High-performance ceramic coatings come in a wide variety. Based on their functional characteristics, they can be broadly classified into three categories: wear-resistant ceramic coatings, corrosion-resistant ceramic coatings, and thermal barrier ceramic coatings. Each type has its own distinct features, so understanding their characteristics will greatly guide related research and applications.
Wear-resistant ceramic coatings mainly include certain oxides, carbides, silicides, nitrides, and borides, represented by materials like Al₂O₃, WC, MoSi₂, AlN, and ZrB₂. The most prominent features of wear-resistant ceramic coatings are their stable chemical properties, high hardness, good high-temperature oxidation resistance, and excellent wear resistance. They are primarily used in applications such as cutting tools, hard tools, and wear- and corrosion-resistant components.
Corrosion-resistant ceramic coatings are used to protect base components from various environmental corrosions, such as the marine environment for offshore equipment, the cutting fluid environment for tools, and the molten zinc environment for galvanizing sink rolls. There isn't a specific category for corrosion-resistant ceramic coatings; most wear-resistant ceramic coatings also possess good corrosion resistance.
Thermal barrier ceramic coatings are coating systems composed of a metallic bond coat and a ceramic thermal barrier topcoat, represented by materials like MCrAlY/ZrO₂-Y₂O₃ and MCrAlY/ZrO₂-CeO₂ (where M refers to Co, Ni, or their alloys). They are currently mainly applied in aircraft engines.
The performance of high-performance ceramic coatings is largely determined by their preparation process. The main preparation methods for ceramic coatings include: wet chemical methods, vapor deposition, solid-phase deposition, and thermal spraying. Among these, thermal spraying accounts for over 50% of the ceramic coating market share.
Ceramic thermal spraying refers to thermal spraying methods that use ceramics as the spraying material. Developed from thermal spraying of metallic materials, it has advanced rapidly due to the many excellent properties of ceramic coatings that are unmatched by metallic materials, playing an increasingly important role in numerous fields.
Aerospace Industry
Thermal barrier coatings are a key technology in modern aircraft engines. Hot section components like flame tubes, afterburners, and turbine blades are often coated with plasma-sprayed Al₂O₃, ZrO₂, or multilayer cermet coatings. In the more demanding aerospace industry, components require materials with even more stringent properties. Ceramic coatings that are stable, reliable, lightweight, and high-performance are used in the thrust chambers of liquid rocket engines and the exhaust nozzles of short-duration solid rocket motors, effectively solving problems related to high-temperature erosion and insulation.
Power Industry
In coal-fired power plants, plasma-sprayed WC/Co cermet coatings on the impellers of forced draft fans and induced draft fans reduce wear in high-speed particulate environments, extending component life by over four times compared to uncoated ones. Piston rods in hydraulic hoists of large water conservancy projects must withstand wear from heavy-duty reciprocating sliding during gate operation and resist corrosion from humid conditions. Traditional chromium-plated piston rods can develop leaks or even seize after a period, directly affecting gate operation and positioning.
Petrochemical Industry
Plasma-sprayed ceramic coatings are widely used on plungers, often employing materials like Cr₂O₃, Al₂O₃, or Al₂O₃-TiO₂. Examples include mud pump plungers in oil exploration, and C-type pump and CO₂ pump plungers in chemical fiber production. To prevent leakage of conveyed liquid media, mechanical dynamic seal rings and shaft sleeves with sprayed ceramic coatings are extensively used in end-face seals within the petroleum, chemical fiber, and fertilizer industries.
Ball valves are critical components for transporting high-temperature, high-pressure fluids containing solid particles and corrosive slurries, demanding stringent sealing performance. Plasma-sprayed Cr₂O₃ or HVOF-sprayed WC/Co coatings effectively solve this challenge, increasing service life by approximately ten times.
Metallurgical Industry
Plasma-sprayed Al₂O₃+25% ZrO₂ composite coatings on hearth rolls in continuous steel annealing furnaces last 6 to 8 times longer than previous high-temperature alloy or graphite rolls. Sink rolls in hot-dip galvanizing, coated with HVOF-sprayed cermet coatings, exhibit excellent resistance to molten zinc corrosion and good wear resistance, lasting up to one month-more than double the life of uncoated rolls. Sink rolls for hot-dip aluminizing, a former technical challenge, now use plasma-sprayed spinel coatings sealed with water glass, significantly improving service life to over 15 days.
Light Industry
To overcome wear caused by yarn and chemical fibers on textile machinery parts, numerous components like rollers, grooved rollers, and friction discs are coated with plasma-sprayed Al₂O₃-TiO₂ or Cr₂O₃ coatings.
Printing & Packaging Industry
In printing, plasma-sprayed Cr₂O₃ coatings are used on ink ducts and rubber-coated rollers, while Al₂O₃-TiO₂ coatings are applied to cast iron printing rollers. Corona treatment rollers for plastic films like polyethylene use plasma-sprayed Al₂O₃ as an insulating coating. In the packaging industry, corrugating rolls are coated with plasma-sprayed Cr₂O₃ ceramic coatings.