Effect of separation distance on cavitation erosion of vibratory and stationary specimens in a vibratory facility

Vibratory cavitation erosion with vibratory and stationary specimens is studied for three materials in tap water at room temperature. The separation distance is varied from 0.127 to 6.096 mm. Test materials were commercially pure lead, soft (1100-O) aluminum and type 316 stainless steel. The double-horn amplitude was 58.4 μm (2.3 × 10^?3in) in a 20 kHz facility. The total duration of all tests was 10 min.The weight loss of both vibratory and stationary specimens of course depends on materials. The weight loss of stationary specimens is best correlated as a function of the reciprocal of the separation distance.     

Mechanisms of Formation of Spheroids Produced by Cavitation Erosion

The prediction, control, and prevention of unscheduled downtime due to wear of industrial equipment is an important engineering problem. The characterization of wear particles and the study of the mechanism of their formation will aid in preventive maintenance. Of particular interest is the mechanism of formation of spherical particles during wear and erosion. It has been suggested that cavitation erosion is a mechanism of formation for these spherical particles. Using both a vibratory apparatus and a jet erosion facility, spherical particles were produced on various materials including aluminum and 52100 steel. Special techniques for isolating and mounting the eroded particles were developed. Spheroids ranging from 0·5 μ (microns) to 30 μ in diameter were observed in the vibratory cavitation method both in distilled water and in SAE 10W nondetergent oil. Much larger spheroids up to 150μ in diameter were observed in clusters with the jet erosion method. Scanning electron microscope studies revealed craters, plastic flow, overflowing lips, and splashing stems. Based on these observations, it is theorized that the high strain rate indentation of the cavitation bubbles leads to the splash of metal into the surrounding liquid where surface tension produces spherical particles. Supporting experimental evidence and calculations are also presented.     

A study of cavitation bubble collapse pressures and erosion part 3: the results in a venturi facility

Cavitation erosion generated in a venturi facility was studied by comparing the erosion loss with the distributions of cavitation bubble collapse pressures (impact loads). The erosion process in the venturi tests is similar to that in the vibratory tests, although its progression is very slow. That is, the surface first deforms and fractures as a result of fatigue with repeated bubble collapse pressures below the threshold pressure needed to form a pit impulsively. By comparing the distributions of impact loads measured using our method with the hypothetical stress-number of cycles curves for fatigue, it is found that the incubation period and the volume loss rate during the stable period follow Miner's law regardless of the venturi, vibratory and cavitation conditions and materials. Therefore we found that we are able to estimate cavitation damage in a flowing system in the same way as damage in the vibratory tests from Miner's law although the distributions of cavitation bubble collapse pressures are markedly different.     

Investigation of the Ring Area Formed Around Cavitation Erosion Pits on the Surface of Carbon Steel

The ring areas formed around micropits in cavitation erosion experiments were investigated. The corrosion behavior and vibratory cavitation erosion tests of mild carbon steel in tap and distilled water were carried out. Thus, the ring areas were densely formed in tap water and scarcely formed in distilled water in cavitation tests. The ring areas formed around micropits in cavitation and free cavitation tests have a similar shape. Moreover, SEM examinations showed that the corrosion products spread within the ring areas. Thus, the ring areas formed around micropits are the result of corrosion effect and are not the result of thermal effects due to bubble collapse.     

文氏管及振动设备的气蚀腐蚀试验结果比较

本文对五种金属材料在振动（不流动）和文氏管（流动）的系统中用自来水作试验的气蚀腐蚀性能作了详尽的比较,不但研究了温度变化（27到93℃）、文氏管喉部流速（34到49米/秒）及振动器双振幅的影响,而且探讨了最大腐蚀速度MDPR max和气蚀孕育期IP与材料的布氏硬度BHN和极限变形能UR（=UTS{sup}2/2E）等机械性能之间的关系。在“腐蚀阻抗”MDPR max{sup}-1和IP与这些机械性能的关系上只获得中等地成功。但是,发现了一个适用于两种设备的MDPR max和IP间的令人满意的关系,其形式是MDPR max{sup}-1＝a×（IP）{sup}n,这里n接近于1（0.94）。由MDPR max量度的气蚀强度在振动设备中要大10到20倍,与振动器的振幅和材料有关。如果对各别的材料分别考虑的话,此数值在5到30之间变化,其中变化最大的是碳钢1018,而最小的是不锈钢316。这表明了在这些气蚀方式间形式上的重大差别,亦表明了对这两种设备中测得的数据进行的比较尚有不精确的地方。     

