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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.
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The erosion process of a 4 µm monolayer CrN coating deposited on 316L stainless steel due to cavitation was investigated using finite element analysis (FEA). To estimate load parameters from cavitation pit geometry resulting from high impact velocity and high strain rate, the explicit dynamic solver was employed. Water microjet impacts at velocities of 100, 200 and 500 m/s were simulated to recreate different cavitation erosion intensities observed in the experiment. The resulting damage characteristics were compared to previous studies on uncoated 316L steel. The relationship between impact velocity and postimpact geometry was examined. Simulations revealed that only impact at 500 m/s can exceed the maximum yield stress of the substrate without penetrating the coating. Subsequent impacts on the same zone deepen the impact pit and penetrate the coating, leading to direct substrate degradation. The influence of impact velocity on the coating degradation process is discussed.
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The scouring and migration of sediments in sewer systems are the key contributors to overflow pollution. Both physical and biological factors affect the erosion and migration of layered sediments. However, the functional characteristics of these factors and their quantification process still need to be further explored. In this study, the physical form and biological metabolism of the sediment are coupled, and the suspension mechanism under the dual action is proposed systematically and deeply. The influence coefficient of scour initiation was redefined as A^/prime, where the physical factors were particle size and mass, and the biological factors were bio-viscosity and internal cavitation. The bio-viscosity of layered sediment particles is provided by Extracellular Polymeric Substances (EPS). The slope value of |ΔD/-Δf| (ΔD: Dissipation; Δf: frequency) of surface EPS decreased from 0.489 to 0.315 when Quartz Crystal Microbalance with Dissipation (QCM-D) was used to analyse EPS viscosity, indicating that biological activities formed a dense biofilm on the sediment surface and enhanced the bond between particles. Meanwhile, by monitoring the accumulation density of sediments at different depths, it was found that the packing density of the bottom layer decreased from 1.50 to 1.45 g/cm3, which was mainly due to the internal cavitation caused by microorganism consuming organic matrix and releasing H2S and CH4. The delamination difference of EPS results in the uneven change of adhesion between different layers. This, combined with the internal erosion characteristics triggered by microbial stratified metabolism, collectively constitutes the biological effects on the sediment structure. Finally, the coupling mechanism of particle distribution and bio-viscous-cavitation erosion was formed, and the correctness of the formula was verified by repeated experiments, which proved the agreement between the theory and the practice and provided a scientific method for systematically analysing the erosion and migration law of sediment in the sewer system.
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The challenge of cavitation erosion (CE) in flow-handling components of marine engineering has promoted the development of advanced materials due to safety incidents and economic costs. High entropy alloys (HEAs), known for high hardness and corrosion resistance, emerge as promising candidates. This paper delved into the CE characteristics of CoCrFeNiMoCu0.1 HEA when subjected to the 3.5 wt% NaCl solution, elucidating the synergistic effect of CE-corrosion. The quantitative analysis revealed that CE-corrosion synergy contributed 48.02% to total CE mass loss, primarily attributed to corrosion-induced CE damage. Meanwhile, electrochemical noise (EN) was utilized to reveal the corrosion behavior of CoCrFeNiMoCu0.1 HEA in 3.5 wt% NaCl solution combined with the morphologies observation and surface roughness. Extended CE time compromised the corrosion resistance of CoCrFeNiMoCu0.1 HEA and diminished the impact of selective phase corrosion on the surface. Eventually, the CE damage mechanism of CoCrFeNiMoCu0.1 HEA was revealed based on pertinent experimental findings. The results showed that with increased CE time, the CoCrFeNiMoCu0.1 HEA transitioned from predominantly extensive exfoliation of the initial FCC phase to further damage of the intermetallic σ and µ phases.
