Stationary Specimen Method Research Articles

Ultrasonic cavitation erosion of CFRP composites

To date, cavitation erosion of carbon fibre reinforced polymer (CFRP) composites has attracted only limited scientific attention. This paper investigates this knowledge gap through a series of experiments, in which unidirectional and bidirectional (2x2 twill) CFRP composites were exposed to cavitation clouds produced by an ultrasonic transducer in distilled water. Both composites were bonded with epoxy resin. Cavitation erosion tests were conducted according to the ASTM G32-16 standard using a stationary specimen method. The effect of water absorption on monitoring erosion damage was studied using saturated and dry specimens. Specimen mass loss measurements and microscopy observations were done at regular intervals throughout testing. Erosion imprint topographies were studied using X-ray computed microtomography. Three distinct erosion stages were identified from the erosion process observations. Nonuniformities in surface geometry and properties facilitated nucleation and accelerated local erosion. Surface epoxy thickness, fibre diameter and packing, and thickness and layup of fibre bundles influenced the erosion process. The erosion mechanisms included cracking and debonding of epoxy, and tunnelling and trenching in fibre bundles. Research findings indicated that the composite internal structure can potentially be designed for reduced water absorption and increased erosion resistance. Acoustic impedance was most efficient in predicting material response to cavitation erosion.

Effect of Nitrogen Ion Implantation on the Cavitation Erosion Resistance and Cobalt-Based Solid Solution Phase Transformations of HIPed Stellite 6.

From the wide range of engineering materials traditional Stellite 6 (cobalt alloy) exhibits excellent resistance to cavitation erosion (CE). Nonetheless, the influence of ion implantation of cobalt alloys on the CE behaviour has not been completely clarified by the literature. Thus, this work investigates the effect of nitrogen ion implantation (NII) of HIPed Stellite 6 on the improvement of resistance to CE. Finally, the cobalt-rich matrix phase transformations due to both NII and cavitation load were studied. The CE resistance of stellites ion-implanted by 120 keV N+ ions two fluences: 5 × 1016 cm−2 and 1 × 1017 cm−2 were comparatively analysed with the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen-implanted HIPed Stellite 6 two times exceeds the resistance to CE than unimplanted stellite, and has almost ten times higher CE reference than stainless steel. The X-ray diffraction (XRD) confirms that NII of HIPed Stellite 6 favours transformation of the ε(hcp) to γ(fcc) structure. Unimplanted stellite ε-rich matrix is less prone to plastic deformation than γ and consequently, increase of γ phase effectively holds carbides in cobalt matrix and prevents Cr7C3 debonding. This phenomenon elongates three times the CE incubation stage, slows erosion rate and mitigates the material loss. Metastable γ structure formed by ion implantation consumes the cavitation load for work-hardening and γ → ε martensitic transformation. In further CE stages, phases transform as for unimplanted alloy namely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of γ phase. The CE mechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviour relies on the plastic deformation of cobalt matrix, starting at Cr7C3/matrix interfaces. Once the Cr7C3 particles lose from the matrix restrain, they debond from matrix and are removed from the material. Carbides detachment creates cavitation pits which initiate cracks propagation through cobalt matrix, that leads to loss of matrix phase and as a result the CE proceeds with a detachment of massive chunk of materials.

Cavitation erosion and sliding wear resistance of HVOF coatings

The aim of the work was to investigate the resistance to cavitation erosion and sliding wear of sprayed HVOF coatings. M(Ni,Co)CrAlY and Cr3C2-NiCr based coatings were deposited using HVOF method onto stainless steel substrate grade AISI 304. As-sprayed coatings’ surface morphology was examined by SEM-EDS and profilometer methods. Cavitationerosion tests were conducted in distilled water with the use of vibratory rig and stationary specimen method. Cavitation erosion curves were plotted as well as cavitational wear mechanism was observed with the use of SEM microscope. Sliding wear tests were performed using the ball-on-disc tribotester with counter-specimen (ball) made of steel 100Cr6. Wearrates and coefficient of friction were computed. Normalized wear resistance with referenceto stainless steel reference sample AISI 304 was calculated. In addition, comparable analysis of wear resistance results was conducted. M(Ni,Co)CrAlY coating presented the highest cavitation erosion resistance, therefore Cr3C2-NiCr coating represented the highest sliding wear resistance of all tested materials.