Cavitation erosion of aluminum considering bubble collapse,pulse height spectra and cavitation erosion efficiency

Water erosion data on 1100-0 aluminum specimens obtained using a cavitating venturi are compared with bubble collapse pulse height spectra measured using a microtransducer. The data are resolved into erosion power and acoustic power. The former is defined in terms of the power applied to the eroded material to cause the observed pitting and volume loss. The ratio between these power quantities is termed the cavitation erosion efficiency η incav and is found to be essentially constant for the range of tests, being approximately 1.4 × 10^?6. The acoustic power which is easily measured can then be used to estimate the eventual material volume erosion rates, i.e. the mean depth of penetration (MDPR), with much greater accuracy than is otherwise possible. The MDPR is measured directly from the weight loss and is calculated from individual pit counts on damaged surfaces. The effects of the degree of cavitation (the extent of the cavitation cloud or the cavitation number) and the throat velocity on the MDPR is examined. An overall velocity damage exponent of n = 4.75 is found.     

An application of bubble collapse pulse height spectra to venturi cavitation erosion of 1100-o aluminum

Venturi cavitation erosion tests were performed and correlated with bubble collapse pulse height spectra measured by a microtransducer. The effects of the throat velocity and the cavitation number σ (referred to the downstream pressure and throat velocity) on the erosion rate (MDPR) were studied. The velocity damage exponent was 4.11 for 0.62 ? σ ? 0.80, while the MDPR is almost independent of velocity for σ = 0.85. The MDPR decreases with increased σ for 0.62 ? σ ? 0.85. The data were reduced to “acoustic power” (from pulse height spectra) and “erosion power” (the ultimate resilience multiplied by the MDPR). A near-linear relationship was found between these. Their reciprocal ratio η_cav ≈ 7 × 10^?11. For σ = 0.62, the data deviated from the others, possibly because of the work hardening of the eroded surface.     

Cavitation erosion in a dilute emulsion

The cavitation erosion of mild steel, brass, and pure iron in emulsions made with distilled water and 1.0% NaCl solution was investigated using a vibratory apparatus operating at 20 kHz and 15 μm amplitude. The emulsion reduced the steady-state erosion rate of mild steel in distilled and salt water to about 80% and 30%, respectively, of the values for no emulsion, but had no effect on brass in distilled water. Changes in the microstructures of the eroded surfaces and in the pH of the solution are presented and discussed in relation to the erosion curves.     

Comparison of cavitation erosion test results from venturi and vibratory facilities

A detailed comparison of cavitation erosion performance in tap water for five alloys in a vibratory (no-flow) system and a Venturi (flow) system was made. The effects of temperature variation (80 – 200 °F), Venturi throat velocity (34 – 49 m s^?1) and vibratory horn double amplitude were studied. Correlations between maximum erosion rate (maximum mean depth of penetration rate (MDPR_max)) and incubation period IP, and the material mechanical properties Brinell hardness and ultimate resilience $\text{UR =}\text{UTS}{}^2\text{2E}$. (where UTS is the ultimate tensile strength and E is the elastic modulus), were examined. Only moderate success was achieved in correlations between “erosion resistance” MDPR_max^?1 and IP and these mechanical properties. However, a good correlation was found between MDPR_max and IP, pertinent to both facilities, of the form MDPR_max^?1 = aIPⁿ, where n is near unity (0.94). The cavitation intensity, as measured by MDPR_max, was found to be 10–20 times greater in the vibratory system, depending on horn amplitude and material. This ratio varies between 5 and 30 if individual materials are considered separately, being greatest for 1018 carbon steel and least for 316 stainless steel. This indicates the important differences in form between these cavitating regimes and the imprecision of material comparisons made in both regimes.     

