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The unsteady cavitating flow past a three-dimensional twisted hydrofoil is numerically investigated by a large eddy simulation to obtain in-depth insight into the bubble dynamics near the cavitation erosion region. Macroscopic cavity evolution is captured by a multiphase flow computing frame, while the bubble oscillations in the cavitating flow are computed by solving the Gilmore bubble dynamic model, in which the driving force for the bubble movement is exported through the application of a discrete phase model. The cavitation erosion potential is then computed by a robust indicator developed based on the energy balance hypothesis. The relevance between the dynamics and the destructive essence of a cavitation bubble and the erosion intensity is thoroughly analyzed. The results show that the unsteadiness involved in the turbulent cloud cavitation is well reproduced, and the main cavitation erosion risk in the middle region of the hydrofoil is also accurately predicted comparing with the painting test results. A localized high-pressure region is identified near the rear part of the attached cavity where the mainstream encounters the primary reentrant jet flows. The peak bubble internal pressure can reach 487 MPa near the middle plane of the hydrofoil, during the stage when the surrounding liquid pressure is continuously increased. The bubbles with the smallest radius, ranging from 23.1 to 26.3 μm after compressing from their initial sizes (R0 = 100–700 μm) in the near wall region, are associated with the extremely high internal pressure, and they are responsible for the cavitation erosion damage on the hydrofoil surface. [ABSTRACT FROM AUTHOR]

In the context of constructing high-head hydro-power stations, the Pelton turbine assumes a critical role as the primary energy converter. This study employs the Eulerian–Lagrangian method to simulate the multi-phase flow occurring within the Pelton turbine bucket. Furthermore, it introduces a novel aspect by investigating and comparing the effects of cavitation on erosion within the bucket region under varying conditions of sediment-water, involving different particle sizes and concentrations. The research findings unveiled several key insights. Primarily, cavitation predominantly influences the flow characteristics of particles at the air–liquid interface, while particles with larger sizes tend to concentrate in the center of the jet. Consequently, cavitation's impact on erosion is more pronounced in the case of smaller-sized particles. Moreover, the study revealed that cavitation can either exacerbate erosion under high particle concentration conditions or mitigate it when particle concentration is low. Furthermore, the investigation highlighted variations in the degree of erosion and the affected area of the bucket based on different position angles. Particularly, at a position angle of 65°, the presence of water vapor induced by cavitation alters particle trajectories, thereby modifying the overall erosion pattern of the bucket. These findings collectively contribute to a deeper understanding of the complex interplay between cavitation and erosion within the Pelton turbine bucket. [ABSTRACT FROM AUTHOR]

Part of the gas phase within the bearing emanates from the gaseous lubricating medium generated by the phase transition of the liquid lubricant under low pressure, while the remaining portion originates from the expansion of gases, such as air, present in the lubricant. This study delves into the impact of vapor and gas cavitation on the stability of the rotor-journal bearing system. Utilizing computational fluid dynamics (CFD), a 3D transient lubrication model is developed for the rotor-journal bearing system. This model integrates a combined cavitation approach, encompassing both vaporous and gaseous cavitation phenomena. Based on a new structured dynamic mesh method, the journal orbits are obtained when the journal moves in the rotor-journal bearing system. In vaporous and gaseous cavitation, shear stress and non-condensable gases (NCG) are incorporated successively. Compared with the combined cavitation model, the basic cavitation model journal orbit amplitude is significantly larger than the combined cavitation model. The carrying capacity of journal bearings under the basic cavitation model is overestimated, leading to a more conservative prediction for system stability. [ABSTRACT FROM AUTHOR]

In this work, we investigate the effect of dissolved gas concentration on cavitation inception and cavitation development in a transparent sharp-edged orifice, similar to that previously analyzed by Nurick in the context of liquid injectors. The working liquid is water, and carbon dioxide is employed as a non-condensable dissolved gas. Cavitation inception points are determined for different dissolved gas concentration levels by measuring wall-static pressures just downstream of the orifice contraction and visually observing the onset of a localized (vapor) bubble cloud formation and collapse. Cavitation onset correlates with a plateau in wall-static pressure measurements as a function of a cavitation number. An increase in the amount of dissolved carbon dioxide is found to increase the cavitation number at which the onset of cavitation occurs. The transition from cloud cavitation to extended-sheet or full cavitation along the entire orifice length occurs suddenly and is shifted to higher cavitation numbers with increasing dissolved gas content. Volume flow rate measurements are performed to determine the change in the discharge coefficient with the cavitation number and dissolved gas content for the investigated cases. CFD analyses are carried out based on the cavitation model by Zwart et al. and the model by Yang et al. to account for non-condensable gases. Discharge coefficients obtained from the numerical simulations are in good agreement with experimental values, although they are slightly higher in the cavitating case. The earlier onset of fluid cavitation (i.e., cavitation inception at higher cavitation numbers) with increasing dissolved carbon dioxide content is not predicted using the employed numerical model. [ABSTRACT FROM AUTHOR]

This research discusses an invented and helpful application of the ultrasonic cavitation process to increase the surface roughness of 2205 duplex stainless steel DSS on small scales, which may be desired for special applications. This was achieved by an ultrasonic system corresponding with the ASTM G-32 standard. An invented edit was added to the horn to scan the entire sample surface and generate a homogenous cavitation effect. The cavitation for 60, 90, and 120 second increased the surface roughness about 18, 26, and 22 times, respectively, based on the Three-Dimensional Surface Roughness Profilometer 3DSRP and Scanning Electron Microscopy SEM results. This increase was caused by plastic deformation, which only happens in the cavitation incubation stage. Wavy damages resulting from repeated and multiple collapsing of bubbles were noted using atomic force microscopy AFM. The average values of roughness were about 179, 261, and 221 nm after 60, 90, and 120 sesond of cavitation, respectively, compared with 10.89 nm for the reference sample. Voltage maps on the sample surface using electrostatic force microscopy EFM show the electrostatic force variations according to the surface roughness, where it recorded 3.2, 7.4, and 4.1 Volt after 60, 90, and 120 second of cavitation, respectively, vs 0.033 Volt for the reference sample. It shows a good agreement in the results and means that cavitation is a good tool for increasing the metal's surface roughness for various purposes. [ABSTRACT FROM AUTHOR]