Some Laboratory Tests Regarding the X20Cr13 Martensitic Stainless Steel Behaviour

In this paper, beside the documentation regarding the many laboratory tests of X20Cr13 steel, the cavitation erosion, dry sliding wear, hardness respectively corrosion of this martensitic stainless steel was investigate. As cavitation erosion aspects, the authors present some preview results and continue to investigate the cavitation erosion resistance of X20Cr13 steel for an extended duration of 900 minutes of the cavitational attack, duration divided into 30 periods of 30 minutes. All this research through the stationary specimen method was done by using a cavitation stand and the obtained results were presented through cumulative mass loss and cavitation erosion rate versus time curves. As dry sliding wear aspects, the research was done with a CSM Tribometer through the pin-on-disk method and the obtained results were presented by means of the coefficient of friction and the wear rate. As hardness aspects, the measurement was made through the Vickers method using a Zwick/Roell microhardness tester. Finally, as corrosion aspects the research was done with a three-electrode cell using potentiodynamic polarization method and the obtained results were presented as corrosion curve in a logarithmic form.

Application of computer image analysis software for determining incubation period of cavitation erosion – preliminary results

The paper discusses the application of image analysis software ImagePro Plus and MetIlo for assessing cavitation erosion wear. The investigation of cavitation damage is performed on a vibratory test rig in compliance with the ASTM G32 standard using the stationary specimen method. Low-alloy steel grade 34CrNiMo6 is used as the test material. Cavitation wear is evaluated by gravimetric and roughness measurements, microscopic observations and computer image analysis in specified exposure times. The computer image analysis of selected surface areas during a predetermined exposure to cavitation time is performed using images captured with a metallographic microscope. Based on the results of scanning electron and stereoscope microscopic observations, the cavitation worn surfaces are qualitatively described. The relations between surface topography, gravimetric measurements and the microscopic results are discussed. The findings obtained by gravimetric and roughness measurements, image processing and microscopic observations are complementary. The results prove the suitability of image analysis for investigating incubation period of cavitation erosion. The quantification of cavitation erosion damage indicates that the incubation period of cavitation erosion of the tested steel lasts for 20 minutes. The results demonstrate that cavitation-worn surfaces at the initial stage of cavitation erosion can be examined using both ImagePro Plus and MetIlo.

Cavitation Erosion Research on the X3CrNi13-4 Stainless Steel

The paper presents ample researches on cavitation erosion of two charges of stainless steel type X3CrNi13-4 on a cavitation stand, through the stationary specimen method. The results of the experimental trials are highlighted in tables and in graphics regarding the reproduction of mass losses and the cavitation erosion rate according to time. The images of the microstructures before the cavitation test and the macrostructures after the cavitation test of the two charges of stainless steel type X3CrNi13-4 are also presented in this paper.

Research through the Stationary Specimen Method of the X20Cr13 Stainless Steel Used for Hydraulic Pumps

This paper presents the cavitation erosion research through the stationary specimen method of the X20Cr13 martensitic stainless steel. Actual research involves a number of 4 different tests for this material and the comparison between these experimental tests is highlighted by the images and graphs forwarded in the paper. All research was done using vibratory apparatus composed from electro-acoustic piezo-converter, acoustic transformer, a titanium sonotrode and the ultrasonic generator DG-2000. The mass loss of the martensitic stainless steel samples was measure with special digital balance.

Roughness measurement as an alternative method in evaluation of cavitation resistance of steels

The purpose of this study was to investigate possible application of roughness measurement in evaluation of resistance of steels in conditions of cavitation effect where these materials are usually applied. Steels which belong to different classes were selected for testing. Cavitation testing was performed by using the ultrasonic vibratory cavitation test set up (stationary specimen method). Mass loss and surface degradation of investigated samples were monitored during the exposure to cavitation erosion. Mass loss was measured by an analytical balance. The morphology of the damaged surfaces with the change of the test period was analyzed using scanning electron microscopy (SEM). The surface roughness tester was used to monitor changes of surface roughness during the test and for obtaining the line profile of surface samples after cavitation tests. Cross-sections of samples were made after testing and optical microscopy was used to obtain complete information about the roughness change and compare the images with the lines of the profile obtained by the measurement of roughness. It can be concluded that the behaviour of steels under conditions of cavitation can be estimated by measuring the change in surface roughness. Conclusions adopted on the basis of roughness changes are consistent with that based on measurements of mass loss and morphology of surface damage during cavitation testing time.

