Mathematical modelling of heat-resistant nickel alloys high temperature corrosion

Abstract

The mathematical modelling of the average corrosion rate () or nickel alloys with different alloying systems (for mono-, directed- and equilibrium crystallization) under synthetic ash conditions at different temperatures has been carried out. Since modern heat-resistant nickel alloys have complex multicomponent compositions, in which all the elements influence on corrosion complexly, the high temperature corrosion (HTC) stability was evaluated by the value of the known parameter Pks(surface resistance coefficient). This made it possible to compare the level of stability of alloys with different alloying schemes. However, this parameter does not cover all the alloying elements that are present in the heat-resistant nickel alloys. Therefore, as a result of analysis and processing of experimental data, the ratio of alloying elements to assess the corrosion resistance has been proposed; this ratio considers the complex influence of the main components of the alloy. Since high temperature corrosion (HTC) is related to the presence of certain elements in the alloy and their concentration, the ratio Kps (surface resistance coefficient) makes it possible to evaluate more adequately the average corrosion rate at different temperatures for multi-component nickel systems. The dependence of the average corrosion rate on Kps for monocrystalline alloys is straightforward, due to the specific character of the alloying systems of this class materials. Characteristic for them is a significantly less amount of chromium (up to 10% by weight) is characteristic of them and a decrease in the content (and in some alloys, absence) of titanium as well, which results in a significant reduction in the high temperature corrosion (HTC)-stability of the material. It has been established that to ensure the required level of high temperature corrosion (HTC) stability of alloys of directed and equilibrium crystallization, the value of the ratio should be not less than Kps ≥ 2, which will provide a non-destructive dense film of corrosion products. So, for the alloys with Kps ≤ 2 the formation of a thick layer of corrosion products, which is easily separated during the operation is characteristic. The obtained regression models give an opportunity to predict the average speed of corrosion depending on the alloying system, both for the development of new heat- resistant nickel alloys for directed crystallization, and in improving the composition of the known industrial alloys within the brand composition. The obtained correlation dependencies are exponential in nature