Advanced Coatings: Enabling Engineering Feats and Overcoming Material Limitations

Jet engines represent a remarkable achievement in human engineering. However, their operation defies conventional material limits, according to Ben Beake, director of materials research at Micro Materials, an equipment testing company based in Wales. He states, “The air coming in is hotter than the melting point of the metal underneath – which is obviously not a good thing,” clarifying that these air temperatures exceed 1,000C. To overcome this challenge, jet engine designers have utilized heat-resistant ceramic coatings on engine blades. Currently, researchers are advancing even more robust coatings, enabling engines to operate at even higher temperatures. Dr Beake notes, “If you get it to go hotter, then there’s a massive saving on fuel and CO2.” He estimates that a temperature increase of approximately 30C could lead to an 8% reduction in fuel consumption. This illustrates the significant impact of coatings – they fundamentally alter the performance and potential of base materials. While their importance is often underestimated, these protective layers and surface treatments can enhance high-performance machinery or safeguard costly equipment in extreme conditions. Dr Beake and his team are responsible for rigorously testing coatings to determine their durability and efficacy. Not all clients receive their desired outcomes. He recounted an instance years ago when he informed a missile manufacturer, “We’ve broken your coating.” Dr Beake added, “They stormed off in a huff.” In addition to subjecting coatings to elevated temperatures, Micro Materials employs a “woodpecker” device, which is a small diamond stylus that repeatedly strikes a coating at various points to assess its resilience. The company recently collaborated with Teer Coatings, located in the UK, to evaluate a product suitable for satellite components such as gears and bearings found in diverse moving assemblies. Xiaoling Zhang, from the company, describes this as a challenging endeavor, as the coating needs to safeguard these components both before launch (when exposed to atmospheric humidity on the ground) and while in orbit, against space dust and radiation. Nevertheless, she asserts that the company has successfully met the requirements. Beyond their role in spacecraft protection, coatings may also prevent illness among astronauts. Biofilms, which are viscous bacterial growths within pipes, proliferate more rapidly in microgravity conditions. This presents a potential issue for water systems or fluid-handling equipment on space stations or future spacecraft. Kripa Varanasi, from the Massachusetts Institute of Technology, states, “Biofilms are known to cause mechanical failures.” He adds, “You don’t want this.” Professor Varanasi and his team have engineered various coatings that render surfaces slick, thereby inhibiting biofilm formation. An experiment conducted on the International Space Station, testing one of these coatings, confirmed its intended effectiveness. The concept behind this coating involves combining a solid substance with a lubricant. This mixture is then sprayed onto the internal surface of a pipe or tube, making the interior exceptionally smooth. Professor Varanasi gained prior recognition for creating comparable coatings for the interiors of toothpaste tubes, enabling complete product extraction. He and his associates have commercialized this technology via their spin-out company, LiquiGlide. The property of slipperiness might be an overlooked characteristic. Nuria Espallargas, along with colleagues at the Norwegian University of Science and Technology, has engineered a silicon carbide-based coating for machinery employed in the production or repair of aluminum. This coating functions similarly to a non-stick frying pan, preventing molten aluminum layers from adhering to costly equipment. However, the exact mechanism of this specific coating remains somewhat enigmatic. Professor Espallargas admits, “To be honest, we really don’t know how it works, the mechanism is unknown at the moment.” Despite this, the coating is commercially accessible through her spin-out company, Seram Coatings. Atlas Machine and Supply, a US company specializing in the manufacture and repair of industrial machinery, has tested it. Jeremy Rydberg, chief innovation officer, states, “The real benefit lies in extending the life of the tools and improving the quality of the products being produced.” He explains that, without the coating, Atlas needs to reconstruct its aluminum-processing roller tools every two days, incurring an annual cost of $4.5m. However, the new coating extends the lifespan of these tools to a full week, rather than just a few days, thereby reducing rebuild expenses to approximately $1.3m per year. While coatings offer remarkable capabilities, they do not consistently perform as expected, observes Andy Hopkinson, managing director at Safinah Group, a company frequently engaged to examine coating failures. He mentions, “We’re seeing a lot of issues at the moment with car parks, where their passive fire protection system is peeling off,” referring to the fire-retardant paint occasionally applied to concrete constructions. Furthermore, his company has discovered that coatings on commercial vessels do not invariably deter barnacles and other marine organisms from adhering to the hull. This issue, termed biofouling, heightens friction, compelling the ship’s engine to exert more effort and consume additional fuel. Even with various promising coatings available, ship owners do not always select the appropriate one for their specific vessel. Dr Hopkinson states that this decision should be based on factors such as the ship’s operational area, its anticipated idle time versus active time, and other relevant conditions. Rectifying such problems can incur costs ranging from many thousands to millions of pounds. Mr Hopkinson explains, “Typically, paint costs between 1 and 2% of the project. The problem is, when it goes wrong, the costs become exponential.” Nevertheless, researchers in this domain assert that substantial opportunities remain for enhancing existing coatings and creating novel ones, which could significantly boost the future performance of machinery or infrastructure.