Performance analysis of retrofitted tribo-corrosion test-rig for monitoring in situ oil condition

Oils and lubricants, once extracted after use from a mechanical system, can hardly be reused, and should be refurbished or replaced in most applications. New methods of in situ oil and lubricant efficiency monitoring systems have been introduced for a wide variety of mechanical systems, such as automobiles, aerospace aircrafts, ships, offshore wind turbines, and deep sea oil drilling rigs. These methods utilize electronic sensors to monitor the “byproduct effects” in a mechanical system that are not indicative of the actual remaining lifecycle and reliability of the oils. A reliable oil monitoring system should be able to monitor the wear rate and the corrosion rate of the tribo-pairs due to the inclusion of contaminants. The current study addresses this technological gap, and presents a novel design of a tribo-corrosion test rig for oils used in a dynamic system. A pin-on-disk tribometer test rig retrofitted with a three electrode-potentiostat corrosion monitoring system was used to analyze the corrosion and wear rate of a steel tribo-pair in industrial grade transmission oil. The effectiveness of the retrofitted test rig was analyzed by introducing various concentrations of contaminants in an oil medium that usually leads to a corrosive working environment. The results indicate that the retrofitted test rig can effectively monitor the in situ tribological performance of the oil in a controlled dynamic corrosive environment. It is a useful method to understand the wear–corrosion synergies for further experimental work, and to develop accurate predictive lifecycle assessment and prognostic models. The application of this system is expected to have economic benefits and help reduce the ecological oil waste footprint

Understanding the Tribocorrosion Behavior of Engineered Surfaces

Wear and corrosion are the most common forms of degradation in automobiles, ships, aircraft, biomedical implants, industrial machinery, and other mechanical systems. The dependence of these mechanical systems on tribological contacts accounts for a global economic wear loss of US$300 billion USD (2017) annually. The losses from fiction and wear are estimated to be 73$2,505 billion, which is equivalent to 3.4% of the global Gross Domestic Product (GDP 2013). Today, with advanced manufacturing and surface processing techniques, it is possible to render a surface functionally resistant to wear or corrosion. A major drawback of such functionalization is that the processing specifically enhances resistance to either wear or corrosion, however, the action of wear and corrosion can lead to a wear-corrosion synergistic degradation, which has been scarcely understood. When functional surfaces are in relative sliding motion in a lubricated environment, they undergo wear and corrosion over extended periods of operation. The oxide layer formed as a result of corrosion is mechanically removed during sliding, thereby exposing a fresh layer of metal to degrade by wear and corrosion. The cycle of synergism between wear and corrosion is called tribocorrosion. The onset of tribocorrosion causes material degradation to occur faster than the action of either wear or corrosion alone. Understanding and characterizing the mechanism of tribocorrosion in various mechanical systems is complicated due to the variability in surface characteristics, lubricants, and tribo-interface conditions. This has also made it challenging to develop a stable wear-corrosion synergism monitoring system and tribocorrosion resistant surfaces for oil and aqueous environments.In the present study, an experimental module to monitor tribocorrosion in-situ is designed and implemented to measure the tribocorrosion behavior of various surface characteristics, lubricants, and tribo-interface conditions. A focus is placed on understanding the mechanism of tribocorrosion and designing surfaces with enhanced tribocorrosion resistance. The effect of surface engineering methods, such as textures and coatings on tribocorrosion, are investigated. More specifically, the surface engineering methods include surface processing using laser shock peening (LSP) on steel and magnesium alloys, and nanocomposite coatings on surfaces using Nickel-Graphene. The environmental conditions include aqueous environments that simulate seawater conditions. The study investigates the mechanochemical and physicochemical behavior of surface characteristics after modification to understand the mechanism of tribocorrosion. The effect of LSP intensity on wear, corrosion, tribocorrosion, surface roughness, and surface energy is discussed, and phenomenological models are proposed. The observed correlation between surface roughness, surface energy, and wear-corrosion synergism in defining the tribocorrosion mechanism is also discussed.This study has enabled (1) understanding of the association between electrochemical and mechanical processes that affect the material and lubricant degradation, (2) application of innovative solutions to mitigate tribocorrosion in advanced manufacturing and material processing applications, and (3) design of material systems that are resistant to tribocorrosion. The study on the tribological behavior of LSP surfaces shows the coefficient of friction (COF) can be reduced by up to 83.25% depending on the applied laser intensity. From the results of this study, it was inferred that the surface roughening effects induced by the laser intensity plays a major role in defining the tribocorrosion behavior of LSP surfaces. The tribocorrosion studies that followed indicate that a change in surface roughness can drastically modify the wettability of the surface, more so in environments susceptible to corrosion. The wettability can be quantified into various components of surface energy. The surface energy was found to be the lowest at lower laser intensities. Lower interfacial surface energy showed decreased wettability, providing enhanced tribocorrosion resistance. However, higher laser intensities increased the surface roughening effect, causing an increase in the interfacial surface energy and wettability of the surfaces, and thereby decreasing the tribocorrosion resistance. Depending on the applied laser intensity, the surface roughness and the profile of the treated area can be precisely controlled, thereby providing a technique to tailor not just tribological properties, but also the tribocorrosion properties. Tribocorrosion studies have also been conducted for electrodeposited nickel-graphene (Ni/GPL) nanocomposite films on steel to understand the wear accelerated corrosion in contaminated oil-lubricated mediums. It was observed that the wear-corrosion synergism for steel with and without the Ni/GPL film was negligible in an uncontaminated oil (synthetic transmission oil). However, when the oil was contaminated, the wear-corrosion synergy was higher on steel than on steel with Ni/GPL. The enhanced resistance to wear corrosion synergy was attributed to the Ni/GPL having refined grains that results in minimal transport of corrosive contaminants, water, and oxygen that inhibits corrosion cracking or pitting to the substrate. Further, the presence of GPL in the film minimized the effects of wear, which resulted in enhanced resistance of Ni/GPL films to tribocorrosion. This study provides insight into the role of surface characteristics, lubricants, and tribo-interface conditions that define the synergism between wear and corrosion. The research will enable the effective utilization and design of a tribo-system that can maximize the tribological performance and inhibit tribocorrosion

