Ultrasonic Vibratory Apparatus Research Articles

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.

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.

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.

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 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.

Evaluation of cavitation erosion resistance of copper alloy in different liquid media

To evaluate the influence of liquid property on cavitation erosion resistance of the copper alloy, an experimental investigation is performed with the ultrasonic vibratory apparatus. Liquid media of deionized water, tap water, and 3.5 wt.% NaCl solution are selected. The cumulative mass loss rate and microhardness are measured and surface morphology observed at different erosion time. The results show that the cumulative mass loss increases consistently with the erosion time, and the highest cumulative mass loss rate is witnessed in tap water. The erosion time at which the maximum cumulative mass loss rate is reached is the shortest with the 3.5 wt.% NaCl solution. Surface morphology testifies the rapid evolution of small cavitation erosion pits into large eroded area in the specimen surface submerged in the deionized water and tap water. In comparison, the specimen surface in the 3.5 wt.% NaCl solution is featured by insignificant cavitation erosion, and plastic deformation remains predominant for a long erosion time. The initiation and development of micro‐cracks are remarkable in tap water. In the 3.5 wt.% NaCl solution, the progression of cavitation erosion is mitigated relative to the other two cases, and cavitation erosion pits remain the predominant constituents of the erosion pattern as the erosion time increases. The hardening layer is found beneath the specimen surface, and the 3.5 wt.% NaCl solution is responsible for the thickest hardening layer. As cavitation erosion develops, the softening phenomenon is salient with consistent flaking off of surface layers.

Formation of cavitation-induced nanosize precipitates on the eroded surface for Inconel 718 alloy

The cavitation erosion of Inconel 718 nickel-base alloy was investigated using an ultrasonic vibratory apparatus. The morphologies and microstructure evolution of the eroded surface were observed by scanning electron microscopy (SEM) and cold field emission scanning electron microscope (FESEM) and the cavitation-induced nanosize precipitates are found in the local zones of eroded surface.

Vibratory cavitation erosion behavior of AISI 304 stainless steel in water at elevated temperatures

The cavitation erosion behavior of AISI 304 stainless steel was investigated using an ultrasonic vibratory apparatus at elevated temperatures and the morphologies of the eroded surface and the cross section were observed by scanning electron microscopy (SEM) and optical microscopy. The results show that the cumulative mass loss increases, shows a peak and then decreases with increase in liquid temperature. The cavitation damage of the eroded surface was relatively uniform at 20–60°C and at 80°C it was localized; the depth of local deeper pit at 80°C was about 1.7 times deeper than at 50°C. The initial results based on the cumulative mass loss could not predict the degree of cavitation damage, and the depth of local erosion pit may be an effective method for judging erosion damage.

Cavitation erosion behavior of Hastelloy C-276 nickel-based alloy

The cavitation erosion behavior of Hastelloy C-276 alloy was investigated using an ultrasonic vibratory apparatus and compared with that of 316L stainless steel. The mean depth of erosion (MDE) and erosion rate (ER) curves vs. test time were attained for Hastelloy C-276 alloy. Morphology and microstructure evolution of the eroded surface were observed by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and the predominant erosion mechanism was also discussed. The results show that the MDE is about 1/6 times lower than that of the stainless steel after 9h of testing. The incubation period of Hastelloy C-276 alloy is about 3 times longer than that of 316L stainless steel. The cavitation-induced nanometer-scaled precipitates were found in the local zones of the eroded surface for Hastelloy C-276. The selective cavitation erosion was found in Hastelloy C-276 alloy. The formation of nanometer-scaled precipitates in the eroded surface may play a significant role in the cavitation erosion resistance of Hastelloy C-276.

Microstructural effect of α-Sialon ceramic on the resistance to cavitation erosion in deionized water

The resistance to cavitation erosion of one Yb-α-Sialon ceramic and two Dy-α-Sialon ceramics (Dy-α-Sialon-1 and Dy-α-Sialon-2) was investigated in deionized water using an ultrasonic vibratory apparatus. The incubation periods of Dy-α-Sialon-1, Dy-α-Sialon-2 and Yb-α-Sialon ceramic were 210min, 300min and 360min, respectively. Surface roughness and area fraction of cavities were found good indicators for the evolution of ceramics erosion. The microstructural features, including main phase (α phase), inhomogeneities of the microstructures and type of rare earth oxide, were correlated to the cavitation erosion behavior. It was found that the elongated α-Sialon grains in Yb-α-Sialon and Dy-α-Sialon-2 produced a self-toughening effect to increase the incubation period. The aggregation of Dy2O3 in Dy-α-Sialon-1 had an adverse effect on the resistance to cavitation erosion. Impurity phases and type of rare earth oxide had impacts on resistance to cavitation erosion. The findings in this work indicate that the cavitation erosion resistance of α-Sialon ceramics could be improved by microstructure optimization.

Evaluating Erosion of Engineering Materials Subject to Cavitation in Liquids on a Ultrasonic Vibratory Apparatus

To evaluate the erosion of various engineering materials subject to cavitation in laboratory, a ultrasonic vibratory apparatus (UVA-1) is designed and manufactured according to ASTM G 32-06. The principle and setup of the UVA-1 are briefed. Some utilities of this apparatus are listed with several good examples.

