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Type Of Thermal Spray Powder
Mar 21, 2018

Thermal spray powders are classified into self-fluxing alloys, self-bonding alloys, corrosion resistant and oxidation resistant alloys, ceramics, cermets and composite powders. Each powder must take into account its particle size composition, particle shape, flowability, and composition. Generally, the deposition rate of the powder during thermal spraying should be between 80% and 95%.

Self-fluxing alloy powder This powder has a very low melting point and can be melted or remelted in the normal atmosphere to combine with the surface of the workpiece to form an essentially non-porous dense layer. Self-fluxing alloys contain boron and silicon flux, acting as a "getter" to prevent the oxidation of nickel-chromium alloys and to form an antioxidant borosilicate "glass." Boron is a nickel fortifier, and can also lower the melting point of nickel-based alloys (as low as 1040 to 1120 °C). Borosilicate flux can significantly improve the fluidity and surface tension of liquid alloys, and is conducive to the formation of dense coatings. The coating hardness range is HRC30~50, and its wear resistance and abrasiveness are 20 times higher than steels with the same hardness. Self-fluxing alloys are further divided into nickel-based, cobalt-based, iron-based, and tungsten carbide-containing powders, which are almost all produced by atomization. Commonly used in workpieces requiring wear resistance, thin corrosion resistance, and high surface finish.

Wear-resistant, corrosion-resistant, high-temperature alloy powder This is an alloy powder containing eutectic carbides in a cobalt-based matrix alloyed with chromium and tungsten. For example, various components of cobalt-chromium-tungsten alloy powder. It can meet wear, corrosion and high temperature requirements. However, as the weight percentage of carbides decreases, its wear resistance and corrosion resistance decrease. This spray powder is expensive. Low-cost alternatives to cobalt or cobalt have now been developed.

Oxidized alloy powders Oxidation resistant alloys cannot be self-melting and are always used in sprayed form. For example, similar to the 316 type of high-quality stainless steel, high chromium stainless steel, nickel-chromium alloy and high-purity spherical copper powder. They are produced almost by atomization and can be used to make bright, dense, high-gloss coatings or to repair work surfaces.

Composite Powders With the development of spraying equipment, a new type of thermal spray material, namely composite powder, has been developed with a wide variety of products and wide applications. It is often commercially available as an exfoliating white adhesive powder. Since then, various high melting point metals, alloys, oxides, carbides, and other non-metallic materials can be thermally sprayed. Composite powders can be various combinations of different materials, from two or more different materials combined into multi-phase heterogeneous particles, according to the powder structure can be divided into two types of coated and non-coated type. The former is a kind of core material whose particle surface is completely and uniformly coated with one or more, one or more layers of other materials; the latter is a relatively coarse secondary powder composed of two or more fine material particles. , More high-energy ball mill mechanical alloying method production. Composite powders are heterogeneous, but the distribution of ingredients and various components between the particles is generally relatively uniform.

The coated type composite powder is a very good thermal spray material and has a broad development prospect. According to its material, performance and application, it can be roughly divided into the following types: (1) Self-bonding type. This kind of powder is made of metal aluminum, titanium, zirconium, chromium and its alloy as the core and coated with nickel or cobalt on the outside to become self-bonding alloy powders such as nickel (cobalt) coated aluminum, titanium coated and zirconium coated. The preparation method of this composite powder includes a liquid phase deposition method, a vapor deposition method, and a solid-phase thermal diffusion bonding method, in which a wet nickel-cobalt-coated composite powder can be directly produced from a nickel or cobalt production process. Take; Vapor deposition of carbonyl production of nickel-coated aluminum powder is also quite successful. (2) wear-resistant type. Such as WC, TiC, BN, Cr3C2, SiC, TiN, diamond as its core, its surface is covered with metallic nickel,

Cobalt, copper or alloys such as Ni-Cr-Al and Co-Cr-Al-Y can be used to make processing tools or wear resistant coatings. (3) can be sealed type. For example, the core is covered with a kind of abradable, relatively soft powder (graphite, diatomaceous earth, calcium fluoride, etc.), and the surface is coated with metal, processed or thermally sprayed to form an abradable coating or Parts to achieve lubrication and sealing purposes. Such powders include nickel-coated graphite (a in the figure), copper-clad graphite, nickel-clad diatomaceous earth, nickel-copper-aluminum-packaged calcium fluoride, and the like. (4) Wear resistant type. For example, titanium, zirconium, chromium, chromium oxide as the core coating of nickel, cobalt, copper, silver, gold and other composite powders for the surface coating of wear resistant parts. (5) Heat and heat resistant type. For example, zirconia, alumina (b in the figure) and titanium oxide, which have good thermal or heat-resistance properties, are coated with metal as a binder, and these oxides and minerals can be improved after thermal spraying. Bonding with the workpiece substrate to form a good heat insulation, heat-resistant coating, in order to improve the heat-resistant wear-resisting erosion resistance of the workpiece surface. This coating has been widely used in aero engines and spacecraft.

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