Gecko-Inspired Adhesive Mechanisms and Adhesives for Robots—A Review

Small living organisms such as lizards possess naturally built functional surface textures that enable them to walk or climb on versatile surface topographies. Bio-mimicking the surface characteristics of these geckos has enormous potential to improve the accessibility of modern robotics. Therefore, gecko-inspired adhesives have significant industrial applications, including robotic endoscopy, bio-medical cleaning, medical bandage tapes, rock climbing adhesives, tissue adhesives, etc. As a result, synthetic adhesives have been developed by researchers, in addition to dry fibrillary adhesives, elastomeric adhesives, electrostatic adhesives, and thermoplastic adhesives. All these adhesives represent significant contributions towards robotic grippers and gloves, depending on the nature of the application. However, these adhesives often exhibit limitations in the form of fouling, wear, and tear, which restrict their functionalities and load-carrying capabilities in the natural environment. Therefore, it is essential to summarize the state of the art attributes of contemporary studies to extend the ongoing work in this field. This review summarizes different adhesion mechanisms involving gecko-inspired adhesives and attempts to explain the parameters and limitations which have impacts on adhesion. Additionally, different novel adhesive fabrication techniques such as replica molding, 3D direct laser writing, dip transfer processing, fused deposition modeling, and digital light processing are encapsulated

Tribocorrosion Behavior of Inconel 718 Fabricated by Laser Powder Bed Fusion-Based Additive Manufacturing

Additive manufacturing (AM) by laser powder bed fusion (LPBF) has gained significant research attention to fabricate complex 3D Inconel alloy components for jet engines. The strategic advantages of LPBF-based AM to fabricate jet components for aerospace applications are well reported. The jet components are exposed to a high degree of vibration during the jet operation in a variable aqueous environment. The combined vibration and the aqueous environment create a tribological condition that can accelerate the failure mechanism. Therefore, it is critical to understand the tribocorrosion behavior of the Inconel alloy. In the present work, tribocorrosion behavior of the LPBF fabricated standalone coating of Inconel 718 in the 3.5% NaCl aqueous solution is presented. The LPBF fabricated samples are analyzed to determine the impact of porosity, generated as a result of LPBF, on the triobocorrosion behavior of AM Inconel 718. The study includes potentiodynamic tests, cathodic polarization, along with OCP measurements. The corrosive environment is found to increase the wear by 29.24% and 49.5% without the initiation of corrosion in the case of AM and wrought Inconel 718, respectively. A corrosion accelerated wear form of tribocorrosion is observed for Inconel 718. Additionally, the corrosive environment has a significant effect on wear even when the Inconel 718 surface is in equilibrium potential with the corrosive environment and no corrosion potential scan is applied. This study provides an insight into a critical aspect of the AM Inconel components

Effect of Gas Propellant Temperature on the Microstructure, Friction, and Wear Resistance of High-Pressure Cold Sprayed Zr702 Coatings on Al6061 Alloy

For the first time, Zr702 coatings were deposited onto an Al6061 alloy using a high-pressure cold spray (HPCS) system. In this work, five different N2 process gas temperatures between 700 and 1100 °C were employed to understand the formation of cold sprayed (CS) Zr coatings and their feasibility for enhanced wear resistance. Results indicated that the N2 processing gas temperature of about 1100 °C enabled a higher degree of particle thermal softening, which created a dense, robust, oxide- and defect-free Zr coating. Across all CS Zr coatings, there was a refinement of crystallinity, which was attributed to the severe localized plastic deformation of the powder particles. The enhanced thermal boost up zone at the inter-particle boundaries and decreased recoverable elastic strain were accountable for the inter-particle bonding of the coatings at higher process gas temperatures. The flattening ratio (ε) increased as a function of temperature, implying that there was a greater degree of plastic deformation at higher N2 gas temperatures. The microhardness readings and wear volume of the coatings were also improved as a function of process gas temperature. In this work, the wear of the Al6061 alloy substrate was mainly plowing-based, whereas the Zr CS substrates demonstrated a gradual change of abrasive to adhesive wear. From our findings, the preparation of CS Zr coatings was a feasible method of enhancing the wear resistance of Al-based alloys