Cavitation erosion behavior of ceramics in aqueous solutions

Significant research has been done in the cavitation behavior of metallic alloys (steel, aluminum, etc.) and to a much lesser degree engineering ceramics. Corrosion will enhance cavitation damage in metallic alloys, whereas ceramics are generally considered to be immune to most types of corrosion and should demonstrate the same cavitation behavior regardless of media. This preliminary study evaluates the cavitation performance of several engineering ceramics (Al 2O 3, Si 3N 4, Macor™ (glass-mica) and ZrO 2) in various media, including: simulated sea water, distilled water and dilute acid and base. Cavitation testing was accomplished using an ultrasonic vibratory apparatus per ASTM G-32-03. Results indicate that Al 2O 3 is influenced by basic solutions and the cavitation resistance of zirconia drops in the presence of acid. The glass-mica (Macor™) ceramic had the lowest cavitation resistance but was not influenced by the media. The relationship between the media, mechanical properties and microstructure of each ceramic and cavitation behavior is discussed.

Cavitation erosion resistance of Fe-26Mn-6Si-7Cr-1Cu shape memory alloy

The cavitation erosion of low stacking fault energy Fe-26Mn-6Si-7Cr-1Cu shape memory alloy has been investigated in water using an ultrasonic vibratory apparatus, and compared with the behaviour of 0Cr13Ni5Mo stainless steel. It is shown that Fe-26Mn-6Si-7Cr-1Cu alloy has higher cavitation erosion resistance than 0Cr13Ni5Mo stainless steel. The cavitation erosion mechanism of Fe-26Mn-6Si-7Cr-1Cu was studied by examining the eroded surface using X-ray diffraction (XRD) and scanning electron microscopy (SEM). During early stages of cavitation erosion, Fe-26Mn-6Si-7Cr-1Cu alloy undergoes strain induced martensitic transformation. Exposure to further cavitation results in the deformation of ϵ martensite. The boundaries of ϵ martensite impede plastic deformation, leading to strain accumulation and subsequent material removal. On the basis of an XRD study and indentation tests, the better cavitaton erosion resistance of Fe-26Mn-6Si-7Cr-1Cu alloy is mainly ascribed to strain induced martensitic transformation, which can absorb impact energy without damage.

Cavitation Erosion and Friction Behavior of Stainless Steel as a Function of Grain Size

ABSTRACTResearch conducted on steels is motivated by a technological need to further improve their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a low yield strength. One way of increasing the yield strength is by grain refining. This work presents a study on the cavitation erosion and friction behavior of AISI 304 austenitic stainless steel characterized by two different grain sizes: 2.5 μm and 40 μm. The cavitation erosion behavior in water with different pH values and at room temperature has been studied by using a 20 kHz ultrasonic vibratory apparatus. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH value; decrease of this value produces an increase in surface damage. Using a precision microtribometer, with applied loads in the μN regime, it was found that capillarity plays a dominant role. At the same loads, in high humidity environments, both the fine and coarse grain steels exhibit high friction relative to measurements performed under dry conditions. At high loads (20 mN and above) a reversal in microfrictional behavior occurs in that friction is higher under dry conditions than under moist conditions.

Cavitation Erosion of Cobalt Alloy Coatings Containing Tungsten Carbide Particles in Hydrochloric and Sulphuric Corrosive Media

Cavitation erosion tests of composite coatings based on vacuum fusion sintered cobalt alloy containing tungsten carbide particles were carried out in 30 percent HCl and 50 percent H2SO4 solutions. The technique used included an ultrasonic vibratory apparatus at 30°C, 25μm amplitude and 30 kHz frequency. Weight loss was measured with an analytical balance and the microstructure was observed with SEM. The test results showed that the cavitation erosion resistance of the composite coatings was increased by increasing the tungsten carbide content. The cavitation erosion is mainly caused by removal of the matrix material. The steady-state erosion rates have a linear relationship with the volume fraction of the tungsten carbide phase.

Cavitation erosion of grey cast irons containing 0.2 and 1.0% phosphorous in corrosive waters

The effect of 0.2 and 1.0% P in a sand cast flake graphite grey iron on the cavitation erosion behaviour in distilled, NaCl, and NaCl/inhibitor waters, has been investigated. Techniques used include an ultrasonic vibratory apparatus at 50°C and 15 μm amplitude, electrochemical polarization, profilometry, and microscopy. Salt in the water increased the electrochemical corrosion rate, the erosion rate, the number of pits/cracks in the surface, the roughness of the surface, and reduced the nominal incubation time. For the 0.2% P iron in 3% salt water the nominal incubation time was reduced by 0.2 times, the steady-state erosion rate increased by 7.0 times and 90% of the increase was due to corrosion-induced erosion. The presence of a continuous brittle phosphide network in the 1.0% P iron had a negligible effect on the erosion rate but reduced the incubation time by a factor of 0.3. The inhibitor eliminated completely the effects of corrosion up to a salt concentration of 0.25%. The processes and mechanisms are discussed.