The bonding force (or bonding strength) of various coatings and substrates is related to many factors such as spraying methods, spraying materials, spraying conditions, and substrate surface treatment.
The bonding strength of several different coatings measured by different test methods is listed below.
The following graphs show the tensile and shear bond strengths of various coatings prepared by air spray on different substrates pretreated in various ways. It can be seen from the table that for the substrate of the same material, the surface roughness (recommended instrument: roughness meter) is treated in different ways, and the bonding strength is also very different.
The molybdenum coating made by plasma jet spraying (relevant instrument: coating Thickness Gauge ), the substrate is mild steel polished and roughened by emery cloth, and the bonding strength of the pulling test is shown in the table. After the test, the molybdenum coating remained on the end surface of the drawn piston, the boundary between the substrate and the coating was not separated, and the damage occurred inside the coating. This shows that the pretreatment of the molybdenum coating, even if only 40 or 80 mesh abrasive cloth is used to polish the surface of the substrate, the bonding strength between the coating and the substrate is greater than the strength of the coating itself.
The bonding strength results of the pull-out test of the carbon steel (0.45% carbon) coating made by gas spraying on the steel substrate roughened by different methods are shown in the table. It can be seen from the table that before the carbon steel is sprayed, the bonding strength of the carbon steel coating is greatly improved due to the molybdenum bottom layer sprayed. The thickness of the molybdenum bottom layer is 0.05-0.08mm.
Table 11-5-5 lists the changes in the bonding strength of beryllium coatings made by plasma jet spraying when only the spraying distance is changed without changing other conditions. It can be seen from the table that the spraying distance has a great influence on the bonding strength. This result is obtained by using a bonding agent to bond the coatings of two base rods with coatings at the ends, and use this as a sample for tensile testing. The bonding strength of sprayed coatings of several materials obtained by this method is shown in Table 11-5-5.
On the mild steel substrate that has been sandblasted, the coatings of alumina, alumina + 2.5% titanium oxide, and zirconia made by plasma jet spraying are the bonding strength results of the bonding agent bonding test method. They are 9.81, 14.71, 4.90-6.86N/mm² respectively. The fractures of alumina and alumina + 2.5% titanium oxide coatings are almost all generated inside the coating, indicating that the bonding force between the coating and the substrate is greater than that of the coating itself. However, the zirconia coating peels off at the boundary between the coating and the substrate surface, indicating that the bonding force of the coating is low. The bonding strength of the tungsten coating deposited on graphite by plasma jet method is 1.96-4.41N/mm². The wire material is sprayed on the substrate after melting. The strength is measured by the pull-out test method.
The bonding strength of carbon steel coatings and aluminum coatings made on several substrates by arc spraying method (adhesive bonding method, substrate rod diameter 40mm) is compared with the bonding strength of the gas spray coating of the same material, as shown in the figure As shown in 11-5-13, it can be seen from the figure that, except for one exception, the bonding strength of the arc sprayed layer is higher than that of the gas sprayed layer. In the test, the fracture of the arc sprayed coating occurred between the particles in the coating, while the damage of the gas sprayed coating was the peeling of the coating at the boundary of the substrate.
