Vibratory Apparatus Research Articles

The effect of compressive stress on cavitation-erosion corrosion behavior of 304 stainless steel

PurposeThe purpose of this paper is to clarify the effect of compressive stress on cavitation-erosion corrosion behavior of 304 stainless steel.Design/methodology/approachCompressive stresses of 60 MPa and 120 MPa were applied to 304 stainless steel through a self-designed loading device, and cavitation erosion-corrosion tests were performed using an ultrasonically vibratory apparatus. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure evolution, and corrosion behavior was studied by electrochemical analysis.FindingsThe cavitation weight loss of 304 stainless steel decreased with the compressive stress. After cavitation corroded for 8 h, the weight loss for the specimen with 120 MPa compressive stress was 5.11 mg/cm2, which was reduced by 56.7% from that of the specimen without loading stress (11.79 mg/cm2). The reason can be attributed to that compressive stress promoted the deformation-induced martensitic transformation during the cavitation process, which could not only provide a cushioning effect by absorbing cavitation impact energy but also improve the hardness of 304 stainless steel.Originality/valueCompressive stress was found to restrain the cavitation damage on 304 stainless steel, and the corresponding mechanism was proposed.

Mechanism of the attack on metal surface in wear under ultrasonic cavtation

Two series of tests of annealed metal materials — copper, brass L60 and aluminum-magnesium alloy AMg4,0 — were carried out. The first series consists first in upsetting the cylindrical samples of the listed above alloys on a press to a different strain rate, then cutting the deformed samples and measuring the microhardness of the area adjacent to the center of the samples. The first series results in constructing the calibration plots of microhardness as a function of strain. During the second series the tests of the same materials for cavitation wear were carried out in the fresh water on the ultrasonic vibratory apparatus. The frequency and amplitude of the apparatus horn vibration amount to 22 kHz and 28 μm respectively. The microhardness of the samples surface exposed to cavitation attack was measured after the definite spans of time within the incubation period and the maximum value of the microhardness was registered. Marking the maximum microhardness value on the calibration plot yields the strain rate reached on the surface under cavitation attack before the removal of wear particles begins. On the basis of the found values of the strain the stress state rigidity of the surface layers under cavitation attack was evaluated. The obtained coefficients of stress state rigidity allowed drawing the conclusion, that cavitation attack on the material being tested on the ultrasonic vibratory apparatus occurs through the microjets impacts.

Cavitation erosion damage of self-fluxing NiCrSiB hardfacings deposited by oxy-acetylene powder welding

This paper comparatively investigates the cavitation erosion damage of two self-fluxing NiCrSiB hardfacings deposited via the oxy-acetylene powder welding method. Examinations were conducted according to the procedure given by ASTM G32 standard. In order to research cavitation erosion (CE), the vibratory apparatus was employed. The cavitation damaged surfaces were inspected using a scanning electron microscope, optical microscope and surface profilometer. The hardness of the A-NiCrSiB hardfacing equals 908HV while that of C-NiCrSiB amounts to 399HV. The research showed that the CE resistance of C-NiCrSiB is higher than that of A-NiCrSiB. The results demonstrate that in the case of multiphase materials, like the NiCrSiB hardfacings, hardness cannot be the key factor for cavitation erosion damage estimation whereas it is strongly subjected to material microstructure. In order to qualitatively recognise the cavitation erosion damage of the NiCrSiB self-fluxing hardfacings at a given exposure time, the following factors should be respected: physical and mechanical properties, material microstructure and also material loss and eroded surface morphology, both stated at specific testing time. The general idea for the cavitation erosion damage estimation of the NiCrSiB oxy-acetylene welds was presented.

