ASTM G32 Research Articles

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 200rpm and 100mm/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 10h, 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 and high-velocity slurry erosion resistance of welded Stellite 6 alloy

The cavitation and slurry erosion resistances of Stellite 6 coatings and 13-4 stainless steel were compared in laboratory. The Cavitation Resistance (CR) was measured according to ASTM G32 standard and the Slurry Erosion Resistance (SER) was tested in a high-velocity erosion tester under several impact angles. The results showed that the coatings improved the CR 15 times when compared to bare stainless steel. The SER of the coatings was also higher for all the impingement angles tested, the highest erosion rate being observed at 45°. The main wear mechanisms were micro-cracking (cavitation tests), and micro-cutting and micro-ploughing (slurry erosion tests).

Observation of Microstructural Deformation Behavior in Metals Caused by Cavitation Impact

To clarify the erosion mechanism of cavitation, we pay attention to the internal changes in grains caused by cavitation impact. The vibratory cavitation test based on ASTM G32 was carried out and the cross section of directly under the eroded surface of a specimen was observed using the electron backscattering diffraction (EBSD) technique. The situations of grain boundaries and the changes in the crystal orientations of grains in aluminum, copper, and steel were analyzed. As a result, the following observations were made. Cavitation impact causes grain refining of sub-micrometer order near the eroded surface. There exist small changes in crystal orientation in grains. In steel, grain boundaries were generated on the eroded surface and were growing inward in the grain. Finally, the mechanism of internal deformation of grains caused by cavitation impact was discussed.

Wear mechanisms of epoxy-based composite coatings submitted to cavitation

Many hydraulic components are exposed to severe conditions such as high speed slurry and cavitation erosion, where the mechanical properties of the material in which they are manufactured, as well as the hydrodynamic profile of the components are crucial factors. These conditions are responsible for high maintenance and stoppage costs and seriously affect the reliability of power generation. In this work, coatings based on epoxy resins were applied onto stainless and plain carbon steel plates and their suitability to protect against cavitation erosion was evaluated. The cavitation erosion resistance was measured according to ASTM G32 standard in an ultrasonic cavitometer with an indirect-type sample positioning setup. The analysis of the microstructure and the worn surfaces of the samples showed that pores, matrix–reinforcement interfaces and cracks acted as nucleation sites for cavitation. The coatings presented good cavitation resistance based on incubation time measurements, but those that lasted longer showed 2 acceleration periods instead of the ordinary S-shaped time-variation curve typical of many metallic materials, which was mainly attributed to adhesion problems.

Cavitation erosion of martensitic and austenitic stainless steel welded coatings

Abstract The cavitation erosion resistance of four alloys used to repair worn turbines by welding was tested in laboratory. AWS E309 alloy (3 layers) and a High-Cobalt stainless steel (2 and 3 layers) were applied by manual process (SMAW) onto ASTM A743 grade CA6NM stainless steel (commonly known as 13-4 steel) and their cavitation resistance was compared to that of conventional alloys E410NiMo (applied by SMAW) and a ER410NiMo (applied by semiautomatic process GMAW). The microstructure of the weld deposits was studied by Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), while the chemical composition was analyzed by Optical Emission (OES) and Energy Dispersive X-Ray Spectrometry (EDXS). Cavitation erosion tests were performed in an ultrasonic tester according to ASTM G32 standard and the worn surfaces were analyzed by SEM and XRD. The best cavitation erosion resistance of all the materials tested was shown by the High-Cobalt stainless steel coating applied in 3 layers, while the AWS E309 presented the highest value of maximum erosion rate. Conventional E410NiMo and ER410NiMo alloys showed an intermediate behavior. Incubation periods were 10.9 h and 21.5 h for High-Cobalt stainless steel in 2 and 3 layers, respectively, and 1.4 h for the 13-4 steel. In High-Cobalt stainless steel samples, occurrence of austenite-to-martensite phase transformation and profuse formation of twins and slip lines at the worn surfaces were observed.

Influence of Phosphorus Concentration and Heat Treatment on Anticavitation Erosion Characteristics in Electroless Nickel Plating

Cavitation erosion has been a serious problem in the use of turbomachineries such as ship propellers. In this paper, we proposed a technique to prevent cavitation erosion using electroless nickel-phosphorus plating (ENP). ENP was plated on JIS CAC703 (Ni-Al Bronze), which is known as a material of ship propellers. We examined the anticavitation property of ENP by a vibratory cavitation apparatus based on ASTM G32. It was found that the mass loss of plated substrate can be decreased ten times less than that of substrate by selecting suitable heat treatment temperature for the concentration of phosphorus in ENP. Finally, the mechanism of erosion of ENP is discussed.

