Surface texture plays an important role in the frictional behavior and transfer layer formation of contacting surfaces. In the present investigation, basic experiments were conducted using an inclined pin-on-plate sliding apparatus to better understand the role of surface texture on the coefficient of friction and the formation of a transfer layer. In the experiments, soft HCP materials such as pure Mg and pure Zn were used for the pins and a hardened 080 M40 steel was used for the plate. Two surface parameters of the steel plates—roughness and texture—were varied in tests that were conducted at a sliding speed of 2 mm/s in ambient conditions under both dry and lubricated conditions. The morphologies of the worn surfaces of the pins and the formation of the transfer layer on the counter surfaces were observed using a scanning electron microscope. In the experiments, the occurrence of stick-slip motion, the formation of a transfer layer, and the value of friction were recorded. With respect to the friction, both adhesion and plowing components were analyzed. Based on the experimental results, the effect of surface texture on the friction was attributed to differences in the amount of plowing. Both the plowing component of friction and the amplitude of stick-slip motion were determined to increase surface textures that promote plane strain conditions and decrease the textures that favor plane stress conditions.
Lubrication for extreme conditions, such as high temperature, cryogenic temperature, vacuum pressure, high load, high speed, and corrosive environments, is a continuing challenge among tribologists and space engineers due to the inadequate friction and wear properties of liquid lubricants. As a result, tremendous research effort has been put forward to study lubrication mechanisms for various machine elements under challenging conditions over the past two decades. Self-lubricating materials have been most widely used for adequate lubrication in extreme conditions in recent years. This review paper presents state-of-the-art of materials for lubrication in extreme condition applications in aerospace, automotive, and power generation areas. More specifically, solid lubricants dispersed in various matrices for lubrication application were analyzed in-depth under challenging conditions. This study also reports the self-lubricating materials and their lubrication mechanisms. Finally, various applications and challenges of self-lubricating materials were explored.
In the present investigation, unidirectional grinding marks were attained on the steel plates. Experiments were then conducted using pins of Al-Mg alloy against the prepared steel plates using an inclined pin-on-plate sliding tester. The goal of the research is to understand the influence of grinding mark direction and inclination angle of hard material on the friction and transfer layer formation during sliding. The inclination angle of the plate was held at 0.2°, 0.6°, 1°, 1.4°, 1.8°, 2.2° and 2.6° in the tests. The pins were slid both perpendicular and parallel to the grinding marks direction. Experiments were conducted under both dry and lubricated conditions on each plate in ambient environment. Results showed that the coefficient of friction and formation of transfer layer depend on the grinding marks direction and inclination angle of the hard surfaces. For a given inclination angle, the coefficient of friction and transfer layer formation were found to be more for the pins slid perpendicular to the unidirectional grinding marks when compared to parallel to the unidirectional grinding marks under both dry and lubricated conditions. The stick-slip phenomenon was observed only under lubricated conditions at the highest tilt angle for the sliding perpendicular to the grinding marks direction. These variations could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding.
Plasma electrolytic oxidation (PEO) is an electrochemical surface modification technique for producing dense oxide layers on valve metals. This review compiles the various modifications to the PEO process that have been used to improve the produced coatings and make them suitable for specific applications, with a focus on examples of aluminum, magnesium, and titanium substrates. An overview of the PEO process is given, highlighting the various process parameters and their effects on the final surface. The challenges with light metals that motivate the use of surface modifications are summarized, along with some of the other modifications that attempt to overcome them. Two broad categories of modifications to the PEO process are presented: in situ modifications, influencing the properties of the coating during its formation, and ex situ modifications, augmenting the properties of an already-formed coating. Finally, specific examples of applications for modified PEO processes are discussed, including battery, biomedical, water treatment, and energy production applications.
Abstract In this work, laser shock peening (LSP) was utilized as a surface-processing technique to modify the tribocorrosion characteristics of cold-spray (CS) 316L SS. Results indicate that with the influence of LSP, the degree of wear–corrosion synergism was effectively decreased. Particularly, the degree of wear loss being accelerated by electrochemical degradation was effectively reduced due to the cumulative effects of refined crystallinity, increased surface hardness, closure of surface pores, and decrease in wettability. Consequentially, the wear mechanism transitioned from being an abrasive type with cracking and delamination to an abrasive type free of any defects. From these findings, it can be inferred that LSP is indeed a viable method to improve the tribocorrosion characteristics of CS 316L SS.
