Cavitation is a wear process in engineering systems caused by the energy release of collapsing bubbles leading to the failure of critical components such as valves, pumps, and propellers. Thermally sprayed coatings can be applied to improve the wear resistance of these components. This investigation considers a WC-NiCrBSi coating composition under cavitation wear, where the WC phase provides the strength and the NiCrBSi matrix offers corrosion resistance in seawater. Coatings were deposited on AISI 440C stainless steel discs of 32mm diameter and 8mm thickness using industrially optimized parameters for the HVOF JP5000 system. Indirect cavitation tests were conducted using a modified ASTM G32 testing procedure on coated test coupons in as-sprayed and Hot Isostatic Pressed (HIPed) conditions. Two tests were performed for each coating using natural seawater of pH 8.19 at room temperature, and averaged wear values are reported to compare the cavitation rate and cumulative mass loss of the coatings. Coating microstructural phases in the as-sprayed and HIPed conditions were identified using X-ray diffraction. The microstructure of the coating substrate system and post-cavitation test wear scars were investigated using Scanning Electron Microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). This investigation provides an understanding of the corrosive-cavitation wear behavior and failure modes of coatings. The cavitation erosion rate and cumulative mass loss results showed that the as-sprayed WC-NiCrBSi coatings improve the cavitation wear resistance of the substrate.

The development of materials and alloys for coatings has been increasingly important for reducing costs in different manufacturing processes. The Inconel alloy is widely used due to its chemical inertness and high resistance to high temperatures, but it does not present adequate resistance to erosive wear. In this context, the resistance to wear from cavitation erosion and slurry erosion was evaluated of samples with depositions obtained by laser cladding (Laser directed energy deposition - L-DED) of Inconel 718 and Inconel 718+10%NiNb. The cavitation erosion wear tests were carried out following the ASTM G32 standard (2016), and the ASTM G73-10 standard (2017) was used to evaluate the resistance to slurry erosion wear. The scanning electron microscopy technique (SEM-EDS), and X-ray diffraction (XRD) were used to characterize the cross-section and the surface after wear. The wear mechanism was checked and identified. Microhardness profiles of the cladding cross-section were carried out. The mass loss and wear rate due to cavitation and slurry jet erosion of Inconel 718 and Inconel 718+ 10% NiNb coatings were determined. It was proven that the addition of 10% NiNb in the formation of the cladding caused a 45% increase in average microhardness in the cross-section of the Inconel 718 cladding. The addition of 10% NiNb to the Inconel 718 cladding caused a decrease in mass loss due to slurry erosion from 38.9 mg to 21.9 mg (33%) when the erodent impact angle was 60°.

This study investigates the cavitation erosion (CE) behavior and fracture morphology of tungsten carbide thermal spray coatings. WC-CoCr and WC-CrC-Ni powders of various sizes were deposited on stainless steel substrates by HVOF spraying using different combustion pressures. Coating samples and Cr steel reference specimens were subjected to vibratory cavitation erosion tests, volume loss was measured, and erosion damages were examined by SEM to assess fracture morphology. The results indicate that CE resistance can be improved by reducing porosity and increasing interparticle bonding strength.

High quality coatings of titanium can be obtained by cold spraying using high process gas temperatures and pressures. However, the performance of cold sprayed coatings is determined not only by the respective material properties and the impact conditions, but also by the temperature and properties of the substrate—including the already deposited— material. In the present study, cold spray of spherical titanium grade II powders was performed on titanium grade II, copper, and stainless steel substrates, using two sets of parameters and three different substrate temperatures. Single impacts and respective particle adhesion were investigated using wipe tests followed by a modified cavitation test. Higher bond strengths were achieved for substrates that were held at higher temperatures during spraying. Moreover, the electrical conductivity of coating, taken as a measure of particle-particle bonding quality within the coating, improved and the porosity decreased for increased substrate temperatures. The findings are discussed in view of the thermal conditions, as well as the mechanical response of the uppermost layer of the substrate/deposit set.

In the present study, spherical Ti-6Al-4V powders were cold sprayed on titanium, aluminum, and magnesium alloy substrates to investigate influences over a wide range of damping conditions and respective deceleration of impacting particles. Single impacts were produced via wipe tests and bonding was evaluated by cavitation testing followed by SEM examination of impact and fracture morphologies. The results show that better bonding is achieved for material combinations with similar properties due to high adiabatic shear instabilities that result in microfusion at the particle-substrate interface. In the case of dissimilar materials, the conditions for bonding can be reached in an intermediate stage, but bonded areas may later separate due to particle movement around the interface.

This study investigates the impact behavior and consequences for coating formation in cold spraying of FeAl intermetallic compound powder. A range of spraying conditions was used to process single impacts in so-called wipe tests and for processing spray layers. In order to avoid brittle failure, high process gas temperatures and varied traverse speeds were used to account for thermal softening of spray particles and already adhering layers. Morphologies of as-impacted particles and partially removed single splats were subsequently investigated by SEM. The study of spray lines indicates that secondary impacts are only successful within an extremely narrow range of impact conditions. Within this narrow parameter regime, thicker and dense coatings are obtained. Hardness testing shows that the properties of the powders were retained.

