Advanced surface coatings are used in situations in which the material of the main component is unable to sustain long life or protect itself from adverse operating environments. Coatings are especially useful for situations when making the bulk of components of a material possessing the desired properties will increase the cost to the point of being prohibitive; in these cases, the practical solution is a surface coating that serves as a protective barrier from the environment and any adverse effects from that environment.
Different materials used for coatings offer properties such as anti-friction and anti-wear, anti-corrosion, thermal resistance, and super hydrophobic capabilities, depending on the operating conditions and the required properties. These materials have been used to overcome unfavorable operating conditions and to enhance the adhesion and surface texturing of coatings.
Graphene has been used for coating materials. Especially modified graphene oxide, which has been shown to improve corrosion performance of materials including epoxies and epoxy coatings. The corrosion resistance of steel substrate was considerably improved under salt spray tests. The use of graphene in the epoxy-composite coatings was studied in adhesion tests and showed improved anti-corrosion performance compared with other epoxy coatings.
In the automotive industry, coatings are used in the structure of the vehicles and the fabrics, as well as in the power generation units. For example, a company like Zircotec develops coatings for the use of materials previously unsuitable for automotive applications that can help solve issues including heat, wear, and electrical insulation. The company's solutions include two categories of composites: the first protects against heat, while the second works to protect against wear and abrasion.
For wear, the solutions are metal-based. For temperature solutions, the coatings are ceramic, such as zirconia. The composite materials that can be used include carbon fiber, sintered nylon, and fiberglass. These can provide lightweight, less expensive materials for use in the automotive industry. As well, plasma-sprayed ceramic coatings can provide lightweight, easily packaged, and durable thermal barriers suitable for a range of environments.
Similar to, and related to, the automotive industry, manufacturers of power generation equipment, such as turbines, compressors, or engines, have seen improved performance with advanced surface coatings. These coatings can limit compressor fouling, protect against corrosion or wear in all power generation units, and reduce the effects of hot corrosion and oxidation; in some cases, the coatings can act as a thermal barrier. Any failures in power generation units of unprotected components can trigger chain reactions within the system and result in damage to coated and protected parts.
Other coatings can also improve the power generation efficiency, beyond just the lengthening of the lifespan of the part and reducing replacement cost. Through the reduction of fouling, which decreases the overall efficiency and output of an engine, these coatings can increase the overall fuel efficiency of an engine.
In renewable energy, similar to the use of coatings in turbines for power generation, corrosion resistant thermal spray coatings can protect the components in the power plants. Water walls and super-heater tubes suffer from heat-temperature corrosion, mainly triggered by gases such as HCl and H2O, often in combination with alkali and metal chlorides produced during field combustion. The use of a dense, defect-free adherent coating through thermal spray techniques can improve the performance of components and increase the thermal and electrical efficiency of these power plants, allowing them to generate more power.
In the textile industry, coatings are often used on the equipment used to manufacture the textiles. The rollers and other equipment that handle the yarn or thread are subject to abrasion, wear, corrosive liquids, and elevated temperatures. This leads to a decrease in the service life of equipment and increases the downtime necessary for repairing machinery. Many of these machines are manufactured using light alloys as they offer a high strength-to-weight ratio, but these alloys do not provide the protective qualities required in the manufacturing applications. These alloys are less resistant to corrosion compared to heavier metals and often have shorter service lifespans.
In these cases, surface coatings are used to protect the light alloys. A popular coating, plasma electrolytic oxidation (PEO), is a type of advanced electrochemical conversion coating that is capable of offering the necessary protection. This involves modifying the anodic film through arc discharges that create a non-columnar microstructure and give it hardness and high wear performance.
Advanced coatings are also used in medical technology, especially in implants, when a surface coating can improve mechanical properties and the biocompatibility of implants. These coatings can include zirconium nitride for surface hardness, which can reduce the wear rate seen in standard implants by 65 percent. As well, these coatings can increase an implant's resistance to scratches, improve the implant's wettability, and improve articulation between load-bearing surfaces.
Coatings can include layers, including transition layers that create resilient elastic properties and an effective metal ion barrier for patients with metal hypersensitivity. Other types of coatings can include lubricants, antimicrobials, and water-repellant polymers that can be customized to the type of device or application, to improve patient outcomes. Some of the more popular coatings include antimicrobial, hydrophilic, fluoropolymer, and anodic coatings. Device manufacturers can use physical vapor deposition, which can create durable, functional coatings for surgical instruments, knee replacements, and dental implants.
