OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 4 2024 coating on the metal surface is less susceptible to relaxation, which allows increasing the service life of the part by 6–8 times. Objectives of the study: to examine the changes in the structure and microstructure of the material of the upper and lower compression piston rings of the HIMSEN 4H21/32 auxiliary marine engine, arising as a result of the operation of these rings under diff erent conditions and diff erent loads; to compare the microstresses arising due to deformations of the surface layer of the upper and lower compression rings, using metallographic methods and the method of X-ray structural analysis. Materials and methods The subject of the study is the end-of-life piston compression rings (upper and lower) of the HIMSEN 4H21/32 auxiliary marine engine. Existing methods of metallographic research and X-ray diff ractometry [14–24] allow studying the stress state and atomic structure, microstrain and particle size variation of the material. In this study, metallographic and X-ray methods were used to investigate the microstructure of compression rings. Changes in the structure of the material of the upper ring during wear caused by the diff erent operating conditions of the upper and lower compression rings results in a loss of mobility of the lower ring. This means that the entire thermal and mechanical load is borne by the hot reserve of the upper ring. The analysis of changes in the material structure of the upper and lower rings will allow confi rming the diff erences in dynamic and thermal eff ects on the material during operation, which will allow determining the technological parameters for the manufacture of rings and its special hardening. Specimens for preparing sections to determine the microstructure and phase composition of the material were made by cutting perpendicular to the ring generatrix (Fig. 1). Since dynamic and thermal loads are equally probable in all radial directions in the ring plane, the location of the cut is of no particular importance. If a possible fracture or crack is present, the location of the cut should be adjacent to the defect. In order to reveal the entire microstructure, etching was carried out with nital solution (4 % alcoholic solution of HNO3) for 1 minute. The quality of etching was controlled using a metallographic microscope MMN-2. The same microscope was used to obtain photographs of the microstructure of the cross-sections of the rings (Figs. 2, 3). X-ray diff raction studies at room temperature were carried out on a Dron-3M diff ractometer. The diffraction profi les were imaged using Bragg-Brentano geometry on CuKα-radiation with a wavelength of 1.5406 Å (the average value of the K-α1,2 Cu wavelength, usually used for processing X-ray radiographs) in the interval of angles 20°< 2θ < 90°, with a scanning step of 0.02° and pulse set time at each point t = 2 s. The diff raction profi les of the compression rings were processed using PowderCell the computer program, version 2.3, and the ICSD database was used to analyze and clarify the structural characteristics. Note that a signifi cant background in the X-ray images is associated with the fl uorescence of iron when its atoms are excited by K-α copper radiation. The lattice parameters, the sizes of coherent scattering regions on the surfaces of the specimens, as well as lattice microdistortions (microstrains) and dislocation density were determined. The Selyakov-Sherrer formula [23] was used to estimate the eff ective sizes D of the coherent scattering regions (mosaic blocks). , cos k D λ = β θ (1) Fig. 1. Ring cutting pattern
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