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In this work study, a comparative analysis was undertaken to investigate investigation into the cavitation erosion (CE) and corrosion behavior of laser powder bed fusion (LPBF) TC4 and as-cast TC4 in 0.6 mol/L NaCl solution. Relevant results indicated that LPBF TC4 revealed a rectangular checkerboard-like pattern with a more refined grain size compared to as-cast TC4. Meanwhile, LPBF TC4 surpassed its as-cast counterpart in CE resistance, demonstrating approximately 2.25 times lower cumulative mass loss after 8 h CE. The corrosion potential under alternating CE and quiescence conditions demonstrated that both LPBF TC4 and as-cast TC4 underwent a rapid potential decrease at the initial stages of CE, while a consistent negative shift in corrosion potential was observed with the continuously increasing CE time, indicative of a gradual decline in repassivation ability. The initial surge in corrosion potential during the early CE stages was primarily attributed to accelerated oxygen transfer. As CE progressed, the significant reduction in corrosion potential for both LPBF TC4 and as-cast TC4 was attributed to the breakdown of the passive film. The refined and uniform microstructure in LPBF TC4 effectively suppresses both crack formation and propagation, underscoring the potential of LPBF technology in enhancing the CE resistance of titanium alloys. This work can provide important insights into developing high-quality, reliable, and sustainable CE-resistant materials via LPBF technology.
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Cavitation erosion is a general phenomenon in the fields of aviation, navigation, hydraulic machinery, and so on, causing great damage to fluid machinery. With the vast requirements in deep ocean applications, it is urgent to study the mechanism of cavitation erosion and the cavitation erosion resistance of different materials under high hydrostatic pressure to predict and avoid the effect of cavitation erosion. In this work, the spatially confined cavitation bubble cloud associated with Gaussian-like intensity distribution sonoluminescence (SL) was produced by a spherically focused ultrasound transducer with two opening ends near metallic plates under different hydrostatic pressures (0.1, 3, 6, and 10 MPa). The cavitation erosion effects on copper, 17-4PH stainless steel and tungsten plates were studied. Through coupling analysis towards the SL intensity distribution, the macro/micro morphology of cavitation erosion, and the physical parameters of different metallic materials (hardness, yield strength, and melting point), it is found that with increasing hydrostatic pressure, the erosion effect is intensified, the depth of cavitation pits increases, the phenomenon of melting can be observed on materials with relatively low melting points, and the cavitation erosion experienced an evolution process from high-temperature creep to fracture. This work has also established a method for the evaluation of materials' cavitation erosion resistance with measurable SL intensity distribution, which is promising to promote the designing and selection of anti-cavitation materials in deep-sea applications.
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Cavitation erosion poses a significant challenge in fluid systems like hydraulic turbines and ship propellers due to pulsed pressure from collapsing vapor bubbles. To combat this, various materials and surface engineering methods are employed. In this study, nano and micro scale particles of silicon carbide (SiC) or boron carbide (B4C) were incorporated as reinforcement at 6% and 12% ratios, owing to their exceptional resistance to abrasive wear and high hardness. Microparticles were incorporated to assess the damage incurred during the tests in comparison to nanoparticles. Wear tests were conducted on both bulk samples and coated aluminum sheets with a 1mm of composite. Additionally, cavitation tests were performed on coated aluminum tips until stability of mass loss was achieved. The results indicated a distinct wear behavior between the coatings and the bulk samples. Overall, wear tended to be higher for the coated samples with nanocomposites than bulk, except for the nano-composite material containing 12% SiC and pure resin. With the coatings, higher percentages of nanometric particles correlated with increased wear. The coefficient of friction remained within the range of 0.4 to 0.5 for the coatings. Regarding the accumulated erosion in the cavitation tests for 100 min, it was observed that for all nanocomposite materials, it was lower than in pure resin. Particularly, the composite with 6% B4C was slightly lower than the rest. In addition, the erosion rate was also lower for the composites.
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The cavitation erosion failure of pumps or valves induces the low efficiency and reduced service life of nuclear reactors. This paper reviews works regarding the cavitation erosion of pumps and valves in the nuclear power industry and academic research field. The cavitation erosion mechanisms of materials of pumps and valves are related to the microstructure and mechanical properties of the surface layer. The cavitation erosion resistance of austenitic stainless steel can be ten times higher than that of ferritic steel. The cavitation erosion of materials is related to the hardness, toughness, and martensitic transformation capacity. Erosion wear and erosion-corrosion research is also reviewed. Erosion wear is mainly influenced by the hardness of the material surface. Erosion-corrosion behavior is closely connected with the element composition. Measures for improving the cavitation erosion of pumps and valves are summarized in this paper. The cavitation erosion resistance of metallic materials can be enhanced by adding elements and coatings. Adhesion, inclusion content, and residual stress impact the cavitation erosion of materials with coatings.
