Showing papers in "Journal of Tribology-transactions of The Asme in 2022"

The Role of Surface Topography and Normal Load in the Initiation of Ratchetting-Peak Friction, Seizure, Scuffing, and Elastic Shakedown

Abstract: Surface topography is a critical parameter that can influence friction and wear in engineering applications. In this study, the influence of surface topography directionality on seizure and scuffing initiation during tribological interactions is explored. Hence, unidirectional sliding wear experiments were carried out in immersed lubrication conditions for various normal loads. The tribological interactions were studied using EN31-60 HRC flats and SAE52100-60 HRC pins in a sphere on flat configuration. The results show that, in some cases, the sliding interactions in the initial cycles lead to a high friction coefficient of up to �0.68 in lubricated conditions, which was termed as �peak friction�, and this was accompanied by scuffing. The existence of peak friction was found to be dependent on surface topography directionality, especially when the directionality in topography was parallel to the sliding direction. Continuous ratchetting was found to be the cause of peak friction, which was accompanied by seizure and scuffing. When the topography directionality was perpendicular or independent of the sliding direction, elastic shakedown occurred at earlier cycles and prevented peak friction initiation and scuffing and also facilitated for higher steady-state friction values. Copyright © 2021 by ASME

Fabrication of In Situ TiN Ceramic Particle Reinforced High Entropy Alloy Composite Coatings by Laser Cladding Processing

Abstract: In situ TiN ceramic particle reinforced FeCoNiCrMnTi high entropy alloy coating was fabricated by laser cladding processing at high purity nitrogen gas atmosphere on the AISI 304 stainless steel substrate. The effect of Ti addition on the microstructure, phase structure, and wear properties of the coatings was investigated. The results showed that the phase structure of the coatings was mainly face-centered cubic (FCC)-type γ phase. A few of cubic or flower-like TiN ceramic were formed after adding titanium into the FeCoNiCrMn powder. When atomic ratio of Ti exceeds 0.5, Laves phases appeared in the coatings. With increasing of Ti, the micro-hardness and wear resistance of the coatings increased, but friction coefficient and crack resistance of the coatings reduced. Suitable Ti content in the FeCoNiCrMnTix, laser composite coating, had higher resistance to adhesive wear, oxidation wear, and cracking resistance.

A Review of Preparation and Tribological Applications of Pickering Emulsion

Abstract: Pickering emulsion is a new type of stable emulsion made by ultrafine solid particles instead of traditional surfactants as stabilizers, which has received widespread attention in recent years. The preparation methods of stator-rotor homogenization, high-pressure homogenization, and ultrasonic emulsification were compared with others in this work. The main factors affecting the stability of Pickering emulsion are the surface humidity of the solid particles, the polarity of the oil phase, and the oil–water ratio. These factors could affect the nature of the solid particles, the preparation process of Pickering emulsion, and the external environment. Consequently, the long-term stability of Pickering emulsion is still a challenge. The tribological investigations of Pickering emulsion were summarized, and the multifunctional Pickering emulsion shows superior prospects for tribological applications. Moreover, the latest development of Pickering emulsion offers a new strategy for smart lubrication in the near future.

Tribological Investigation of Composite MoS2-TiO2-ZrO2 Coating Material by Response Surface Methodology Approach

Abstract: Molybdenum disulfide (MoS2) is popularly used in tribological applications because of its excellent lubricating properties. However, its performance needs to be further improved. In the present study, an attempt has been made to improve the wear resistance of pure MoS2 coating by incorporating TiO2 and ZrO2 nanoparticles as a reinforcement material into the MoS2 base matrix. The composite MoS2-TiO2-ZrO2 coating was applied onto substrate surface by the bonding technique. The tribological performance of the coated specimens was evaluated by employing various operating conditions (such as wt% of compounding elements, contact pressure, and sliding speed) using pin-on-disc friction and wear test rig. A statistical model was developed to identify the significant factors affecting the friction coefficient (COF) and wear-rate of the composite coating material. The design of experiment (DOE) was formulated by response surface methodology (RSM) approach to cut down the number of experiments and to develop a mathematical model between the key process parameters such as wt% of compounding elements, contact pressures, and sliding speeds. Analysis of variance (ANOVA) was executed for checking the adequacy of the empirical models developed. It was discovered that the COF and wear-rate of composite MoS2-TiO2-ZrO2 coating significantly affected by the wt% addition of ZrO2. The SEM and optical microscopy analyses of the worn surfaces and transfer films indicated that the tribological properties of composite MoS2-TiO2-ZrO2 coating were significantly improved compared to pure MoS2 coating.

