Solid State Phenomena Vol. 223

Abstract: Al–Si alloys are among the most popular casting metals. Two-component aluminium alloys with silicon are not suitable for direct use after melting. Subject to their silicon content, Al Si alloys have a coarse-grained eutectic phase, and alloys with more than 13% Si content also feature large crystallites or β-phase needles. The β-phase is hard, but also fragile. Large crystallites are good planes of division, and they reduce the mechanical properties of alloys.In this study, the Al-9% Si alloy was refined with a sodium modifier. The modifier was added to the mould by the in-mould method. The modifier's influence on the microstructure and mechanical properties of the alloy was presented graphically. The results of the analysis indicate that the compound modifier influenced the evaluated properties of the Al-9%Si hypoeutectic alloy.

Abstract: The article presents a proposal of a mathematical model describing the complex heat flow within the area of steel bar bundles. The model is based on an analysis of the thermal resistances defined for mechanisms of heat transfer present in the discussed medium. A bundle is considered a porous medium with a granular structure. Taking into account the modes of heat flow, we consider the following: thermal conduction in a solid phase (steel and scale), thermal conduction in a liquid phase (gas), and thermal radiation and the contact conduction in the areas of bar contact. The essence of the discussed model is the consideration of the phenomenon of scale, which is formed on the surface of the heated bars. The final result of the described calculation procedure is the value of the effective thermal conductivity k_ef. This parameter quantitatively expresses the heat flow in the area of the bars bundle and constitutes its basic thermal property. The value of k_ef is necessary for the optimization of heating a bundle of bars.

Abstract: The paper describes issues related to the use of dilatometric methods for the study of thermo-mechanical properties of PVD gradient coatings. Tests were conducted on three types of CrCN / CrN coatings, which differed in the nature of the change of physico-chemical parameters in the gradient transition layer, deposited on a molybdenum substrate with the use of the cathodic arc evaporation method. The scope of the experimental studies included an analysis of the changes of the thermal “extortion” of the substrate – PVD coating system during annealing processes. In parallel, for comparison purposes, a mathematical description was proposed of gradient coatings containing the transition functions of material parameters. These functions describe the changes of such parameters as the Young's modulus, the Poisson's ratio, the thermal expansion coefficient, and the density as a function of spatial variables. Using the mathematical description proposed, numerical calculations of the state of thermal stress and strain for coatings are represented, respectively, by the transition function forms (a stepped, square, and square root) were carried via FEM. Based on the experimental and computational results obtained, the comparison between the elongation of the tested samples, and the state of thermal stress and strain in the substrate-gradient coating systems analysed were all specified.

Abstract: Diffusion layers produced on low-carbon steel and iron surfaces by means of vacuum titanizing process have been studied. A new technological process combining a vacuum titanizing with a preliminary electrolytic deposition of cobalt has been proposed to increase the corrosion resistance of layers. As a result, diffusion duplex layers of a Ti+Co type on the low-carbon steel and iron surfaces have been obtained. The layers microstructure, their thickness, phase composition and concentration depth profiles of elements in the diffusion zone of these layers have been investigated. Microstructure studies of these layers were performed by metallographic microscopy, X-ray diffraction, and a SEM electron microscope with a BSE and an EDS spectrometer. In addition, the layers hardness and their corrosion resistance have been determined. Corrosion measurements were performed in 0.1 M H₂SO₄ by means of potentiodynamic polarization and electrochemical impedance tests. The highest corrosion resistance was observed for steel samples with the Ti+Co type duplex layers, which showed the least passive current density and the highest charge transfer resistance, whereas the titanized layers, and the steel without any layer, corroded actively.

Abstract: Diffusion chromizing of tool steel has been investigated, using a powder method modified by the use of low pressure during the process for the avoidance of the oxidation of the batch. Innovative chromizing novel processes have been carried out in a hot-wall vacuum oven. The processes have been performed in a chromium chloride atmosphere at a low pressure range from 1 to 800 hPa, with treatment temperatures of 850 to 950°C. Studies of layer thickness, its phase composition, and Cr, Fe, and C depth profiles in the diffusion zone of chromized layer have been conducted. The effect of the process parameters, such as time and temperature, on the growth kinetics of diffusion layers has also been investigated. A comparison was made between the layer thickness produced on the tool steel surface using the novel chromizing method, under low pressure, and a traditional chromizing process, by the pack powder method. Chromizing conducted at low pressure was found to be more effective for maximizing the growth rate of diffusion layers than that for chromizing by the traditional pack cementation method.