Pulsed laser ablation in liquids (PLAL) is a colloidal synthesis technique attracting significant interest from the scientific community due to the quality of the nanoparticles being produced. In this type of synthesis protocol, the cavitation bubble plays a vital role during the synthesis of nanoparticles. This work studied the effect of the laser beam power on cavitation bubble lifetime. Three different laser beam power values (5.8 W, 7.5 W and 10.5 W) were used to irradiate a pure nickel target in de-ionized (DI) water to synthesize nickel-based nanoparticles. The optimal repetition rate maximizing the production of nanoparticles was determined by atomic emission spectroscopy for each laser beam power. It was determined that the optimal repetition rate increased exponentially with laser beam power, while the cavitation bubble lifetime decreased logarithmically with the laser beam power. Moreover, the effect of the laser beam power on the cavitation bubble lifetime also had an effect on the size distribution of the nanoparticles being produced; the smallest size distribution was obtained at the highest laser beam power. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical, experimental and numerical study of the dynamics of cavitation bubbles inside a droplet suspended in another host fluid. On the theoretical side, we provided a modified Rayleigh collapse time and natural frequency for spherical bubbles in our particular context, characterized by the density ratio between the two liquids and the bubble-to-droplet size ratio. Regarding the experimental aspect, experiments were carried out for laser-induced cavitation bubbles inside oil-in-water (O/W) or water-in-oil (W/O) droplets. Two distinct fluid-mixing mechanisms were unveiled in the two systems, respectively. In the case of O/W droplets, a liquid jet emerges around the end of the bubble collapse phase, effectively penetrating the droplet interface. We offer a detailed analysis of the criteria governing jet penetration, involving the standoff parameter and impact velocity of the bubble jet on the droplet surface. Conversely, in the scenario involving W/O droplets, the bubble traverses the droplet interior, inducing global motion and eventually leading to droplet pinch-off when the local Weber number exceeds a critical value. This phenomenon is elucidated through the equilibrium between interfacial and kinetic energies. Lastly, our boundary integral model faithfully reproduces the essential physics of the non-spherical bubble dynamics observed in the experiments. We conduct a parametric study spanning a wide parameter space to investigate bubble–droplet interactions. The insights from this study could serve as a valuable reference for practical applications in the field of ultrasonic emulsification, pharmacy, etc. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pore opening-induced pore blocking is the mechanism for the limit to LCP. • LCP is described for desorption of condensate from closed cavities with wedge-like opening. • Experimental LCP for carbons at P/P 0 ∼ 0.4 is reproduced in simulations at boiling points. • Experimental LCP for silica at P/P 0 ∼ 0.5 is described correctly in simulations. • LCP is relatively insensitive to the geometrical aspects of the cavity. The limit to the lower closure point (LCP) observed experimentally in the desorption isotherm of gases in porous solids has been commonly attributed to the homogeneous cavitation of the condensate in cavities. It was proposed recently that the experimental limit to LCP could be described in simulations with the ink-bottle pore, provided that the length of the uniformly sized conduit connecting the closed cavity to the surrounding is shorter than 2 nm, and the evaporation is by way of pore blocking mechanism, rather than homogeneous cavitation. To substantiate this assertion, that deviates from the commonly belief of homogeneous cavitation, we further investigated in this paper with cavities having wedge-like pore opening , that better mimics real solids, and offer further explanation on the limit of the LCP to the pore blocking as the mechanism of evaporation with simulations of argon and nitrogen adsorption over a range of temperatures that are commonly used experimentally. It was found that simulation results correctly captured the experimental observations for carbon-based materials and silica-based materials in that the limit of LCP shifts to higher reduced pressures for weaker adsorbing silica, compared to stronger adsorbing carbon and for a given adsorbent it also shifts to higher reduced pressure for higher temperatures. [ABSTRACT FROM AUTHOR]

The surface treatment technology is one of the methods to protect the metal materials from erosion which is one of the most common surface damage of mineral processing equipment. In this paper, ultrasonic surface rolling extrusion (USRE) was used to investigate the effect of the USRE process on the erosion behavior of 304SS. Different USRE passes were conducted on the 304SS samples to characterize the microstructure, micromorphology, phase transition, surface hardness and residual stress, respectively. On this basis, the passivation film of the samples before and after USRE were studied and the erosion mechanism of the USRE samples was explored. The results show that better erosion resistance of the USRE samples can be attributed to phase transformation, grain refinement, strengthened surface hardness. The results of this paper provide a theoretical basis for the design of erosion resistant metal materials. [ABSTRACT FROM AUTHOR]

The proposed method simulates the growth and collapse mechanisms of lasers or sparks cavitation bubbles based on a double-distributed pseudo-potential thermal lattice Boltzmann method, which gives a high-temperature spot equal to or larger than the critical temperature of the fluid. This technique offers valuable insights into both the hydro- and the thermodynamics evolution of near-wall bulk bubbles. Our findings indicate that the dimensionless bubble-wall distance and the maximum radius share a correlative relationship, expressible via a piecewise function. The critical radius required for bubble inception exhibits a direct correlation with surface tension. We also observe a power-law relationship between surface tension and the maximum radius: lower surface tension results in increased deformation and a larger jet volume. The simulation results reveal the significant influence of initial input temperature on the pressure dynamics within the gas nucleus, leading to varied surface expansion velocities. However, this factor only marginally affects the surface wall expansion velocities. An increased input temperature results in intensified collapse mechanisms. Nevertheless, the elevated temperature during the initial collapse may cause an increase in pressure within the remaining bubble components, potentially leading to oscillations in the bubble radius. • A segmental relationship between bubble-wall distance and maximum radius is delineated. • A mathematical relationship, governed by a power-law, between surface tension and maximum radius is elucidated. • An extensive analysis of the influence of initial input temperature on bubble pressure dynamics is presented. • A comprehensive examination of the effect of initial input temperature on surface expansion velocities is conducted. [ABSTRACT FROM AUTHOR]

To improve the high-temperature erosion wear resistance of 304 stainless steel, this study designed and fabricated bionic samples based on the erosion wear resistance characteristics of the desert scorpion body surface. Uniformly distributed ridged bionic units were fabricated on the surface of 304 stainless steel by laser cladding 25% WC-NiCrBSiFe. The experiments were conducted using self-designed high-temperature erosion wear equipment to compare the erosion rates of bionic and untreated samples from room temperature to 1000ºC. The results showed that the erosion rate of the bionic samples was significantly lower than that of the untreated sample at different temperatures. The erosion rate of bionic units slowly increased from room temperature to 1000ºC, showed a decreasing trend at 400–600ºC, and reached a maximum value at 1000ºC, which is 50% of the untreated sample. The bionic unit's wear mechanism mainly includes chiseling, plowing, and removal of the oxide film, as well as hard phases. Subsequently, the mechanisms of the unit on high temperature erosion wear resistance improvement were suggested: (i) the unique microscopic structure of bionic units with alternating distribution of soft and hard phases can weaken the impact of solid particles, the hard phase resists the plastic deformation and the soft phase absorbs impact energy and hinders crack propagation;(ii) the uniformly distributed ridged units can generate air cushion and shielding effects during high temperature erosion, which can weaken the chiseling and plowing effects of solid particles on the surface of bionic samples. [ABSTRACT FROM AUTHOR]

