Characteristics of thermal spray materials
Thermal spray materials are distinguished by their diverse compositional diversity, allowing for the design and adjustment of their composition to suit specific application requirements, resulting in coatings with a wide range of superior properties. Whether using a single metal, alloy, ceramic, or metal-ceramic composite, thermal spray materials can be used to create coatings. For example, to meet the need for high-temperature wear resistance, a tungsten carbide -cobalt alloy powder can be prepared. Tungsten carbide provides high hardness and wear resistance, while cobalt, as a binder phase, provides toughness. The synergistic effect of these two allows the coating to maintain excellent wear resistance even at high temperatures. To adapt to corrosive environments, a nickel-chromium-molybdenum alloy can be selected. The addition of chromium and molybdenum significantly improves the coating’s resistance to acid and alkali corrosion. This diverse compositional range enables thermal spray materials to meet diverse performance requirements, from ambient to high temperatures, from wear resistance to corrosion protection, and from electrical conductivity to insulation. These materials can meet the diverse performance requirements of coatings in virtually every complex industrial environment. Furthermore, by adjusting the material composition ratio, continuous performance control is possible. For example, gradually increasing the chromium content in a nickel-based alloy will gradually improve the coating’s oxidation resistance, providing precise material selection for applications in diverse temperature environments.
Thermal spray materials are highly adaptable in form and can be manufactured in a variety of forms, including powder, wire, and rod, to meet the diverse requirements of the thermal spray process. This ensures stable feed and excellent melt atomization in all spraying processes. Powder materials are the most widely used form, and their particle size and morphology can be optimized based on the spraying process. For example, plasma spraying requires powders with good flowability and a moderate particle size (10-50μm) to ensure sufficient heating and acceleration in the plasma arc. Supersonic flame spraying requires finer powders (5-30μm) to facilitate rapid melting and dense coating formation in the high-velocity flame. Wires are primarily suitable for arc spraying and flame spraying processes. Wire diameters typically range from 1.2-3.0mm, and they offer continuous feed, enabling highly efficient coating deposition. For example, arc spraying zinc wire can achieve deposition rates of 5-10kg/h, significantly exceeding those of some powder spraying processes. Rods are suitable for specific flame spraying equipment. By feeding the rods into the flame to melt and atomize them, they are suitable for spraying brittle materials such as ceramics. For example, zirconia rods can form a uniform thermal insulation coating during flame spraying. The different forms of thermal spray materials complement each other, making thermal spray technology flexible for a variety of applications. Whether it’s coating small precision components or anti-corrosion spraying large steel structures, the right material form and spraying process can be found.
Thermal spray materials offer excellent performance designability. By manipulating the material composition and microstructure, coating properties can be precisely customized to meet the specific requirements of different operating conditions for various properties, such as hardness, toughness, corrosion resistance, and high-temperature resistance. For example, by adjusting the ceramic phase content in the metal-ceramic composite, the hardness and toughness of the coating can be controlled. When the tungsten carbide content increases from 70% to 90%, the coating’s hardness increases from HRC55 to HRC65, while the toughness decreases slightly. Therefore, the appropriate composition ratio can be selected based on the severity of the wear conditions. In terms of high-temperature resistance, by selecting different ceramic materials, coatings suitable for different temperature ranges can be prepared. Alumina coatings are suitable for environments below 600°C, zirconium oxide coatings can be used for long-term use at temperatures above 1200°C, and hafnium carbide coatings can even withstand extreme temperatures exceeding 2000°C. In terms of corrosion resistance, by selecting materials such as nickel-based alloys and titanium alloys and adjusting the content of alloying elements such as chromium, molybdenum, and tungsten, coatings resistant to different corrosive media, including strong acids, strong bases, and salt spray, can be produced. This designability enables thermal spray materials to be tailored to solve various industrial challenges. For example, spraying a wear-resistant and corrosion-resistant composite coating on the surface of oil drilling equipment not only resists rock abrasion but also prevents corrosion from drilling fluids, significantly extending the service life of the drill bit.
Thermal spray materials possess excellent bonding properties, forming a strong bond with various metal substrates (such as steel, aluminum, copper, and titanium). This ensures that the coating resists peeling during use and fully demonstrates its protective properties. This bonding is primarily due to a combination of mechanical bonding, physical adsorption, and micrometallurgical bonding. When molten or semi-molten material particles impact the substrate surface at high speed, they undergo dramatic plastic deformation, forming a mechanical bond with the substrate’s surface structure. This is the primary bonding mechanism for thermal spray coatings. Furthermore, physical adsorption between the particles and the substrate surface at high temperatures can further enhance the bonding strength. For certain materials, such as nickel-aluminum composite powders, an exothermic reaction occurs during the spraying process, forming intermetallic compounds and achieving micrometallurgical bonding, significantly improving the coating’s bonding strength. For example, arc-sprayed nickel-aluminum composite wires can achieve a bonding strength of 30-50 MPa to the steel substrate, far exceeding the 10-20 MPa of conventional zinc-aluminum coatings. Plasma-sprayed zirconium oxide coatings can achieve bonding strengths exceeding 20 MPa by using a nickel-chromium alloy transition layer, meeting the requirements for high-temperature thermal insulation coatings. Good bonding performance is the key to the long-term and reliable operation of thermal spray materials under various complex working conditions such as dynamic loads, vibrations, and temperature changes, ensuring that the coating can effectively protect the substrate and extend the service life of components.
Thermal spray materials have a wide range of applications and can form uniform, continuous coatings on a variety of substrate materials and component shapes, meeting a wide range of spraying needs, from tiny electronic components to large engineering structures. Thermal spray materials bond well to metal substrates, whether ferrous (such as carbon steel and cast iron) or non-ferrous (such as aluminum alloys and copper alloys). Thermal spraying can also be applied to certain non-metallic substrates, such as ceramics, plastics, and composites, through appropriate surface pretreatment (such as sandblasting and priming). For example, spraying a metal coating on the surface of a plastic part can achieve conductive or decorative properties. Regarding component shape, thermal spray materials are suitable for various shapes, including flat and curved surfaces, pipe inner walls, and complex cavities. For example, a rotary spray gun can form a uniform coating on the surface of shaft parts, and special spray gun accessories can be used to spray the inner walls of pipes, meeting the corrosion protection requirements of long-distance pipelines. Furthermore, thermal spray coatings can be adjusted over a wide range of thicknesses, from functional coatings of a few microns to repair coatings of several millimeters. For example, spraying a 1-2mm thick nickel-based alloy coating on a worn journal can restore its original dimensions and performance. This wide range of applications has made thermal spray materials crucial for numerous industries, including aerospace, machinery manufacturing, petrochemicals, electric power, and automotive transportation, making them indispensable key materials in the field of surface engineering.
