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Cavitation erosion, as a mechanical effect of destruction, constitutes a complex and critical problem that affects the safety and efficiency of the functioning of engineering components specific to many fields of work, the most well-known being propellers of ships and maritime and river vessels, seawater desalination systems, offshore oil and gas drilling platforms (including drilling and processing equipment), and the rotors and blades of hydraulic machines. The main objective of the research conducted in this paper is to experimentally investigate the phenomenology of this surface degradation process of maritime ships and offshore installations operating in marine and river waters. To reduce cavitation erosion of maritime structures made from Duplex stainless steels, the study used the deposition by welding of layers of metallic alloys with a high capacity for work hardening. The cavitation tests were conducted in accordance with the American Society for Testing and Materials standards. The response of the deposited metal under each coating condition, compared to the base metal, was investigated by calculating the erosion penetration rate (MDER) through mass loss measurements over the cavitation duration and studying the degraded zones using scanning electron microscopy (SEM), the energy-dispersive X-ray analysis, and hardness measurements. It was revealed that welding hardfacing with austenitic manganese alloy contributes to an approximately 8.5–10.5-fold increase in cavitation erosion resistance. The explanation is given by the increase in surface hardness of the coated area, with 2–3 layers of deposited alloy reaching values of 465–490 HV5, significantly exceeding those specific to the base metal, which range from 260–280 HV5. The obtained results highlighted the feasibility of forming hard coatings on Duplex stainless-steel substrates. [ABSTRACT FROM AUTHOR]

Laser beam remelting is a relatively simple and highly effective technique for the physical modification of surfaces to improve resistance to cavitation erosion. In this study, we investigated the effect of laser remelting on the surface of cast stainless steel with 0.40% C, 25% Cr, 20% Ni, and 1.5% Si on cavitation erosion behavior in tap water. The investigation was conducted using a piezoceramic crystal vibrator apparatus. Base laser beam parameters were carefully selected to result in a defect-free surface (no porosity, material burn, cracks) with hardness capable of generating better resistance to cavitation erosion. The experimental results were compared with those of the reference material. Surface morphology and microstructure evolution after cavitation tests were analyzed using an optical metallographic microscope (OM), scanning electron microscope (SEM), and hardness tests to explore the mechanism of improving surface degradation resistance. The conducted research demonstrated that surfaces modified by laser remelting exhibit a 4.8–5.1 times greater increase in cavitation erosion resistance due to the homogenization of chemical composition and refinement of the microstructure, while maintaining the properties of the base material. [ABSTRACT FROM AUTHOR]

The paper presents the results of the cavitational erosion research carried out on two stainless steels intended for the manufacture of parts strongly subjected to cavitation, such as the vanes and rotors of hydraulic turbines and pumps. In accordance with the new trends, to reduce carbon below 0.1%, for both categories the carbon content was kept at the value of 0.038%. The researches are carried out in the Cavitation Erosion Research Laboratory of the Politehnica University of Timisoara, on the magnetostrictive vibrating device with a nickel tube. The behaviour and resistance to cavitation erosion are evaluated based on the comparison of curves and specific parameters with those of OH12NDL stainless steel, as a reference for the parts subjected to cavitation, as well as on the basis of microstructural images, obtained by optical and electron microscopy. The results show similarities and differences of microstructural damage between the two steels. The comparison of the specific curves and the values of the reference parameters, with those of the reference steel OH12NDL, shows that both steels can be successfully used in the manufacture of vanes and rotors of hydraulic machines. [ABSTRACT FROM AUTHOR]

Aluminum-based alloys are known for their applications in most fields, due to their physicalmechanical properties and their technological capability to lend themselves to the realization of various parts, with geometrical configurations ranging from simple to complex. These parts include those working in hydrodynamic flow fields, characterised by certain degrees of destruction by erosion created by microjets and shock waves. Such parts are the propellers of motor boats, the impellers of household pumps, radiators and pumps in the cooling system of motor vehicles. As erosion causes the surface of the part to change, causing it to fail, research is currently being developed to increase service life by increasing the resistance of the structure to cavitation erosion. This is the direction of the present work, the results of which show the effect of artificial ageing treatment at 140 °C, with a holding time of 12 hours, of aluminium alloy 2017 A. Comparison with similar results obtained previously on the delivery condition and on artificial ageing at the same temperature, with holding times of one hour and 24 hours, shows that the structure obtained by the analysed heat treatment regime is a variant for increasing the service life to cavitational stresses. [ABSTRACT FROM AUTHOR]

The use of volume heat treatments aims to change the microstructure and the values of the mechanical properties, with homogeneous distribution in the volume of the part, so as to confer resistance to various stresses. From the point of view of the hydrodynamic stresses of the microjets generated by the cavitation mechanism, these treatments ensure an increase in the life of the required surface. In the case of aluminum-based alloys, volume thermal treatments do not produce important changes in the structural phase, but they cause important changes in the values of the mechanical properties. As these alloys have small specific masses and good mechanical properties, research is currently being resumed aimed at extending their use to parts that work in cavitation such as: propellers of motor boats and pleasure boats, pump rotors in the cooling system of thermal engines and aircraft wings. In this sense, the vibratory cavitation tests are carried out on aluminum alloy 7075 subjected to volumetric thermal treatment of artificial aging at 1800C with a holding time of 24 hours. The comparison with the results previously obtained on the delivered state and the regime with the same temperature and duration of one hour shows that the effect of increasing the duration of the heat treatment leads to a significant increase compared to the state of delivery and slightly different from that obtained by the one with a duration of one hour. [ABSTRACT FROM AUTHOR]