Pistol shrimp generate cavitation bubbles. Cavitation impacts due to bubble collapses are harmful phenomena, as they cause severe damage to hydraulic machinery such as pumps and valves. However, cavitation impacts can be utilized for mechanical surface treatment to improve the fatigue strength of metallic materials, which is called "cavitation peening". Through conventional cavitation peening, cavitation is generated by a submerged water jet, i.e., a cavitating jet or a pulsed laser. The fatigue strength of magnesium alloy when treated by the pulsed laser is larger than that of the jet. In order to drastically increase the processing efficiency of cavitation peening, the mechanism of pistol shrimp (specifically when used to create a cavitation bubble), i.e., Alpheus randalli, was quantitatively investigated. It was found that a pulsed water jet generates a cavitation bubble when a shrimp snaps its claws. Furthermore, two types of cavitation generators were developed, namely, one that uses a pulsed laser and one that uses a piezo actuator, and this was achieved by mimicking a pistol shrimp. The generation of cavitation bubbles was demonstrated by using both types of cavitation generators: the pulsed laser and the piezo actuator. [ABSTRACT FROM AUTHOR]

Thermocavitation, the creation of a vapor bubble by heating a liquid with a continuous-wave laser, has been studied for a wide range of applications. Examples include the development of an actuator for needle-free jet injectors, as the pumping mechanism in microfluidic channels and nanoparticle synthesis. Optimal use in these applications requires control over the bubble dynamics through the laser power and beam radius. However, the influence of the laser beam radius on the bubble characteristics is not fully understood. Here, we present a way to control the beam radius from an optical fiber by changing the distance from the glass–liquid interface. We show that the increase in the beam size results in a longer nucleation time. Numerical simulations of the experiment show that the maximum temperature at nucleation is 237 ± 5 °C and independent of laser parameters. Delayed nucleation for larger beam sizes results in more absorbed energy by the liquid at the nucleation instant. Consequently, a larger beam size results in a faster growing bubble, producing the same effect as reducing the laser power. We conclude that the bubble energy only depends on the amount of absorbed optical energy and it is independent of the beam radius and laser power for any amount of absorbed energy. This effect contrasts with pulsed lasers, where an increase in the beam radius results in a reduction of bubble energy. Our results are of relevance for the use of continuous-wave laser-actuated cavitation in needle-free jet injectors as well as other applications of thermocavitation in microfluidic confinement. [ABSTRACT FROM AUTHOR]

Accurate determination of high strain rate (>103 1/s) constitutive properties of soft materials remains a formidable challenge. Albeit recent advancements among experimental techniques, in particular inertial microcavitation rheometry (IMR), the intrinsic requirement to visualize the bubble cavitation dynamics has limited its application to nominally transparent materials. Here, in an effort to address this challenge and to expand the experimental capability of IMR to optically opaque materials, we investigated whether one could use the acoustic signature of the time interval between the bubble's maximum radius and first collapse time point, characterized as the bubble collapse time, to infer the viscoelastic material properties without being able to image the bubble directly in the tissue. By introducing a modified Rayleigh collapse time for soft materials, which is strongly dependent on the stiffness of the material at hand, we show that, in principle, one can obtain an order of magnitude or better estimate of the viscoelastic material properties of the soft material under investigation. Using a newly developed energy-based theoretical framework, we show that for materials stiffer than 10 kPa the bubble collapse time during a single bubble cavitation event can provide quantitative and meaningful information about the constitutive properties of the material at hand. For very soft materials (i.e., shear modulus less than 10 kPa), our theory shows that unless the collapse time measurement has very high precision and low uncertainties, the material property estimates based on the bubble collapse time only will not be accurate and require visual resolution of the full cavitation kinematics. [ABSTRACT FROM AUTHOR]

This study investigates the influence of viscoelasticity on the collapse of aspherical vapor bubbles near a solid boundary through numerical simulations. A fully compressible three-dimensional finite volume method is employed, incorporating a single-fluid homogeneous mixture cavitation model and the simplified linear Phan-Thien Tanner viscoelastic constitutive model. The collapse dynamics, liquid jetting, shock wave formation, and associated pressure impact are analyzed, and the viscous and viscoelastic stress fields are presented. A comparison of viscoelastic to Newtonian dynamics reveals significant differences in collapse behavior and shock wave formation due to viscoelasticity. Viscoelasticity can induce jet piercing, which is not observed in the Newtonian collapse, and increases vapor re-evaporation after the first collapse. The effect of changing the initial standoff distance is examined for both viscoelastic and Newtonian fluids, where a second jet formation is present only for the viscoelastic collapse, and the second collapse's intensity is increased due to increased vapor production during rebound. Additionally, the variation of elasticity in the viscoelastic case demonstrates a correlation between the amount of vapor produced during rebound and the relaxation time for the investigated cases. [ABSTRACT FROM AUTHOR]

The fluid dynamics of liquid droplet impact on surfaces hold significant relevance to various industrial applications. However, high impact velocities introduce compressible effects, leading to material erosion. A gap in understanding and modeling these effects has motivated this study. We simulated droplet impacts on solid surfaces and proposed a new analytical model for impact pressure and droplet turning line, targeting at predictions for enhanced cavitation. The highly compressed liquid behind the droplet expands sideways, causing lateral jetting. As the droplet encounters a shock wave, it reflects as a rarefaction wave, leading to low-pressure zones within the droplet. These zones converge at the droplet's center, causing cavitation, which, upon collapse, induces another shock wave, contributing to erosion. Using the well-established model for the low-velocity impact shows a significant discrepancy. Hence, an analytical model for the turning line radius is introduced, incorporating the lateral jetting's characteristic length scale. Comparing our model with existing ones, our new model exhibits superior predictive accuracy. [ABSTRACT FROM AUTHOR]

