Papers by Keyword: Cavitation Erosion

Abstract: Aluminum alloy 6082 is known for its use in the manufacture of structures that require welding interventions, high mechanical properties, resistance to pressure and corrosion, such as: boilers, truck structures, bicycles and motor boats. The recent research, regarding the cavitation resistance of the this alloy structure, shows a poor behavior of the semi-finished structure and somewhat improved by artificial aging volumetric heat treatment regimes. On the line of increasing the resistance of the this alloy structure, to the erosive demands of cavitation, they sign up of the rechearch results of the this paper, regarding the behavior and resistance of the vibratory cavitation of the aluminum alloy 6082 structure , obtained by WIG remelting. Comparing with the results obtained on the structures in the semi-finished state and through volume thermal treatments of artificial aging state, using the established parameters, recommended by the ASTM G32-2016 norms, a significant increase in the resistance to cyclic cavitation stresses is found, as a result of the increase in the surface hardness value. The novelty of the work consists in motivating the use of the remelting procedure of the surface structure of aluminum alloy 6082, through WIG remelting in order to increase the surface hardness, with a direct effect on increasing this structure resistance to the cyclical fatigue stresses of shock waves and microjets developed through the hydrodynamic mechanism of cavitation.

Abstract: The paper presents the results of the behavior and resistance to the erosion by cavitation of the 2017 A aluminium alloy structure, obtained by the WIG remelted method. The research is in step with the new directions of study and aims to extend the aluminum alloy 2017 A to the manufacture of parts that work in the cavitation regime, such as: pistons and valves of thermal engines, respectively various pump rotors or motor boat propellers. The analysis performed on the basis of the specific curves, constructed according to the indications of the ASTM G32-2016 normas, shows that structure, obtained by the WIG remelting, confers a constant behavior to the cyclic stresses of microjets generated by the hydrodynamics of the vibratory cavitation. The comparison of the results, based on the specific parameters, used in the laboratory and indicated by the ASTM G32-2016 norms shows a resistance to cavitation erosion, clearly superior to the semi-finished structure and those obtained by artificial aging heat treatment at 1800C and 120 0C, with duration of one hour.

Abstract: Aluminum alloys are known for their wide application in the automotive, river and marine boat constructions, but also in hydraulic systems (radiators/oil coolers). Their use is made by manufacturing parts directly from the semi-finished state, with or without certain volumetric heat treatments and surface hardening, depending on the functional role and the physical-mechanical characteristics pursued. Some of these parts work in hydrodynamic conditions, where cavitation manifests itself through erosion, such as: propellers of boats and barges, pump rotors in water cooling systems of automobiles. Visual analyzes performed on sailboat and powerboat propellers, after identical durations and operating conditions, showed cavitation erosion damage, different depending on the type of aluminum alloy. As a result, the paper presents and analyzes the behavior and resistance to erosion by vibratory cavitation of 4 types of aluminum alloys in the state of rolled semi-finished products. To highlight the differences in the destruction of structures under the cyclic stresses of cavitational microjets, macro and microscopic images of the eroded structure are used, as well as the curves with the values of the parameters specific to cavitation, recommended by the ASTM G32 -2016 norms and used in the research laboratory's custom. The analysis of the results shows that the resistance of the structure to cavitation erosion is dependent on the type of alloy, the degree of brittle intermetallic compounds and the mechanical properties specific to toughness.

Abstract: The good mechanical properties of aluminum alloy 2017 A have determined its use in a wide range of applications in which cavitational solocitations occur, such as hydraulic actuation installations, heat engine blocks, boat propellers and sloops, pumps in the cooling system of thermal engines, wings and ogives of airplanes. Currently, research is focused on the development of procedures for improving the resistance to cavitational erosion of these materials. This paper presents the results of the research on the cavitation erosion behavior of the material subjected to thermal aging treatment at different temperatures of 140 °C and 180 °C respectively and a constant holding time of 12 hours. The research was carried out according to the ASTM G32-2016 norms, on a vibrating device with piezoceramic crystals from the Cavitation Laboratory of the Polytechnic University of Timisoara. The research results, based on characteristic curves, mechanical properties, micro and macro structural images, showed that the sample kept for 12 h at a temperature of 180 °C is weaker than the control sample, during the sample time kept for 12 h at a temperature of 140 °C, has a small increase, even if, compared to the control sample (without heat treatment), the hardness is lower.

Abstract: The use of aluminum alloys in the manufacture of hydropneumatic systems components is very known. However, the knowledge of their behavior under cavitational demands, determinated of flow of the working liquid, is limited. For this reason, in recent years, the older research, carried out on this type of material and on some of its alloys, regarding the resistance to cavity erosion, has been resumed, especially since the mechanical properties and reduced mass are an advantage for the parts that work in this conditions (ship propellers, pumps and bodies of hydraulic devices, etc.). Therefore, the results of this paper are in step with the new researches, highlighting the behavior and resistance to the erosion produced by vibrating cavitation on the aluminum alloy 6082 subjected to the thermal aging treatment at 140 °C, with a holding time of 12 hours. The performance evaluation is based on the characteristic curves of the cavity, the specific parameters and the macro and microstructural investigations. The comparison with the delivered state shows a double increase in resistance from the cavitational erosion created by the shock waves and microjets.

