Jen Fin Lin

Experimental analysis of the tribological behavior of electroless nickel-coated graphite particles in aluminum matrix composites under reciprocating motion

Abstract Pure graphite particles and graphite particles coated with an electroless nickel (EN) film were introduced into an aluminum alloy via powder metallurgy to form two kinds of 6061 aluminum alloys. Tribological performances exhibited in unlubricated frictional contacts and in oil lubricated contacts were compared for both alloys. Variations in seizure resistance, friction behavior, wear mechanism, wear particle size, and wear loss were studied related to variations in graphite content of the aluminum composite material. A wear test machine equipped with an electrical contact resistance (ECR) function, in combination with the measurement of wear displacement, was used to investigate friction and wear performances and the wear mechanism. Wear rates and friction coefficient for the two kinds of alloys were compared to evaluate the tribological effect of the coated particles. The optimum graphite content in the alloys under both lubrication regimes was also determined.

The tribological characteristics of titanium nitride, titanium carbonitride and titanium carbide coatings

Abstract The tribological behaviors of TiN, TiC and Ti(C,N) coatings prepared by differing mass flow rates of nitrogen and acetylene during the coating process are studied in this work. The lower specimens were coated with titanium film as the underlayer and with TiN, TiC or Ti(C,N) film as the top layer. They were deposited by the cathodic arc ion plating process. The chemical compositions of eight types of ceramic coatings were determined by the wavelength-dispersive X-ray analysis. The influence by changing the mass flow rate ratio of N2 and C2H2 gases on specimens tribological behavior, microhardness, coating morphology, and adhesive strength was investigated. The three-body abrasive wear more often appeared at the temperatures that the ceramic coating was not yet softened by the frictional heat. Increasing the mass flow rate ratio of the acetylene gas in the coating process is favorable for more ions to react with the titanium, thus resulting in noticeable rises of the C/Ti atomic ratio; conversely, it is disadvantageous for nitrogen ions to react with the titanium. The wear rate of the lower specimen with the TiN film is the lowest of the three kinds of ceramic coatings; however, its friction coefficient is relatively higher than that of the TiC film.

The tribological characteristics of titanium nitride coatings. Part I. Coating thickness effects

The tribological behavior of specimens coated by two layers, titanium nitride film as the top layer and titanium film as the underlayer, is studied. The coating layers of the bottom specimens were deposited using the cathodic arc ion plating process technique. Experiments were carried out on a wear test machine using a thrust-washer adapter to simulate the surface contacts between the steel ring (the upper specimen) and the titanium nitride coated washer (the bottom specimen). We address the subject about the influence of the thickness of the two coating layers on tribological behavior, wear mechanism, specimens hardness and adhesive strength. A thin titanium nitride film in combination with a thick titanium film attenuates the adhesive strength, resulting in a significant increase in wear rate. The influence of the titanium nitride or titanium thickness on the friction coefficient is quite limited at higher sliding speeds. The specimens hardness is increased by thickening the titanium nitride layer, but is lowered by increasing the titanium thickness. When the specimens sliding speed is increased, both the wear rates and the friction coefficients show significant decline.

Tribological characteristics of titanium nitride and titanium carbonitride multilayer films. Part I. The effect of coating sequence on material and mechanical properties

In this study, the specimens in disc style were prepared by changing the coating sequence and coating thickness of titanium nitride and titanium carbonitride films on S45C steel substrate as the top and the second layers of a multilayer system. These arrangements were made in order to investigate the mechanical properties of the composite films like the adhesion strength, load carrying capacity, hardness, surface topography and surface microstructure. The experimental results show that the specimens with the Ti/Ti(C,N)/TiN film have a relatively higher composite hardness than the Ti/TiN/Ti(C,N) film. The trend exhibited in the coating film hardness of ceramic coating film is similar to the composite hardness. The specimens with the Ti/Ti(C,N)/TiN film have a lower critical friction force and critical track distance compared with the Ti/TiN/Ti(C,N) film. For the specimen with the Ti/Ti(C,N)/TiN film, peaks protruding over the flat surface are quantitatively increased by the increase in the coating film thickness. Nevertheless, either the peak parameter Rz or the amplitude parameter Ry after coating thick films is strongly affected by the Ra value of steel substrate before coating and the uniformity of the surface morphology can thus be improved. However, for the specimens with the Ti/TiN/Ti(C,N) film, increasing the total film thickness decreased the asperity, but also eliminated the morphological uniformity.

Tribological characteristics of titanium nitride and titanium carbonitride multilayer films: Part II. The effect of coating sequence on tribological properties

The effect on the tribological behavior of the lower specimen (disc) with different total film thickness and different coating sequences of two ceramic films was examined. The tribological behavior in response to the above two factors are expressed in terms of the wear rate of the upper and lower specimen, friction coefficient, wear mechanism, wear debris size and wear displacement. The lower specimen wear rates can be regressed by two straight lines or two curves as a function of the friction power parameter. Friction coefficients can be expressed as two linear functions in terms of the parameter T/LV where T is the specimens ultimate temperature, L is the applied load and V denotes the sliding velocity. The characteristics exhibited in the wear rate of the lower specimen and friction coefficient in each subregion of the friction power parameter (fLV) and the parameter T/LV, respectively can be interpreted by the alterations in wear mechanism. The wear rate of the lower specimen where the Ti(C,N) film is the top layer is equal to or lower than that with the TiN film as the top layer if they are both evaluated at the same thickness and under the same operating conditions.

