High-performance ceramic spray coating is a general term for a category of non-metallic inorganic coatings, which emerged after organic resins, metals and alloys. Over the past half-century, with the development of cutting-edge technologies such as aerospace engineering and electronic military industries, high-performance ceramic coatings have also achieved sustained and rapid development. Coated parts fabricated by combining these new high-temperature materials with metal substrates are fully integrated. Ceramic materials feature the merits of ceramic coatings including superior heat resistance, high plasticity and good electrical conductivity. The base metallic materials can complement them mutually while retaining the structural strength of the original substrate materials.
Forming Methods ① Solid-state deposition: e.g., self-propagating high-temperature synthesis (SHS). ② Vapor deposition: e.g., Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD). ③ Wet chemical methods: sol-gel process, electroless plating, composite electroless plating, etc. ④ Thermal spraying: such as plasma spraying and flame spraying. This method accounts for more than 50% of the ceramic coating market share. Advantages: ① It can flexibly combine the high temperature resistance, wear resistance, corrosion resistance and other properties of ceramic materials with the high strength, toughness, machinability, electrical and thermal conductivity of metallic materials. It leverages the strengths of each material to offset weaknesses and maximizes the overall comprehensive performance to meet the structural and environmental protection requirements of mechanical products. ② A wide variety of materials are available for preparing ceramic coatings. Ceramics combined with ceramics, ceramics with metals, ceramics with plastics and other material combinations can be adopted as needed. Moreover, it can be easily adapted to existing metal processing conditions to realize technical upgrading for enterprises. ③ Ceramic coatings are easy to form with fast deposition rates and controllable coating thickness. Different sintering processes can be applied to spray the surfaces of thin-walled parts, hollow parts and special-shaped components, and localized spray strengthening of products can also be realized. ④ Ceramic coatings with favorable machinability can be deposited on different substrates. Examples include various metals, cement, refractory materials, gypsum and other inorganic materials; plastics and organic materials; wood, paperboard, etc. Their performance can be improved via ceramic spraying. After the ceramic coating is damaged, the metal substrate can be reused, and ceramic coating can be re-sprayed on it (the same applies to other substrates if they remain intact and fit for secondary use). ⑤ Reduced material consumption. Ceramic coatings generally range in thickness from tens of micrometers to several millimeters. Ceramic materials feature low density, resulting in low material consumption yet high added value. ⑥ Not limited by workpiece size or construction site. Sprayed workpieces can be large or small with unrestricted shapes. Spraying can be carried out either in a thermal spraying workshop or on-site. Disadvantages: ① Poor plastic deformation capacity, sensitivity to stress concentration and cracks, inferior thermal shock resistance and fatigue resistance. ② Ceramic coating materials and metallic materials differ greatly in thermal expansion coefficient and thermal conductivity. Diverse stress states generated during service will affect service life. ③ The coating bonds to the substrate through mechanical interlocking or molecular attraction, which leads to inconsistent bonding strength. Application Fields ① Aerospace Industry: Thermal barrier coatings constitute one of the core technologies for modern aero-engines. Hot-section components of aero-engines such as flame tubes, afterburners and turbine blades commonly adopt plasma-sprayed Al₂O₃, ZrO₂ or multi-layer cermet composite coatings. More sophisticated components in the aerospace sector impose stricter requirements on materials. Stable, reliable, lightweight high-performance ceramic coatings are applied to thrust chambers of liquid-fuel rocket engines. The nozzles of solid rocket engines rely on these coatings to resolve high-temperature corrosion and thermal insulation issues within short operating cycles. ② Power Industry: Plasma-sprayed WC/Co cermet coatings are applied on forced draft and induced draft fan blades of pulverized coal boilers in thermal power plants to mitigate blade abrasion in high-speed dusty environments. Their service life is more than four times longer than that of uncoated blades. The piston rods of hydraulic hoists for large water conservancy projects must withstand reciprocating sliding wear under heavy loads during gate opening and closing, as well as long-term corrosion by water vapor. Traditional chrome-plated piston rods tend to leak oil or even jam after a period of operation, which directly interferes with gate movement and positioning. ③ Petrochemical Industry: Plasma-sprayed ceramic coated plungers are widely adopted, typically using Cr₂O₃, Al₂O₃ or Al₂O₃-TiO₂ ceramic coatings. Representative examples include mud pump plungers for oil exploration, C-type pump plungers and CO₂ pump plungers for chemical fiber production. To prevent leakage of conveyed liquid media, mechanical sealing rings and shaft sleeves are manufactured with ceramic sprayed components. Their end-face sealing structure is widely used in oil, chemical fiber and fertilizer production. Ball valves are critical components for transporting high-temperature, high-pressure corrosive slurries containing solid particles, with stringent sealing requirements. Plasma-sprayed Cr₂O₃ or HVOF-sprayed WC/Co coatings effectively address this challenge and extend service life by roughly 10 times. ④ Metallurgical Industry: Continuous annealing rolls Specialized furnace rolls for steel plates adopt plasma-sprayed Al₂O₃ + 25% ZrO₂ composite coatings, whose service life is 6–8 times that of conventional superalloy and graphite rolls. Sinking rolls for hot-dip galvanizing use HVOF-sprayed cermet coatings, which deliver outstanding molten zinc corrosion resistance and good wear resistance. The service life of this new type of sinking roll exceeds that of the original rolls by more than twofold, lasting around one month. Concave rolls for hot-dip aluminizing were once a bottleneck technology for this process. Plasma-sprayed spinel coatings together with water glass sealing treatment greatly prolong the service life to more than 15 days. ⑤ Light Industry: To reduce abrasion caused by yarn and chemical fibers on textile machinery parts, many components in the textile industry are coated with ceramic coatings, such as rollers, grooved rolls and friction plates. Plasma-sprayed Al₂O₃-TiO₂ or Cr₂O₃ coatings are commonly used. ⑥ Printing and Packaging Industry: In the printing sector, ink fountain rollers and offset rollers adopt plasma-sprayed Cr₂O₃ ceramic coatings; cast iron printing rollers use Al₂O₃-TiO₂ coatings. Corona rollers used for plastic films such as polyethylene are coated with plasma-sprayed Al₂O₃ as an insulating layer. Corrugating rolls in the packaging industry use plasma-sprayed Cr₂O₃ ceramic coatings.