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This study focuses on unraveling the failure mechanisms of three distinct polymer-coating structures applied to mortar substrates: an epoxy coating (MEP1), an epoxy coating with an intermediate epoxy mortar layer (MEP2), and a polyurea coating with an intermediate epoxy mortar layer (MPU). Ultrasonic cavitation experiments are conducted to investigate the initial stages of cavitation erosion. The damaged surfaces of these three coating structures are meticulously investigated and characterized. An in-depth analysis is performed on the distribution characteristics of cavitation pits and the evolutionary patterns of these pits. The results indicate that the introduction of epoxy mortar as an intermediate layer significantly enhances the material's cavitation resistance by improving its energy absorption capacity. This enhancement delays the formation of cavitation pits on the coating surface. Additionally, the superior adhesive properties of the intermediate epoxy mortar with the mortar substrate prevent direct cavitation erosion from forming on the substrate, even when brittleness failure occurs and coating erosion is observed on the surface epoxy polymer. The polyurea coatings demonstrate exceptional elastic-plastic deformation capabilities. When combined with the intermediate epoxy mortar layer, MPU can withstand prolonged and repetitive cavitation impacts, resulting in minimal coating erosion.
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This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering.
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In this article, the WC-10Ni coatings were fabricated by HVOF spray, then the ultrasonic cavitation erosion performances of the coatings in distilled water and 3.5â¯wt% NaCl solution with various Na2S concentrations (0, 20 and 200â¯ppm) were investigated. The results of the cumulative volume loss of the coating in different mediums showed that the coating exhibited enhanced cavitation erosion resistance with the increase of Na2S concentrations in medium. The reason for the improvement on the cavitation erosion performance was the growth of corrosion product films containing sulphide. In comparison with the coating after cavitation erosion in medium without Na2S, no large craters and deep grooves were observed on the eroded coating surface in medium with Na2S. The ultrasonic cavitation damage of the coating manifests as the spall of the metal binder phase (Ni) and exposure of the hard phase (WC).
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The present study emphasizes the role of sulphide on ultrasonic cavitation erosion-corrosion (UCE-C) behaviors of HVOF-sprayed WC-Cr3C2-Ni coating in 3.5 wt% NaCl solution with different sulphide concentrations. The results indicated that the ultrasonic cavitation erosion (UCE) resistance of the coating decreased significantly with increasing sulphide concentration. The coating reacted with oxygen and anion those transferred by UCE, and the cavitation impact force led to the lack of support for tungsten carbide particles, which resulted in the reduction in the mass of the coating. There were two main factors those affected the UCE-C mechanism, in which the passivation film helped to reduce the mass loss of the coating, while the impact force caused by cavitation destroyed the passivation film, led to the accelerated anion diffusion and ultimately accelerated the mass loss of the coating. Mechanical erosion dominated the UCE-C of the coating in all tested solutions.
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It is known that a number of parts that operate in liquid media, such as the propellers of motorboats and pleasure river vessels, as well as the rotors of household pumps and the radiators and pumps in the cooling system of motor vehicles are made, as a rule, of aluminum-based alloy. Research during maintenance leads to the conclusion that, in certain operating conditions, due to the turbulent character of the flow, with pressure drops to below the vaporization level, it inevitably reaches the threshold of cavitation, which manifests itself through its effects, especially through erosion. To increase the lifetime, these alloys are currently subjected to techniques to improve the structure's resistance to the cyclic stresses of cavitational microjets. Among these techniques are volumetric heat treatments, which lead to changes in the microstructure and mechanical property values, with an effect on the behavior and resistance to cavitation erosion. This paper studies the influence of heat aging treatments on the cavitation erosion behavior of an aluminum alloy type 6082, in the cast state. The heat treatments applied were 140 °C/1 h, 12 h, 24 h and 180 °C/1 h, 12 h, 24 h. The MDEmax and MDERs parameters were determined and a correlation could be made between the values of the mechanical-resilient characteristics and the resistance to cavitation erosion in the case of aluminum alloy 6082.
