What material to choose for thermal spraying bottom layer of stainless steel, copper alloy, aluminum magnesium alloy and non-metallic materials

       When the base material is ordinary carbon steel, alloy steel, stainless steel, nickel-chromium alloy, aluminum, magnesium, titanium, niobium and other materials, spray powder with "self-bonding" effect can be selected as the bonding base material, and the coating is very dense , the porosity is low, and the bonding strength between the surface working layer and the substrate can be significantly improved. However, it should be noted that this type of bonding bottom layer is not corrosion-resistant in acidic, alkaline and neutral salt electrolytes, and is not suitable for use as a bonding bottom layer under such liquid chemical corrosion conditions.



When the base material is copper and copper alloy, aluminum bronze should be preferred as the bonding bottom layer. Due to the exothermic reaction between Cu and Al during the thermal spraying process, intermetallic compounds are formed. Therefore, aluminum bronze has a certain self-adhesion on the surface of copper and copper alloys, which is beneficial to improve the relationship between the coating and the substrate. high bonding strength, and the coating has good thermal shock resistance and oxidation resistance.



When the substrate is a plastic or polymer matrix, in order to avoid "coking" on the surface of the substrate by being scorched by high-temperature particles, thus affecting the bonding between the working layer and the plastic substrate, low melting point metals (such as Zn, Al, etc.) are often selected. etc.), or plastic plus stainless steel composite powder as the bonding base material. Plastic plus stainless steel composite powder is a powder composed of plastic powder and stainless steel powder. It is mainly used as the bonding base material when spraying high melting point metal, ceramic or cermet coating on plastic substrates. Among them, the plastic component is soft and has good leveling, which makes the coating and the base plastic have good bonding strength, and minimizes the heating of the plastic base; while the stainless steel component has good chemical corrosion resistance, can form hard particles embedded in the plastic coating,



It is beneficial to form a rough surface and provide an ideal "anchor" structure for the spraying working layer; in addition, the stainless steel component is also conducive to dissipating the heat of the spraying flame, thereby avoiding local overheating or coking of the plastic matrix, which is beneficial to improving the adhesion. The bonding strength of the bottom layer to the substrate is favorable.



When the substrate is a graphite substrate, in order to prevent the graphite and tungsten from reacting at high temperature to form tungsten carbide and cause graphite embrittlement, tantalum can be sprayed as the bonding bottom layer. In addition, a self-adhesive bond can also be formed between the tantalum coating and the steel substrate.



It is worth noting that in thermal spraying technology, molybdenum (Mo) is also widely used as an adhesive primer with self-adhesive effect. This is because Mo oxidizes rapidly at 400 °C to generate volatile MoO3, resulting in rapid sublimation. The exposed molybdenum droplets have excellent wetting and spreading properties on clean and smooth surfaces of most metals and their alloys. Thereby forming a self-adhesive effect. In addition to metals, it can also bond to non-metallic surfaces such as ceramics and glass, except for copper and copper alloys, plated surfaces, nitrided surfaces and ferrosilicon surfaces.



In addition, NiCr alloy with excellent high temperature oxidation resistance and corrosion resistance, although it does not have self-bonding effect, is also a widely used bonding base material.