CSA Ceramics Abstracts (iki 2021 m.)

This work presents a comparative study of the surface mechanical properties and tribological wear resistance of polymeric sliding materials. The authors focused on the application of polymeric materials in producing spare parts for vehicles that are still in use but for which original components are no longer manufactured or are disproportionately expensive compared to the vehicle’s market value. The subject of the study was frictional interactions between the timing chain and the sliding element. Three commercial materials were tested, designated: PA6G, PA6G+MoS2, PE 1000. A commercial lubricant PMO 5W40 Extreme 100 % (intended for vehicles without a particulate filters) was used. The coefficient of friction and wear were analyzed under dry friction and oil bath. The lowest coefficient of dry friction was obtained for the PA6 G, whereas PE 1000 exhibits the highest. Under oil lubrication, however, PE 1000 demonstrated the lowest coefficient of friction. Microscopic analysis of wear scars was performed. The extent of wear depends on the type of material used and the nature of the interaction (dry friction, oil-bath friction). Wear under dry friction was lower than under oil-bath conditions, possibly due to the influence of the Rebinder effect.

The rheological properties and stability of cement‐based materials determine the technological properties of concrete mixtures and significantly influence concrete properties. Polycarboxylate ether (PCE) and other plasticizing admixtures are widely used in construction practice to plasticize concrete mixtures. Experimental research on the rheological characteristics of cement mortar modified with PCE and air‐entraining admixtures (AIRs) was carried out with a rotation rheometer with coaxial cylinders and water bleeding tests. Herschel–Buckley or modified Bingham models were used to approximate experimental flow curves and assess rheological parameters such as yield stress, plastic viscosity, and shear thinning/thickening index. The rheological test was carried out at 5 and 90 min after mixing the cement mortar. The rheological test established that the modification of cement mortar by PCE in a dosage of 0.2% (in dry material) leads to a decrease in plastic viscosity of 25.0% with a reduction in water demand of 18% for the same workability. Modification of cement mortar by AIR in 0.3% dosage leads to a decrease in yield stress by 37.7% and a decrease in plastic viscosity by 35.4% compared to the control specimen without PCE. The combined modification by PCE and AIR admixtures shows a synergistic effect. It leads to a significant decrease in yield stress of cement mortar by 92.2% and a decrease in plastic viscosity to about 0  Pa·s. In addition, there is a significant coefficient of water bleeding reduction up to 0%, when additional water reduction was carried out in the mixture while maintaining the same workability. The cement mortar, with or without PCE and AIR, exhibited shear‐thinning characteristics for up to 90 min after mixing. The solid, liquid, and gas (air) phases’ influence yield stress and plastic viscosity in the analysis mixtures are presented in this paper. It has been established that a modified exponential Mooney dependency can be used to predict the yield stress and plastic viscosity of the modified cement mortar (both plasticized and air‐entrained).

This paper presents the results of computer simulations and experimental studies, aiming to increase the mechanical strength of sheet metal parts manufactured from high-quality structural carbon steel by means of local laser processing. 0e effects of laser processing on the strength of steel sheet plates and their ability to resist bend load after laser treatment were studied. 0e results of bending experiments and computer simulations of elastoplastic deformation establish that local laser processing with surface melting can be used to increase the mechanical strength of structural elements made from thin sheet steel C22E and to decrease its deflection under similar workload, as an alternative to the application of complex geometric shapes, additional strengthening elements, or heat treatment.

In this work we have evaluated the feasibility of the magnetic field pressing technology for formation of Cu-Nb joints for further pulsed power applications. The electrical and mechanical properties of joints have been investigated. The structure of Cu-Nb conductors joints was investigated using optical and scanning electron microscopy. The mechanical characteristics have been evaluated using tensile tests. It has been determined that the maximum tensile strength of 350 MPa could be achieved, which is 30,4 % of a Cu-Nb wire strength. The applied pressing technology allowed minimizing the defects in the microcomposite structure due to solid-state joining process, however the resultant decrease of conductivity by 10 % influenced an increase of the Joule heating. After a 2 min 200 A current flow the difference of 54,4 °C between the conductor and the joint area was observed. It was concluded that the Cu-Nb joints formed by magnetic field pressing are applicable for pulsed magnet setups where non-destructive joints are required.

In the present work, plasma-spray technology was applied as a means to improve the durability of Al-Mg alloy parts. NiCrSiBFe coatings deposited on aluminium-magnesium alloy substrates with different thickness values were studied. Before spraying, the surfaces of aluminium-magnesium alloy were modified upon applying different surface pre-treatment methods. The phase composition, microstructure, microhardness, porosity and adhesion of the deposited coatings were characterized. Ball-on-plate wear tests of the NiCrSiBFe coatings were carried out in dry and lubricated conditions, using a scanning electron microscope to characterize the worn track and the wear mechanism. The correlation of the coating porosity and the adhesion strength with the thickness of a deposited layer was determined. The results revealed that the plasma-sprayed NiCrSiBFe coatings, compared with the uncoated Al-Mg substrate, provide both a stable friction coefficient and an improved wear resistance, which is about two times better under dry sliding and about five times better under lubricated sliding.