Coated Mcralx Coating Stripping And Repair Technology

The removing and recoating technologies for overlay coatings (HY1, HY3, HY5) on super-alloy substrates, including physical and chemical removal methods as well as their effects on mechanical properties of substrates, were studied on this paper. Hot corrosion resistance, high temperature oxidation resistance and other properties of the recoated coatings were evaluated via various high temperature tests, such as high-temperature corrosion, high-temperature oxidation, and thermal shocking. Different chemical removal methods for overlay coatings were also investigated and compared. The mechanisms behind the physical and chemical methods were discussed.Cross-section and surface microstructure, the phase structures, and the elemental distribution of the coatings were studied by SEM, XRD, XPS etc. From our results, the HNO₃ and FeCl₃ solution could remove the overlay coatings successfully and did not make any damage on the substrate's microstructures and mechanical properties. Our results from high-temperature oxidation, corrosion, and thermal shocking tests showed that the recoated coatings had a good high temperature performance as the coatings without any removing process did.This study focuses on the coatings removed and recoated on substrates before and after high temperature oxidation. The removal solutions were selected based on the coating's concentration and microstruces. As our results showed, the concentration of each element in the coating was changed as Cr was enriched tremendously in the coating after a high temperature oxidation. Therefore, the HF/HNO₃/Fe solution could effectively remove the coating before a high temperature oxidation, whereas the HNO₃/FeCl₃ solution is more suitable for removing the coating after a high temperature oxidation.The removing rates and the relationship between removal time and the coating weight loss were investigated by measuring the weight loss of the overlay coatings. The concentration of the dissolved element from the coatings, such as Ni,Cr,Al,Si,Y etc, was monitored by the plasma emission spectrum to understand the removing mechanism behind. Due to the different E^°values of each elements, each elements could be removed at different rates. When the removing technique applied to certain parts with complex structure, certain uncoated area should be protected to avoid corrosion introduced by the chemical removal solution.