Analysis of the Quality of Sulfomolybdenum Coatings Obtained by Electrospark Alloying Methods

The authors of this paper have attempted to improve the quality of surface layers applied to steel elements of machine parts constituting friction couples. The main goal of the research was to investigate an electrospark alloying method process for obtaining abrasion-resistant tribological coatings containing molybdenum disulfide on a steel surface. A substance in the form of sulfur ointment with a sulfur content of 33.3% was applied on the surfaces of C22 and C40 steel specimens. In order to determine the influence of the energy parameters of ESA equipment on the quality parameters of coatings, the ESA process was carried out using a molybdenum electrode with discharge energies Wp = 0.13; Wp = 0.55; Wp = 3.4 J. The following tests were carried out on specimens with such coatings: metallographic analysis, microhardness tests, surface roughness, and local X-ray diffraction microanalysis. The experiments revealed that sulfomolybdenum coatings consist of four zones with different mechanical properties. Depending on the discharge energy and the substrate material, the hardness of these zones varies from approx. 1100 to over 10,000 MPa. Differences in the distribution of, among others, sulfur and molybdenum in the obtained coatings, as well as differences in the microstructure of the observed coatings, were observed

Assessment of Technological Capabilities for Forming Al-C-B System Coatings on Steel Surfaces by Electrospark Alloying Method

In this paper, the possibility of applying the electrospark alloying (ESA) method to obtain boron-containing coatings characterised by increased hardness and wear resistance is considered. A new method for producing such coatings is proposed. The method consists in applying grease containing aluminium powder and amorphous boron to the surface to be treated and subsequently processing the obtained surface using the ESA method by a graphite electrode. The microstructural analysis of the Al-C-B coatings on steel C40 showed that the surface layer consists of several zones, the number and parameters of which are determined by the energy conditions of the ESA process. Durametric studies showed that with an increase in the discharge energy influence, the microhardness values of both the upper strengthened layer and the diffusion zone increased to Wp = 0.13 J, Hµ = 6487 MPa, and Wp = 4.9 J, Hµ = 12350 MPa, respectively. The results of X-ray diffraction analysis indicate that at the discharge energies of 0.13 and 0.55 J, the phase composition of the coating is represented by solid solutions of body-centred cubic lattice (BCC) and face-centred cubic lattice (FCC). The coatings obtained at Wp = 4.9 J were characterised by the presence of intermetallics Fe4Al13 and borocementite Fe3 (CB) in addition to the solid solutions. The X-ray spectral analysis of the obtained coatings indicated that during the electrospark alloying process, the surface layers were saturated with aluminium, boron, and carbon. With increasing discharge energy, the diffusion zone increases; during the ESA process with the use of the discharge energy of 0.13 J for steel C40, the diffusion zone is 10–15 µm. When replacing a substrate made of steel C40 with the same one material but of steel C22, an increase in the thickness of the surface layer accompanied by a slight decrease in microhardness is observed as a result of processing with the use of the ESA method. There were simulated phase portraits of the Al-C-B coatings. It is shown that near the stationary points in the phase portraits, one can see either a slowing down of the evolution or a spiral twisting of the diffusion-process particle

Technological Features for Controlling Steel Part Quality Parameters by the Method of Electrospark Alloying Using Carburezer Containing Nitrogen—Carbon Components

A new method of surface modification based on the method of electrospark alloying (ESA) using carburizer containing nitrogen—carbon components for producing coatings is considered. New processes have been proposed that include the step of applying saturating media in the form of paste-like nitrogenous and nitrogenous-carbon components, respectively, onto the surface without waiting for those media to dry, conducting the ESA process with the use of a steel electrode-tool, as well as with a graphite electrode-tool. Before applying the saturating media, an aluminium layer is applied onto the surface with the use of the ESA method at a discharge energy of Wp = 0.13–6.80 J. A saturating medium in the form of a paste was applied to the surfaces of specimens of steel C22 and steel C40. During nitriding, nitrocarburizing and carburization by ESA (CESA) processes, with an increase in the discharge energy (Wp), the thickness, micro hardness and continuity of the “white layer” coatings, as well as the magnitude of the surface roughness, increase due to saturation of the steel surface with nitrogen and/or carbon, high cooling rates, formation of non-equilibrium structures, formation of special phases, etc. In the course of nitriding, nitrocarburizing and CESA processing of steels C22 and C40, preliminary processing with the use of the ESA method by aluminum increases the thickness, microhardness and continuity of the “white layer”, while the roughness changes insignificantly. Analysis of the phase composition indicates that the presence of the aluminum sublayer leads to the formation of the aluminum-containing phases, resulting in a significant increase in the hardness and, in addition, in an increase in the thickness and quality of the surface layers. The proposed methods can be used to strengthen the surface layers of the critical parts and their elements for compressor and pumping equipment

