Kostyk K. Scientific basis of surface hardening technologies of machine parts by controlled composition powder mixtures

The thesis for the scientific degree of doctor of technical sciences, specialty 05.02.08 – technology of mechanical engineering (13 – mechanical engineering). – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2020. In the thesis a set of studies was aimed at solving an important scientific and technical problem in the field of engineering technology: the development of innovative and short-term technologies of machine parts surface hardening with controlled composition powder mixtures to ensure the performance properties of products at a high level with a significant reduction in the cost of their production. Mathematical models and nomograms of existing technologies of steels surface hardening were created to determine the specific conditions of ChTT (temperature and duration) based on a given depth of the diffusion layer or the surface hardness of steels, which significantly affects the efficiency of the strengthening processes. The general methodological approach of management of technological processes of details surface hardening by powder mixes of the controlled structure at saturation of surface layers with nitrogen, carbon and boron on the basis of use of innovative technologies and the system analysis at the minimum expenses was developed that allowed to increase operational properties of products at considerable reduction of ChTT duration. ChTT was designed the complex, which significantly reduces the fragility of boriding layers due to a more gradual decrease in hardness from surface to core products from steels to improve the operational properties of the goods and service life of machine parts and tools. It was created a mathematical model of the temperature distribution in the depth of the diffusion layer to determine the nature of the dependencies and obtain data on the temperature distribution in the depth of the product under different processing conditions. It was improved boriding pastes technology of titanium alloys through the use of nanodispersed environment, thereby reducing the boriding process 2-3 times and to shorten the manufacturing process of components by combining two operations: boriding and titanium alloy hardening. The solutions of boundary value diffusion problems by the boundary element method were proposed, which allowed to create a mathematical model of the distribution of boron concentration over the thickness of the hardened titanium alloy. The processes of heating by high-frequency currents and due to the preliminary laser treatment of parts were intensified, which allowed to obtain high performance properties of the surface layers with a significant reduction in the duration of treatments. A comparative analysis of the influence of existing and developed hardening treatments on the change in the depth of the layer, the surface hardness and wear resistance of the surface layer of steel 38Ch2MoAl was done. It was established that the developed complex hardening treatment based on the process of diffusion saturation with boron can provide wear resistance of the surface layers at a high level with abrasive wear. Keywords: technological process, formation of surface quality of machine parts, integrated and innovative technology, surface strengthening, performance properties, surface hardness, diffusion layer, wear resistance, nanodisperse powder mixture, mathematical modeling.