aircraft construction, was investigated. Fretting damages were investigated between the contact surface of the plates and between the plate and the rivet contact surface.

Experiments were carried out using a computer controlled Instron testing machine with 200 kN static and 100 kN dynamic load capacity. Max package computer program was used for the control of the experiments. Fretting scars, width of wear scars, microstructure was investigated by metallographic techniques and scanning electron microscopy.

It was found that fretting damages were occurred between the plates contacting surface and between the plate and rivet contact surface. As load and cycles increased, fretting scars increased. Fretting wear initially begins with metal-to-metal contact. Then, the formed metallic wear particles are hardened by oxidation. These hard particles spread between surfaces, causing three-body fretting wear. Fretting wear surface width increases with increasing load and number of cycles.

The useful life of many tribological joints is limited by wear or deterioration of the fretting components due to fretting by oscillating relative displacements of the friction surfaces. Such displacements are caused by vibrations, reciprocating motion, periodic bending or twisting of the mating component, etc. Fretting also tangibly reduces the surface layer quality and produces increased surface roughness, micropits, subsurface microphone.

Stimulated by previous reference, which proposed making straight line of regression to test gear gravimetric wear loss sequence distribution, this paper aims to propose using straight line of regression to fit gear gravimetric wear loss sequence based on stationary random process suppose. Faced to that the stationary random sequence suppose had not been proved by previous reference, and that prediction did not present high precision, this paper proposes a method of fitting non-stationary random process probability distribution function.

Firstly, this paper proposes using weighted sum of Gauss items to fit zero-step approximate probability density. Secondly, for the beginning, this paper uses the method with few Gauss items under low precision. With the amount of points increasing, this paper uses more Gauss items under higher precision, and some Gauss items and some former points are deleted under precision condition. Thirdly, for particle swarm optimization with constraint problem, this paper proposed improved method, and the stop condition is under precision condition.

In experiment data analysis section, gear wear loss prediction is done by the method proposed by this paper. Compared with the method based on the stationary random sequence suppose by prediction relative error, the method proposed by this paper lowers the relative error whose absolute values are more than 5%, except when the current point sequence number is 2, and retains the relative error, whose absolute values are lower than 5%, still lower than 5%.

Finally, the method proposed by this paper based on non-stationary random sequence suppose is proved to be the better method in gear gravimetric wear loss prediction.

This paper aims to address the influence of tribofilms and running-in on failures and friction of gears. The operation regime of gears is increasingly shifted to mixed and boundary lubrication, where high local pressures and temperatures occur at solid interactions in the gear contact. This results in strong tribofilm formation due to interactions of lubricant and its additives with the gear flanks and is related to changes of surface topography especially pronounced during running-in.

Experiments at a twin-disk and gear test rig were combined with chemical, structural and mechanical tribofilm characterization by surface analysis. Pitting lifetime, scuffing load carrying capacity and friction of ground spur gears were investigated for a mineral oil with different additives.

Experimental investigations showed a superordinate influence of tribofilms over surface roughness changes on damage and friction behavior of gears. Surface analysis of tribofilms provides explanatory approaches for friction behavior and load carrying capacity. A recommendation for the running-in of spur gears was derived.

Experimental methods and modern surface analysis were combined to study the influence of running-in and tribofilms on different failures and friction of spur gears.