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Aluminum intermetalide coatings on magnesium alloys can be used mainly as interlayers in composite coatings to improve corrosion resistance.
Aluminum intermetalide coatings can be applied by various methods – from powders, alloys, etc. With these methods, coatings are mainly produced from pure aluminum. Vaccines obtained by vacuum methods, in particular (PVD), are more suitable for obtaining multicomponent coatings.
PVD technology allows you to effectively control the properties of the products to be coated, obtaining both single-layer and multi-layer coatings.
At elevated temperatures of 300-400°C, aluminide coatings are subject to absorption, which significantly affects their properties, as absorption leads to the formation of diffusion (mainly intermetallic) layers, which increase the adhesion of the coatings. Additional alloying elements affect both the absorption rate of the precipitated layers and the final properties of the coatings. This effect is even more effective when several layers of different chemical composition are applied. As a result, it is possible to obtain combined coatings in which each layer (diffusion, modified applied) fulfills its specific function.
Changes in the chemical composition of multi-component PVD coatings during heat treatment were investigated during this phase of the project.
All coatings were obtained using an upgraded NNV-6.6-I1 vacuum ion-plasma setup. During PVD application, electric arc sources for titanium and niobium application and a magnetron sputter for aluminum and silicon application were used simultaneously. Precipitation of pure metals was performed under argon at 7×10-4-1×10-3 mm Hg. The nitride coating was applied under an argon atmosphere at a pressure of 3×10-3 with the addition of nitrogen at a partial pressure of 2×10-3 mm Hg.
Figure 1. Appearance of samples 173,176,177,179 (a) before heat treatment and (b) after heat treatment at 330 ° C.
The changes of the most important parameters of the chemical composition – magnesium content in the coating and Mg / Al ratio% from the thawing time are shown in Fig. 2. And the morphology of the surface microstructure is shown in Fig3.
Figure 2. Mg / Al ratios for different samples
Fig 3 sample 173 changes in surface morphology during heat treatment.
Fig 4 sample 176 changes in surface morphology during heat treatment.
During the heat treatment, the Mg / A% ratio in the coating changes due to mutual diffusion. Aluminum enters the sample, but magnesium tends to the surface. The largest change in the ratio is observed in sample 173, and the Mg / Al% ratio after testing is 75%. The smallest change in the Mg / Al% 29% ratio is observed for sample 176.
The microstructure of all studied coatings did not change significantly within 4 hours.
The homogeneity of the coatings is maintained and there is no local damage to the coatings, as spherical formations with a high magnesium content appear on the surface. For samples 173 and 176, only a slight graininess is observed. After an 8-hour test, small semicircular formations form on the surface of sample 173, indicating the onset of spherical formations with an elevated magnesium content in the sample. middle of the coating. Coating 177 showed high stability in both composition and structure for up to 4 hours of testing due to surface (TiAl)nFor the nitride layer, only local delamination of the nitride coating is observed, which takes up a significant amount after only 8 hours. surface area. Therefore, the Mg / Al% concentration ratio increases rapidly to 44%. As the value of the inner layers increases, the chemical composition of the surface is measured.
Being implemented with the financial support of the ERDF.