What is the principle of plasma spraying? Plasma spraying uses a rigid non-transferred plasma arc as the heat source to heat the powder material to be sprayed to a molten or semi-molten state, and then spray it on the surface of the pretreated workpiece after being atomized and accelerated by a high-speed flame flow. , A thermal spray surface processing method to form spray coating.

The principle of plasma spraying is mainly to generate a plasma flame flow through a plasma spray gun (also known as a plasma arc generator). The tungsten electrode (cathode) and nozzle (anode) of the spray gun are respectively connected to the negative and positive electrodes of the power supply (the workpiece is not charged), and the arc is ignited by a high-frequency spark, so that the working gas (Ar or N2) supplied to the spray gun is ionized under the action of the arc. plasma. Under the combined action of mechanical compression effect, self-magnetic compression effect and thermal compression effect, the arc is compressed to form a non-transferred plasma arc. The powder-feeding stream transports the powder sprayed material into the plasma arc, and is quickly heated to a molten or semi-molten state, and hits the surface of the pretreated substrate at high speed with the plasma stream, and forms a firm spray coating on the surface of the substrate. So that the sprayed surface of the parts can obtain various special physical and chemical properties such as different hardness, wear resistance, heat resistance, corrosion resistance, insulation, heat insulation, lubrication, etc., to meet the requirements of different working conditions of the parts.

In the process of forming a coating, a single molten particle is the basic unit to form a coating, and its behavior basically reflects the characteristics of the formation of the coating. The behavior of a single particle includes three basic processes: first, the process of sending the spraying material into the heat source; then the interaction process between the spraying material and the heat source. Under the action of the heat source, the material is heated, melted, and accelerated, and at the same time, high-temperature, high-speed particles and The process of environmental atmosphere, especially for metal materials, the entrainment of air in the heat source will cause the sprayed particles to react with the atmosphere, such as oxidation, etc.; finally, the high-temperature and high-speed molten particles collide with the collective, horizontal flow flattening, and rapid cooling and solidification. This process is generally completed in a very short time of tens of microseconds.

The bonding mechanism of "coating" includes the bonding of the coating to the surface of the substrate and the cohesive bonding of the coating. The bonding strength of the coating is called the bonding force, and the bonding strength of the coating and the basic surface is called the cohesion.

Research and experience have shown that the "macro" interface between the coating and the surface of the substrate is mainly mechanically bonded, with physical and chemical bonding as a supplement. The "micro" interface between the layered particles of the coating may belong to physical-chemical Combine more ingredients.