We show numerically that large amplitude, shape deformations imposed on a spherical-cap, incompressible, sessile gas bubble pinned on a rigid wall can produce a sharp, wall-directed jet. For such a bubble filled with a permanent gas, the temporal spectrum for surface-tension-driven, linearized perturbations has been studied recently in D. Ding and J. Bostwick ["Oscillations of a partially wetting bubble," J. Fluid Mech. 945, A24 (2022)]. in the potential flow limit. We reformulate this as an initial-value problem analogous in spirit to classical derivations in the inviscid limit by Kelvin ["Oscillations of a liquid sphere," Math. Phys. Papers 3, 384–386 (1890)], Rayleigh ["On the instability of jets," Proc. London Math. Soc. s1-10, 4–13 (1878)] or by Prosperetti ["Viscous effects on small-amplitude surface waves," Phys. Fluids 19, 195–203 (1976)] and Prosperetti ["Motion of two superposed viscous fluids," Phys. Fluids 24, 1217–1223 (1981)] for the viscous case. The first test of linear theory is reported here by distorting the shape of the pinned, spherical cap employing eigenmodes obtained from linearized theory. These are employed as the initial shape distortion of the bubble in numerical simulations. It is seen that linearized predictions show good agreement with nonlinear simulations at small distortion amplitude producing standing waves, which oscillate at the predicted frequency. Beyond the linear regime as the shape distortions are made sufficiently large, we observe the formation of a dimple followed by a slender, wall-directed jet, analogous to similar jets observed in other geometries from collapsing wave troughs [Farsoiya et al., "Axisymmetric viscous interfacial oscillations–theory and simulations," J. Fluid Mech. 826, 797–818 (2017) and Kayal et al., "Dimples, jets and self-similarity in nonlinear capillary waves," J. Fluid Mech. 951, A26 (2022).] This jet can eject with an instantaneous velocity exceeding nearly 20 times that predicted by linear theory. By projecting the shape of the bubble surface around the time instant of jet ejection, into the eigenspectrum we show that the jet ejection coincides with the nonlinear spreading of energy into a large number of eigenmodes. We further demonstrate that the velocity-field associated with the dimple plays a crucial role in evolving it into a jet and without which, the jet does not form. It is also shown that evolving the bubble shape containing a dimple but zero initial velocity-field everywhere, via linear theory, does not produce the jet. These conclusions accompanied by first principles analysis provide insight into the experimental observations of Prabowo and Ohl ["Surface oscillation and jetting from surface attached acoustic driven bubbles," Ultrason. Sonochem. 18, 431–435 (2011)], where similar jets were reported earlier, albeit via acoustic forcing. Our inferences also complement well-known results of Naude and Ellis ["On the mechanism of cavitation damage by nonhemispherical cavities collapsing in contact with a solid boundary," J. Fluids Eng. 83, 648–656 (1961)] and Plesset and Chapman ["Collapse of an initially spherical vapour cavity in the neighbourhood of a solid boundary," J. Fluid Mech. 47, 283–290 (1971)] demonstrating that wall-directed jets can be generated from volume preserving, shape deformations of a pinned bubble. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) is difficult to machine due to its high hardness and chemical inertness, and surface modification is a key pre-step in chemical mechanical polishing (CMP), SiC single crystal surface modification can promote surface material removal and increase surface flattening rate. To promote SiC surface oxidation efficiency, a green enhanced oxidation method named ultrasonic-assisted plasma electrochemical oxidation (UAPECO) that combines ultrasonic vibration and plasma electrochemical oxidation (PECO) is proposed. Experiments were conducted to evaluate the UAPECO performance and investigate the enhanced oxidation mechanism in UAPECO. The results confirmed that ultrasonic vibration effectively promotes SiC oxidation rate in UAPECO, and the oxidation rate of UAPECO was 24% higher than that of PECO under 200 V oxidation voltage. Combined with physicochemical effect of ultrasonic vibration, the oxidation enhancement mechanisms in UAPECO are that the ultrasonic high-frequency vibration in electrolyte promotes the electrolyte temperature on SiC surface and causes the cavitation effect and acoustic-chemical effect, and the compound effect enhances the oxidation reaction on SiC surface. UAPECO is a promising surface modification technology for SiC single crystal that can greatly improve the polishing efficiency applicable for CMP. [ABSTRACT FROM AUTHOR]

The purpose of this research is to study the possibility of enhancing the multifunctionality of permanent degraded grasslands by overseeding, with special look on economic efficiency. The experience that is the subject of the research was organized in the Research and Development Station for Meadows, Vaslui area, on a Dichanthium ischaemum (L.) Roberty meadow. In the study area there are large areas of permanent meadows, at different stages of degradation, due to the positioning on surfaces with different degrees of inclination, eroded or subject to erosion process, due to abandonment or non-rational use, with an inappropriate load of animals and failure to apply maintenance or improvement measures. Due to these aspects, the production is small and the floral composition is dominated by species with medium and low fodder value. In order to increase the production of permanent grassland in the area, it was considered necessary to apply organic fertilizers, and their effect was compared to that of abandonment, mulching or simple use, and with overseeding measures. Biological material used (a mixture of: 70% Bromus inermis Leyss. + 30% Onobrychis viciifolia Scop. - 30 kg·ha-¹ + 25 kg·ha-1). Total expenses, net income and profitability rate (rate of return) were calculated. The lowest costs were recorded when the biomass was only harvested, no other action being performed. When overseeding and fertilization were overlapping the costs were the highest, the economic efficiency being carried close to zero, but more likely, the effect of fertilization has been greatly diminished due to poor climatic conditions. [ABSTRACT FROM AUTHOR]

The life-limiting fitness for service of high-temperature components is of interest in design, fabrication and later assessments of remaining creep life. Of the associated indicators, strain reflects creep in design and in service, while the discontinuities like creep cavities are targeted in the in-service inspections. Microstructure and hardness can provide supporting information on the material condition. Here, we assess such indicators for the creep-associated damage, particularly at the early stages. Improvements appear possible, e.g. in microscopy to support metallographic inspections and in utilising the widening inspection experience on newer materials. The present work successfully integrated the Wilshire/LCSP creep strain and rupture models with FE analysis for predicting creep strain evolution. Since the model applies for the whole creep curve, it can be used for early stages of creep down to the limit of negligible creep and to the lower limit of the window where creep cavitation damage can be observed. [ABSTRACT FROM AUTHOR]

To investigate the machining effect of ultrasonic honing microjets on a titanium–tantalum alloy surface, a cavitation microjet flow impingement model was established using the smoothed particle hydrodynamics–finite element method (SPH–FEM) coupling method including the effects of wall elastic–plastic deformation, the ultrasonic field and the honing pressure field. Simulation analysis was conducted on a single impact with different initial speeds and a continuous impact at a constant initial speed. The results showed that the initial speed of the microjet needed to reach at least 580 to 610 m/s in order to obtain an obvious effect of the single impact. The single impact had almost no effect at low speeds. However, when the microjet continuously impacted the same position, obvious pits were produced via a cumulative effect. These pits were similar to that obtained by the single impact, and they had the maximum depth at the edge rather than the center. With the increase in the microjet's initial speed, the total number of shocks required to reach the same depth gradually decreases. When the number of impacts is large, with the increase in the number of impacts, the growth rate of the maximum pit depth gradually slows down, and even shows no growth or negative growth at some times. Using the continuous impacts of the microjet by prolonging the processing time can enhance titanium–tantalum alloy machining with ultrasonic honing for material removal. [ABSTRACT FROM AUTHOR]

