Self-bonding powder

The self-bonding powder refers to an alloy powder which can produce micro-metallurgical bonding characteristics with the surface of the substrate during spraying. In order to obtain the self-bonding between the sprayed particles and the substrate, the spraying material with the following characteristics is advantageous(this is also the basis for the design of the self-bonding alloy)

(1)High melting point, high density metal alloys which can be heated and melted under thermal spraying conditions, such as molybdenum and other high density refractory metals which have a high melting point. When such a metal is sprayed, the temperature of the sprayed particles is higher, thereby increasing the interaction temperature between the sprayed particles and the substrate, and high energy transfer is beneficial to metallurgical bonding. 

(2)The exothermic reaction of the sprayed material during spraying also helps to improve the interaction between the sprayed particles and the surface of the substrate. For example, aluminum reacts with nickel during the spraying process, the aluminothermic reaction exotherms.

There are 3 common kinds of Self-bonding powders:

A: Molybdenum and its alloy self-bonding powder

Thermal spraying of such powders has self-bonding properties on the surface of the steel material, and the coating has friction reducing properties. When spraying on steel as a working coating, in most cases no need the bottom layer. The thermal spray coating of molybdenum-based alloy powder is mainly used to withstand sliding frictional wear between metals. Such as the engine piston ring. At present, the molybdenum-based alloy powders used in the world mainly include the following:

(1) Pure molybdenum powder(Pure moly powder, Mo≥99.5%)

(2) Carbon-containing: Mo3%C

(3) Mo25% (NiCrBSiFe) mixed powder with self-fluxing alloy powder

B: Exothermic reaction type self-bonding powder.

They are mainly some aluminum alloy powders, such as Ni-Al, FeNi-Al alloy powder. The Ni 95% Al 5% powder (NiAl95/5 powder)is mostly aluminum coated nickel powder. When the powder is heated in the flame stream, it reaches the melting point of aluminum (660℃) very quickly, and a strong exothermic reaction occurs between Al and Ni to form Ni-Al compounds (Ni3Al, NiAl, NiAlg). The Ni 80% Al 20% powder(NiAl80/20 powder) and Ni 70% Al 30% powder(NiAl70/30 powder) are mostly Ni coated aluminum powder. The two powders are heated in the flame during thermal spraying. When the temperature in the center rises above 660℃, the aluminum core will melt, infiltrate outward, and react intensely with the outer nickel to form NiAl compounds.These NiAl compounds and unreacted Al react intensely with oxygen in the flame stream or spraying onto the surface of the substrate (exotherm is above 1670 kJ/mol). It is beneficial to combine with matrix. Good micro-metallurgical bonding can be achieved with ordinary carbon steel, alloy steel, stainless steel, cast iron, cast steel, nickel and nickel  alloys, titanium and titanium alloys, copper and copper alloys and even nitriding steel. The coating structure obtained is NiAl alloy distributed with NiAl compounds, and the coating has good oxidation resistance, corrosion resistance and wear resistance.It can be used as a self-bonding layer or a wear-resistant and corrosion-resistant working layer. It can be used for out-of-tolerance repair and surface strengthening of various, transmission parts, machine guides, fan blades and aircraft engine components.

C: MCrAIYX series high temperature coating self-bonding alloy powder

The development of such alloy coating materials began in the 1950s with the aim of producing heat-resistant, oxidation-resistant and wear-resistant thermal spray coatings on aero-engine components. The M in the alloy is Ni or Co or Fe. Or Ni-Co, Ni-Fe, etc., are the basic elements of the alloy and form an alloy matrix with other alloying elements. It is widely used in aerospace, metallurgy, energy, chemical and other industries.