Дослідження структури та властивостей високоентропійних сплавів системи AlCrFeCoNiCu[x]

The peculiarities of the structure formation of alloys of the system AlCrFeCoNiCuх (where x = 0, 0.5, 1, 2, and 3 moles) were studied. Durometric studies of alloys of this system were carried out. Established that an alloy AlCrFeCoNiCu0.5 has the highest microhardness (6.1 GPa). Heat resistance tests showed that AlCrFeCoNi and AlCrFeCoNiCu have the highest heat resistance. The connection between the scale composition after the test and the mechanism of oxidation of this alloys revealed.Досліджені особливості структуроутворення сплавів системи AlCrFeCoNiCuх (де x = 0, 0,5, 1, 2, 3 моль). Як і фазовий склад, мікроструктури сплавів по мірі збільшення кількості міді зазнають істотних змін. В усьому досліджуваному концентраційному інтервалі зміни вмісту міді спостерігається різна морфологія фаз. Підтверджено, що при збільшенні концентрації міді змінюється характер кристалізації сплавів даної системи. Проведені дюрометричні дослідження сплавів даної системи. Встановлено, що найвищу мікротвердість 6.1 ГПа має сплав AlCrFeCoNiCu0.5. Випробування на жаростійкість показали, що найвищу жаростійкість мають сплави AlCrFeCoNi та AlCrFeCoNiCu. Результати рентгенофлуорисцентного аналізу свідчить про високий вміст алюмінію в окалині. Отже, високу жаростійкість сплавів можна пояснити утворенням на поверхні захисної плівки Al2O3

Температура солідусу та гаряча твердість стопів Ti–Nb–Mo

Eight alloys of the Ti–Nb–Mo system are synthesized by the arc remelting method. As shown, they have dendritic microstructures typical of casting. The phase composition and lattice periods of the formed phases are determined. Using the method of differential thermal analysis (DTA), phase transformations in the solid state are investigated, and the temperatures of the onset of melting and crystallization are determined. For alloys, the solidus temperature of which is above 2000°C, together with DTA, the Pirani–Althermum pyrometric method is also used. Based on the experimental data, the temperature dependences of the hardness of the alloys are constructed and the activation energies of deformation of the material under the indenter are calculated. The analysis of the curves of the dependence of the hardness of the alloys is carried out and the temperature of the sharp softening of the material is determined. As shown, that the α→β transition in titanium alloys with an unstable β-phase does not lead to a significant change in hardness.Методою дугового перетопу одержано 8 стопів системи Ti–Nb–Mo. Показано, що вони мають типові для лиття дендритні мікроструктури. Визначено фазовий склад та встановлено періоди ґратниць утворених фаз. Використовуючи методу диференціальної термічні аналізи (ДТА) досліджено фазові перетворення у твердому стані, а також визначено температури початку топлення та кристалізації. Для стопів температура солідуса яких вище 2000°С разом з ДТА була також використана пірометрична метода Пірані–Альтермума. На основі експериментальних даних побудовані температурні залежності твердости стопів та розраховано енергії активації деформування матеріалу під індентором. Проведено аналізу кривих залежності твердости стопів та визначена температура різкого знеміцнення матеріалу. Показано, що α → β-перехід в стопах системи Ti–Nb– Mo з нестабільною бета фазою не призводить до суттєвої зміни твердості за даної температури переходу