Cavitation damage incubation with typical fluids applied to a scroll expander system

During the operation of a scroll expander system overpressure may occur resulting in cavitation damage. Impacts due to implosion of cavitation bubbles near to suction ports can result in damage to the scroll plate in the expander. The accumulation of cavitation pits across the scroll plate leads to cavitation erosion hence efficiency drop. An experimental analysis to identify the mechanical damage of the cavitation on various steel surfaces with different liquid environments was conducted.Three liquid environments and four steel grades were utilised experimentally. The liquids used for the tests were distilled water, used as a reference liquid, and the two working fluids of the scroll expander a synthetic lubricant and a high molecular refrigerant. The steel grades were a high carbon (AISI 1085) and low carbon (AISI 1010) martensitic steel with retained austenite, a chromium martensitic steel (AISI 52100) and a martensitic scroll plate (SP) sample. An ultrasonic transducer was utilised to produce cavitation conditions using a 5 mm diameter probe. The comparison of the results revealed the most hostile liquid environment according to the morphology evaluation of the incubation pits. The cavitation mechanisms are discussed and the cavitation resistance of the steel grades is evaluated. The best performing steel material against cavitation is determined for the conditions described.     

Cavitation damage incubation with typical fluids applied to a scroll expander system

During the operation of a scroll expander system overpressure may occur resulting in cavitation damage. Impacts due to implosion of cavitation bubbles near to suction ports can result in damage to the scroll plate in the expander. The accumulation of cavitation pits across the scroll plate leads to cavitation erosion hence efficiency drop. An experimental analysis to identify the mechanical damage of the cavitation on various steel surfaces with different liquid environments was conducted.Three liquid environments and four steel grades were utilised experimentally. The liquids used for the tests were distilled water, used as a reference liquid, and the two working fluids of the scroll expander a synthetic lubricant and a high molecular refrigerant. The steel grades were a high carbon (AISI 1085) and low carbon (AISI 1010) martensitic steel with retained austenite, a chromium martensitic steel (AISI 52100) and a martensitic scroll plate (SP) sample. An ultrasonic transducer was utilised to produce cavitation conditions using a 5 mm diameter probe. The comparison of the results revealed the most hostile liquid environment according to the morphology evaluation of the incubation pits. The cavitation mechanisms are discussed and the cavitation resistance of the steel grades is evaluated. The best performing steel material against cavitation is determined for the conditions described.     

Effect of liquid metal composition and hydrodynamic parameters on cavitation erosion

Cavitation erosion testing machine for low-temperature melting alloy liquid was developed by using a vibratory apparatus. The erosion tests of SUS304 were carried out in three kinds of lead–bismuth and deionized water. We defined a relative temperature as the percentage between freezing and boiling points. At relative temperature at 14 °C, the erosion rate is 10–12 times in various lead–bismuth alloys, and 2–5 times in sodium, as compared with that in deionized water. When SUS304 was exposed to a cavitation in PbBi, the surface was work hardened 20% harder compared with original surface. In deionized water, SUS304 was work hardened by 5%. Therefore, we can conclude that larger collapse pressure can be estimated to act on the specimen surface in lead–bismuth, as compared with that in water.We discussed the effect of hydrodynamic properties on cavitation erosion in a flowing system. It is considered that the erosion rate in sodium is in proportion to 1st to 6th power of flow velocity similarly to that in mercury. The incipient cavitation number is approximately unity irrespective of test liquids. Furthermore, the relation between MDER and cavitation number is expressed as power low of function with an exponent of 2.5.     