Corrosion is a persistent challenge in the aviation industry, affecting the safety, performance, and maintenance costs of aircraft. While composite materials have gained widespread use due to their lightweight properties and corrosion resistance, certain critical parts, such as the wing and empennage leading edges and the engine inlet, demand alternative solutions. Aluminum, titanium, and stainless steel emerge as mandatory materials for such components, given their exceptional strength and durability. However, protecting these metallic components from corrosion remains crucial. In this paper, we present a study aimed at evaluating the corrosion resistance of stainless steel, employed as an erosion shielding panel for a composite vehicle's wing, layered with a superhydrophobic coating. The samples with and without coating have been characterized by contact angle measurements, microscopy (optical and electronic), and visual inspection after immersion in two solutions, NaCl and NaOH, respectively. The application of the superhydrophobic coating demonstrated a significant reduction in corrosion extent, especially in the demanding NaCl environment. This was evidenced by diminished formation of ripples and surface roughness, decreased iron oxide formation from oxidative processes, and a lower Surface Free Energy value in both liquid environments. Notably, the surface maintained its superhydrophobic properties even following an 8-day immersion in NaCl and NaOH solutions, demonstrating the reliability of the superhydrophobic coating offering as a potential solution to enhance the longevity and reliability of aircraft structures. [ABSTRACT FROM AUTHOR]

The paper reveals the problem of measuring reactive oxygen (ROS) and nitrogen (RNS) species' concentrations in plasma treated water Milli-Q. We investigate the features of the FOX method for hydrogen peroxide concentration measurement and the Griess method for nitrite ions concentration spectrophotometric measurement using two different ways of an aqueous solution treatment. In the first case, the electrode (non-conducting high-temperature ceramics) was above the aqueous solution and the discharge was in the gas phase. In the second case, the electrodes were fixed around the perimeter inside the cylindrical chamber filled with water, and working gas (air, argon) was injected into interelectrode space. Varying the duration of exposure (2–10 min) leads to changes in the chemical composition and biological activity of the liquid medium, and this approach is effective for proving of the methods in complex liquids. We found the erosion of the electrodes (stainless steel, duralumin) with the injection of argon and air. The erosion can affect reactions of the methods used, as a result, it makes a contribution to measured concentration. For further applications, it is necessary to consider these features to obtain the correct and reproducible results. When plasma exposure occurs with an electrode that is above the surface of the liquid and does not erode, both methods work in the proper way. But when erosion is present ions of eroded materials (iron, aluminum) contribute to the measurement of hydrogen peroxide concentration using the FOX method. A method with xylenol orange is proposed for taking this feature into account by measuring the concentration of metal ions. In the Griess assay it is possible to obtain strongly erroneous results due to visually similar color and close values of absorbance at the chosen wavelength (525 nm) for both low concentration of nitrites (within linear part of the calibration curve) of nitrites and high concentration (far beyond linear part of the calibration curve). In our research concentration of nitrites does drastically change in the experiment after changing material of the electrodes from stainless steel to duralumin. The Griess assay leads to the formation of a stable fluorescent complex when erosion of the metal electrodes is present. [ABSTRACT FROM AUTHOR]

This paper reports the microstructure and corrosion behavior of a Nb-containing stainless steel surfacing layer prepared by tungsten inert gas (TIG) powder surfacing. The focus was to achieve a clear understanding of the relationships between the Nb-addition and cavitation erosion behavior. In order to eliminate the microstructure inhomogeneity of as-welded samples, solution heat treatment was carried out. It is considered to set the heat treatment temperature at 1150 °C and 1250 °C to minimize the precipitation phase. Results showed that due to the Nb addition the as-welded 22Cr9Ni3MoNb surfacing layer had higher hardness, a lower pitting potential, and better cavitation erosion resistance. Because of the existence of a great quantity of precipitates, heat treatment at 1250 °C had an adverse effect on the mechanical properties and cavitation erosion resistance of surfacing layer samples. [ABSTRACT FROM AUTHOR]

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Applying a focused ultrasonic field on a free liquid surface results in its growth eventually leading to the so-called acoustic fountain. In this work, a numerical approach is presented to further increase the understanding of the acoustic fountain phenomenon. The developed simulation method enables the prediction of the free surface motion and the dynamic acoustic field in the moving liquid. The dynamic system is a balance between inertia, surface tension and the acoustic radiation force, and its nonlinearity is demonstrated by studying the relation between the ultrasonic excitation amplitude and corresponding liquid deformation. We show that dynamic resonance is the main mechanism causing the specific acoustic fountain shapes, and the analysis of the dynamic acoustic pressure allows us to predict Faraday-instability atomisation. We show that strong resonance peaks cause atomisation bursts and strong transient deformations corresponding to previously reported experimental observations. The quantitative prediction of the dynamic acoustic pressure enables us to assess the potential of cavitation generation in acoustic fountains. The observed local high acoustic pressures above both the cavitation and the atomisation threshold hint at the coexistence of these two phenomena in acoustic fountains. [ABSTRACT FROM AUTHOR]

Nowadays, naval propellers are made in Ni-Al or Mn-Al bronzes, which are affected by high cavitation erosion. In this study, the possibility of adopting 6xxx alloy with different superficial treatments obtained through fluidised beds and laser surface texturing was investigated. 6xxx alloy series is known for its versatility due to an excellent mix of mechanical and physical properties, combined with ease of processing, welding, and good chemical resistance; however, its main drawback is low resistance to cavitation erosion. In this study, a total of 4 different surface treatments were produced and characterized such as fluidised bed coatings (Al2O3, S280) and laser textured samples (0–30% overlap). Moreover, the effect of a heat-treatment was evaluated for each kind of specimen analysed. The study was divided into two steps: in the first phase, the samples were morphologically and mechanically characterised through roughness measurements, micro-hardness, scratch, wear, and wettability tests. Successively, a modified ASTM-G32-10 standard was adopted to assess the cavitation erosion resistance; in particular, for each sample, mass and volume loss were analysed and compared to the as-built sample. Results showed a drastic reduction of the wear evaluated through pin-on-disk tests with the application of the high hardness coatings (Al2O3, S280) while a reduction of the cavitation erosion volume of about 20% lower was obtained through the best laser texturing treatment. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced aluminum matrix composites (C f /Al) are widely used in various industries. But they are difficult to join because it is hard to realize the wetting and continuity of the carbon fiber in joint. To solve this problem, C f /Al are joined by ultrasonic soldering in this work. Results show that the C f /Al can be wetted within 5 s under ultrasonic. Transmission electron microscope result shows that the surface of the wetted carbon fiber is covered by an amorphous-nanocrystalline layer, which is formed due to the high solder velocity, temperature and pressure caused by cavitation. Carbon fibers flow into the solder after the Al matrix is eroded, guaranteeing its continuity in the joint. Limited carbon fibers flow into the joint at low ultrasonic power of 333.3 W, while a fully carbon fiber reinforced composite joint is obtained at 1000 W. The soldered joints have higher strength than the C f /Al substrate, and its formation mechanism is discussed. [ABSTRACT FROM AUTHOR]