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In many industrial processes that include fluid flow, cavitation erosion of different engineering structures (pumps, turbines, water levels, valves, etc.) during their operation is expected. Metallic, ceramic, and composite materials are usual candidates considered for application in such extreme conditions. In this study, the idea is to synthesize refractory ceramic material based on talc with the addition of zeolite for utilization as protective coatings in cavitating conditions. Two talc-based refractories with zeolites from two Serbian deposits were produced. The behaviors of the samples in simulated cavitation conditions were examined by an advanced non-destructive methodology consisting of monitoring mass loss and surface degradation using image analysis compiled with principal component analysis (PCA), interior degradation by ultrasonic measurements, and the microstructure by a scanning electron microscope (SEM). Lower mass loss, surface degradation level, and modeled strength decrease indicated better cavitation resistance of the sample with Igros zeolite, whereby measured strength values validated the model. For the chosen critical strength, the critical cavitation period as well as critical morphological descriptors, Area and Diameter (max and min), were determined. A Young's elasticity modulus decrease indicated that surface damage influence progressed towards interior of the material. It can be concluded that the proposed methodology approach is efficient and reliable in predicting the materials' service life in extreme conditions.
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Marine flow-passing components are susceptible to cavitation erosion (CE), and researchers have worked to find ways to reduce its effects. Laser Shock Peening (LSP), a material strengthening method, has been widely used in aerospace and other cutting-edge fields. In recent years, LSP has been used in cavitation resistance research. However, the current LSP research does not realize a comprehensive predictive assessment of the material's CE resistance. This paper uses m stresses to develop a comprehensive set of strengthening effect prediction models from LSP to CE using finite element analysis (FEA). Results show that the LSP-1 sample (4 mm spot, 10 J energy) introduced a compressive residual stress value of 37.4 MPa, better than that of 16.6 MPa with the LSP-2 sample (6 mm spot, 10 J energy), which is generally consistent with the experimental findings; the model predicts a 16.35% improvement in the resistance of LSP-1 sample to water jet damage, which is comparable to the experimental result of 14.02%; additionally, interactions between micro-jets do not predominate the cavitation erosion process and the final CE effect of the material is mainly due to the accumulation of jet-material interaction.
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This study used electrochemical noise technology to analyse the effects of surface damage induced by cavitation erosion (CE) on the pitting and passivation behaviours of TA31 Ti alloy. According to the results, TA31 Ti alloy exhibited high corrosion resistance in NaCl solutions. However, the residual tensile stress layer generated during grinding and polishing reduced its passivation ability. Subsequently, the residual tensile stress layer was eliminated after CE for 1 h, improving the passivation ability of the material. Thereafter, pitting corrosion was initiated on the material surface. Increasing the CE time from 1 h to 2 h gradually decreased the passivation ability of the alloy. A large number of CE holes promoted the transition from pitting initiation to metastable pitting growth. which gradually dominated the surface of TA31 Ti alloy. The damage mechanism of uniform thinning increased the passivation ability and stability of the alloy with the increase in CE time from 2 h to 6 h. Therefore, the surface of TA31 Ti alloy was dominated by the initiation of pitting corrosion.
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Nickel-based superalloys are frequently used to manufacture the components that operate under cavitation erosion conditions, such as aircraft gas turbine construction, nuclear power systems, steam turbine power plants, and chemical and petrochemical industries. Their poor performance in terms of cavitation erosion leads to a significant reduction in service life. This paper compares four technological treatment methods to improve cavitation erosion resistance. The cavitation erosion experiments were carried out on a vibrating device with piezoceramic crystals in accordance with the prescriptions of the ASTM G32-2016 standard. The maximum depth of surface damage, the erosion rate, and the morphologies of the eroded surfaces during the cavitation erosion tests were characterized. The results indicate that the thermochemical plasma nitriding treatment can reduce mass losses and the erosion rate. The cavitation erosion resistance of the nitrided samples is approximately 2 times higher than that of the remelted TIG surfaces, approximately 2.4 times higher than that of the artificially aged hardened substrate, and 10.6 times higher than that of the solution heat-treated substrate. The improvement in cavitation erosion resistance for Nimonic 80A superalloy is attributed to the finishing of the surface microstructure, graining, and the presence of residual compressive stresses, factors that prevent crack initiation and propagation, thus blocking material removal during cavitation stresses.
