R. S. Mardarevych

A device for multi-cycle fatigue testing of metals is developed. The influence of technological processing on the surface quality and fatigue strength of the Ti–6Al–3Mo alloy has been established. It is shown that after milling and single-shot wire electrical discharge machining (WEDM), the parameters of the alloy surface profile are worse than the regulatory requirements, and the fatigue strength does not exceed 191 MPa. The сhemical polishing of Ti–6Al–3Mo alloy made by single-shot WEDM eliminates the surface defect zone (Ra = 0.2–0.3 mkm and Rv = –1.2 mkm), which contributes to an increase in its fatigue limit in two times compared to unpolished samples.

Corrosion-resistant electrodeposited Ni–Mo–B coatings of various chemical compositions were obtained from a self-regulating electrolyte, and their micromechanical, tribological, and tribocorrosion properties were investigated. The influence of electrodeposition parameters on the composition, structure, and characteristics of Ni–Mo–B coatings was studied. They exhibit a fine-grained structure with 8–27 wt% Mo and 1.3–3.39 wt% B, free of pores and cracks. It was established that an increase in molybdenum content enhances the corrosion resistance of the coatings in chloride-containing media. The micromechanical properties of coatings with 8 and 16 wt% Mo were examined using scratch testing and dynamic nanoindentation, while their tribological and tribocorrosion characteristics were evaluated under a “plane–ball” configuration in air and in 3% NaCl solution, respectively. It was revealed that coatings with 8 wt% Mo perform better under dry friction conditions, whereas coatings with 16 wt% Mo are more effective under tribocorrosion loading. Ni–Mo–B coatings can serve as an environmentally friendly alternative to hard chromium.

The influence of chemical and electrochemical polishing on the surface roughness of the Ti–6Al–3Mo alloy obtained after wire electroerosion cutting are investigated. After electrochemical polishing in mixtures of perchloric and acetic acids, the surface roughness of the alloy Ra corresponds to 0.8 mkm, but due to the inhomogeneous distribution of the electric field, rounding of the edges and macro-unevenness occurs. The composition of the electrolytes and the modes for chemical polishing of the alloy are recommended. After such treatment, the arithmetic mean of the profile deviations does not exceed 0.6 mkm.

Introduction. In power engineering, there is a need to improve the performance of gas coolers in contact with explosive atmospheres to ensure reliable operation of turbogenerators. Problem Statement. Important problems that require constant improvement of equipment are local corrosion, hydrogenation, etc., in particular, of pipe joints with pipe boards, which is characterized by the emergence and development of cracks under the influence of simultaneous mechanical stress and corrosive environment. The cracks promote depressurization that leads to emergency stop of turbogenerator. Purpose. To develop a new design of sealing joints of heat exchange tubes and tube sheet with increased corrosion and corrosion-mechanical resistance. Materials and methods. The samples made of steel 09G2S, M2 copper, steel 09G2S with a clad layer of copper M2, cupronickel МNZhМC 30-1-1, brass L68 have been tested. The vacuum extraction of hydrogen under elevated temperature, corrosion-fatigue, metallographic, and X-ray spectral test methods have been used. Results. A new structural element of gas coolers with improved characteristics has been designed. It is based on a welded-rolled joint of a copper tube with a copper-clad tube sheet, which does not cause deformation of the structure and crack formation. The studies of the effect of different modes of flaring of such joints on their resistance to failure under the simultaneous action of cyclic loads and the environment have shown that as the degree of flaring of copper tubes 19 1.5 and 19 1 mm increases, the crack generation period and durability combined with connections grows ~1.5 times. Conclusions. The new structural element reduces the probability of corrosion and mechanical destruction of parts of heat exchange equipment and helps to extend the period of its trouble-free operation.