Papers by Keyword: Cavitation Wear

Abstract: In order to meet the expectations of the global industry in areas such as: energy, heating, aviation, automotive, railway, chemical, petrochemical, oil, gas, river and marine sectors, where material wear processes may occur due to the flow of water gas and steam or their mixtures with various degree of saturation at different pressures, the authors of this article have conducted research on the resistance to cavitation wear of a low-friction composite anti-wear PVD coating in the form of chromium nitride and tungsten carbide (CrN+WC/C) deposited by a physical method on the surface of structural elements in the form of cavitation generators operating in extreme conditions of cavitation wear. Structural elements were examined made of steel with the ferritic-perlitic structure of the P265GH grade and with the austenitic chromium-nickel structure of the X2CrNi18-9 (304L) grade with a protective composite low-friction coating applied onto their surfaces by the Physical Vapour Deposition (PVD) technique, intended for operation in the cavitation wear environment. In order to obtain the results, the investigations of mass loss and roughness profile changes were conducted and the analysis of structural-metallographic morphology changes on the surfaces of structural elements was performed using a scanning electron microscope at voltages accelerating from 5 to 20kV using secondary electrons detection. The results of cavitation wear on the surface of structural elements were obtained using a digital microscope operating in 4K technology with a progressive scanning system.

Abstract: Evaluation of cavitation erosion resistance of is carried out by using various testing stands, that differ by the way of cavitation excitation and its intensity. These various testing conditions have led to a standardization of some part of laboratory stands, that in turn allows a direct comparison of results obtained in different laboratories. The aim of this study was to determine the course of cavitational destruction of MgAl2Si alloy samples tested on three different laboratory stands. The research was conducted on a vibration stand according to ASTM G32, where cavitation is forced by the vibrating element; in the cavitation tunnel reflecting actual flow conditions, and on a jet impact stand- simulating the impact microjet in the final phase of the cavitational bubbles implosion. Each laboratory stand has given a different course of cavitational destruction.

Abstract: Copper alloys due to their very good corrosion properties are often used to a fabrication of components that are subjected to both a cavitational destruction and a corrosive action of an environment, e.g.. ships’ propellers, sliding elements, pump parts etc. The course of cavitational destruction depends mainly on a material’s structure (a grain size, a type of inclusions, morphology and phase distribution, etc.) but also on the load distribution, and a possible activity of chemical, electrochemical and thermal processes near cavitation bubbles. Properties of a material that is subjected to the cavitational damage are strongly affected by its structure formed upon manufacturing or applied processing. In the present paper, results of the cavitational resistance analysis of CuZn10 alloy in the as cast state (the grain size of 200 μm) and after thermomechanical processing (the grain size of 10 or 200 μm) evaluated on vibrational laboratory stand in accordance with ASTM G-32 standard, are shown.

Abstract: A cavitation erosion is the process based on an impact of pressure pulses on a material’s surface caused by the phenomenon of cavitation. The term cavitation is defined as a phenomenon of formation, growth and disappearance (implosion) of bubbles due to cyclic pressure variations in a liquid. The cavitation initiators are embryos (cavitation nuclei with a size up to 50 μm), located in the water or on wetted surfaces that lead to decreasing of the liquid ability to transfer tensile stresses. The role of embryos is played by micro gas bubbles, fine solid particles, micro-organisms or gas-filled pores on a surface of solid body embedded in a liquid. A rapid pressure drop occurring within the liquid and a presence of cavitational kernel causes rupture the continuity of the liquid and thus lead to the formation of steam-gas mixture areas, a so called cavitation bubbles. A cavitation bubble may be filled with a gas, a vapor or a steam/gas mixture.A course of cavitation depends on a cavitation type. In thepresent work, a mechanism of cavitiational destruction of 99,7 % titaniumtested on vibrational and jet-impact valaboratory stands, is analyzed. Results of thecavitational resistance evaluation of Ti99.7 titanium carried out onvibrational and jet-impact stands have revealed different mechanisms of acavitation destruction caused by various forms of cavitation. It was found thata surface of titanium samples tested on the vibratory stand was covered by verylarge number of microcracks which in a later stage of the research leads to theerosion of the material. The cavitational destruction of Ti samples on the jet-impact stand is initiatedby a plastic straining of subsurface area, which in the further stage leads toan erosion represented by the detachment of whole grains anda formation of deep pits on the material’s surface. Additionally, results of conducted studies have confirmed the fatigue character of the cavitationaldestruction process.

Abstract: Electroplated nickel coatings provide ductility, excellent corrosion resistance and good wear resistance, which qualifies them to meet complex demands of engineering, microtechnology and microelectronics. The co-deposition of particles is a promising alternative to deposit layers with adequate microstructure and properties avoiding the rise of residual stress. The incorporation of the sufficient quantity of particles, monodisperse distribution and downsizing to nanometre scale affect the amount of strengthening by dispersion hardening. To avoid agglomeration in the electroplating bath as well as in the layer is a challenge which has been met by simple Watts nickel electrolyte with a minimum of organic additives and adequate bath agitation comprising sonication, i.e. the exposure of the bath to high-frequency sound waves. Well-dispersed hard particles (titanium oxide and silicon carbide) were incorporated in nickel films. The focus was set on the correlation between the gained microstructure of the composites with particles from micron to nanometre scale and the electrochemical and mechanical properties. Corrosion was quantified from polarisation curves and volumetric erosion measurements. Wear resistance was evaluated by scratch energy density studies, oscillating sliding wear testing and cavitation wear testing and compared to indentation hardness results. Sonication and particle downsizing result in matrix grain refinement and dispersion hardening. Incorporation of different particles with respect to different material and size proved to meet different demands. Submicron TiO2 is best for high corrosion resistance, sonicated nickel without particle incorporation is best for high abrasion resistance, nano TiO2 is best for oscillating sliding wear resistance and submicron SiC is best for cavitation wear resistance.