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Components made of aluminum alloys operating under cavitation erosion conditions have low performance and therefore a reduced lifetime. The degradation of these components is a consequence of the repetitive implosion of cavitation bubbles adjacent to the solid surface. In this paper, the effect of the rapid re-melting and solidification modification of the surface microstructure of parts of an Al-based alloy strengthened by artificial ageing on the reduction of material loss through cavitation erosion was investigated. The heat source used was the electric arc generated between a tungsten electrode and the workpiece (i.e., TIG). Local surface melting was performed at different values of linear energy (El = 6600-15840 J/cm), varying the current between 100 A and 200 A, at a constant voltage of 10 V. The obtained results showed an increase in the surface microhardness at values of 129-137 HV0.05 and a decrease in the erosion rate from 0.50 µm/min, characteristic of the artificial ageing heat treatment, to 0.10-0.32 µm/min, specific to TIG re-melted layers. For the study of the cavitational erosion mechanism, investigations were carried out by optical microscopy and scanning electron microscopy. The results showed that the improvement of the cavitational erosion resistance by surface melting was a consequence of the increase in microstructural homogeneity and grains refinement.
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The phenomena of cavitation and cavitation erosion affect hydraulic machines, increasing their maintenance costs. Both these phenomena and also the methods of preventing the destruction of materials are presented. The compressive stress in the surface layer created from the implosion of cavitation bubbles depends on the aggressiveness of the cavitation, which in turn depends on the test device and test conditions, and also affects the erosion rate. Comparing the erosion rates of different materials tested using different tests devices, the correlation with material hardness was confirmed. However, no one simple correlation was obtained but rather several were achieved. This indicates that in addition to hardness, cavitation erosion resistance is also affected by other properties, such as ductility, fatigue strength and fracture toughness. Various methods such as plasma nitriding, shot peening, deep rolling and coating deposition used to increase resistance to cavitation erosion by increasing the hardness of the material surface are presented. It is shown that the improvement depends on the substrate, coating material and test conditions, but even using the same materials and test conditions large differences in the improvement can be sometimes gained. Moreover, sometimes a slight change in the manufacturing conditions of the protective layer or coating component can even contribute to a deterioration in resistance compared with the untreated material. Plasma nitriding can improve resistance by even 20 times, but in most cases, the improvement was about two-fold. Shot peening or friction stir processing can improve erosion resistance up to five times. However, such treatment introduces compressive stresses into the surface layer, which reduces corrosion resistance. Testing in a 3.5% NaCl solution showed a deterioration of resistance. Other effective treatments were laser treatment (an improvement from 1.15 times to about 7 times), the deposition of PVD coatings (an improvement of up to 40 times) and HVOF coatings or HVAF coatings (an improvement of up to 6.5 times). It is shown that the ratio of the coating hardness to the hardness of the substrate is also very important, and for a value greater than the threshold value, the improvement in resistance decreases. A thick, hard and brittle coating or alloyed layer may impair the resistance compared to the untreated substrate material.
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Rough surfaces have been widely considered as negative factors affecting cavitation erosion resistance. However, this study presented the opposite result. Here, 316L stainless steel substrates and the arc-sprayed 316L stainless steel coatings were subjected to a specific grinding process that introduced scratches on the surfaces. The surface hardness values of these ground specimens were measured to evaluate the influence of the grinding-induced strain hardening. The cavitation erosion performance of the specimens was evaluated. The results showed that rough surfaces with scratches could enhance the cavitation erosion resistance, particularly at the early stage of cavitation erosion. The scratches had a greater effect on the cavitation erosion resistance of the coatings than on the substrates. Moreover, rough surfaces with initial surface scratches could extend the incubation period of the 316L stainless steel substrates due to the inhibition of the plastic deformation. The SEM observation showed that the scratch structure of the coating surface inhibited the growth of cracks and the propagation of cavitation pits. This study could also serve as a reference for investigating the cavitation erosion behaviors of materials with a particular surface feature.