Abstract: Aluminum-based alloys, due to their high properties compared to pure aluminum, have expanded their use in building the aircraft strength structures, in the automotive construction and in the naval field. Some of these, such as the radome (aircraft nose) and the wings of the airplane, are exposed also to intense stress from the erosion created by the impact with the raindrops. The literature considers this type of damage to be assimilated by the erosion trough cavitation. Therefore, the paper presents the results of the behavior and resistance to erosion trough vibratory cavitation of the 7075 - T651 aluminum alloy structure, heat treated by artificial aging at 140 °C for 12 hours. The research has been carried out on a standard device that complies with the requirements described in ASTM G32-2016. The structure strength obtained through the researched heat treatment, is evaluated through comparison with the state obtained by artificial aging at 180 °C with a similar duration of 12 hours. The evaluation is done by comparing the parameters recommended by the ASTM G32-2016 norms of the two heat treatments. The results show that the achieved gain is slightly increased.

Abstract: The present paper analyzes the differences in behavior and resistance to erosion through vibrating cavitation, between the bronze structures CuSn-12C resulting from two volumetric thermal treatments of hardening and tempering. The analysis was performed on the basis of macro and microscopic images, as well as on the basis of the histogram in which the values ​​of the reference parameters used in the laboratory custom and prescribed by the international norms ASTM G32-2016 are compared. This shows the dependence of the degree of erosion as a function of the temperature of tempering heat treatment, after hardening, as a result of microstructural changes and the hardness of the surface attacked by cavitation. The experimental research is performed on the standard vibrating device within the Cavitation Erosion Research Laboratory of the Politehnica University of Timișoara.

Abstract: Among other parts made of brass there are also the blades and the rotors of the hydraulic machines, respectively ship propellers, which during operation are degraded by cavitation erosion. As a result, most of the researches, including the most recent ones, are focused on the morphological analysis of structures eroded under the impact of micro-jets and shock waves, produced by cavitation hydrodynamics. The goal is to create new materials, but also to use new treatment technologies to increase cavitation resistance. As the literature is quite poor in studies related to the materials resistance to cavitation erosion, respectively treatments and technological procedures of it’s improvement, this paper presents the research results on the behavior of vibration cavitation erosion, carried out on three sets of CuZn39Pb3 brass samples, subjected to volumetric heat treatments of hardening for putting in solution at 800°C, followed by tempering at 250°C, 400°C and 600°C. The characterization of the behavior and the cavitation resistance of the structures resulting from the applied heat treatments is performed based on macroscopic images, taken at different representative periods, SEM images at the end of the test duration and values ​​of specific parameters recommended by ASTM G32-2016. The analysis highlights the differences caused by the change in structure by varying the temperature, but also the hardness of the surface exposed to the cavity. Thus, of the three treatments, it is found that the best resistance to cavitation is conferred by the structure resulting from hardening at 800°C, with tempering at 250°C.

Abstract: Using ammonium persulfate as an oxidant and nano-silica as dispersing medium,o-toluidine was oxidized to form a core-shell structure poly (o-toluidine)/nano-SiO₂ particle. Investigation of particle yield by ICP-AES method, the adhesion method was used to study the adhesion between coating and cylinder liner. The cavitation resistance of the coating cylinder was studied by the vibration gas cavitation method. The results showed that poly(o-toluidine) was uniformly coated around the nano-silica particles to which forms stable poly (o-toluidine)/nano-SiO₂ with core-shell structure, when m(SiO₂):m(POT)=1:8，n((NH₄)₂S₂O₃):n(POT)=1:1,and the temperature was controlled from 10 to 15°C, the composite poly(o-toluidine)/nano-SiO₂ particles were prepared and the yield reached 85%. Composite poly(o-toluidine)/nano-SiO₂ particles as a functional component and epoxy resin as a film-forming agent were used to prepare composite poly(o-toluidine)/nano-SiO₂/epoxy resin coated cylinder liner with good cavitation resistance, t₁₀₀=885min.

Abstract: The authors investigated the effect of ultrasonic cavitation on the surface of St3, 20, 45 steels. It was found that cavitation causes a change in the structure and properties of the surface layer of the samples. A refinement of the grain and an increase in the microhardness of the surface layer similar for the investigated materials were revealed. The dependences of dynamics of the increase in microhardness under the action of ultrasound were given, which show that there was a steady state, characterized by an indicator of relative microhardness of 1.3...1.5. The results of changes in the parameters of roughness and sub-roughness were given. Studies showed that cavitation erosion leads to an increase in altitude and step parameters of the surface microgeometry. The research results can be used for development and creation of ultrasonic technological processes carried out in liquid media.