Properties of Thermal Spray Coatings

1.Chemical composition

Because the coating material will interact with the surrounding medium at high temperature during the melting and spraying process to form oxides. Nitride, and decomposes at high temperature, so the composition of the coating is different from the composition of the coating material, and affects the performance of the coating to a certain extent. For example, the oxidation of MCrAIY will affect its corrosion resistance, while the wear resistance of WC-Co will decrease after oxidation and high temperature decomposition. This phenomenon can be avoided and mitigated by the choice of spraying method. For example, the use of low-pressure plasma spraying can greatly reduce the oxidation of coating materials, while high-speed flame spraying can prevent the pyrolysis of carbides.

2.Porosity

Pores inevitably exist in thermal spray coatings, and the size of porosity is related to the temperature and velocity of particles, as well as spraying parameters such as spraying distance and spraying angle. Generally speaking, the porosity of flame sprayed and arc sprayed coatings with low temperature and speed is relatively high, generally reaching a few percent, or even up to ten percent. The high-temperature plasma sprayed coating and high-speed supersonic flame sprayed coating have lower porosity. The minimum can be less than 0.5%.

3.Hardness

Due to the chilling and high-speed impact during the formation of the thermal spray coating, the grain refinement of the coating and the distortion of the crystal lattice make the coating strengthened, so the hardness of the thermal spray coating is higher than that of the general material. It will also vary depending on the spraying method.

4.Bonding strength

The bonding of the thermal spray coating to the substrate mainly depends on the mechanical engagement with the rough surface of the substrate (scratch effect). The cleanliness of the substrate surface, the particle temperature of the coating material and the speed at which the particles hit the substrate, as well as the residual stress in the coating will affect the bonding strength of the coating and the substrate, so the bonding strength of the coating is also related to the spraying applied. method related.

5.Thermal fatigue properties

For some workpieces used in the state of cooling and heating cycles, the thermal fatigue resistance (or thermal shock) performance of the coating is very important. If the thermal shock resistance of the coating is not good, the workpiece will be difficult to use It will crack or even peel off very quickly. The thermal shock resistance of the coating mainly depends on the difference between the thermal expansion coefficient of the coating material and the base material and the strength of the bonding between the coating and the base material.