Machines operating in aqueous environments may be subjected to cavitation damage during operation. This study aims to evaluate the cavitation resistance of WC-10Co4Cr and WC-20CrC-7Ni coatings under cavitation erosion conditions with additional electrochemical effects. The coatings were deposited on AISI 1040 steel substrates using a high velocity air fuel thermal spray process. The microstructure of the coatings was observed by a scanning electron microscope, while their phase composition was analyzed using an energy-dispersive microanalysis system. In addition, the microhardness of the coatings and substrate was measured, and the surface topography of the eroded surface layers was observed using a 3D optical profilometer. The results revealed that the cavitation resistance of the WC-20CrC-7Ni coatings was better than that of the WC-10Co4Cr coatings. The observation of the structure and surface topography made it possible to identity the reasons for the differences between the cavitation resistance of both coatings: The WC-20CrC-7Ni coatings had a finer grain structure, lower pore density, and lower as-sprayed surface roughness. These differences, along with the presence of a high Cr and Ni content in the feedstock powder, that increased the coating corrosion resistance, contributed to improving the cavitation resistance and reducing the material loss of the WC-20CrC-7Ni coatings.Keywords cavitation erosion resistance Á HVAF coatings Á microstructure Á surface topography Á ultrasonic vibration method Á WC-10Co4Cr Á WC-20CrC-7NiThis article is an invited paper selected from presentations at the 2021 International Thermal Spray Conference, ITSC2021, that was held virtually May 25-28, 2021 due to travel restrictions related to the coronavirus (COVID-19) pandemic. It has been expanded from the original presentation.

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Low carbon ferrite-bainite pipe steels of the K65 (Kh80) strength grade produced by two manu facturing companies have been studied using different mechanical tests and fractographic analysis of frac tured surfaces. The results demonstrate that the energy capacity a (a c ) and the true relative reduction at frac ture ϕ f upon tensile tests, as well as the level of KCV -40 ≥ 250 J/cm 2 and the relative width of the zone of homo geneous ductile fracture L C /B at the fracture surface of Charpy samples upon impact bending tests, can be used as the laboratory criteria of crack resistance.

The ultrasonic vibratory test was carried out to evaluate the cavitation erosion/corrosion resistance of welded-deposited austenitic stainless steel/E308L-17. Three layers of the E308L-17 electrode were deposited onto AISI 1040 substrate utilizing Shielded Metal Arc Welding (SMAW) process. The eroded surfaces of the E308L welded deposit/coating and AISI 1040 substrate steel have been analyzed by evaluating surface topography, as well as scanning electron microscope (SEM) micrographs. In addition, the cumulative weight loss and erosion rate curves were attained to evaluate the cavitation resistance of the tested materials. The cavitation results showed that the E308L-17 deposited stainless steel has lost about 15 mg as a cumulative weight, while the loss of AISI 1040 substrate was about 123 mg. This is equal to 0.12% and 1.0% of the original test specimen weight for the E308L-17 and AISI 1040, respectively. Consequently, E308L-17 austenitic stainless steel can be effectively used as a protective material for surfaces exposed to cavitation wear, since the AISI 1040 substrate has been enhanced by 8 times using E308L stainless steel.

In this study, two Ni-based coating materials, namely NiCrMoNb and NiCrBSi, have been applied using High Velocity Air Fuel (HVAF) thermal spraying process. The performance of the coated surface in resistance to cavitation erosion-corrosion of both coating materials, has been evaluated using an ultrasonic vibratory method. The cumulative material loss and erosion rate curves of the two coatings have been discussed. Surface topography, microhardness, macroscopic images, and scanning electron microscope (SEM) micrographs were used to characterize the coatings before and after the cavitation test. The cavitation results showed that the NiCrMoNb coating surface has exhibited better performance than the NiCrBSi coating surface under the same test conditions. The total cumulative weight loss of the NiCrMoNb coating was about 1/3 that of the NiCrBSi coating. SEM micrographs of the eroded surfaces showed that the surface layer of the NiCrBSi coating was more damaged, compared to layer of the NiCrMoNb coating. Overall, the NiCrMoNb coating can be effectively used against the cavitation wear, due to its superior performance.