Cavitation erosion of silver plated coatings in a low-temperature environment

Abstra ct It is well known that cavitation occurs in inducer pumps used for space rockets. The silver plated coating on the inducer liner faces erosion damage. In this study, we carried out cavitation erosion tests on seven silver plated coatings with the stationary specimen method using a vibratory apparatus. We analyzed the erosion behavior of these coatings and discussed their erosion resistance. The erosion resistance of silver plated coatings can be evaluated in terms of material hardness and was ranked between pure aluminum and pure copper. Moreover we carried out erosion tests using the vibrating specimen method in deionized water, liquid nitrogen and ethanol for the silver coating which showed the highest erosion resistance in the stationary specimen method. We found that erosion occurred in low-temperature ethanol, but not in liquid nitrogen.

Bubble Structures Between Two Walls in Ultrasonic Cavitation Erosion

The cavitation bubble structures for the stationary specimen method were clarified for various distances, h, between the stationary specimen and the horn-tip surface. The generated cavitation bubbles constituted a huge number of tiny bubbles and bubble clusters of different sizes. The maximum cluster size was 1.4 mm. The observed cavitation patterns systematically changed during tests from the subcavitating state to the supercavitating state with respect to the separation distance, h. For h <4 mm, the bubbles have a definite trajectory, and the pressure patterns manifest a circular shape as a result of streaming induced by ultrasonic cavitation. The feature morphology of the eroded surfaces revealed that the predominant failure mode was fatigue. In the light of the material failure features and the cavitation patterns, it is also deduced that the important mechanism to transfer the cavitation energy to the solid is shock pressures accompanied by collapsing clusters.

Cavitation Erosion of Silver Plated Coatings in a Low-Temperature Environment

It is well known that cavitation occurs in inducer pumps used for space rockets. Silver plated coating on the inducer liner faces the damage to erosion. In this study, we carried out cavitation erosion tests for seven silver plated coatings in stationary specimen method using a vibratory apparatus. We analyzed the erosion behavior of these coatings and discussed the erosion resistance. The erosion resistance of silver coating could be evaluated in terms of material hardness and was ranked between pure aluminum and pure copper. Moreover, we carried out erosion tests using vibrating specimen method in deionized water, liquid nitrogen and ethanol for the silver coating which showed the highest erosion resistance in stationary specimen method. We found that erosion occurred in low-temperature ethanol, but not in liquid nitrogen.

Experimental study and analytical model of the cavitation ring region with small diameter ultrasonic horn

Experiments of cavitation erosion are performed on a surface using the “stationary specimen method”. A small diameter horn of 5 mm is selected instead of using the standard horn of 15.9 mm. The experiments are performed according to these parameters: an excitation frequency of the horn of 20 kHz, a gap between the horn and the specimen within the range from 0.05 to 0.5 mm and the displacement amplitude of the horn within a range of 15–50 μm. After examination of the samples, two erosion patterns can be clearly distinguished, one circular shape centred in the origin and a ring shape around. Moreover, it has been observed that the diameter of this ring shape, the cavitation ring region, is a function that depends on the amplitude and the gap. Existence of the cavitation ring region under the mentioned conditions is explained using a theoretical model based on the combination of Fluid Mechanics and Analytical Mechanics. Results after application of this model reveal the satisfactory agreement between the numerical output and the experimental data.