A spiral axial-flow blade pump (SABP) is an indispensable device in the closed gathering and transporting technology of oil and natural gas exploitation; it can not only transport a gas–liquid mixture with a high gas content, but also transport a gas–liquid–solid mixture containing a small amount of sand. However, due to the large vortices that often appear in the flow channel of the SABP, cavitation is induced extremely easily. This paper presents a numeric calculation of the cavitation performance of an SABP to reveal the law governing the impact of cavitation on its internal flow. The impact of tip clearance with different sizes on the dynamic and static head of the SABP was analyzed, and the change rules of the absolute velocity, relative velocity, and dynamic and static head were revealed under different cavitation stages, too. [ABSTRACT FROM AUTHOR]

The comparative study of as-rolled untreated and solution-treated 23-8N nitronic steel was studied. The results obtained from mechanical characterization revealed that the solution-treated nitronic steel specimens have shown higher toughness and ductility with marginal reduction in hardness as compared to as-rolled untreated nitronic steel specimens. The erosion behavior with surface characterizations of nitronic steel specimen has been evaluated by air jet and slurry jet erosion test rig at four different impingement angles (15°, 45°, 60°, and 90°) and (30°, 45°, 60°, and 90°), respectively. It is observed that the air jet and slurry jet erosion rate for untreated and solution-treated specimens, decreases as the impingement angle increases. The potentiodynamic polarization test in 3.5 wt.% NaCl aqueous solution has been conducted to evaluate the corrosion rate of specimens. The as-rolled solution-treated steel exhibits better corrosion resistance as compared to untreated steel. The surface characterization of eroded specimens was analyzed using scanning electron microscope and possible erosion mechanisms have been studied on untreated and solution-treated specimens. [ABSTRACT FROM AUTHOR]

The static and dynamic corrosion of TiAl-Nb coating in molten zinc could be divided into incubation period and rapid corrosion period. It has a long incubation period during which no corrosion occurs in molten zinc. After the incubation period, the corrosion occurs rapidly and rapid corrosion period is controlled by reaction–diffusion and dissolution mechanisms. The lifetime of TiAl-Nb coating primarily depends on the incubation period, which is not available for other materials. This type of corrosion has not been reported in other literature; we first refer to it as "incubation style" corrosion. The lifetime of TiAl-Nb coating in static corrosion was 41 days, and the lifetime was prolonged in dynamic corrosion. Compared with the static corrosion, the contact probability between the flowing molten zinc and the coating was reduced, the molten zinc was difficult to wet the coating, and the incubation period of dynamic corrosion was prolonged. After the incubation period, the mechanical scouring effect of flowing molten zinc accelerated the loss of corrosion product and spalled TiAl-Nb splats, which shortened the rapid corrosion period. As the erosion speed increased from 100 to 500 r/min, the micromechanical scouring effect of flowing molten zinc was intensified, the incubation period was increased by 27%, and the rapid corrosion period was shortened by 25%. [ABSTRACT FROM AUTHOR]

This study focuses on the additive manufacturing technique of selective laser melting (SLM) to produce Ti-6Al-4V-Zn titanium alloy. The addition of zinc at 0.3 wt.% was investigated to improve the strength and ductility of SLM Ti-6Al-4V alloys. The microstructure and mechanical properties were analyzed using different vacuum heat treatment processes, with the 800-4-FC specimen exhibiting the most favorable overall mechanical properties. Additionally, zinc serves as a stabilizing element for the β phase, enhancing the resistance to particle erosion and corrosion impedance of Ti-6Al-4V-Zn alloy. Furthermore, the incorporation of trace amounts of Zn imparts improved impact toughness and stabilized high-temperature tensile mechanical properties to SLM Ti-6Al-4V-Zn alloy. The data obtained serve as valuable references for the application of SLM-64Ti. [ABSTRACT FROM AUTHOR]

Precessing vortex rope (PVR) plays a key role in inducing hydraulic resonance in Francis turbines operating at partial load, possibly degrading power plant stability and availability. Air injection into the runner cone is a suitable mitigating alternative; however, the influence mechanism of air injection on PVR remains unclear. The principal objective of this study was to establish response relationships between the characteristic parameters and air injection by the method of computational fluid dynamics (CFD) considering the fluid components of water, water vapour and air. The findings show that cavitation flow can be completely suppressed by slight air injection; however, the helical vortex structures are persisted at 1.0% and 2.0% air volume fractions, and the static pressure recovery is improved together with a slight increase in the hydraulic loss. At 3.0% air volume fraction, the vortex structure completely disappears, leaving an umbrella-shaped structure, with no pressure vibration arising in the turbine. Moreover, the physical mechanism of reducing the pressure amplitudes is clarified. This results clarify the influence mechanism of air injection on PVR, and contribute to steadily extending the flexibility of the operating range of the turbine during the engineering application. [ABSTRACT FROM AUTHOR]

Pneumatic drive bellows pumps (PDBPs) are a crucial fluid control component in the semiconductor industry. However, when dealing with specific chemical mechanical polishing (CMP) slurries, agglomeration of particles can occur, leading to scratches, particle residues, pits, and other defects on the wafer surface. The leading cause of agglomeration has been proposed to be cavitation and excessive shear in PDBPs. A high-fidelity multiphase computational fluid dynamics (CFD) model, which fully resolves the response of check valves under hydrodynamic and other external loads, was established to evaluate cavitation behaviour and shear distribution in PDBPs. Moreover, a test rig was built to visualize cavitating flow patterns in PDBPs and verify the accuracy of the CFD model. Among different cavitation regions captured by high-speed visualization, the region near the inner leading edge of the end-ring of the inlet valve is dominant, with high intensity, long duration, and complex morphology evolution. Detailed initiation and development process of cavities in the dominant region are analysed numerically. The shear rate in different domains of PDBPs is estimated, and the inlet valve domain stands out from the other. The strongest shear rate is observed near the leading edge of the end-ring. Furthermore, an analysis of the relationship between cavitation and shear indicates that the high-intensity vortices generated owing to strong shear account for the inception of cavitation. This study contributes to understanding inner flow details in PDBPs and provides a guideline for further optimization of similar pumps. [ABSTRACT FROM AUTHOR]