AN ANALYSIS OF THE EFFICIENCY OF USING A PLANETARY VIBRODRIVE WITH KINEMATICALLY UNBALANCED MASSES IN A VIBRATORY APPARATUS FOR MIXING LIQUID MEDIA

The purpose of the research is to analyze the efficiency of using a planetary vibrodrive (vibratory drive) with kinematically unbalanced masses in a vibratory apparatus for mixing liquid media. The article gives a theoretical justification of the effectiveness of supplementing the configuration of a vibrodrive with an additional inertia block and presents the results of computer simulation of the oscillatory processes arising in the system, which reflect the predominant features of the proposed design solution. The use of a planetary vibrodrive with kinematically unbalanced masses allows one to create high-frequency controlled circular oscillations of the working body. At the same time, the inclusion of an additional rotatable body into the system increases the range of controlling the oscillation parameters of the working body and enables to regulate independently the oscillation amplitude and frequency. The independence of the vibration parameter control allows one to ensure a uniform distribution of the velocities of the stirred liquid motion to obtain a homogeneous dispersion medium. The proposed design solution increases the efficiency of the ongoing vibromechanical processes and adds a supplementary cavitation factor of influence on the liquid medium. Hydrodynamic cavitation, which is created due to the liquid pulsation when the slots on the rotating elements of the vibrodrive are closed, eliminates the presence of stagnant zones in the mixed medium. Due to the use of a planetary vibrodrive with a rotating support body in a vibratory apparatus for mixing liquid media, the technological process of obtaining medium and highly dispersed emulsions is intensified at minor changes in the design of the apparatus. The improved technological capabilities of the process of mixing liquid mixtures allow one to mix substances with different properties of the dispersion phase. In this case, dispersion phases can be both liquid and solid, which are crushed and mixed in a dispersion liquid medium. Conclusion. The use of a planetary vibrodrive with kinematically unbalanced masses in a vibratory apparatus for mixing liquid media increases the efficiency of the technological process and simultaneously increases the quality indicators of the resulting emulsions and suspensions.

The Limited Role of Pit Formed by Microjet in Evolution of Cavitation Erosion in the Incubation Period

AbstractStepwise cavitation erosion is used to study pits formed by microjets. The aim is to determine the role of the pit in the development of cavitation erosion damage, including geometrical features of the pitted area and pit counting. The study also identified the dominant feature in the development of cavitation damage. We used a vibratory cavitation apparatus to perform cavitation erosion damage on a stainless steel, SUS 304, in tap water with scanning electron microscopy (SEM) at 5-min intervals from t = 0 min to t = 45 min. We then analyzed and characterized the pits formed by impacting the surface with a microjet. These results showed that individual pits and clusters of pits are characterized by a black spot surrounded by plastic deformation, and both are irregular in shape. This suggests that the microjet is hitting the wear surface in an oblique direction. Over the course of the test time, neither the shape nor the size of the microjet pits and their clusters change; pit diameters approximately 2 μm or less. The area of pits and their clusters does not exceed 1% of the worn surface. All these features demonstrate that the pit and its clusters do not impact the evolution of cavitation damage. Our results also indicated that slip bands were caused by a shock wave. Slip bands are large (>10 μm) and account for about 30% of the wear surface. This confirms that slip bands are predominantly responsible for the development of cavitation; the predominant cavitation mechanism is fatigue due to multiple shock waves.

High Energy Ball Milling and Liquid Crystal Template Method: A Successful Combination for the Preparation of Magnetic Nano-Platforms.

In this study, we present the preparation of superparamagnetic ordered mesoporous silica (SOMS) for biomedical applications by the combination of high energy ball milling (HEBM) and the liquid crystal template method (LCT) to produce a material comprised of room temperature superparamagnetic Fe₃O₄ nanoparticles in a MCM-41 like mesostructured silica. In a typical synthesis, a mixture of Fe₂O₃ and silica was sealed in a stainless-steel vial with steel balls. Ball milling experiments were performed in a vibratory mill apparatus. The milling process produced nanocomposites with an average size ranging from ∼100-200 nm, where the Fe₃O₄ nanoparticles (4.8 nm size) are homogeneously dispersed into the amorphous SiO₂ matrix. The obtained nanocomposite has been used for the preparation of the SOMS through the LCT method. Structural, morphological and textural characterization were performed using X-ray powder diffraction, transmission electron microscopy and nitrogen sorption analysis. Field dependence of magnetization was investigated and showed superparamagnetic behaviour at 300 K with a value of saturation magnetization (Ms) that is of interest for biomedical applications.