Revision of cavitation erosion database and analysis of stainless steel data

Cavitation erosion data have been accumulated in our laboratory for about 32 years since 1970. The database was constructed as electronic data in MS Excel files. The data files are able to offer quick search in terms of the test material, test method and test conditions from among 859 data. In this study, 131 data since 2003 were newly added to the database constructed in our previous study. The stainless steel data were analyzed, including various stainless steels such as ferritic, austenitic, duplex and martensitic stainless steels. Vibratory cavitation test results for different stainless steels, obtained with varying test conditions of frequency, amplitude and attachment of specimen, were converted analytically to obtain average erosion rates under assumed standardized conditions of a stationary specimen test with 1 mm standoff distance, and with frequency and amplitude as specified by ASTM G32. The average of erosion rate under the standardized condition (ASTM G32, stationary specimen method, standoff distance 1 mm) was determined for different stainless steels. The erosion resistance was defined as a reciprocal of erosion rate, and the correlation between erosion resistance and hardness of the specimen after erosion test was better than with the other mechanical properties. The erosion resistance is equal to 2.6E−07 × (HV × F mat) 2.4 (HV; Vickers hardness, F mat; material factor), and the correlation coefficient is 0.98. It was concluded that the erosion resistance of different stainless steels could be estimated with high reliability from the material hardness and the material factor.

Construction of Database on Cavitation Erosion and Analyses of Stainless Steel Data

Cavitation erosion data have been accumulated in our laboratory for about 34 years since 1970. The database was constructed as electronic data in Excel file. The data file is able to offer quick search in terms of test material, test method and test condition from among 986 data. The stainless steel data were analyzed, including various stainless steels such as ferritic, austenitic, duplex and martensitic stainless steel. The average of erosion rate under the standardized condition (ASTMG32, stationary specimen method, standoff distance 1 mm) was determined for different stainless steels. The erosion resistance was defined as a reciprocal of erosion rate, and the correlation between erosion resistance and hardness of eroded area after erosion test was better than with the other mechanical properties. The erosion resistance is equal to 2.6×10-7× (HV×.Fmax) 2.4 (HV;Vickers hardness, Fmat; Material factor), and the correlation coefficient is Q.98. It was concluded that the erosion resistance of different stainless steels could be estimated precisely from the material hardness and material factor.

935 キャビテーション壊食データベースの構築と炭素鋼データの解析

Cavitation erosion data has been accumulated in our laboratory since 1970 for about 30 years. The database was constructed in the electrical data of the Excel file. The data file is able to offer the quick search in terms of test material, test method and test condition among 859 data. The carbon steel data were analyzed, excluding stainless steels that exhibit the high work hardening. The average of erosion rate under the standardized condition (ASTM G 32, stationary specimen method, standoff distance 1 mm) was determined for different carbon steels. Since the coefficient of variation was obtained in the range from 0.1 to 0.3, the standard deviation can be easily estimated for these steels. The erosion resistance was defined as a reciprocal of erosion rate, and it was normalized with the erosion resistance of SUS 304 steel. The normalized erosion resistance is equal to 2.1 E-06 x HV2.4 (HV, Vickers hardness), and the correlation coefficient is 0.92. It was concluded that the erosion resistance could be estimated precisely by the material hardness for carbon steels.

Cavitation Erosion of Ti-Ni Shape Memory Alloy Coating.

Cavitation erosion tests were carried out for Ti-Ni shape memory alloy solid and coating using stationary specimen method of vibratory apparatus. The alloy coating was made by sputter deposition and was heat-treated at 300, 500 and 700°C. The coatings without heat treatment and with treatment at 300°C were completely peeled off after reaching the substrate due to cavitation, and the coatings heated at 500 and 700°C were strong enough to have high resistance of the erosion. A transition of mass loss rate was observed against the temperature of heat treatment. The mass loss rate changes from high to low at 400°C, because of the crystallization at this temperature. The mass loss rate of the coatings heat treated at 500 and 700°C corresponds well with that of the alloy solid. It was concluded that the erosion resistance in Ti-Ni shape memory alloy coating is about 20 times superior to that of stelite 6B.

K-0411 Ti-Ni形状記憶合金被覆材のキャビテーション壊食(S08-3 環境適合性)(S08 形状記憶合金の製造・加工技術と機能発現)

Cavitation erosion tests were carried out for Ti-Ni shape memory alloy solid and coating using stationary specimen method of vibratory apparatus. The alloy coating was made by sputter deposition and was heat treated at 300, 500 and 700℃. A transition of mass loss rate was observed against the temperature of heat treatment. The mass loss rate changes from high to low at 400℃, because of the crystallization at this temperature. The mass loss rate of the coating heat treated at 500 and 700℃ corresponds well with that of the alloy solid. It was concluded that the erosion resistance in Ti-Ni shape memory alloy is about 30 times superior to that of stelite 6B.