Castolin Eutectic, a company based in Belgium, has introduced a new thermal spraying service called XupersoniClad. This service utilizes supersonic spraying technology to provide enhanced protection against abrasion, erosion, and wear for components, vessels, and structures. XupersoniClad offers unique advantages in the European market and can be applied to various industries, including recycling, concrete production, and vessel interiors. The service also includes the ability to apply coatings to the internal diameter of pipes and utilizes a faster and more energy-efficient surface preparation method. [Extracted from the article]

Bubble dynamics near a rigid boundary at Reynolds numbers of O(10–100) exhibit significant viscous effect, associated with ultrasonic cavitation and cavitation damage. We study this phenomenon experimentally using high-speed photography of spark-generated bubble oscillation in silicone oils, whose viscosity is about three orders larger than water. Comparing to bubbles in water, bubble surfaces in silicone oil are more stable and thus more cycles of oscillations may be observed and studied. Additionally, we investigate this phenomenon numerically using the volume of fluid method. We propose a non-reflective boundary condition, reducing the computational domain's dimensions tenfold based on the far-field asymptotic behavior. This paper pays particular attention in the mechanism for the bubble jetting, the vortex sheet, and the vortex ring development. Initially, a stagnation point at the bubble center moves away from the wall owing to asymmetric bubble expansion, leaving the bubble around the moment the bubble reaches its maximum volume. During this process, a vortex sheet forms inside the bubble. As the vortex sheet approaches the bubble interface, it transfers momentum to the gas–liquid interface, influencing the flow near the bubble wall. The high-pressure zone at the stagnation point drives the distal bubble surface to collapse first and fastest subsequently. This asymmetric collapse generates circulation around the bubble's side cross section, leading to the development of a vortex ring within the bubble gas at the outer rim of the decaying vortex sheet. The vortex ring, with its core inside the bubble gas, functions like a bearing system in accelerating the jet. [ABSTRACT FROM AUTHOR]

Dispersed vapor bubbles are the dominant rheology in cloud cavitation, and their size distribution is directly associated with cavitation noise and erosion. However, the numerical resolution of large numbers of dispersed bubbles remains a challenge. In this work, we establish a new cavitation model based on the population balance equation (PBE) that can predict the size distribution and spatiotemporal evolution of bubbles within cloud cavitation under different cavitation numbers. An expression for the phase transition source term without empirical parameters is derived based on the bubble size distribution (BSD) function, enabling the coupling of mass transfer in the governing equations with the PBE cavitation model. The cavitation model is solved alongside the Eulerian homogeneous mixture flow. The mass transfer between water and vapor, and the bubble coalescence and breakup under turbulent flows, are modeled to determine the BSD. The numerical model is carefully validated through comparisons with experimental results for cavitation flows on a wedge-shaped flat plate, and good agreement is achieved with respect to the pressure distribution, void fraction, and BSD. This confirms that our proposed cavitation model can accurately predict the void fraction and BSD within the cloud cavitation region. [ABSTRACT FROM AUTHOR]

Building a chute aerator is an efficient way of protecting the chute bottom from cavitation damage in large flood-discharging hydraulic structures, but it sometimes fails to provide sufficient protection to the side-walls. In this study, basic air–water flow properties were investigated for discharge flows over an offset chute aerator model, with particular focus on the near-bottom and near-wall regions, for a range of discharge velocities over the offset brink (3.58 m/s < V < 8.02 m/s), Froude numbers (4.8 < Fr < 12.0) and Reynolds numbers (8.0 × 104 < Re < 9.2 × 105). The results indicated little transverse variations in air–water flow properties except near the jet impact perimeter. The bottom air concentration and bubble frequency decreased at different rates downstream of the impact point; the influence of Reynolds number on the bubble size and density should not be ignored. The shape of the clear-water core between the upper and lower aeration layers was identified with the aid of high-speed imaging and air concentration calibration against the wall. A formula to predict narrowing of the jet core until its end position was developed. [ABSTRACT FROM AUTHOR]

Cavitation erosion and corrosion-cavitation synergism behavior of CoCrFeNiMnTix (x = 0.5, 1.0, 1.5, 2.0 in atomic ratio) high entropy alloy coatings were analyzed. The sample with x = 1.0 showed the best cavitation erosion resistance due to the low weight loss and the maximum erosion rate. The protective ability of passivation film also displayed an increased first and then decreased tendency with the increase of Ti content as indicated by corrosion-cavitation synergism determined by open circuit potential method under cavitation erosion and quiescence condition. The sample with x = 1.0 displayed good re-passivation ability of passivation film according to open circuit potential behavior under cavitation erosion and quiescence condition. In general, the sample with x = 1.0 exhibited the highest cavitation erosion, the best self-repairing ability of the passivation film under the corrosion-cavitation synergism condition, which showed a great potential in the application of ocean engineering field as fluid-passing parts. [ABSTRACT FROM AUTHOR]

In order to alleviate the impact of environmental erosion on the properties of concrete, this experiment modified high-strength concrete with polyvinyl alcohol (PVA) fiber and studied its salt corrosion resistance. The test results show that with the progress of the salt corrosion test, the compressive strength of all specimens increases first and then decreases. Among them, the initial compressive strength of concrete with 0.2% and 0.3% PVA content is 50.6 MPa and 47.5 MPa, respectively, which is 11.9% and 5.1% higher than that of the benchmark specimen. The maximum compressive strength of the test specimen with 0.2% PVA content reaches 52.7 MPa, which is 25.8% higher than that of the benchmark test. The relative mass of each specimens first decreases and then fluctuates, and the 0.2% PVA specimen is the most stable. The relative dynamic elastic modulus of each specimen first increases significantly and then fluctuates up and down. The optimum volume content of polyvinyl alcohol fiber is 0.2%, which can improve the compressive strength of concrete, reduce mass loss and increase dynamic elastic modulus. At this time, the salt corrosion resistance of concrete material is the best. [ABSTRACT FROM AUTHOR]

