Prediction of high temperature corrosion of nickel-based superalloys

Abstract

Purpose. Establish a correlation between the rate of corrosion and the ratio of alloying elements based on the mathematical treatment of experimental values of foundry heat resisting nickel alloys (ZNS) under synthetic ash conditions.Methods of research. Experimental values were processed in the Microsoft Office program suite in the EXCEL package with the least squares method, with the result of correlation dependencies of the “parameter-property” type with the obtaining of mathematical equations of regression models that optimally describe these dependencies and the construction of trend lines.Results. Since modern ZNS have complex multicomponent compositions, in which there is a complex influence of elements on corrosion, the evaluation of the stability of the corrosion was carried out per the size of the known parameter Кпс. This allowed to compare the level of stability of alloys with different doping schemes. However, this parameter does not cover all the doping elements that are present in the ZNS. Therefore, because of the analysis and processing of experimental data, the ratio of alloying elements to assess corrosion resistance is proposed, which considers the complex influence of the main components of the alloy. Since VTK is related to the presence of certain elements in the alloy and their concentration, the ratio Kпс allows more adequately to evaluate, for multi-component nickel systems, the average rate of corrosion at different temperatures. The dependence of the average corrosion rate on Kпс for monocrystalline alloys is straightforward, due to the specificity of the doping systems of the materials of this class. Characteristic for them is a significantly smaller amount of chromium (up to 10% by weight) and lowering of the content (and in some alloys, absence of) titanium, which leads to a significant reduction in the VTK-stability of the material. It is established that in order to ensure the required level of VTK-stability of alloys of directed and equilibrium crystallization, the value of the ratio should be not less than Кпс ≥ 2, which will provide a nondestructive dense film of corrosion products. So, for alloys with Кпс ≤ 2, the formation of a thick layer of corrosion products is characteristic, which is easily evaporated during the operation. The obtained regression models give an opportunity to predict the average speed of corrosion depending on the alloy alloy system, as in the development of new ZNS for directed crystallization, and in improving the composition of known industrial compositions within the branded composition. The obtained correlation dependencies are exponential in nature.Scientific novelty. For the first time, the ratios of Kпс are proposed, by which one can adequately predict the average corrosion rate for different temperatures of the multicomponent ZNS compositions.Practical value. An effective solution is proposed for predicting the average corrosion rate for different temperatures of alloys, both in the development of new formulations of ZNS, and in the development of well-known industrial brands.