Kaplun P. Scientific and applied fundamentals of application of hydrogen-free ion nitriding to enhance contact strength of tribosystems

This work solves scientific and technical issue of enhancing contact endurance and durability of coated structural elements at rolling friction by optimizing the properties of cover-base composition under developed concept. This concept features application of gradient coatings with optimal properties and residual compressing strain on the surface under hydrogen-free technology and obtaining of maximum base hardness by thermal processing methods. In order to achieve the set goal, a new integrated technological process has been proposed and implemented. It includes the technology of ion nitriding in hydrogen and hydrogen-free media and ion oxidation, thermal activation of nitrated cases at steel quenching temperature with exposure at given temperature during optimal time followed by quenching in industrial oil and low temperature tempering. Research on the process of ion nitriding in hydrogen-free media for specific structural steels was performed with determining regularities of influence of technological process parameters of ion nitriding on thickness, hardness, chemical and phase composition, and residual compressing strain in nitrated case. Optimal technological regimes of ion nitriding under criteria of maximum value of thickness and hardness for each steel were determined. Regularities of distribution of microhardness and residual stresses by nitrated case thickness were researched and experimental and calculation methodology for their determination at any site of nitrated case cross-section was developed. Based on theoretical research on thermal activation of nitrated cases, new technology of ion nitroquenching and oxyquenching, which satisfy the requirements of the proposed concept. Multipurpose experimental plant for testing contact endurance at rolling friction with sliding was developed. It was used to perform a research on wearability kinetics and contact endurance of various steels in various media (industrial oil, aggressive, abrasion, at dry friction). Effect of hydrogen on contact endurance at ion nitriding in hydrogen media was researched. Developed technology was tested under industrial conditions.