The paper presents the results of the experiment of behavior and resistance to vibration cavity erosion, carried out on cast aluminum alloy 5083 heat treated by hardening at 450 °C and maintained for 12 hours at the artificial aging temperature of 180 °C. Following the experiment carried out in the Cavitation Erosion Research Laboratory of the Politehnica University of Timișoara, it is found that the duration of 12 hours is insufficient to increase the resistance to cavitation erosion, as evidenced by the destruction of caves in the shape of pits. [ABSTRACT FROM AUTHOR]

Among the applications of aluminum-based alloys is that in the field of hydraulic installations and equipment. Some components of their structure, such as the rotors of the cooling pumps of motor vehicles, or the blades of propellers from the engines of fishing boats, or pleasure boats, and even the radiators of motor vehicles are subject to corrosion by the cavity created during operation. Among the aluminum alloys used in the manufacture of such components is the alloy 5083. These parts can be made by casting (rotors / pump housings and steam propeller) or laminated semi-finished products, such as blades for rotors / propellers with adjustable vanes. Cavitation operation inevitably leads to damage by erosion caused by cyclic stresses of micro-jets and shock waves generated by the implosion of cavitation bubbles. As a result, the paper presents the results regarding the degradation by vibration cavitation of alloy 5083, in the form of cast and rolled semi-finished product. The curves and parameters specific to the resistance of the alloy to cavity erosion, as well as the images of eroded surfaces, show, surprisingly, that the cast semi-finished product has a higher resistance than the laminated one, due to the mechanical properties and the type of microstructure. [ABSTRACT FROM AUTHOR]

Aluminum based alloy type 5083 have a large applicability in the area of automobile and naval constructions (such as: Shipbuilding, Rail cars, Vehicle corps, Type truck body, Mine skips and cages, Pressure vessel). The components of these parts are sometimes required for high aggressiveness factors. Thus, during operation, both the pump rotors and the propellers are subjected to hydrodynamic stresses of the cavity, which, by erosion, leads to their removing, completely or until repair. At the same time, to increase the service life, chemical corrosion of the liquid environment, these others contain various alloying elements, which change the structure and improve the chemical, physical and mechanical properties. In order to increase the resistance to erosion and mechanical stresses of the cavitational current, heat treatments are applied which also modify the microstructure and the values of the mechanical properties. The study presents the results of research on its vibrating cavity of another 5083 cast, subjected to the heat treatment of the solution at 350°C followed by artificial aging at 180°C with different maintenance times (one hour, 12 hours, 24 hours). The analysis of the results, based on the specific curves used in the Cavitation Erosion Research Laboratory in Timișoara, recommended by ASTM G32-2016, as well as macro images of eroded surfaces for 165 minutes, shows the dependence of cavitation erosion resistance of the microstructure type results from heat treatment and not of durable value, respectively of resilience, properties with great influence on the resistance to cavitation stresses, as happens, most often, in the case of steels. [ABSTRACT FROM AUTHOR]

Very many components operating in liquid environments are manufactured from copper-based alloys, i.e. brass and bronze. Most often, these alloys are selected based on their resistance to chemical corrosion and their high level of heat transfer capability. Some of these components are subject to cavitation stress. In consideration of the above, this paper presents the different resistances to vibratory cavitation erosion-corrosion of brass (CuZn39Pb3) and bronze (CuSn12-C) in semi-finished state, used to manufacture the components of valves installed in the cooling systems and hydrodynamic power transmission of railway vehicles. To show these differences in the behavior and resistance of the material when it is subject to cavitation microjets from the vibratory cavitation process, we are using SEM and photographic images of the eroded surface structure. The assessment of the difference in resistance is made based on the MDE(t) curves and the specific parameters: average erosion depth, cavitation resistance and the average roughness, as appearing in the profile diagram for the eroded surface. The experiments were performed using the standard piezoelectric crystal assembly, available in the Cavitation Research Laboratory at the Polytechnic University from Timisoara. [ABSTRACT FROM AUTHOR]

Manufacturing hydraulic machinery runners with improved cavitation erosion resistance and in the same time with good welding ability is a great challenge for the specialists in design and maintenance of such devices. A good choice is the use of steels with austenitic structures having in the chemical composition 10% of nickel and 2% to 24% of chromium. Upon these types of steels, in the Cavitation Laboratory of the Timisoara Polytechnic University were undertaken extensive researches. It resulted that the best behavior was obtained with the steels having in the structure both austenite and martensite. For such steels the hardness of the attacked areas receives increased hardness as a result of the implosion of cavitation bubbles. [ABSTRACT FROM AUTHOR]

Regardless if the erosion phenomenon takes place in a laboratory facility or in an industrial device cavitation erosion intensity depends on two different factors: the quality of the steel and the intensity of the cavitation. Researches to obtain better materials are done every time in laboratory devices in which the cavitation intensity is very great and the research time is reduced. In most cases, the intensity of cavitation in industrial devices is smaller. The present laboratory researches upon eight stainless steels with great content of austenite are important because such materials are used to repair by welding the affected details. The chemical compositions were established as follows: the Nickel content approximately the same 10%, two contents of carbon 0.1% and 0.036% and eight different Chromium contents between 6 to 24 %. The laboratory facility is a device with piezoelectric crystals respecting the ASTM G32-2010 Standard. The laboratory results show that all the tested steels have very good cavitation erosion resistance; the best obtained result is for the steel having 6% Chromium and 0.1% Carbon with the structure having 32% martensite and 68% austenite. It is interesting to note that this result is better than that obtained for steels with greater content of martensite. [ABSTRACT FROM AUTHOR]