Computational Efficiency Improvement of Dimple Textured Hydrodynamic Journal Bearing Using Progressive Mesh Densification Method

Abstract: There is a considerable amount of study carried out on textured hydrodynamic bearings. The numerical solution of textured bearings is a matter of concern for the researchers. There are several methods used to estimate the performance parameters of textured bearings. However, progressive mesh densification (PMD) method is not yet used for textured bearings while it has been used for mixed elastohydrodynamic lubrication (EHL) and thermo-EHL problems. In the present analysis, the PMD method is implemented to estimate the performance parameters of the textured journal bearing. It is compared with the multigrid and the fixed mesh methods and found to be very effective in improving computational efficiency.

Comparative Study of the Wear Behavior of B4C Monolayered and CrN/CrCN/DLC Multilayered Physical Vapor Deposition Coatings Under High Contact Loads: An Experimental Analysis

Abstract: There are several ways to characterize the wear resistance of coatings in the laboratory, almost all of them applying relatively low contact pressure, both punctually and over surface contact. Pin-on-disc, reciprocal sliding, and micro-abrasion wear tests are quite common configurations for this purpose. Thus, a gap was identified in terms of characterization of hard physical vapor deposition (PVD) coatings subject to higher levels of contact pressure. This study aims to study and compare the wear behavior of two different coatings made by PVD, a B4C (Boron Carbide) monolayer, less used, and another following a multilayer structure of CrN/CrCN/DLC, to identify the wear mechanisms involved in quite different coatings. Both coatings were initially characterized in terms of chemical composition, thickness, morphology, structure, hardness, and adhesion to the substrate, being subsequently tested in laboratory equipment for wear tests following the block-on-ring configuration and relatively high levels of contact pressure, with a view to study the failure mechanisms of the coatings and their wearrate. CrN/CrCN/DLC multilayered coatings presented a better overall wear behavior, whereas B4C coating showed a good wear behavior regarding the load and configuration used, but in line with the behavior already observed when other wear testing configurations had been used. Thus, under the conditions imposed, CrN/CrCN/DLC coating is the best option when high contact pressure is applied to the coated surfaces.

Experimental Study on the Coefficient of Friction of the Ball Screw

Abstract: The coefficient of friction (COF) is a key factor to estimate the performance of ball screws. Pieces of research focus on the experimental study of the COF, leading to the COF chosen empirically in many studies. To acquire the COF of the ball screw, a measuring system is conducted to detect the friction torque under different preloads and rotational speeds and the effects of the applied axial load and rotational speed on the COF are analyzed. By the curve fitting method, the Stribeck curve of the ball screw is obtained. The experimental results show that the lubricating state can be divided into two categories: the mixed lubrication state and the elastohydrodynamic lubrication state. This study is beneficial to choose a suitable working condition for a different performance of the ball screw.

Dry Sliding Wear Behavior of Magnesium Nanocomposites Using Response Surface Methodology

Abstract: In this study, a pure magnesium material reinforced with 0.5, 1, 1.5, and 2 w% of CaO was prepared through disintegrated melt deposition technique (DMD process). Nanocomposites were investigated for their sliding wear behavior in dry condition at room temperature. The amount of CaO, load, sliding distance, and sliding velocity were selected as input design parameters at their five level in central composite design using minitab 18.1 statistical software. The influence of design parameters on wear loss is reported through the response surface methodology (RSM). Analysis of variance (ANOVA) was used to confirm the soundness of the developed regression equation. The results indicate the contribution of linear, quadratic, and interaction terms of design parameters on response. Three-dimensional response surface and two-dimensional contour plots indicate the interaction effect. The result shows that an increase in the sliding velocity contributes to a decrease in the wear loss of the composites because of the emergence of protective oxidative layer at the surfaces of the pins, which is confirmed through field emission scanning electron microscope and energy dispersive X-ray analysis analyses of the pin surfaces. Wear loss of the material decreased as the amount of CaO increased. The ANOVA analysis concluded that the sliding distance and load contribute significantly to wear loss of the composites, and their percentage of contribution is 64.02% and 3.69%.