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•Stress-induced phase transformation was observed in 304 SS during cavitation erosion.•A possible exacerbation mechanism of corrosion on cavitation erosion was suggested.•Cavitation ...erosion did not start at the pre-existing pores (formed during casting).•The evolution of cavitation erosion crack was studied via in-situ SEM observation.
This study investigated the effect of stress on the microstructure evolution of austenitic stainless steels (316L SS and 304 SS) subjected to cavitation erosion and cavitation erosion-corrosion. Results show that continuous accumulation of stress of austenitic stainless steels at the early stage of cavitation erosion was observed from the samples tested in deionised water (DIW) but not in artificial seawater (ASW), which is due to stress release induced by ASW. In addition, a stress-induced phase transformation from austenite to martensite during the cavitation erosion tests in both DIW and ASW was observed in 304 SS, but not in 316 SS. Furthermore, primary cavitation craters formed during the cavitation erosion were not expanded directly but shrank first and then expanded due to re-accumulation of stress. More importantly, this study reports for the first time that pre-existing pores are not initiation points of cavitation erosion damage, possibly because of the ductility of austenitic stainless steels, which resulted in continuous shrinkage of the pores caused by the accumulated stress. Our findings provide new insights into understanding the failure mechanisms of austenitic stainless steels subjected to cavitation erosion, which will inform the development of high-performance cavitation erosion-resistant materials.
Yttria-stabilized zirconia (YSZ) and TiO2- doped YSZ (TiYSZ) coatings were prepared using Atmospheric Plasma Spraying (APS) at different power levels to protect of flow passage components from ...cavitation erosion. We analyzed, the effects of TiO2 doping and spraying power on the coatings' phase structure, microstructure and mechanical properties using XRD, Raman spectroscopy, SEM, Vickers hardness and nano-indentation. We tested the cavitation erosion behavior of TiYSZ coatings and YSZ coatings (as a reference) in a laboratory setting employing vibration-induced cavitation in accordance with ASTM standard G32-16. The results showed that the YSZ coating contained 50% c-phase and 50% t-phase, while the TiYSZ coating contained approximately 78 % c-phase. Spraying power hadlittle effect on the phase structure of either coating. However, higher spraying power increased the density of the coating, leading to greater microhardness. TiYSZ coatings were denser than YSZ at any power level and did not exhibit a distinct microcolumnar grain structure, unlike YSZ. Additionally, TiYSZ coatings displayed better mechanical properties, including higher hardness, elastic modulus, toughness, and fracture strength compared to YSZ. As a result, the cavitation resistance of TiYSZ coatings improved by about 50% compared to YSZ. Furhermore, we found that chemical degradation of YSZ-based ceramics under cavitation erosion conditions plays a role in cavitation erosion. We also observed that cavitation-induced amorphization is a key mechanism contributing to this degradation.
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•A spatially confined cavitation with sonoluminescence (SL) was taken to study the erosion resistance of metals.•The erosion effect is intensified with deeper pit depth and appearance ...of melting effect under high hydrostatic pressure.•A method for evaluating materials’ erosion resistance with measurable SL intensity was established.•This work is benefit to predict and avoid the cavitation erosion in deep-sea applications.
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.
•Cavitation erosion-corrosion behavior of Al0.1CoCrFeNi HEA is investigated.•Al0.1CoCrFeNi HEA showed 1/9th erosion rates compared to SS316L steel.•Al0.1CoCrFeNi HEA showed 1/4th erosion-corrosion ...rates compared to SS316L steel.•Compared to SS316L, passive layer stability was higher for the HEA.•Better performance of HEA due to high work hardening and corrosion resistance.
