Study of structure and properties of aluminized layer during the renewal of gas turbine first stage blades

The blades of a gas-turbine engine are one of its main elements. To protect the blade surface from erosive wear and high-temperature sulphide-oxide corrosion, diffusion saturation by aluminum is applied. The structure, phase composition and properties of the protective layer of blades made of heat-resistant alloy ZhS6K are investigated. The aluminized layer on new products, after their operation and after renewal is studied. It is found that during operation the protective layer of the gas-turbine engine blade is depleted unevenly. Depletion occurs in the alloying elements of the alloy of the base material zone under the coating which affects the properties of the restored aluminized layer. It is shown that on the new blades even after the protective coating restoration the structure of aluminized layer and the way of hardness distribution change with depth. It is revealed that the quality of the obtained protective coating is heavily conditioned by the preliminary surface preparation. The influence of surface roughness obtained by polishing, hydroabrasive treatment and sandblasting on the properties of the restored layer is investigated. For commercial purposes, hydroabrasive preliminary treatment is preferable due to its low cost, high productivity and moderate facilities requirements. It protects surface layer from defects such as bumps or pits. The tests reveal the optimum pressure of a paint sprayer during slurry aluminizing to obtain a satisfactory layer. These operations make it possible to improve the quality of protective layers of the turbine first stage blades during the renewal.