Tribology Future – Are Coatings Important?

20.05.2024

Introduction

Tribology is need of hour in many instances and it greatly impacts the economy of any country. The significant economic impact of tribological issues on a nation’s economy is from the concurrent energy and material losses occurring across mechanical apparatuses. The losses on individual machines may seem small but when multiplied across a large number of similar machines, the costs become substantial. For example, over 200 years ago, Jacobs Rowe suggested that implementing rolling element bearings in carriages could halve the number of horses needed in the United Kingdom, resulting in potential annual savings of around one million pounds at early 18th-century prices. In the modern times a simple analysis reveals that providing lubricants that increase mechanical efficiency by 5% to all worm gear drives in the United States could save approximately US$0.6 billion annually. Recognizing the extent of economic losses due to friction and wear, researchers and engineers have begun to challenge conventional limitations attributed to mechanical performance. They are exploring new materials and lubricants to overcome these constraints, with some advancements potentially revolutionizing entire technologies and economies.

Figure-1 Types of composite materials and the functional improvements addressed [3]

How is this developing?

In recent years, there have been significant advancements in the fields of tribological and solid lubricant coatings, offering promising solutions for the increasingly demanding conditions of future tribosystems. These coatings are uniquely designed to perform under specific application conditions, although none can work universally across all conditions. Performance and durability vary greatly depending on factors like test environment, temperature, and sliding conditions. To address these challenges, researchers have been developing novel coating architectures with features like multi-layers, micro-surface texturing, nano-structures, and composites. These advanced coatings often outperform traditional ones in machining and sliding contact applications, with some nano-composite coatings exhibiting superhard properties and improved performance across a range of conditions. Maintaining a significant space between coatings and substrates is crucial for extending service life, and modern deposition methods with mixed processing capabilities ensure strong adhesion between coatings and substrates. Research into newer and improved tribological and hard lubricant coatings will continue in the coming years, driven by the increasingly challenging application conditions of future mechanical systems. A particularly exciting trend is the development of coatings for dry and near-dry machining applications, leveraging existing knowledge and technological resources to bring these coatings to market in the near future.

Future Need

The fundamental mechanisms of friction involve adhesion and mechanical deformation, though their relative importance is subject to ongoing debate. Frictional energy is primarily dissipated through the deformation of surface layers via elastic, plastic, and viscoelastic processes, as well as through micro-fracture of surface materials and possibly shear fracture of adhesive interface bonds. Adhesion plays a significant role in friction, particularly in high-vacuum environments and instances of seizure. Surface films and boundary adhesion due to contamination can also influence friction by affecting the quantity and nature of local deformation generated by friction. Efforts are ongoing to better understand these fundamental mechanisms and to minimize friction by optimizing material properties to achieve the lowest possible friction values.

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Figure-2 Schematic representing the main five characteristics of coatings required for the high-temperature tribological applications [4]

Simulation techniques are valuable for understanding nano-scale interactions and obtaining quantitative results for various system models and working conditions. However, there are still several challenges that need to be addressed to achieve simulation outcomes closer to real-world scenarios. These limitations of numerical simulations are expected to be overcome in the coming years with advancements in processor technology and the development of more sophisticated algorithms.

References

[1] Findik, F., 2014. Latest progress on tribological properties of industrial materials. Materials & Design, 57, pp.218-244.

[2] https://www.bruker.com/en/news-and-events/webinars/2022/assessing-the-surface-metrology-of-orthopaedic-implants.html

[3] Hogmark, S., Jacobson, S. and Larsson, M., 2000. Design and evaluation of tribological coatings. wear, 246(1-2), pp.20-33.

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[4] Zakeri, A., Bahmani, E. and Ramazani, A., 2022. A review on the enhancement of mechanical and tribological properties of MCrAlY coatings reinforced by dispersed micro and nanoparticles. Energies, 15(5), p.1914.

 

I am currently working as a Postgraduate Researcher at the University of Leeds, where I am actively involved in research activities. Prior to this, I successfully completed my master's degree through the renowned Erasmus Mundus joint program, specializing in Tribology and Bachelor's degree in Mechanical Engineering from VTU in Belgaum, India. Further I handle the social media pages for Tribonet and I have my youtube channel Tribo Geek.

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