Marian Chuchman

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.

Удосконалено склад комплексного електроліту для формування високолегованих молібденом нікелевих по­криттів. Встановлено, що для формування бездефектних покриттів з вмістом Mo понад 40 мас. % оптимальним є такий склад електроліту: 0,2 М NiCl2; 1,0 M Na3C6H5O7; 1 г/л сахарину, 1 г/л Na2MoO4, SrMoO4 (нас.), рН 9,0. Такі покриття характеризуються підвищеною корозійною тривкістю порівняно з система­ми Ni—Mo з меншим вмістом молібдену та Ni—Mo—B, а також покращеними електрокаталітичними властивостями, що свідчить про їхню перспективність як недорогих катодів для лужного електролізу та можливу заміну хастелоїв і твердого хромування.

The effect of heat treatment on the development of micromechanical and tribocorrosion properties of electrodeposited Ni–Mo–B coatings was examined. The Ni–Mo–B coatings were electrodeposited onto low-carbon steel from a citrate electrolyte containing amorphous boron. Isothermal annealing was performed at 950°C for 2 hours in an argon atmosphere. The coatings were analyzed using SEM/EDS, XRD, dynamic nanoindentation, and tribocorrosion tests in a 3% NaCl solution. It was found that heat treatment induces a diffusion transformation of amorphous boron into a matrix-filled composite consisting of a Ni(Mo) solid solution and strengthening phases (Ni3B and Mo2NiB2). Increasing the Mo content from 8 to 16 wt.% resulted in a 3.75-fold increase in the Mo2NiB2 ternary boride phase. This structural change led to a significant increase in microhardness (up to 11.67 GPa) and the elastic modulus (292.5 GPa). In tribocorrosion tests, the coating with 16 wt.% Mo demonstrated better stability: the wear track width decreased by 46%, and the coefficient of friction remained more consistent (around 0.2) compared to the coating with 8 wt.% Mo. Additionally, increasing boride phase content shifted the wear mechanism from oxidative-adhesive with microdeformation to a mixed process, with oxidative wear dominating. The study shows that high-temperature annealing of Ni–Mo–B coatings enhances their phase composition by forming complex borides. Coatings containing 16 wt.% molybdenum offer improved resistance to mechanical and corrosion damage, making them suitable for oil and gas, chemical, and utilities industries.

Corrosion and tribocorrosion of 17G1S-U (17Mn1Si) steel in a chloride-acetate solution bubbled with hydrogen sulfide, air, and their mixtures at a ratio of partial pressures PH2S : Pair 1:1 and 1:10 were investigated. At low oxygen concentrations, the corrosion rate of steel is lower than in a saturated hydrogen sulfide solution due to the interaction of H2S and O2 and a decrease in the conсentration of both components. At oxygen high concentrations, steel corrosion accelerates due to the oxidation of sulfide films on the surface and the deterioration of their protective properties. Hydrogenation of steel decreases with oxygen partial pressure increase due to decreasing sulfide concentration in the solution. Tribocorrosion of steel in the solution at a ratio of partial pressures 1:1 depends on a combination of anodic dissolution and hydrogen cracking, and at a ratio of 1:10 – mainly on anodic dissolution. The combined effect of pitting corrosion, iron oxides and hydroxides in the corrosion products determines the abrasive mechanism of tribocorrosion.

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.