Anthropogenic underwater vibrations are sensed and stressful for the shore crab Carcinus maenas

Acoustic pollution in aquatic environments has increased with adverse effects on many aquatic organisms. However, little work has been done considering the effects of the vibratory component of acoustic stimuli, which can be transmitted in the substrate and propagated into the aquatic medium. Benthic marine organisms, including many invertebrates, are capable of sensing seabed vibration, yet the responses they trigger on organism have received little attention. This study investigates the impact of underwater vibration on the physiology and behaviour of a ubiquitous inhabitant of coastal areas of the northern hemisphere, the shore crab Carcinus maenas. We developed a novel vibratory apparatus with geophones supported on a softly sprung frame to induce a seabed vibration of 20 Hz frequency, as observed during dredging, piling and other anthropogenic activities. The geophone internal mass caused the frame to vibrate in a controlled manner. Our results show that transition from ambient to anthropogenic vibrations induced an increase in activity and antennae beats in shore crabs, indicating perception of the vibratory stimulus and a higher stress level. There was also a trend on sex-specific responses to anthropogenic vibration, with males showing a higher activity level than females. However, no effect of anthropogenic vibrations was found upon oxygen consumption. These results show that anthropogenic underwater vibration induces behavioural responses in Carcinus maenas. This highlights the importance of evaluating man-made vibratory activities on coastal invertebrates and the necessity of evaluating anthropogenic effects on both sexes.

Influence of atomic migration mode at different temperatures on the microstructure, mechanical and cavitation erosion behaviors of Co-based alloy coating

Heat treatment (HT) was used to regulate atomic migration modes to optimize the microstructure and improve the cavitation erosion (CE) durability of thermal-sprayed CoCrAlYTaCSi coating. The structure evolution was analyzed by XRD, SEM and TEM. The mechanical and CE behaviors were characterized by a Vicker’s hardness tester and vibratory apparatus. Results demonstrated that the migration, oxidation and precipitation of atoms were effectively interfered by changing HT conditions, which significantly affected the phase structure and properties of coatings. Splat interfaces provided a convenient path for atoms migration, and the inward migration of oxygen was faster at 600 °C, causing serious oxidation of internal structure. But directional long-range migration of Al was activated at higher temperatures, and thus a continuous oxide layer mainly composed of Al2O3 was generated on the coating surface, which could prevent oxygen from diffusing into the coating. Meanwhile, through the migration of atoms within the coating, especially at 950 °C, the splat interfaces were fused together, and many nano-carbides were precipitated at grain boundaries, finally favoring to improve the hardness and CE-resistance greatly.

Effects of microstructure and mechanical properties on cavitation erosion resistance of NiCrWMoCuCBFe coatings

NiCrWMoCuCBFe coatings were prepared by high velocity oxy-fuel (HVOF) spraying technology with the microstructures and mechanical properties characterized in detail. Besides, an ultrasonic vibratory apparatus was employed to investigate the cavitation erosion resistance of the coating in deionized water and its cavitation erosion mechanism was revealed. The results show that there were some inherent defects existed on the coating surface but its microhardness was more than triple that of 316 L stainless steel. In the initial stage of cavitation erosion, these inherent defects of coating surfaces were damaged at first, leading the incubation period of the coating was shorter than 10 min. With the prolongation of cavitation erosion time, many cracks interpenetrated and finally led to the exfoliation of coatings. When the cavitation erosion time extended to 10 h, the erosion rate of the coating was almost stable and reached maximum about 1.32 ± 0.08 μm/h, which was less than that of 316 L stainless steel (2.62 ± 0.18 μm/h). That is, the inherent defects influenced the cavitation erosion resistance in the incubation period of the coating but the mechanical properties played a dominant role in the long-term cavitation erosion of the coating.

Correlation between microstructural characteristics and cavitation resistance of Stellite-6 coatings on 17-4 PH stainless steel prepared with supersonic laser deposition and laser cladding