The tribological performance of 6061 aluminum alloy/graphite composite materials in oil lubrications with EP additives

Abstract A thrust-on-washer adapter was applied to simulate surface contracs under oil lubrications. The upper, ring-style specimens were prepared using A356.0 aluminum alloy material; the lower, disk-style specimens were prepared using a composite material of 6061 aluminum alloy and graphite. The load applications were increased so that friction contacts ranged from hydrodynamic or mixed lubrication to boundary lubrication. The tribological mechanism and antiseizure performance of oil with different extreme pressure (EP) additive concentrations was shown to relate closely to friction coefficients, Stribeck curves, electrical voltage variations, wear mechanisms, and chemical products in wear debris. The experimental results reveal that the occurrence of surface seizure is dependent upon the value of the oil temperature rise per second, rather than the oil temperature itself. When the initial oil temperature was kept at 25°C, raising the EP additive concentration shortened the time before surface seizure occurred. When the initial oil temperature was 70 °C, an increase in the EP additive concentration fully prevented surface seizure. Under boundary lubrication conditions, the EP additive alone was unable to generate chemically reactive films regardless of oil temperatures; the antiwear performance occurred only in tribosurfaces when operating in hydrodynamic or mixed lubrication regimes.

Evaluation of lubricants for cold strip rolling

Abstract The lubrication characteristics during roll bite were evaluated by studying the friction coefficient, forward slip, rolling force and drive torque. Experiments were conducted on a laboratory rolling mill to assess the effects of these factors and the oil viscosity, surface roughness, reduction ratio and rolling speed on rolling behavior. Favorable lubrication conditions, indicated by a smaller forward slip and friction coefficient, were found when the reduction ratio or rolling speed was quite large. Cold rolling using a high viscosity lubricant is beneficial in reducing forward slip and friction coefficient. Increasing the isotropic surface roughness of the rolling strip can increase the friction coefficient and forward slip.

Analysis of wear behaviour of titanium carbonitride coatings

Abstract The kinetics of chemical reactions occurring during the coating process and the wear behaviour of Ti(C,N) coatings, including variations in wear displacement with the temperature of the lower specimen, were investigated in this work. The variations in the wear displacement and the temperature of the lower specimen are regressed by an eight-order polynomial function. The lower specimens were coated by a titanium film as underlayer and three kinds of coating material including TiN, Ti(C,N) or TiC were deposited as the top layer. The Ti(C,N) coatings were prepared by varying the gas flow rates of nitrogen and acetylene to form eight kinds of specimen. The tribological behaviour demonstrated by these eight specimens is discussed. The experimental data for the atomic ratios of [C] and [N] can be well expressed using the theory of diffusion rate and the theory of reaction rate for the deposition of ceramic coatings. The variations in the wear displacement gradient with the temperature of the lower specimen can give information on the adhesive behaviour arising before and after three-body wear. The wear rates of the upper and lower specimens due to adhesive wear are dependent on the operating conditions. The specimen with a higher final wear displacement was likely to produce on the upper specimen a higher wear rate when operating at 0.705 m s −1 . The thicker the adhesive layer, the lower the wear rate of the lower specimen produced. When the sliding speed was elevated to 1.41 m s −1 , the specimen with a higher final wear displacement often produced a lower wear rate on the upper specimen, and also caused higher wear rates on the lower specimens.

Analysis of the tribological behaviour and wear mechanisms of titanium nitride coating

Abstract Experiments were conducted on a test machine that used a thrust-washer adapter, where a rotating upper specimen was pressed against a stationary lower specimen. This setup was used to simulate the surface contacts between the steel (of the ring) and the titanium nitride coating (on the washer). Further, the existence of an electroless nickel interlayer on the washer was also investigated. The effect of the coating layers on tribological behaviour was evaluated for different thickness combinations of the titanium nitride layer (top layer) and the electroless nickel layer (interlayer). The interlayer was found to increase the wear volume, but was advantageous for strengthening resistance against chemical corrosion. The wear volume was controlled by the thickness of the two coating layers. A thicker TiN layer in conjunction with a thinner interlayer constituted the appropriate combination for two coating layers from the viewpoint of lowering wear volume. The friction coefficients arising from the TiN coating generally varied in the narrow range between 0.5 and 0.55, regardless of the interlayer thickness. Both the friction coefficient and wear volume were affected very much by the applied load and sliding speed. In the testing operating conditions, the primary wear mechanisms of the coating layers, such as microabrasion, semicircular or curved cracking, plucking and grooving, formed the surface failures. The surface failures due to friction and wear that occurred within the top layer appeared to be nearly independent of the adhesive strength of the interface.

The Effect of Surface Irregularities on the Tribological Behavior of Steel Rollers Under Rolling-Sliding Contact

Experiments were conducted utilizing a gear-cam adapter to simulate line-contact lubrication and wear. Roller specimens with various asperity heights and roughness patterns were riding on the rollerplates and sliding over the two lands of the lower specimen. The experimental results reveal that the roughness pattern and the asperity height are of importance in determining the friction coefficient, whereas asperity height is more related to the wear rate. The temperature rise of the lubricant seems to be seldom affected by the foregoing factors, but is governed by the combined effect of applied load and drivers rotational speed