Noha V. Development of an automated process control system for producing complex-profile nickel alloy castings

Dissertation for the degree of Doctor of Philosophy in the specialty 136 Metallurgy (13 – Mechanical Engineering). – Institute of Physics and Technology of Metals and Alloys of the National Academy of Sciences of Ukraine, Kyiv, 2026. The dissertation is devoted to the study of the processes of obtaining castings from heat-resistant alloys for parts of critical purpose, in particular for blades of gas turbine engines (GTD), and multifactor optimization of the production cycle of obtaining complex-profile parts of gas turbine engines (GTD blades) using automated control and monitoring of melting parameters to reduce product defects and save electricity based on a software system of our own development. Existing technologies for casting parts of gas turbine engines from heat-resistant alloys with a polycrystalline structure currently do not allow obtaining heat resistance and long-term strength in accordance with the constantly growing requirements of the modern energy market and the industry as a whole. It should be noted that in such elements as the working blades of a gas turbine engine, dynamic loading is carried out along the axis of the parts. A significantly smaller plane of transverse boundaries in alloys with an oriented structure reduces the likelihood of the formation of local defects during creep, and increased plasticity facilitates the relaxation of stresses in the material. During the study, it was found that increasing the crystallization rate of castings from 5 to 10 mm/min contributes to the grinding of the dendritic structure. At the same time, an increase in the volume fraction of the strengthening intermetallic γ′-phase is observed, a decrease in the size of its particles and the average cross-section of the γ//γ′-eutectic islands, as well as an increase in the number of dispersed carbides of the MC type in the interdendritic spaces. It was established that the formation of a regular directional structure is ensured at a speed of movement of the crystallization front within 5–10 mm/min. The results of tests of the reference samples for short-term and long-term strength after heat treatment according to standard methods confirmed the compliance of the mechanical properties with the requirements of the technical documentation for the product. In order to study the influence of technological parameters and directed crystallization processes on the structure of the heat-resistant alloy, the SM88 alloy was chosen as a model material. This alloy is widely used for the manufacture of critical parts, in particular, the working blades of first and second stage gas turbine engines. In order to establish the influence of technological parameters and directed crystallization processes on the structural characteristics of the SM88 alloy, a series of experiments were conducted. Melting and pouring were carried out in a vacuum furnace UVNK-8P, since it implemented the crystallization process using a liquid metal cooler (LMC), with varying the crystallization rate of castings at 2 levels: 5 and 10 mm/min. The pouring temperature of the metal was 1550-1570 °C. Local values of the parameters of the directional crystallization process during the melts were calculated from the temperature distribution in the volume of the casting, which was measured experimentally at five points along the axis, using tungsten-rhenium thermocouples (BP 5/20, electrode diameter 0.30 mm). The study of the macrostructure of the experimental samples obtained as a result of the experiment showed that with the selected optimal crystallization parameters, a regular dendritic structure is formed along the entire length of the product, including the transition section. During visual inspection of the outer and inner surfaces of castings from a heat-resistant alloy and metallographic studies, no micropores, blockages, shells, non-metallic inclusions were detected. Since an increase in the crystallization rate entails a significant increase in the level of liquation of elements in the alloy, the appearance of large areas of the eutectic high-temperature γ΄ eut.-phase is observed in the structure. Its volume fraction, determined by statistical metallography in 10 fields of view, was 2-4% at Vkr.=5mm/min and 6-8% at Vkr.=10mm/min. The amount of secondary dispersed γ΄ - phase localized in interdendritic spaces decreased significantly with increasing crystallization rate. It is crushed, retaining mainly a shape close to spherical, changing its size from 04-06 microns to 02-03 microns. As part of the study, a software prototype was developed. The results of theoretical and experimental research obtained in the process of work can be implemented at domestic enterprises in the gas turbine industry in order to optimize the consumption of energy resources and materials necessary to obtain the final product.