Abstract: One of the most perspective directions of the development of surface engineering is related to hybrid technologies. The best-known and widely used hybrid surface treatment technology is a combination of a gas or plasma nitriding process with the process of the deposition of hard antiwear coatings by means of PVD methods. The paper presents the influence of the thickness of layers in the multilayer coating on tribological properties of hybrid layers – PN + AlCrTiN_multinano obtained on the EN X32CrMoV3.3 hot working steel. The research methods concentrated on the analysis of mechanical properties, surface topography and microstructure, and tribological properties. The studies on mechanical properties included tests on hardness using the nanoindentation method and tests on adhesion using the scratchtest. The analysis of surface topography and microstructure was examined by scanning electron microscopy and scanning transmission electron microscopy. The tribological properties were examined using the ball-on-disc method. The coating was tested with alumina balls as counterparts at room temperature. The authors indicate that the PN + AlCrTiN_multinano hybrid layers are characterized by excellent mechanical properties and tribological resistance. In this paper, the authors confirmed that the thickness of layers in a multilayer coating is important in shaping the mechanical and tribological properties of the PN + AlCrTiN_multinano hybrid layer.

Abstract: The PVD magnetron sputtering method is one of the most efficient methods enabling the spraying of the multi-component materials and almost unlimited setting of the chemical composition of coatings. The micro-and nanocrystalline coating structure favours the selective diffusion of chromium and other alloy additions that form compact oxide layers. The paper presents the study of coatings made in the process of magnetron sputtering of AISI310S grade chromium-nickel steel. The study covered coatings of the steel's composition with additions of 2-5% Si and of 2-5% Al. The resistance of the coatings at temperatures induced by electric current flow was assessed. The coatings provided a resistance element in the electric circuit, and the measurementof their temperature was made by the voltage drop indirect method. It was found that the steel coatings had a resistance of 0.176 Ω within the entire range of testing temperature, and their failure occurred at a temperature of 350°C due to cracking and delamination from the substrate. Introducing the Si or Al addition to the coatings resulted in an increase in coating resistance and temperature stability, respectively, to 450 and 400°C. Changes of coating’s phase composition and texture were not found. The resistance of the coatings with the Al and Si additions decreased with temperature due to their oxidation.

Abstract: The paper presents a prototype system for modifying surface of a film that can be used in various industries. System allows for two-sided modification of the surface of the film under reduced pressure with a low temperature plasma use. During the surface treatment process, it is possible to dispense chemicals into vacuum chamber in gaseous form, which can create a thin coating on the surface of the film. The system enables the film modification process parameterization while monitoring its key parameters.

Abstract: This paper presents the purpose, concept, principles of functioning, design and construction of a stand intended for testing the durability of rotational elements of office chairs. It shows the use of the stand for certification tests in accordance with the PN-EN 1335:2009 standard. It also discusses how tests on swivelling and the durability of wheels and the base of office chairs should be conducted using the developed stand. The authors present test conditions and discuss the instrumentation necessary to induce static loads during the investigations. They also identify the possibilities to perform other tests on the stand by introducing to the existing research instruments additional instrumentation necessary from the point of view of the above listed standard. The possibility of adjusting the stand to the prospective changes in normative requirements and the needs of individual users are also described.

Abstract: Motion elements of refrigerating compressors, depending on the applied oils and refrigerants, can be exposed to various wear processes. The presence of refrigerant makes lubricating and anti-wear properties of the mixture of oil and refrigerant much worse than in the case of oil with no refrigerant. Regulations concerning the application of substances weakening the ozone layer, valid at present, demand the withdrawal of operating synthetic agents refrigerating installations type HCFC – among others the popular R22. This paper presents the influence of different mixtures of oils and refrigerants on the moment of friction and the surface condition of cast iron and aluminium PA6. The tests were carried out on a friction machine with the use of a node type block-on-ring, which is located inside a pressure chamber that simulates the refrigeration compressor inside. The results of the performed tests confirm the possibility of using green refrigerant R290 (propane) as a substitute for R22, while keeping the existing mineral oil in the refrigerating installation.