Cavitation erosion resistance of high nitrogen stainless steel in comparison with low N content CrMnN stainless steel

Abstract

The cavitation erosion (CE) of a high nitrogen stainless steel (HNS) and a low nitrogen CrMnN stainless steel in both distilled water and 3%NaCl solution at 20±1°C was investigated by using a magnetostrictive induced cavitation facility. The evolution of CE with test time was analysed by morphology observation by SEM and roughness measurement after different CE intervals. The possible phase transformation of austenite to martensite due to cavitation was analysed by XRD, and cross-sectional microhardness after cavitation was also measured to evaluate the work hardening ability. The role of corrosion was analysed by polarisation curve. The test results indicated that HNS had a relatively higher CE resistance than CrMnN steel, which was mainly attributed to its higher work hardening ability, thicker wok hardening layer and lower stacking fault energy. Different from that of the HNS, many tiny cracks could be clearly seen in the cross-section of eroded CrMnN steel especially at the ferrite zones. The pure erosion dominated the whole cavitation damage process, and the synergistic effect between corrosion and erosion was relatively small for both steels. The CE behaviour of HNS was relatively more sensitive to the corrosion media than that of CrMnN steel. Therefore, it should be a little bit careful when HNS was used in corrosive media.     

Resistance to wear and cavitation erosion of bearing alloys

Sliding wear and vibratory cavitation erosion tests in paraffin oil were carried out on bearing alloys, i.e. tin-based and lead-based white metals, Cu-Pb alloy and leaded bronze. In lubricated wear under mild conditions the surface is worn smooth and a slight difference exists between the wear resistances of the four alloys. In cavitation erosion an eroded surface which is much rougher than the worn surface is formed. Cavitation erosion is affected strongly by the composition and crystal structure of the alloy and thus the erosion resistances of the four alloys differ greatly, the ranking of resistance being lead-based white metal < Cu-Pb alloy < tin-based white metal < leaded bronze. The surface damage, which is caused by the joint action of cavitation erosion and wear, was also investigated by rubbing the eroded surfaces which had been exposed to cavitation erosion for various times. This damage becomes larger with increasing cavitation damage. The resistance to this damage differs much more in the four alloys tested and tends to correlate with the results of the erosion tests rather than those of the wear tests. Therefore, it is clear that the cavitation erosion resistance should be considered in the selection of bearing materials.     

Vibratory cavitation erosion in aqueous solutions

Vibratory cavitation erosion tests on AISI-SAE 1018 carbon steel in tap water and in mild (0.1 M) aqueous solutions of CaCO₃, CaO, NaHCO₃ and NaOH were conducted at a temperature of 80 °F (27 °C), a double amplitude of 1.38 × 10^?3 in (35.1 μm) and a pressure of 1 atm. For the maximum (150 min) test duration the weight loss in tap water (no additive) is the smallest. However, this is not the case for shorter test times. The biggest difference between weight losses among the various solutions is about 10% – 30%, which is somewhat beyond natural data scatter for such vibratory tests. Released gases and also particles may play an important role in the results.There are three easily distinguishable damage regions for all cavitated surfaces, i.e. generally undamaged rim, central heavily damaged region and transition region, as for most vibratory tests. The relative areas of the three regions are about 53.5%, 0.13% and 46.4% respectively for the present tests.The erosion rate and extent of the damaged regions do not depend substantially on the solute tested. The very small area of the heavily damaged central region is presumably due to the relatively low horn amplitude used in these tests. The increase in damage rate with respect to tap water is about 50% for the maximum test duration.Surface photographs and scanning electron microscopy photomicrographs (for a test duration of 150 min) are presented. Cracks, intercrystalline fractures and single-blow craters are most concentrated in the central region, as would be expected.     

1100-0铝和1018碳钢文氏管空蚀试验的流速指数和空化数

本研究的目的是要估价一下文氏管喉部流速在空化数不变时对试件空化侵蚀的影响。此处的空化数是根据文氏管的出口条件算出的。最近在密执安大学高速空蚀试验装置中曾用27℃的自来水对1018碳钢和1100－0铝进行了试验。目前的试验结果与密执安大学过去所得的结果很符合,表明对于流速范围为10～49米/秒的情况,流速破坏指数在±1～5的范围内变动。     