Cavitation erosion and corrosion of structural materials are serious concerns for marine and offshore industries. Durability and performance of marine components are severely impaired due to degradation from erosion and corrosion. Utilization of advanced structural materials can play a vital role in limiting such degradation. High entropy alloys (HEAs) are a relatively new class of advanced structural materials with exceptional properties. In the present work, we report on the cavitation erosion behavior of Al0.1CoCrFeNi HEA in two different media: distilled water with and without 3.5wt% NaCl. For comparison, conventionally used stainless steel SS316L was also evaluated in identical test conditions. Despite lower hardness and yield strength, the HEA showed significantly longer incubation period and lower erosion-corrosion rate (nearly 1/4th) compared to SS316L steel. Enhanced erosion resistance of HEA was attributed to its high work-hardening behavior and stable passivation film on the surface. The Al0.1CoCrFeNi HEA showed lower corrosion current density, high pitting resistance and protection potential compared to SS316L steel. Further, HEA showed no evidence of intergranular corrosion likely due to the absence of secondary precipitates. Although, the degradation mechanisms (formation of pits and fatigue cracks) were similar for both the materials, the damage severity was found to be much higher for SS316L steel compared to HEA.
This study aims to investigate the correlation between flow velocity and cavitation erosion (CE) characteristics of high-velocity oxygen-fuel (HVOF) sprayed Cr3C2-NiCr (CN) and WC-Cr3C2-Ni (WCN) ...coatings in 3.5 wt% NaCl medium, except for the microstructures, mechanical properties and electrochemical behaviors. In comparison with the CN coating, the WCN coating shows higher values of elastic modulus (E), hardness (H), H/E and H3/E2 as well as lower porosity, resulting in lower volume loss rate (VLR) and enhanced CE resistance in NaCl medium at each value of flow velocity. The VLR values of both coatings increase as the flow velocity increases. The change of the CE progresses in NaCl medium of the CN coating is the formation of cavitation pinholes, pits, craters and oxidation films coupled with the exfoliation of chromium carbide particles when the flow velocity is 23.4 and 33.5 m s−1 as well as the brittle fracture structure with layers delamination accompanied by the oxidation films when the flow velocity is 41.9 m s−1. In a wide flow velocity range, the formation of cavitation pinholes, pits and micro-cracks along with the oxidation films are addressed as the dominant CE mechanism in NaCl medium of the WCN coating.
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.
The objective of the present study is to investigate by model tests the erosion caused by blade root cavitation for a set of three marine propellers. Experiments have been carried out using soft ...paint technique together with cavitation observations in the UNIGE cavitation tunnel. Three standard cameras and one high speed camera have been used to observe the damage patterns and cavitation dynamics, respectively. Standard cameras are fixed on the top of test section to continuously monitor the effect of erosion damage on the blade root, the high-speed camera has been placed at different positions to investigate detailed evolution and collapse of bubbles on pressure and suction side of propeller blades. Soft paint results showing damages pattern have been analysed simultaneously with the high speed videos, and showed remarkable agreement between the occurrence of damage on the blades and the bubble collapse of cavitation. The proposed methodology allows comparing different propellers in terms of cavitation aggressiveness. The comparison of these results with full-scale data provides useful indications to propeller designers when root cavitation cannot be avoided.
•Cavitation dynamics of three different model scale propellers working in inclined shaft configuration.•Soft paint tests to study the damage patterns on suction and pressure side of propeller blades.•Experiments are carried out using three standard cameras and one high speed camera simultaneously to correlate the damage patterns and cavities dynamics.•Results exhibited remarkable agreement between the occurrence of damage on the blades and the bubble collapse of cavitation.