The effect of plasma spray parameters on the cavitation erosion of Al2O3–TiO2 coatings

This paper reports a study of how the choice of plasma spray parameters, used during deposition of Al2O3–13%TiO2 coatings on carbon steel, influences the cavitation erosion properties of such coatings. The parameters studied are the power feeding rate and hydrogen flow rate. The surface and cross section of coatings before and after cavitation were also observed by scanning electron microscopy (SEM). The phases present in the coatings were characterized by X-ray diffraction method (XRD). The microscopic observations were used to study the inter-lamellar connection, porosity, unmelted particles and so on inside the coating. We also measured the roughness, microhardness, adhesion strength and cavitation erosion of the coatings. The XRD results showed that the coating includes different allotropes of Al2O3 such as α and γ. The cavitation erosion studies of the coatings were conducted by ultrasonic cavitation testing on the basis of ASTM G32 standard. It was found that cavitation erosion is accelerated around the unmelted particles and porosities. The results reveal that the cavitation resistance of the coating is determined by its microstructure and that increasing discontinuities (inside the coating) reduce its cavitation resistance. We have found that the coating obtained at hydrogen gas flow rate of 16L/min and powder feeding rate of 20g/min has the best cavitation resistance.

Cavitation resistance, microstructure and surface topography of materials used for hydraulic components

The cavitation resistance of a stainless steel and two flame thermal spray coatings was tested in laboratory according to ASTM G32 standard. The time–variation curves of cumulative volume loss, erosion rate and roughness parameters were related to the microstructure of the samples and to the wear mechanisms. Pores, unmelted particles and other microstructure defects prevented the coatings from showing an incubation period during the tests, while the stainless steel exhibited the expected incubation, acceleration and maximum rate stages. In the stainless steel, a correlation between the transition from incubation to acceleration stage and the R sm / R q and R y / R q ratios was established.

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.

Slurry and cavitation erosion resistance of thermal spray coatings

The slurry and cavitation erosion resistance of six thermal spray coatings were studied in laboratory and compared to that of an uncoated martensitic stainless steel. Nickel, chromium oxide and tungsten carbide coatings were applied by oxy fuel powder (OFP) process and chromium and tungsten carbide coatings were obtained by high velocity oxy fuel (HVOF) process. The microstructure of the coatings was analyzed by light optical microscopy (LOM) and scanning electron microscopy (SEM), as well as by X-ray diffraction (XRD). The cavitation erosion resistance of the coatings was measured in a vibratory apparatus according to ASTM G32 standard and the slurry erosion tests were carried out in a modified centrifugal pump in which the samples were conveniently placed to guarantee grazing incidence conditions, as well as in a high velocity jet erosion testing machine. The results showed that the slurry erosion resistance of the steel can be improved up to 16 times by the application of the thermally sprayed coatings. On the other hand, none of the coated specimens showed better cavitation resistance than the uncoated steel in the experiments. The main mass removal mechanisms observed in all the coatings submitted to slurry erosion were micro-cutting and micro-ploughing as well as detachment of hard particles. In cavitation erosion, OFP coatings showed brittle fracture and microcracking, and in nickel-based coatings some ductile deformation was also observed. In HVOF coatings, detachment of small particles led to coalescence of pores in WC/Co coatings while in CrC coatings the main wear mechanism was brittle fracture of particles.

Cavitation erosion of electroplated nickel composite coatings

The cavitational wear resistance of electroplated nickel composite layers was tested following ASTM G32. Particles of different hardness (titania and silicon carbide) and different sizes from micro-scale to nano-scale were incorporated up to 30 vol.% into a nickel matrix. Martens hardness is improved by grain refinement via particle incorporation. Compared to pure electroplated nickel films the composite layers strengthened by submicro-scale silicon carbide particles exhibit a decreased mass loss of one order of magnitude after 8 h testing time. Remarkably, layers with nano-scaled titania particles show a similar performance. Apart from particle adherence failures, reduced mass loss of the composite layers correlate with improved hardness of the composite due to grain refinement of the matrix and dispersion hardening effects.

Cavitation erosion resistance of various material systems

Advancement in both the design and construction of high-speed ships necessitates the evaluation of cavitation erosion resistant materials. Given their weight advantages, aluminum and laminated composite materials are often chosen as construction materials for high-speed designs. Historically, neither of these materials performs well in a cavitating environment. The objective of this effort is to evaluate potential cavitation erosion protection alternatives. Screening of the various material alternatives was performed using a modified ASTM G32 ultrasonically induced cavitation test method. A relative ranking is provided for materials including metals, composites, elastomers, polymers, and hard ceramic coatings using the maximum erosion rate as a parameter. A potential solution identified during this study involves the use of a durable elastomer material as a protective barrier. Results also show that a sandwich core composite system can be used to increase the cavitation erosion resistance of laminated composite materials.

Construction of database on cavitation erosion and analyses of carbon steel data

Cavitation erosion data have been accumulated in our laboratory for about 30 years since 1970. The database was constructed as electronic data in 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. Carbon steel data were analyzed, excluding stainless steels that exhibit high work hardening. Vibratory cavitation test results for different carbon 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. Since coefficients of variation were obtained in the range of 0.1–0.3, the standard deviation can be easily estimated for these steels. The erosion resistance was defined as the reciprocal value of the erosion rate, and it was normalized with the erosion resistance of SUS304 steel. The normalized erosion resistance is equal to 2.1 E – 06 × HV 2.4 (HV; Vickers hardness), and the correlation coefficient is 0.92. It was concluded that the erosion resistance of carbon steels can be estimated with high reliability from the material hardness.