Stellite-6 coatings were deposited on 17-4 PH stainless steel substrate by supersonic laser deposition (SLD) and laser cladding (LC) to improve cavitation resistance of the substrate. The microstructural characteristics of the as-deposited coatings were analyzed on the basis of OM, SEM, EBSD, XRD, Vicker’s hardness and nano-indentation results. The cavitation erosion performances in 3.5 wt% NaCl solution were comparatively investigated by a vibratory apparatus for the coatings prepared by SLD and LC technologies. The underlying mechanisms for differences of cavitation behavior between these two samples were elucidated in terms of grain size, dilution level, phase composition, hardness, elastic modulus and topographical features of the worn surfaces. Results show that SLD coating has finer grain, lower dilution and higher ratio of hardness to modulus. By analyzing the eroded surfaces, it is found that the pores formed due to mechanical bonding between particles in SLD coating are the priority position of cavitation where bubbles nucleate, grow and collapse. Repeated impact force from bubble collapse produces cracks and makes cracks propagation, leading to particle detachment and finally material removal. Although the porosity of SLD coating is higher than that of LC coating, its content is only less than 0.4%. Therefore, the negative effect of porosity is weaker than the positive effect of grain refinement, low dilution ratio and high hardness on cavitation performance. Consequently, SLD coating has better cavitation resistance than LC coating.

Method and means of cavitation erosion tests under abnormal conditions

The monitoring method for erosion resistance of metals and protective coatings under cavitation exposure in abnormal operating conditions is proposed. This method extends the scope of the standard ASTM G32-10 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. The specialized ultrasonic device has been developed for the study of cavitation destruction of materials and coatings at high pressures, temperatures up to 1000 °C and in liquid media with various properties (including aggressive ones) for implementing the monitoring method. The control system based on continuous monitoring of electric parameters of piezoelectric vibratory system was used to providing the necessary vibration amplitude in the process of cavitation under all changes of liquids parameters. The control system (based on changes monitoring of liquid active resistance) was used for equal efficiency of cavitation process on the surface. Practical recommendations for testing of cavitation erosion of metals and protective coatings in abnormal conditions are given.

Morphology and mechanisms of cavitation damage on lamellar gray iron surfaces

Engine parts in contact with liquids may suffer cavitation erosion damage. Understanding its mechanisms in realistic operating environments is necessary for improvements in the service life and durability of materials for heavy-duty diesel engines. This work illustrates the cavitation erosion behavior of a cylinder liner material with a follow-up of detailed, high-magnification SEM images of damaged sites on the surface. The cylinder liner encloses the piston and combustion chamber in the engine of large trucks and its material of choice is usually a lamellar gray cast iron, its microstructure consisting of flake-shaped graphite, a pearlitic matrix and some steadite. Testing was carried out using an ultrasonic vibratory apparatus, and the liquid of choice was a commercial engine coolant composed of water, glycol and inhibitors. Based on observations of tested surfaces, a sequence of damage patterns is proposed as an explanation of the material’s cavitation erosion behavior. Initiation consists of: chipping at graphite cluster centers, graphite flake removal, pitting along graphite flakes and direct matrix pitting. Development consists of: evolution of chipped spots into matrix-damaging pits, radial pit expansion, pit merging and surface roughening. It can be concluded that presence and morphology of graphite are critical to the cavitation erosion behavior of LGI.

The interaction mechanism of cavitation erosion and corrosion on HVOF sprayed NiCrWMoCuCBFe coating in artificial seawater

When flow passage components were used in the ocean, it was inevitable that they could be damaged by the coupling effect of cavitation erosion and corrosion. It is necessary to explore the interaction mechanism between cavitation erosion and corrosion of the protective coating in marine. In this study, NiCrWMoCuCBFe coating was prepared on 316L stainless steel by high velocity oxy fuel (HVOF) spraying technique. The microstructures and three-dimensional morphologies of coatings were observed. And its cavitation erosion resistance was evaluated by means of a vibratory apparatus in artificial seawater. The influence of corrosion on cavitation erosion of NiCrWMoCuCBFe coating was also investigated. In addition, an electrochemical workstation equipped with a three-electrode system was used to measure the electrochemical properties of this coating after different time cavitation erosion, revealing the effect of cavitation erosion on corrosion. Results show that with the increase of cavitation erosion time of NiCrWMoCuCBFe coating in artificial seawater, many particles with nanometer sizes of NiO, Cr2O3, MoO3 and Mo2C were generated on the cavitation erosion region of coatings because of the coupling effect of corrosion and cavitation erosion, which played an important role on slowing down the rate of cavitation erosion and improving corrosion resistance.