Plastic packaging has shown its advantages over ceramic packaging and metal packaging in lightweight, thin, and high-density electronic devices. In this paper, the reliability and moisture diffusion of Sop-8 (Small Out-Line Package-8) plastic packaging devices are studied, and we put forward a set of complete optimization methods. Firstly, we propose to improve the reliability of plastic packaging devices by reducing the amount of cavitation and warpage deformation. Structural and process factors were investigated in the injection molding process. An orthogonal experiment design was used to create 25 groups of simulation experiments, and Moldflow software was used to simulate the flow mode analysis. Then, the simulation results are subjected to range analysis and comprehensive weighted score analysis. Finally, different optimization methods are proposed according to different production conditions, and each optimization method can reduce cavitation or warpage by more than 9%. The moisture diffusion of the Sop-8 plastic packing devices was also investigated at the same time. It was determined that the contact surface between the lead frame and the plastic packaging material was more likely to exhibit delamination under the condition of MSL2 moisture diffusion because the humidity gradient was easily produced at the crucial points of different materials. The diffusion of moisture is related to the type of plastic packaging material and the diffusion path. [ABSTRACT FROM AUTHOR]

Earlier studies have shown that 30 L steel, used for the manufacture of hydraulic machinery equipment elements, has greater resistance to cavitation wear than 20 GL steel. This paper presents the results of experimental studies of the solid particle erosion resistance of 30 L structural steel samples with different surface modifications based on nitriding and boriding processes. The characteristics of the modified near-surface layers were determined. The results of the solid particle erosion resistance tests carried out according to the ASTM G76-13 standard are presented. The research results demonstrated that boriding processes worsen the solid particle erosion resistance of 30 L steel at flow impact angles of 30° and 90°. All the considered variants of surface nitriding at an impact angle of 90° do not worsen the solid particle erosion resistance of 30 L steel samples, while at an impact angle of 30°, they increase the solid particle erosion resistance by at least 10–20%. [ABSTRACT FROM AUTHOR]

In this study, TiN/Ti coatings with various modulation ratios (TiN/Ti-4:1, TiN/Ti-1:1, and TiN/Ti-1:4) were deposited on 2A70 aluminum to improve its sand erosion performance. The structural design of ion implantation + high thickness Ti transition layer + TiN/Ti coatings was applied to alleviate the differences in physical properties between hard nitride coatings and 2A70 aluminum. Surface roughness, XRD, elastic modulus, hardness, and the sand erosion failure mechanism of each coating were evaluated. The hardness of TiN/Ti-4:1, TiN/Ti-1:1, and TiN/Ti-1:4 on aluminum was 26.99 GPa, 21.70 GPa, and 10.99 GPa. Sand erosion test results showed that TiN/Ti-1:1 had the highest erosion rates due to its rougher surface. Under a 90° incident angle, TiN/Ti-4:1 and TiN/Ti-1:4 both exhibited vertical cracks parallel to the coating growth direction in the bottom TiN layer at the initial erosion stage. Also, a lateral crack caused by TiN layer crack deflection emerged due to a higher crack resistance in the thicker Ti layer of TiN/Ti-1:4. Furthermore, in comparison with the layer-by-layer spalling failure behavior of TiN/Ti-1:4, overall spallation induced by the crack coalescence of the TiN layer was exhibited in TiN/Ti-4:1. In addition, cracks formed and intersected in the inner TiN layer in TiN/Ti-1:1 and TiN/Ti-4:1, resulting in layer-by-layer spallation under a 45° incident angle. [ABSTRACT FROM AUTHOR]

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.

Herein, cavitation erosion tests were carried out on 2205 and 2507 duplex stainless steels (DSSs) in distilled water and artificial seawater using ultrasonic cavitation erosion equipment. Optical microscope (OM), X-ray diffractometer (XRD), and scanning electron microscope (SEM) were used to observe the microstructure and cavitation erosion morphology of the specimens. Cavitation erosion and corrosion behaviors of the specimens were analyzed and the synergistic effect between cavitation erosion and corrosion in artificial seawater was also examined. The results show that the cavitation erosion resistance of 2507 DSS is better than that of 2205 DSS in all kinds of solutions. The destruction occurs first in ferrite due to its lower plasticity. The synergistic effect of cavitation erosion and corrosion accelerates the destruction of the material, and the mass loss caused by cavitation erosion-corrosion synergy for 2205 DSS is higher than that of 2507 DSS.

During operation， hydraulic turbines are continuously subjected to long-term impact from sediment-laden water flows.The combined damage from sediment erosion and cavitationerosion significantly impairs the flow components，compromising the safe and stable operation of the unit.Surface protection of the flow components by means of high-elastic polymer coatings is an economical and practical strategy.In this paper，firstly， the anti-cavitation protective polymer coatings on the surfaces of flow components were reviewed， especially research progress on polyurethane and epoxy resin coatings.Considering the important influence of the erosive and abrasive effects of sediment-laden water flows in the damage of hydraulic turbines，the research progress of polymer/ceramic composite coatings in the synergistic resistance to cavitation and erosion was reviewed； finally， the problems of polymer coatings in the protection of hydraulic turbine flow components were described.

Different from additive manufacturing and subtractive manufacturing, iso-material manufacturing (also named isovolumetric manufacturing) is applied to 304 stainless steel (304SS) by laser surface melting (LSM) at four energy density (51 J/mm2, 44 J/mm2, 39 J/mm2, 37 J/mm2), aiming at improving the resistance to corrosion and cavitation erosion without any addition of precious metals. The experimental results show that the microstructure presents the transformation from plane crystal → columnar crystal → equiaxed crystal from interface to top surface. All the samples exhibit austenite+martensite+Cr23C6, and the martensite content is increased from 9.3% to 40.8% with the energy density decreasing after iso-material manufacturing. In addition, low angle grain boundary is increased, and nano-mechanical properties also show an increasing trend. The decreasing of energy density also enhances the residual tensile stress of the melting layer. The sample obtained at energy density of 51 J/mm2 displays the highest corrosion resistance in 3.5 wt% NaCl solution, which can be attributed to its low galvanic corrosion degree and small residual tensile stress. The sample obtained at energy density of 39 J/mm2 exhibits the highest cavitation erosion resistance (Re) and its passivation film displays better self-repairing and re-passivation ability as indicated by synergistic cavitation erosion-corrosion behavior. The high cavitation erosion resistance can be attributed to the proper compromise of the constituent phases and higher self-repairing of the passivation film for the melting layer. Moreover, the 304 stainless steel prepared in this study exhibits a high or comparable corrosion and cavitation erosion resistance in comparison with the samples prepared by other fabrication method reported previously.