Special spraying technology
Specialty spraying technology is a general term for spraying processes with specialized capabilities or suitability for extreme environments, compared to traditional flame spraying and arc spraying. These technologies primarily include supersonic flame spraying, cold spraying, and laser spraying, playing an irreplaceable role in high-end sectors such as aerospace, new energy, and precision manufacturing. These technologies transcend the performance limitations of traditional spraying through innovative heat source configurations, particle acceleration methods, and material systems. For example, supersonic flame spraying achieves flame velocities of 1500-2000 m/s, enabling semi-molten tungsten carbide particles to impact the substrate at high speed, forming a coating with a density exceeding 95% and wear resistance 3-5 times greater than that of traditional flame sprayed coatings. The core advantage of specialty spraying technology lies in its ability to produce high-performance, multifunctional coatings that meet technical specifications difficult to achieve with traditional processes, such as ultra-high-temperature oxidation resistance, ultra-low-temperature thermal insulation, and ultra-hard wear resistance.
High velocity oxygen fuel (HVOF) spraying is the most widely used specialty spraying technology. It generates a supersonic flame through the high-pressure combustion of oxygen and a fuel (such as kerosene or propane). This accelerates the powdered material to supersonic speeds before depositing it to form a coating. Compared to plasma spraying, HVOF’s flame temperature is lower (approximately 3000°C), which reduces oxidation and phase transformation of the powder particles, making it particularly suitable for the preparation of carbide cermet coatings. For example, HVOF tungsten carbide-cobalt coatings sprayed on oil drilling bits can achieve a hardness of up to HRC65, extending their service life more than twice that of traditional carbide drill bits when drilling in granite formations. This coating achieves a bond strength of 70-100 MPa and a porosity of less than 1%. Applications on high-speed components such as automotive engine valves and turbocharger rotors can withstand centrifugal forces exceeding 10,000 rpm without flaking. Tests conducted by an engine manufacturer showed that the wear resistance of HVOF-coated valves is four times that of chrome-plated valves, significantly reducing the frequency of engine maintenance.
Cold spray technology, a solid-state deposition process, is a revolutionary breakthrough in specialty spray coatings. It uses high-pressure gases (nitrogen or helium) to accelerate powder particles to 300-1200 m/s. The particles, while completely unmelted, impact the substrate, achieving bonding through plastic deformation. This characteristic preserves the material’s original microstructure, making it particularly suitable for the preparation of nanostructured coatings and heat-treated, hardened alloy coatings. For example, cold-sprayed nanocrystalline aluminum coatings maintain an average grain size below 50 nm, exhibit a 40% increase in hardness compared to traditional thermally sprayed aluminum coatings, and exhibit no oxidation. Their application in corrosion protection for spacecraft fuel tanks effectively mitigates the risk of hydrogen embrittlement. In titanium alloy component repair, cold spray technology can deposit titanium powder at room temperature, achieving a bond strength exceeding 50 MPa and a heat-affected zone (HAZ) of less than 10 μm on the substrate, eliminating the thermal deformation associated with welding repairs. An airline used cold spray to repair engine blades, achieving a cost of only one-fifth that of a new component and restoring fatigue life to over 90% of that of a new one.
Laser spraying technology uses a high-energy laser beam as a heat source to melt a pre-set or synchronously fed powder material, rapidly solidifying it to form a coating. This technology boasts high energy density, rapid heating rates, and strong coating-substrate bonding. This technology’s concentrated heat input allows for precise control of the melt pool size, making it suitable for producing ultra-thin coatings ( 5-50μm ) on precision component surfaces. For example, thermal barrier coatings for aircraft engine blades can achieve a thickness tolerance of within ±2μm for laser-sprayed zirconia coatings . Laser spraying boasts cooling rates as high as 10⁶ °C /s , creating fine-grained or amorphous structures that significantly improve coating performance. For example, laser-sprayed iron-based amorphous alloy coatings offer corrosion resistance over 10 times that of 304 stainless steel . Applications on chemical pumps and valves offer resistance to strong acid and alkali corrosion. Furthermore, laser spraying offers high flexibility, enabling robotic manipulation to achieve localized coating of complex three-dimensional parts. For example, selectively spraying a wear-resistant coating on gear teeth ensures wear resistance while preserving the toughness of the core, extending the gear’s service life by over three times.
Suspension plasma spraying is a specialized technology developed for nanomaterials and ceramics. Nanopowders are dispersed in a liquid medium to form a suspension, which is then atomized, melted, and deposited using a plasma flame. This overcomes the problem of nanopowder agglomeration that often occurs in conventional spraying. This technology can produce coatings with unique microstructures, such as porous gradient thermal barrier coatings, where the porosity can vary from 10% on the substrate to 30% at the surface . This ensures bonding strength while reducing thermal conductivity to below 0.1 W/(m · K) . Application to gas turbine blades can reduce heat loss by 30% . Zirconia coatings produced using suspension plasma spraying exhibit a well-developed columnar crystal structure and excellent thermal shock resistance. They withstand 1000 cycles from 1100 °C to room temperature without cracking, far exceeding the 300 cycles achieved by conventional plasma sprayed coatings. In the field of solid oxide fuel cells (SOFCs), this technology can produce dense electrolyte layers (5-10μm thick) and porous electrode layers, increasing battery energy conversion efficiency by 15% and promoting the development of new energy technologies. The continuous innovation of special spraying technology is providing more and more solutions for high-end manufacturing, pushing product performance to a higher level.