Deposition and cavitation erosion behavior of multimodal WC-10Co4Cr coatings sprayed by HVOF

Cavitation erosion is one of the major failure modes for engineering components operating in the marine environment. In this study, WC-10Co4Cr coatings with multi-scale WC particles were prepared on 304 stainless steel substrates by two high velocity oxygen fuel (HVOF) systems differentiated by the types of fuel. The splat formation process of the multimodal cermet particles was investigated, as well as coatings' porosity, microhardness, fracture toughness and electrochemical performance. In addition, the cavitation erosion resistance of the coatings was evaluated by ultrasonic vibratory apparatus in 3.5 wt% NaCl solution. The results show that the splats sprayed by high velocity oxygen liquid fuel (HVOLF) had a more disk-like shape, leading to much lower porosity and superior mechanical properties in the corresponding coating. The low porosity also significantly hindered the formation of cavitation sources and reduced the cavitation rate. More importantly, the synergistic effect of corrosion on cavitation erosion made the coating much more vulnerable in NaCl solution than in fresh water.

ВЛИЯНИЕ КОРРОЗИОННОГО ФАКТОРА НА КАВИТАЦИОННУЮ ИЗНОСОСТОЙКОСТЬ СПЛАВОВ ДЛЯ ГРЕБНЫХ ВИНТОВ

The resistance of the stainless steel 08H14NDL, the bronze BrA8Mts11Zh3N2L and the brass LTs40Mts3Zh to cavitation erosion was investigated in fresh water and artificial sea water. The tests were carried out on an ultrasonic vibratory apparatus. The horn of the vibratory device resonated at approximately 22 kHz, a peak-to-peak amplitude being changed from 24 to 54 μm. The distance between the horn butt-end and the specimen surface equaled 0.5 mm. It was shown, that the increase in the amplitude of vibration leads to the decrease in the difference between the cavitation wear in fresh water and the sea water. It was demonstrated that under the cavitation attack of high intensity the wear of the brass in the sea water can be essentially lower than the one obtained in the fresh water. The demonstrated paradox may be attributed to the peculiarities of the cavitation impact on the ultrasonic vibratory apparatus combined with the plasticizing action of the aggressive liquid. The ultrasonic frequency of the shock waves action on the surface increases dislocations mobility, whereas the stripping the surface layers with sea water alleviates the discharge of the dislocations on the surface: the chemomechanical effect takes place.

Cavitation erosion behavior of HVOF sprayed WC-10Co4Cr cermet coatings in simulated sea water

Mechanical equipment operating in the ocean is vulnerable to cavitation erosion damage. The coatings fabricated by high velocity oxygen fuel (HVOF) spraying technology can remarkably improve the resistance of cavitation erosion. In this study, WC-10Co4Cr coatings with two structures (conventional and bimodal) were prepared on 35CrMo steel substrate, respectively. The morphologies and structures of the powders and as-sprayed coatings were analyzed by SEM and XRD, and microhardness, porosity and surface roughness were also studied. The corrosion resistance of the coatings was evaluated by using potentiodynamic polarization. More importantly, the cavitation erosion resistance in simulated sea water was studied by the ultrasonic cavitation vibratory apparatus and the cavitation erosion failure mechanisms were also explored. The results show that the bimodal coating has better quality and cavitation erosion resistance. Moreover, the effect of corrosion on cavitation erosion is not obvious.

Cavitation erosion mechanisms in Co-based coatings exposed to seawater.

The cavitation erosion (CE) of most materials in seawater is more serious than in fresh water due to the onset of corrosion; however, in a previous study we reported results that contradict this widely accepted trend. In this research our objective is to provide fundamental insight into the mechanisms that may be responsible for these earlier results. To accomplish this objective, two types of Co-based coatings, prepared by high velocity oxygen fuel (HVOF) spraying system, were used to further investigate the underlying corrosion-mitigating CE mechanism in seawater. Accordingly, the influence of spraying parameters on microstructure, composition and mechanical properties of the coatings was analyzed on the basis of SEM, XRD, Raman spectroscopy, Vicker's hardness and nano-indentation results. Electrochemical corrosion tests were used to evaluate the corrosion behavior of the Co-based coatings. Their CE performances in seawater and deionized water were comparatively studied by a vibratory apparatus. Results demonstrated that a higher flame temperature facilitated the oxides formation with associated improvements in compactness, hardness and toughness of the coatings. The presence of alumina in combination with the oxides formed in-situ facilitated the formation of an oxidation film on surfaces, and effectively enhanced the charge transfer resistance of the coating, thereby significantly improving the corrosion resistance in seawater. Metallic Co was not only more easily oxidized but also more readily corroded than the alloyed Co. Compactness was identified as an important factor affecting CE resistance of coatings in deionized water, because defects facilitate the nucleation and eventual collapse of bubbles. Moreover, bubble collapse produced a transient high temperature spike in excess of 600 °C that also caused Co and Cr elements to oxidize. Because the CE tests were carried out in seawater, additional Co3O4 and Cr2O3 were generated owing to corrosion that more effectively increased the surface compactness and mechanical properties of the coatings. This behavior was particular notable for coatings with metallic Co and Cr, which should be why seawater corrosion could weaken the CE of Co-based coatings.

