Металознавство та обробка металів (Sep 2020)
The distribution of alloying elements in secondary carbides of heat-resistant nickel alloys
Abstract
The work is devoted to the study of the specificity of the distribution of alloying elements in the structural components of heat-resistant nickel alloys, namely between secondary carbides, since the role of carbides in the formation of the properties of these alloys is complex. The theoretical modeling of thermodynamic processes of separation of excess phases using the CALPHAD method in the JMatPro software shell is carried out. As well as a practical study of the structure and distribution of chemical elements in carbides, depending on the alloying of the alloy using a scanning electron microscope REM-106I. It is established that in typical M23C6 and M6C carbides, for the ZhS6K alloy, there is a tendency for degeneration and phase reactions depending on the level of doping by the given elements. The mathematical dependences of the influence of alloying of the alloy on the temperature of carbide separation (dissolution) and the change of the chemical composition of the alloy on the content of elements in the carbides have been established. When the content of chromium is increased, the M6C carbide gradually degenerates and disappears at 11%. It is revealed that when the content of 3% molybdenum in the alloy in the structure is formed TSH phase, and at 8% carbide M6C approaches the monocarbide based on molybdenum. Depending on the amount of tungsten in the alloy, the dependences of the temperature (dissolution) of the carbides were calculated. An increase in tungsten in the alloy was found to increase the release (dissolution) temperatures of all carbides in the alloy. It was also found that at a concentration of 11% in the tungsten alloy, TSH phase is released, which adversely affects the properties of the system under study. The dependences obtained were tested on a heat-resistant alloy based on ZS6K. The stoichiometric formulas of the carbides were calculated and the theoretical and practical results were compared, which gave considerable similarity. It is recommended to use the mathematical models obtained not only in the design of new nickel-based heat-resistant alloys, but also in the improvement of known branded compositions within the stated concentrations.
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