Be careful when choosing a spray process. To make sure that the coating meets the requirements of your application, you should consider the working conditions of the parts, and the composition, properties and process characteristics of various coating materials to determine the appropriate spraying materials.
There are many thermal spraying methods, but each method has its own advantages and limitations. Different methods of thermal spraying process selection from different angles will yield different results. Taking high-speed flame spraying as an example, when metal, alloy, and ceramic materials are sprayed by the HVOF process, high-quality coatings with high bonding strength (70 MPa), high density (void ratio <1%), and low oxide content can be obtained. Layer; however, the process has the disadvantages of high operating cost, high heat for the basic number of people, and inability to spray oxide ceramics. Therefore, when selecting the thermal spray process, specific analysis should be carried out for specific needs. The following analysis is carried out in three aspects: coating performance, spray material type, and spray economy.
1) If the spraying performance is not high, the use environment has no special requirements, and the melting point of the spraying material is lower than 2500 °C, the oxygen-acetylene flame spraying process with simple equipment and low cost can be selected, such as general workpiece size repair and conventional surface protection.
2) If it is a valuable or critical component with high spraying performance and poor working conditions, plasma spraying process can be used. Compared with the oxyacetylene flame spraying, the plasma spraying flame has a high temperature, sufficient melting, non-oxidation, high coating bonding strength, and low void ratio.
3) If the coating is required to have high bonding strength and very low void ratio, a high-speed flame (HVOF) spraying process may be selected for the metal or cermet coating; and a high-speed plasma spraying process may be selected for the oxide ceramic coating (eg Plaz Jet plasma spray). If spraying an easily oxidizable metal or cermet, a controlled atmosphere or a low pressure plasma spray process such as Ti, B4C or the like must be used.
Spray material type
1) When spraying metal or alloy materials, the arc spray process is preferred.
2) When spraying ceramic materials, especially oxide ceramic materials or carbide or oxynitride ceramic materials with a melting point exceeding 3000 °C, the plasma spraying process should be selected.
3) When spraying oxide coating, especially WC-Co, Cr3C2-NiCr nitride coating, high speed flame spraying process can be used, and the coating can obtain good comprehensive performance.
4) When spraying bio-coating, it is advisable to use controlled atmosphere or low-pressure plasma spraying process.
Price and cost
Under the condition that the cost of spraying raw materials is not much different, the relative process cost of arc spraying is the lowest in all thermal spraying processes, and the process has the characteristics of high spraying efficiency, high bonding strength between coating and substrate, and is suitable for on-site construction. The arc spray process should be used whenever possible.