Cavitation Erosion Mechanism Research Articles

Cavitation erosion mechanism of S31600 stainless steel laser surface-modified with unclad WC

Laser surface modification of UNS S31600 stainless steel using coarse unclad WC powder (particle size ≈60 μm) for enhancing cavitation erosion resistance was attempted. WC powder was preplaced on as-received S31600 substrate and irradiated by a high-power CW Nd:YAG laser to form a metal-matrix composite (MMC) layer on the substrate. By varying the laser fluence, MMC layers consisting of 3–28 vol.% of WC particles were formed. The microstructure, composition, and the phases present in the modified layer were studied by optical microscopy (OM), energy-dispersive spectrometry (EDS), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The cavitation erosion resistance R e in 3.5% NaCl solution was determined using an ultrasonic vibratory facility. R e was found to attain a maximum value (10.7 times that of as-received S31600) at 9 vol.% of WC. The damaged surface after the cavitation erosion test was studied by SEM to identify the damage mechanism. The variation of R e with the volume fraction of WC was explained in terms of the erosion mechanism of the matrix and the WC particles.

1205 ロングオリフィス出口における壊食メカニズムの解明 : 気泡崩壊過程の観察

1205 ロングオリフィス出口における壊食メカニズムの解明 : 気泡崩壊過程の観察

The final stage of the collapse of a cavitation bubble close to a rigid boundary

The final stage of the collapse of a laser-produced cavitation bubble close to a rigid boundary is studied both experimentally and theoretically. The temporal evolution of the liquid jet developed during bubble collapse, shock wave emission and the behavior of the “splash” effect are investigated by using high-speed photography with up to 5 million frames/second. For a full understanding of the bubble–boundary interaction, numerical simulations are conducted by using a boundary integral method with an incompressible liquid impact model. The results of the numerical calculations provided the pressure contours and the velocity vectors in the liquid surrounding the bubble as well as the bubble profiles. The comparisons between experimental and numerical data are favorable with regard to both bubble shape history and translational motion of the bubble. The results are discussed with respect to the mechanism of cavitation erosion.

Cavitation erosion mechanisms and quantitative evaluation based on erosion particles

Cavitation erosion mechanisms were studied through the observation of removed particles for annealed S15C (equivalent to AISI 1015) steel and heat-treated S55C (AISI 1055) steels. In the initial and the incubation stages, single impact loads removed many small sharply edged particles. During the acceleration and the maximum rate stages, large striated particles were observed due to cyclic loads. The volume fraction of particles exhibiting fatigue fracture in these stages amounts to 70 or 80% irrespective of the material including pure copper and pure aluminum. The exponent of the crack growth rate determined from the fracture is almost the same as that obtained from a regular fatigue test. The fatigue crack growth rate for many metals is inversely proportional to the square of Young's modulus, E−2. The particles fall off from the protrusive surface and their sizes depend on the unevenness in relation to the hardness of the material. The average diameter of erosion particles decreases inversely with the square root of Vickers hardness, HV−1/2. Therefore, the volume is proportional to HV−3/2. Thus, the dependence of the volume loss rate in the maximum rate stage is well described by HV−3/2E−2. The conclusion is that cavitation erosion can be evaluated in terms of the hardness of the material and the fatigue crack growth rate.

Study on the influences of bubbly oil on the cavitation erosion in journal bearings of engines

A simulating experimental device for journal bearin gs of engines is established by use of the mechanism of ultrasonic vibrationTh is device can make the pressure inside the oil film changed at ultrasonic freque ncy,which enable the specimen surface to be damaged by cavitation erosion in a c omparatively short timeConnecting with the bubbly oilproducing device,this r ig can investigate the influence of bubbly oil on the cavitation erosionThroug h detailed experimental research it is found that the bubbly oil decreases the c avitation erosion in journal bearings of enginesThis result is analyzed reason ably from mechanism of cavitation erosion

A Fundamental Study on Cavitation Erosion Using a Magnesium Oxide Single Crystal. Effect of Surface Roughness.