Cavitation erosion is a common phenomenon that occurs in hydraulic turbine blades and result in mass loss. Welding is the most common technique used to recover the geometrical profile of these cavitation eroded turbine blades, however it is known that tensile residual stress can develop. The development of manufacture process that could reduce or eliminate the residual stress level will contribute for a longer service life of this component. It is aimed in this study evaluate cavitation erosion mechanism of Fe- Mn-Cr-Si-Ni arc thermally sprayed coating. Coatings were analyzed by optical and scanning electronic microscopy, microhardness, cavitation tests (ASTMG32-92) and the analysis of eroded surface areas after ultrasonic cavitation tests with DRX and SEM. The results showed that lamellae morphology, oxide volume fraction and porosity modified by changings in parameters deposition, modified cavitation mass loss mechanisms. After ultrasonic cavitation tests, it was verified that mass loss occurred by interlamellae oxide removal and splats surface deformation in initial stages, followed by rupture and finally detachment of the lamellae. Splashing droplets promote greater mass loss in some localized areas because they lower intersplat cohesion.

Damage of marine screw propeller parts made of aluminum bronze cast material caused by cavitation erosion is one of the serious problems. Erosion resistant thermal spray coating on aluminum-bronze material is expected to extend lifetime of such propellers. In this study, Cobalt-based alloy coatings sprayed by; (a) atmospheric plasma spraying (APS), (b) low pressure plasma spraying (LPPS) and (c) high velocity oxy-fuel (HVOF) spraying and aluminum bronze cast material were evaluated by cavitation erosion test using magnetostrictive cavitation test equipment. Fracture morphology of cavitation eroded coating surfaces were analyzed by surface observations with SEM and also the amount of volume loss was measured. Cobalt-based alloy coatings sprayed by LPPS exhibited superior cavitation erosion resistance compared to aluminum bronze cast material and coatings by APS and HVOF. Moreover, mechanical properties of Cobalt-based alloy coatings were investigated in detail by nanoindentation technique. It is found that cavitation erosion resistance of coatings is subjected to interparticle cohesive strength.

The cavitation erosion result mass loss. Welding is the most common technique used to recover the geometrical profile of the blades. However it is known that tensile residual stress can develop. The search for manufacture process that could reduce or eliminate the residual stress level will contribute for a longer life service. The target in this study to evaluate the potential of ASP thermal spray to recover surfaces. The influence of processing parameters on the cavitation resistance and mechanisms was evaluated for three alloys, AWS309LT1, AWS410NiMo and a Co stainless steel known as Cavitec. Coatings were analyzed by optical and electronic microscopy, microhardness and cavitation tests regarding the effect of air pressure. The results showed that lamellae morphology, oxide volume fraction and cavitation resistance were modified by the ASP parameters. The increase in the pressure modified the oxide fraction from 26 to 37% in AWSI309LT1, 23 to 31% for AWS410NiMo and 16 to 23% for Cavitec. Mass loss varied from 3.5 to 4.8 mg/h for AWSI309LT1, 6.65 to 18.19 mg/h for AWS410NiMo, and 3.4 to 4.0 mg/h for Cavitec; the best performance occurred with Cavitec and was associated with higher pressure of deposition and minor oxide volume fraction.

Diamond films have been deposited on WC - 6% Co hard metal tools by the DC plasma jet CVD synthesis. The parameters of the process (gas composition, temperature of the gas phase and the substrate, process pressure) as well as of the substrate surface (material, pretreatment) are related to the diamond film growth. For machining abrasive materials the hard and wear resistant diamond coatings must adhere good to the substrate. The wear behaviour of thin diamond films on hard metals under cavitation treatment has been examined. Thus the conditions of diamond synthesis have been varied especially concerning the coating duration and the process pressure and engineering. The cavitation test reacts more sensitive to coating defects of pm size than the conventional testing methods (scratch test, indenter method) and considers the microstructure of the material. Paper text in German.

The cavitation erosion of various hardfacing coatings was investigated by using a vibratory cavitation apparatus according to ASTM G 32. Coatings of austenitic stainless steel containing 10 % cobalt were applied by arc welding. High velocity oxy-fuel spraying (HVOF) was employed to produce coatings of various kinds of cermets and metallic alloys. For each coating, the steady state erosion rate was determined and the effect of process parameters and alloy composition on the microstructure and erosion rate was investigated. The morphology and microstructure of the coatings before and after cavitation testing were analysed by metallographic methods in order to study the erosion mechanism. It is demonstrated that the high resistance to cavitation erosion of the cobalt-alloyed steel can even further increase when the fluxed core arc welding process and an improved pulsed power source are used to produce the coatings. The erosion resistance of the HVOF coatings, however, was limited by pores, microcracks and oxides and did not significantly exceed the level typical for bulk stainless steel 316 L.

The proposed paper reports a series of experiments to investigate the cavitation erosion mechanism of HVOF coatings. Vibratory cavitation erosion tests according to ASTM G 32 have been carried out with several HVOF coatings including cermets, oxides and metallic alloys. The steady state erosion rate for each coating was determined and the effect of coating composition and microstructure on the erosion rate was investigated. The morphology and microstructure of the various coatings before and after cavitation testing were analyzed by means of light optical and scanning electron microscopy in order to study the erosion mechanism. The results demonstrate that HVOF coatings of NiCrFeBSi, WC-17Co, Cr 3 C 2 -25NiCr and Cr 2 O 3 can exhibit a rather high resistance against cavitation erosion and should be considered for application as a protective surface layer against cavitation. Furthermore, it is shown that cavitation testing can provide a useful tool to study and characterize the bond strength between individual splats as well as the brittleness of the individual phases present in the coating.