Russian Scientists Propose Technology to Reduce Friction and Equipment Wear

11:45, January 12, 2024

Technology has improved bearing durability and outperformed Japanese counterparts

A group of scientists from Udmurt State University, institutes of the Ural Branch of the Russian Academy of Sciences, Udmurt State Agrarian University, and Ural Federal University have presented a technology for reducing friction and wear in sliding bearings. These bearings work in tandem with steel shafts and are used in machines to reduce friction and wear of moving parts. Plain bearings are commonly used in various industries, such as automotive (connecting rods, engines), aviation (landing gear control systems, fuel pumps, and aircraft engines), electric motors, generators, hydropower, shipbuilding, electronic industry, and household appliances. The research breakthrough results were published in Scientific Reports, one of the world's largest scientific journals. The Russian Science Foundation financially supported the research (project No. 19-79-20012).

In their scientific study, the scientists utilized plain bearings with steel and bronze shafts and bushings. Their objective was to demonstrate the consistent efficiency of the bearing coupling when operating without lubrication. Bismuth oxide of varying concentrations was added to the steel shafts at the points of contact with the bronze bushings. The authors suggest that bismuth is suitable for creating a film between bronze and steel. Bismuth is completely immiscible with iron and copper, even in the liquid state. To introduce bismuth into the surface layers of steel shafts, the researchers used high-energy short-pulse laser treatment.

"The main feature of high-speed laser treatment is the use of highly dispersed powders and lasers with pulse durations of tens of nanoseconds or milliseconds. The material surface is rapidly heated to temperatures up to 3500 °C or higher, followed by intensive cooling that results in the high-speed solidification of metal alloys and various ceramics. This process leads to the forming of strongly non-equilibrium states and supersaturated solid solutions. A solid solution of iron and copper was obtained using a specific technology. This technology also allowed for strong adhesion of nanosized particles of bismuth to iron. Manganese oxide was used as a catalyst to introduce bismuth oxide into the surface layers of steel. The surface roughness was reduced by diamond lapping after laser treatment. Both operations took less than 10 minutes in total," says Evgeny Kharanhevsky, Professor at the UdSU Department of General Physics, head of the research group in Izhevsk that proposed the high-speed laser treatment technology, and co-author of the paper.

The effect of five different bismuth oxide coating formulations on the coefficient of friction and wear of a steel disk under unlubricated sliding friction over bronze at high loads and speeds was determined by scientists. The bismuth-modified steel exhibited excellent friction and wear resistance, remaining serviceable after 200 km of linear sliding at a specific load of 12.5 megapascals (approximately 127.5 kg per cm2) and a sliding velocity of 9 m/sec. Simulating harsh conditions of significant oil shortage, the coefficient of dry sliding friction was reduced to as low as 0.03.

"We verified the effectiveness of our method in tests on modified (bismuth alloyed) steel shafts used to equip a turbocharger of an internal combustion engine. A laboratory bench was developed for the tests, on which the operating conditions of the turbocharger bearing unit can be fully simulated. After the tests, the turbocharger, which rotated at a speed of 75 thousand revolutions per minute, was disassembled for inspection," adds Aleksey Ipatov, Associate Professor at the UdSAU Department of Machine Operation and Repair, participant in the research and co-author of the article.

The test results confirmed the ultra-low coefficient of friction and the ability of bismuth-doped steel shafts to operate without lubrication for extended periods. The shafts showed no damage after five hundred unlubricated test cycles.  The turbocharger remained in serviceable condition after testing.

"At the same time, a Japanese-made turbocharger that has not been modified can only withstand five test cycles, even with boundary lubrication. Therefore, we can conclude that bismuth alloying provides excellent antifriction properties and long-term reliability when sliding at high speeds (75,000 rpm) without any kind of lubricant (liquid or solid) by reducing adhesion through interaction, in this case, with copper. In various situations, such as high rotational speeds and loads, extreme temperatures, or when maintaining the necessary thickness of the lubricating layer is impossible, the advantages of high-speed laser treatment technology allow for an infinite number of cycles of shaft rotation under load without causing material fatigue failure or significant wear losses", emphasizes Aleksey Makarov, Head of the Department of Materials Science of M.N. Mikheev Institute of Metal Physics (UB RAS), Chief Researcher of Institute of Engineering Science (UB RAS), Professor of the Department of Foundry Engineering and Hardening Technologies of the Ural Federal University, Head of the research group.

The proposed technology of applying superhard ceramic coatings based on new scientific principles, methods, and approaches provides a breakthrough result in reusable improvement of material properties. As a result, the service life of tools (steel rollers) for hot-pressing of metallic and ceramic materials for the electronics industry is increased from several days to several months.

The authors suggest that the developed method of bearing modification can significantly extend the service life of equipment in various areas of mass machine-building production, including aerospace, automotive, and energy industries. They emphasize the importance of properties such as simplicity, economy, and reliability in achieving this goal. Tests on the actual equipment have demonstrated that the application of a superhard ceramic coating preserves the heat resistance of the valve component of the internal combustion engine up to a temperature of 1000°C. Additionally, the resistance to oxidative and abrasive wear increases by 480 percent, and the service life of the components is increased by 10 times. The application of the high-speed laser treatment technology increased the resource of the hydraulic motor shaft by 30 percent, increased the resistance of punches for manufacturing polymer pipelines by 100 times, and almost halved the process's productivity.

Scientists from universities and institutes of the Branches of the Russian Academy of Sciences in Izhevsk and Ekaterinburg have developed a series of unique ceramic coatings using boron carbides and nitrides, zirconium nitrides and borides, and various oxides. This article describes the bismuth oxide technology as one of the variants.

"The low-friction effect of superhard ceramic coatings is typically observed at high temperatures. However, by adjusting the composition of the powder mixture, which is melted using a short-pulse laser, positive results can be achieved at room temperature. This can be accomplished, for instance, by incorporating lithium compounds," the scientists believe.

Reference

Lubrication is crucial for the operation of plain bearings. Insufficient lubrication can cause significant wear of components, up to abrasion and irreversible damage, and ultimately lead to seizure of the interacting surfaces. In moving mechanical components, macroscale friction and wear are major sources of energy dissipation and significantly reduce the service life of machines and mechanisms. In the case of automobiles, it is estimated that approximately one-third of the fuel is consumed solely to overcome friction.

Plain bearings have the disadvantage of requiring lubrication, which makes them unsuitable for use under dynamic load conditions and at extreme temperatures. Additionally, friction must be overcome, which leads to increased energy consumption and carbon dioxide emissions.

Alexander Zadorozhny

The news article was translated by UrFU International Marketing Office.
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