Scientists Have Come Up With a Way to Improve Wear Resistance of Steel in Seawater

An aggressive environment, such as seawater or friction, eventually destroys even very durable stainless steel products. A method of protection of steel surfaces was proposed by a group of scientists from the National University of Science and Technology (NUST MISIS) together with their counterparts from the Czech Republic.

The researchers believe that the coverage they have developed can significantly enhance the protection of marine and coastal infrastructure, and reduce the risk of accidents and breakdowns of equipment. The study was published in the "Wear" journal.

The marine industry, shipbuilding, and coastal infrastructure require a large number of mechanisms (such as pumps, screws, winches, bolts, etc.), which are susceptible to wear due to contact with saltwater. Many such parts are said to be made of corrosion-resistant steels containing such elements as chromium, nickel, and molybdenum.

However, such protection has a significant disadvantage, as explained by the experts. The corrosion resistance is provided by the finest, just a few nanometres thick coverage on the surface of steel parts, which is formed on its own like the coverage of aluminium oxide on aluminium products. It is worn out if a part is under friction. Therefore, it needs to be additionally protected by increasing the hardness of the surface layer.

Russia's Magnitogorsk Iron and Steel Works

Scientists have developed a coating that meets all the necessary requirements and can protect the surface layer due to perfect adhesion, high hardness, and thickness. It consists of sprayed tantalum-zirconium carbides fixed with a metal layer.

When there is no friction, carbide particles have little effect on corrosion resistance, and when under friction, they mechanically protect the surface layer. According to the experts, it is often more profitable and efficient to refine the top layer than to improve the detail itself.

"Imagine a water pump. The majority of these devices break down due to the tribocorrosion of the shaft in a stuffing box. The water then enters the drive motor and shuts it down. The developed solid coating applied to this part of the turbine shaft can dramatically increase the service life of the entire pump. Protection of a critical area is always better than refining the whole detail. Moreover, sometimes it is not even possible", the senior researcher at the Department of Powder Metallurgy and Performance Coatings at NUST MISIS, Konstantin Kuptsov, commented.

The scientists used an electro-spark alloying method resembling a welding process to apply the coating. This method has long been known, but the specialists at NUST MISIS have proposed to carry out the process in a vacuum. This provides protection against oxidation and significantly improves the quality of the coating. The proposed technology is protected by two patents, the researchers noted.

In the future, the specialists plan to give water-repellent properties to the coating and to prevent contact of metal surfaces with a corrosive medium. It will significantly facilitate the task of selecting the most solid compositions for protection against wear and will help to prevent the surface layer from being covered with ice in polar latitudes.

“The coating is being developed mainly for marine and coastal infrastructure. However, these coatings can be used in other areas, such as the urban environment and transport, which face significant challenges due to corrosion caused by ice-melting products. Protection against corrosion and wear is also indirectly related to safety, as it reduces the risk of various accidents caused by equipment breakdowns”, Kuptsov noted.

The work was carried out within the framework of the Russian Science Foundation project on the "Development of solid hydrophobic coatings intended for the protection of marine and coastal infrastructure against tribocorrosive, abrasive and cavitational wear".