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Thermal spraying powders
Nov 08, 2018

Metal, alloy and composite powder commonly used in thermal spraying hard surface technology.Use oxygen acetylene flame, plasma flame or oxygen acetylene flame thermal spraying (welding) methods, such as powder instant heating, make these unique characteristics in molten or semi-molten state, with high heat flux was in cold or hot spray deposition on the surface of workpiece, the formation of surface strengthening layer, to improve surface wear and corrosion resistance, heat resistance, oxidation resistance or repair the dimensions, etc.This is an economical, practical and efficient process technology, which has been widely used.

Brief thermal spraying technology first originated in 1910, and was pioneered by Dr. M V Schoop of Switzerland with oxyacetylene flame gun for metal spraying.In the 1940s and 1950s, with the advent of new spraying equipment, spraying materials gradually developed from wire to metal powder, especially atomized prealloy powder and coated composite powder.

The types of thermal spraying powder are divided into self-fusion alloy, self-bonding alloy, corrosion and oxidation resistant alloy, ceramics, metal ceramics and composite powder.The effects of particle size composition, particle shape, fluidity and composition must be considered for each powder.Generally, the deposition rate of powder in the process of thermal spraying should be between 80% and 95%.

The powder has a very low melting point and can be melted or remelted in the normal atmosphere and combined with the surface of the workpiece into a dense layer essentially free of pores.The fusible alloy contains boron and silicon fluxes that act as an "getter" to prevent oxidation of the nickel-chromium matrix alloy and form an antioxidant boron silicate "glass".Boron is nickel enhancer, and can reduce the melting point of nickel-based alloy (as low as 1040 ~ 1120 ℃).The borosilicate flux can significantly improve the fluidity and surface tension of liquid alloy, and is conducive to forming a compact coating. The coating's hardness range is hrc30-50, and its anti-wear and abrasion resistance is 20 times higher than that of steel with the same hardness.The self-fusion alloy is divided into nickel base, cobalt base, iron base and tungsten carbide powder.It is often used for workpieces that need wear - resistant, corrosion - resistant thin coating and high surface finishing.

An alloy powder containing eutectic carbides in a cobalt base alloy of chromium and tungsten.For example, various components of cobalt - chromium - tungsten alloy powder.It can meet the requirements of wear resistance, corrosion resistance and high temperature.However, as the percentage of carbides weight decreases, the wear resistance and corrosion resistance of the carbides decrease.The powder is expensive to spray.Cheap alternatives with or without cobalt have been developed.

Non - oxidizing alloy powder non - oxidizing alloy can not be self - melting, and is always used in spray mode.For example, type 316 is similar to 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 shiny, dense, high-gloss coatings or to repair working surfaces.

With the development of spraying equipment, composite powder has been developed into a kind of new thermal spraying material with a wide range of applications, namely composite powder.It is often presented as an exothermic white-bonded powder.Since then, all kinds of metals, alloys, oxides, carbides and other non-metallic materials with high melting point can be used for thermal spraying.Composite powder can combine various materials into heterogeneous particles by combining two or more different materials.The former is a core material whose particle surface is completely and evenly coated with one or more, one or more layers of other materials.The latter is a coarse secondary powder composed of more than two kinds of fine material particles.Composite powders are heterogeneous, but the distribution of components and components between particles is generally relatively uniform.


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