To combat cavitation erosion-corrosion damage inflicted upon mechanical components in marine applications, NbC nanocrystalline coatings were synthesized by a double cathode glow discharge assisted ...reactive sputtering method. The coating comprised equiaxed B1-NaCl-type NbC grains with an average grain size of ~10 nm and a strong NbC (200)-oriented texture by TEM observation. The electrochemical response of the coating exposed to a 3.5 wt% NaCl solution with and without the influence of cavitation was monitored by electrochemical noise (EN) measurements, in addition to open circuit potential and cyclic polarization. To differentiate the cavitation erosion-corrosion resistance between the NbC coating and a reference Ti-6Al-4V alloy substrate, the EN data were further evaluated, based on a series of analyses, including frequency domain, time-domain, shot noise and wavelet transform. For the Ti-6Al-4V alloy, with increasing output power, the noise resistance (Rn) and slope (k values) of potential and current power spectral density (PSD) decreased, and the average charge in each corrosion event (q) and the total energy of d series crystals increased markedly at the output power levels above 400 W, indicative of a high propensity of pitting corrosion for this alloy. Conversely, the Rn and k values for the NbC coating were found to be almost independent of the output power, and the charge of the corrosion event and the total energy of the d series crystals were much lower than that of the Ti-6Al-4V alloy. The findings garnered from analyzing the EN signals is in accord with what were uncovered from examining the eroded surface morphologies, suggesting that the EN method might offer a reliable and effective tool to probe the cavitation erosion-corrosion behavior in developing durable material.
•The coating increases H/E value and elastoplasticity of uncoated Ti-6Al-4V.•No hysteresis loop appears on cyclic polarization curves for the NbC coating.•The coating increases the noise resistance of bare Ti-6Al-4V by an order of magnitude.•The k values of all the PSD plots for the coating are lower than −20 dB/decade.•The total energy of the d series crystals for the coating is 2 orders of magnitude lower than that for bare Ti-6Al-4V.
We numerically investigate the erosion potential of a cavitating liquid jet by means of high-resolution finite volume simulations. As thermodynamic model, we employ a barotropic equilibrium ...cavitation approach, embedded into a homogeneous mixture model. To resolve the effects of collapsing vapor structures and to estimate the erosion potential, full compressibility is considered. Two different operating points featuring different cavitation intensities are investigated and their erosion potential is estimated and compared. Different methods are used for this purpose, including collapse detection (Mihatsch et al., 2015), maximum pressure distribution on the wall, and a new method of generating numerical pit equivalents. The data of numerical pit equivalents is analyzed in detail and compared with experimental data from the literature. Furthermore, a comprehensive grid study for both operating points is presented.
•Numerical assessment of cavitation erosion.•Fully compressible simulations.•High-resolution simulations of a cavitating liquid jet.•Numerical counterparts to experimental erosion pits.•Detailed data on erosion pit formation.
•An intensified collapse by self-focusing of shockwaves emitted during the collapse is proposed as main mechanism of cavitation erosion of hard materials.•Cavitation erosion occurs only for bubble ...collapses at close stand-off below γ≲0.2 where the self-focusing mechanism develops.•Jetting mitigates cavitation erosion.•Conditions to enhance the energy focusing and collapse intensity are presented.
The ability of cavitation bubbles to effectively focus energy is made responsible for cavitation erosion, traumatic brain injury, and even for catalyse chemical reactions. Yet, the mechanism through which material is eroded remains vague, and the extremely fast and localized dynamics that lead to material damage has not been resolved. Here, we reveal the decisive mechanism that leads to energy focusing during the non-spherical collapse of cavitation bubbles and eventually results to the erosion of hardened metals. We show that a single cavitation bubble at ambient pressure close to a metal surface causes erosion only if a non-axisymmetric energy self-focusing is at play. The bubble during its collapse emits shockwaves that under certain conditions converge to a single point where the remaining gas phase is driven to a shockwave-intensified collapse. We resolve the conditions under which this self-focusing enhances the collapse and damages the solid. High-speed imaging of bubble and shock wave dynamics at sub-picosecond exposure times is correlated to the shockwaves recorded with large bandwidth hydrophones. The material damage from several metallic materials is detected in situ and quantified ex-situ via scanning electron microscopy and confocal profilometry. With this knowledge, approaches to mitigate cavitation erosion or to even enhance the energy focusing are within reach.
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