|
Nickel-based superalloy because of its excellent high temperature strength, fatigue resistance and fracture toughness of the many advantages of the wide application field of aerospace. However, with the improvement of engine operating temperature, nickel-based superalloy high temperature oxidation resistance need to be further improved. Preparation of coating in the surface of the alloy is a commonly used to improve the high temperature oxidation resistance. And in the preparation of the coating method, the pack cementation method because of its operation is simple, multicomponent permeation many advantages, such as wide application. Nevertheless, most of the traditional pack cementation method at higher temperatures and last a long time, it would seriously damage the mechanical properties of the alloy. Based on this point, the study of low-temperature pack cementation is particularly important. The essence of the pack cementation method on an in situ chemical vapor deposition method. This paper studies the feasibility of low temperature at the surface of the nickel-based alloy embedded infiltration, and a detailed study of the experimental factors on the coating structure, composition and thickness. The results show that the coating is uniform, dense layer structure, the outer layer of coating composition by Al3Ni2, Al3Ni and a small amount Al86Cr14 the inner main Al3Ni2 phase composition. Component (except catalyst content), the experimental temperature and deposition time, and other experimental factors are not affect the coating structure and phase composition of the penetration-enhancing agent, but a great influence on the thickness of the coating. Coating thickness and deposition time roughly parabolic relationship coating formation is controlled by diffusion. , Coating thickness, and the reaction temperature is the reciprocal of the linear relationship exists between the reaction time under certain conditions. The low-temperature pack cementation aluminide coatings high temperature oxidation resistance has also been studied, and the results show that the coating has excellent high temperature oxidation resistance. Belongs entirely antioxidant levels. In the initial stage, dominated by the growth of the coating surface θ-Al2O3, resulting in oxidation weight gain faster. But with oxidation, and metastable θ-Al2O3 transition to the steady-state α-Al2O3. The decline in the rate of oxidation, the oxidation weight gain curves flatten. The use of conventional pack cementation method on the surface of the bulk material of the nickel base alloy of Al-Si nitrocarburizing, and obtained the structure and composition of the coating was analyzed. The results show, Al-Si coating is a double layer structure, the outer layer by the Ni2Si phase composition, phase composition of the inner layer by the the Ni2Si phase and Ni0.9Al1.1 nitrocarburizing. Between the substrate and coating with a layer of buffer layer, the buffer layer by the the Ni2Si phase and Ni-Cr-Si ternary phase composition. Using the same experimental program, the use of self-designed equipment and in-situ chemical vapor deposition method, the paper succeeded in nickel-base alloy hollow cylindrical workpiece cavity surface Al-Si nitrocarburizing. The structure of the coating obtained, and the same as the Al-Si coating composition with the surface of the bulk material, but the layer thickness is substantially reduced.
|