When a material is exposed to cavitation for a long time, the sueface is eroded like a sponge, which is one of the evidences of cavitation damage. However, the mechanism of the spongelike surface formation remains unclear. A magnesium oxide single crystal is useful to understand the fundamental mechanisms of cavitation erosion. In this study, magnesium oxide single crystal(100)surface were polished with four grades of emery paper to prepare test specimens. The test specimens were exposed to vibratory cavitation. Many dislocation rows with various lengths which intersect the specimen surface at 45 degrees were observed uniformly on a(010)or(001)cross section for an as-cleaved specimen. On the other hand, the dense dislocation rows were localized at the roots of surface irregularity for rough specimens. The depht of surface roughness increases with exposure time and the acceleration is hogher for rougher specimens. It is concluded that the dense dislocation rows intiated at the roots of irregular surface is responsible for the growth of the spongelike eroded surface.

Cavitation erosion mechanism of NiTi coatings made by laser plasma hybrid spraying

NiTi intermetallic compound is known to be a high cavitation erosion-resistant material. The erosion behaviors of NiTi intermetallic compound coatings made by laser plasma hybrid spraying (LPHS) were studied. The erosion resistance of the NiTi coatings depended strongly on the chemical composition of the coatings and the laser irradiation condition, because the NiTi phase and the microstructure of the coatings were varied by those conditions. The best erosion-resistant coatings were obtained with the conditions of nickel composition richer than that of equiatomic NiTi and irradiated laser power density greater than 6×10 8 W/m 2. The cavitation erosion resistance of the coating was about 380-fold that of a titanium alloy substrate. High erosion resistance of these coatings was obtained due to a combination of two factors, namely, super elasticity due to austenite-phase NiTi and high work hardenability due to excess soluble Ni.

Cavitation Erosion Mechanisms and Its Quantitative Evaluation Based on Erosion Particles.

Cavitation erosion mechanisms were studied through the observation of erosion particles for carbon steels. In the initial period and the incubation period, many small sharply-edged particles were produced by single impact loads. In the accumulation period and the steady-state period, large striated particles were observed due to cyclic loads. The volume fraction of fatigue fracture is 70% to 80% in these periods incubation pure copper and pure aluminum. The exponent of the crack growth rate observed on the cross section of the eroded specimen is almost the same as that obtained from a regular fatigue test. The fatigue crack growth rate for many metals depends on a reciprocal of the square of Young's modulus (1/E2). The particles fall off from the tip of uneven surface. The maximum diameter of erosion particle decreases inversely to the square root of Vickers hardness (1/HV1/2), thus the volume is proportional to 1/HV3/2. Therefore, the volume loss rate in the steadystate period corresponds well with the 1/(HV3/2·E2). It was concluded that cavitation erosion can be evaluated in the terms of the material hardness and the fatigue crack growth.

Cavitation erosion by single laser-produced bubbles

In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary (γ=2, where γ=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances (γ[les ]0.7). In this region, the impact velocity rises to 83 m s−1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at γ>1, the impact velocity is smaller than 25 m s−1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when γ<2 and at the moment of first collapse when γ<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range γ=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At γ[les ]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the circumference of the torus, the observed damage is circular as well. Bubbles in the ranges γ[les ]0.3 and γ=1.2 to 1.4 caused the greatest damage. The overall diameter of the damaged area is found to scale with the maximum bubble radius. Owing to the possibility of generating thousands of nearly identical bubbles, the cavitation resistance of even hard steel specimens can be tested.

Cavitation erosion and damage mechanisms of alloys with duplex structures

The cavitation erosion characteristics of alloys with duplex structures such as super duplex stainless steel (UNS S32760) and α+ β brass (Cu–40%Zn) in 3.5% NaCl solution at 23°C were investigated by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 50 μm. Austenitic stainless steel (UNS S30400) with single phase structure was also investigated for comparison purpose. The effect of heat treatment on the cavitation erosion characteristics of these alloys was also studied. Heat treatment of brass and S30400 stainless steel increases the grain size and ductility, and decreases the mechanical strength of these alloys, leading to an increase of erosion loss. For S32760, the effect of heat treatment on the mechanical properties and grain size is minimal and therefore erosion loss is unaffected. Hardness, tensile strength, engineering strain energy and grain size of the heat-treated alloys correlate well with the cavitation erosion resistance R e by linear regression.