Scaling study of cavitation pitting from cavitating jets and ultrasonic horns

Cavitation erosion prediction and characterization of cavitation field strength are of interest to industries suffering from cavitation erosion detrimental effects. One means to evaluate cavitation fields and materials is to examine pitting rates during the incubation period, where the test sample undergoes localized permanent deformations shaped as individual pits. In this study, samples from three metallic materials, an Aluminum alloy (Al 7075), a Nickel Aluminum Bronze (NAB) and a Duplex Stainless Steel (SS A2205) were subjected to a vast range of cavitation intensities generated by cavitating jets at different driving pressures and by an ultrasonic horn. The resulting pitted sample surfaces were examined and characterized with a non-contact 3D optical scanner and the resulting damage computer-analyzed. A statistical analysis of the pit population and its characteristics was then carried out. It was found that the various cavitation field strengths can be correlated to the measured pit distributions and that two characteristic quantities: a characteristic number of pits per unit surface area and unit time, and a characteristic pit diameter or a characteristic pit depth can be attributed to a given “cavitation intensity level”. This characterization concept can be used in the future to study the cavitation intensity of the full scale and to develop methods of full scale predictions based on model scale erosion data.     

Susceptibility of type 431 stainless steel to erosion-corrosion by vibratory cavitation in corrosive media

By utilizing the structural characteristics of type 431 stainless steel, which reveals a wide range of strength as well as corrosion resistance with tempering after quenching, its susceptibility to erosion-corrosion was investigated as a function of tempering temperature. Tests were conducted under a vibratory cavitation condition of 6.5 kHz with a double amplitude of 75 /gmm or of 20 kHz and 50 μm in cavitation media of 3% NaCl solution, 0.1N HCl and 0.1N H₂SO₄ at 22°C. As a preliminary investigation, the mechanical properties and corrosion resistance, in the same solutions as the cavitation media, were also determined as a function of the tempering temperature.The results indicated that the susceptibility to erosion-corrosion depended predominantly upon the mechanical strength but there were some exceptions for which attention should be paid to the corrosion resistance.     

Improvement of cavitation erosion resistance of a duplex stainless steel through friction stir processing (FSP)

The cavitation erosion (CE) resistance of an UNS S32205 duplex stainless steel (DSS) was improved through microstructural modification using friction stir processing (FSP). As-received material was processed using 200 rpm and 100 mm/min spindle and travel speeds, respectively. The cavitation erosion tests were performed in a vibratory apparatus according to ASTM G32 standard. The incubation period, the maximum erosion rate and the variation of surface roughness during the tests are reported and the results are compared with those obtained for the base metal samples (BMS). The worn surfaces were characterized using roughness measurements and scanning electron microscopy (SEM). After a CE testing time of 10 h, FSP samples showed a 70% diminution of the mass loss when compared to the BMS. Moreover, a 200% enhancement of incubation time and 100% reduction in the erosion rate were achieved after FPS. The improvement of CE performance is related to the recrystallized and refined microstructure, as well as to the modification of the elongated α/γ interfaces.     

Cavitation erosion resistance of Cr–N coating deposited on stainless steel

Results of investigation on cavitation-erosion resistance of Cr–N coating deposited on stainless steel X6CrNiTi18-10 (1H18N9T) by means of the cathodic-arc method are presented. The evaluation of Cr–N coating resistance to cavitation erosion is based on the investigation performed in a cavitation tunnel with a slot cavitator and tap water as a medium. The investigation was performed at variable-cavitation intensity and the estimated cavitation resistance parameters of coatings were the incubation period of damage and the instantaneous erosion rate after exposure of specified duration. It has been confirmed that the incubation period of the Cr–N coating damage is approximately 50% longer than that of the uncoated X6CrNiTi18-10 steel, and the instantaneous erosion rate after exposure of specified duration is comparable in both cases. The scanning microscope analysis indicates that the damage of Cr–N coating is due mainly to its delamination, while the erosion of deeper parts of the coating is of minor importance. The character of the coating and substrate damage in multiple locations indicates that the hard coating microparticles torn-off during the cavitation bubbles implosion hit against the coating and the revealed areas of substrate. As a result, the coating and especially the substrate of relatively low hardness are subject to cavitation erosion and to solid particle erosion with the hard torn-off microparticles of coating. The results of the investigation and the analysis indicate that the factors mainly responsible for a long incubation period and low cavitation erosion rate of the steel substrate/hard coating systems are the gained high hardness of substrate and high level of coating adhesion.