Cavitation Erosion and Sliding Wear Mechanisms of AlTiN and TiAlN Films Deposited on Stainless Steel Substrate

The resistance to cavitation erosion and sliding wear of stainless steel grade AISI 304 can be improved by using physical vapor deposited (PVD) coatings. The aim of this study was to investigate the cavitation erosion and sliding wear mechanisms of magnetron-sputtered AlTiN and TiAlN films deposited with different contents of chemical elements onto a stainless steel SS304 substrate. The surface morphology and structure of samples were examined by optical profilometry, light optical microscopy (LOM) and scanning electron microscopy (SEM-EDS). Mechanical properties (hardness, elastic modulus) were tested using a nanoindentation tester. Adhesion of the deposited coatings was determined by the scratch test and Rockwell adhesion tests. Cavitation erosion tests were performed according to ASTM G32 (vibratory apparatus) in compliance with the stationary specimen procedure. Sliding wear tests were conducted with the use of a nano-tribo tester, i.e., ball-on-disc apparatus. Results demonstrate that the cavitation erosion mechanism of the TiAlN and AlTiN coatings rely on embrittlement, which can be attributed to fatigue processes causing film rupture and internal decohesion in flake spallation, and thus leading to coating detachment and substrate exposition. At moderate loads, the sliding wear of thin films takes the form of grooving, micro-scratching, micro-ploughing and smearing of the columnar grain top hills. Compared to the SS reference sample, the PVD films exhibit superior resistance to sliding wear and cavitation erosion.

Cavitation erosion resistance enhancement of martensitic stainless steel via low-temperature plasma carburizing

This work presents the potential of low-temperature plasma carburizing treatments for improving the cavitation erosion resistance of martensitic stainless steel (MSS). As-hardened AISI 420 MSS samples were treated via dc plasma carburizing at 450 °C for 12 h. The cavitation erosion behaviors were compared with that of an untreated steel sample tempered at 220 °C for 1 h. Cavitation erosion tests were performed with an ultrasonic vibratory apparatus in accordance with the ASTM G32-10 standard. The nominal incubation period of the carburized samples was approximately three times higher than that of the untreated sample (23 h versus 7.8 h, respectively). The cavitation erosion behavior was discussed in terms of mechanical surface properties (hardness (H) and elastic modulus (E)) obtained via the nanoindentation technique and respective H/E, H2/E, and H3/E2 ratios.

Statistical analysis of cavitation erosion impacts in a vibratory apparatus with copulas

A method of analysis of cavitation peaks (impact events) using copulas is developed. Impact events, otherwise known as peaks, are defined as maximum in the pressure amplitude applied to a material surface. These impact events were measured using a high speed pressure sensor in a cavitation apparatus based on the ASTM G32 standard. A total of 46180 impacts were measured over 100 realizations of 4ms long recording. First, the impact duration and amplitude’s joint marginals are modeled as gamma distribution (part of the exponential family), determined by a Kolmogorov-Smirnov test (KS test). Then, copulas enable the study of the dependence structure of the measured impacts characteristics. The measured parameters are shown to not be independent but instead have a complex, asymmetric dependence structure. There are almost no impacts that have a combination of a high amplitude (>12MPa) and low duration (<5µs). The Tawn copula best fitted the data, as determined by a maximum likelihood method. An extension of the KS test to two dimensions demonstrated that the copula is a better fit compared with a joint distribution of independent marginals.