Mechanisms of cavitation erosion of TiAl-based titanium aluminide intermetallic alloys

The modes and controlling mechanisms of cavitation erosion of plasma arc-melted TiAl-based titanium aluminide intermetallic alloys, Ti52Al (at.%) and Ti48Al2Mn2Nb (at.%) were studied and compared to those of the Ti3Al-based alloy, Ti25Al10Nb3V1Mo (at.%) and other comparative materials. The accumulation of cavitation damage during the initial stages of cavitation erosion was monitored and the work hardening produced in steady state erosion conditions was measured on 5° taper sections. The cavitation erosion resistance of the titanium aluminide alloys is discussed in terms of their microstructure and mechanical properties. The superior cavitation erosion resistance of the TiAl-based titanium aluminide alloys compared to Ti25Al10Nb3V1Mo (at.%) is ascribed to their ability to twin and to their greater work hardening ability during cavitation erosion.

Cavitation erosion of laser-melted ductile iron

The influence of laser processing on the cavitation erosion of ductile iron, a material employed extensively for components in marine applications, including diesel-engine cylinder liners, valves and pumps, is addressed here. Pearlitic ductile iron has only modest resistance to cavitation erosion; the mean depth of penetration rate (MDPR) was 10 12 μm h −1 in distilled water. Ferritic ductile iron had consistantly better resistance to erosion than pearlitic iron, particularly in corrosive media. The cavitation erosion rates in an aqueous slurry of 35 wt%. 220 grit SiC, Synthetic sea water (3.4 wt%) and centinormal dilute H 2SO 4 were 24.40 and 86 μmh −1 respectively, whilst the corresponding rates were reduced to 3, 6 and 12 μm h −1 for laser-melted samples. The synergistic effect of corrosion and cavitation erosion was more pronounced in the dilute acid than in the salt water. The cavitation erosion rates decreased linearly with increase in the pH value of the cavitation bath. Laser treatment was very effective in bringing about a nearly seven-fold enhancement of the erosion resistance of ductile iron in mild corrosive media. This has enabled the delineation of the mechanism of cavitation erosion of ductile iron before and after laser processing, particularly in corrosive baths. A comprehensive review of published technical literature concerning the influence of laser surface treatment on the cavitation erosion of selected steels and cast irons in different baths is included.

Bubble Behavior near Collapsing Period of Cavitation Bubble under Flow Condition. Simultaneous Measurements with Impulsive Force.

The cavitation erosion problem in liquid flow systems is investigated by many engineers and scientists from the viewpoints of engineering applications as well as basic scientific interest. At the present stage, the mechanism of cavitation erosion is not completely elucidated. One of the most important points is that most investigations have not been conducted under real flow conditions. In the present investigation, simultaneous measurements of cavitation bubbles with impulsive force were realized in flow using a new system combining a high-speed video camera with an impulsive pressure sensor. Thus, some new findings have been revealed concerning the characteristics of bubble behavior near the bubble collapsing period.

Fatigue failure of SUS 304 caused by vibratory cavitation erosion

Abstract The mechanism of cavitation erosion is investigated in detail for SUS 304 stainless steel, a typical erosion-resistant material. Systematic observations of eroded surfaces and dislodged particles show that the predominant failure mode in cavitation erosion is fatigue. Characteristic features of such failures include (1) packets of slip bands, (2) cracks that nucleate at regions of high stress (strain) concentration, (3) cracks that propagate first at an inclination to the surface and then parallel to the surface, and (4) fatigue striations and ‘tire tracks’ on the rupture surfaces. These last two features are the most indicative of a fatigue process. It is also deduced that massive voids accompanying pressure shock-rings are the most erosive kind of cavitation.

腐食環境下におけるエポキシ樹脂のキャビテーション・エロージョン損傷機構

腐食環境下におけるエポキシ樹脂のキャビテーション・エロージョン損傷機構

Laser surface processing and the cavitation erosion of a 16 wt.% Cr white cast iron

The cavitation erosion of a 16 wt.% Cr white cast iron in distilled and 0.02% and 3.0% NaCl water at 50 °C has been investigated using a 15 μm amplitude 20 kHz ultrasonic facility, and the corrosion behaviour during erosion in the 3.0% salt solution measured electrochemically. The effects of prolonged annealing, laser surface melting, laser surface hardening and plasma nitriding of the cast iron were also investigated. Salt in the water increased the erosion rate considerably, and only 0.02% salt increased the rate by over three times. Prolonged annealing at 1040 °C reduced the erosion rate in distilled water but had a negligible effect on the erosion rate in salt waters. Laser processing reduced the rate considerably. For laser surface melting, the reduction in the erosion rate in distilled and 3.0% salt water was by factors of 0.07 and 0.2 respectively. Nitriding did not reduce the erosion rate of the cast material, and it eliminated the beneficial effects of laser melting. Corrosion currents obtained under static and cavitating conditions allowed the contributions of erosion, of corrosion-enhanced erosion and of corrosion to the total cavitation damage to be estimated. For each material, corrosion-enhanced erosion was the major component of damage in 3% salt water. The results of detailed metallographic examination of the erosion damage are also presented, and the mechanism of cavitation erosion is discussed.

Optical and acoustic investigations of the dynamics of laser-produced cavitation bubbles near a solid boundary

The dynamics of laser-produced cavitation bubbles near a solid boundary and its dependence on the distance between bubble and wall are investigated experimentally. It is shown by means of high-speed photography with up to 1 million frames/s that jet and counterjet formation and the development of a ring vortex resulting from the jet flow are general features of the bubble dynamics near solid boundaries. The fluid velocity field in the vicinity of the cavitation bubble is determined with time-resolved particle image velocimetry. A comparison of path lines deduced from successive measurements shows good agreement with the results of numerical calculations by Kucera & Blake (1988). The pressure amplitude, the profile and the energy of the acoustic transients emitted during spherical bubble collapse and the collapse near a rigid boundary are measured with a hydrophone and an optical detection technique. Sound emission is the main damping mechanism in spherical bubble collapse, whereas it plays a minor part in the damping of aspherical collapse. The duration of the acoustic transients is 20-30 ns. The highest pressure amplitudes at the solid boundary have been found for bubbles attached to the boundary. The pressure inside the bubble and at the boundary reaches about 2.5 kbar when the maximum bubble radius is 3.5 mm. The results are discussed with respect to the mechanism of cavitation erosion.

Empreintes dues à l'implosion de bulles isolées : Etude paramétrique expérimentale

With the aim of gaining a better understanding of the significance of various parameters on the cavitation erosion mechanism, an experimental study has been conducted on the marking of polished materials subjected to the collapse of a vapour bubble engendered by a discharger inside a pressurizable vessel. The parameters studied are: the pressure inside the vessel P, the distance relating to the centre of a (d/R max < 1.5) sample bubble, the material (99.99 % aluminium and 316 L stainless steel). Several conclusions can from now on be drawn: * The implosion of a bubble can engender many holes, which demontrates that the collapse in the form of a torus plays a determining part. * The maximum marking is obtained for a d/R value of less than 1.1. * For a given material, there exists a maximum permissible pressure below which no implosion is marked of about 0.07 MPa for aluminium and 0.15 MPa for steel.

A peculiar behavior of cavitating flow around a butterfly valve.

To clarify more precisely the mechanism of cavitation erosion as well as vibration, the flow patterns and the multitudinous constitution of the cavitation were carefully observed in a typical bounded flow around a butterfly valve by using a technique of high-speed photography simultaneously from two sides, under a prescribed nuclei distribution, various hydrodynamic quantities and rolling-up of high-speed flow from a so-called orifice side. In the region where the flow impacts on the downstream pipe-wall from the valve-disk, a large number of vortex cavitations take place predominantly, and the region corresponds well to the region where actual erosion occurs. There are several types of cavitation with their own aspects and behavior as well as occurrence zones in each constructional parts of the valve.

Spatial distribution of cavitation-shock-pressure around a jet-flow gate-valve.

To make clear the mechanism of cavitation erosion, the spatial distribution of cavitation shock pressures were quantitatively measured by a pressure sensitive sheet in the l/l0 scale model of a jet-flow gate-valve, for various valve-openings and cavitation numbers. The dynamic pressure response of the sheet was corrected by the shock wave generated from detonation explosives. It is made clear that the erosive shock pressures are distributed in a limited part of the whole cavitation region, and the safety region without the fatal cavitation erosion is defined.