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Cavitation erosion degrades the surface of engineering components when the material is exposed to turbulent fluid flows. Under conditions of local pressure fluctuations, a nucleation of gas or vapor bubbles occurs. If the pressure suddenly drops below the vapor pressure, these bubbles collapse violently when subjected to higher pressure. This collapse is accompanied by the sudden flow of the liquid, which is manifested by stress pulses capable of causing plastic deformations on solid surfaces. Repeating these stress conditions can cause material removal and ultimately failure of the component itself. The present study aims to reduce the negative impact of this phenomenon on the mechanical systems components, using the TIG local surface remelting technique. Cavitation erosion tests were performed in accordance with the ASTM G32-2016 standard on samples taken from a cast high-alloy stainless steel. The alloy response for each melting current value was investigated by measuring mass loss as a function of cavitation attack time and by analyzing the damaged surfaces using optical and scanning electron microscopes. It was highlighted that the TIG remelted layers provide an increase in cavitation erosion resistance of 5–6 times as a consequence of the fine graining and microstructure induced by the technique applied. [ABSTRACT FROM AUTHOR]

Cavitation erosion of structural materials is a form of wear damage that affects the performance and life of components used in the aerospace, nuclear, and automotive industries, leading to an increase in the frequency of maintenance operations and redesign costs. The cavitation erosion behaviour of the nickel-based superalloy, Nimonic 80 A, was investigated using a piezoceramic crystal vibrator, according to the requirements of ASTM G32-2016. The results showed that plasma nitriding leads to a reduction in the mean erosion penetration depth by approximately ten times and of the erosion rate by the order of six times, compared to the solution heat-treated samples. Typical topographies of cavitation-eroded surfaces show a preferential degradation of the grain boundaries between the γ solid solution phases, of the twins' boundary, and of the interface between the precipitated particles and the γ solid solution matrix. In the nitrided samples, the cracking initiation is determined by nitride particles, which are hard and brittle. Due to the high mechanical strength of the solid solution γ with the fcc crystal lattice, the appearance of the cavitation surface is uniform, and the fracture has a ductile character. [ABSTRACT FROM AUTHOR]

This study aimed to reduce cavitation erosion effects by improving the surface properties of high-alloyed steel cast parts using the tungsten inert gas (TIG) surface physical modification technique. Local surface melting was performed at different linear energies (El = 4080–8880 J/cm) by varying the current between 100 and 200 A at a constant voltage of 10.2–11.1 V. Hardness increased from 210 to 390 HV5 when a TIG current of 150 A with a linear energy of El = 6630 J/cm was implemented. Using this technique, a surface layer with increased resistance to cavitation erosion was formed. This new surface absorbed large amounts of impact energy owing to a favourable combination of microstructural changes, leading to improved elastic and plastic properties, work hardening, cracking, and failure response. The cavitation erosion performance of the re-melted surface layer was analysed using a piezoceramic vibrating device according to the ASTM G32–2016 standard. Following TIG surface re-melting, the average penetration depth of erosion and the cavitation erosion rate increased by approxmately 6.8 times. Based on optical and electronic metallographic analyses, hardness measurements, and X-ray diffraction, it was shown that the morphology of the surface layer following cavitation erosion tests was affected. Microcraters tended to develop at locations where carbide particles from the alloying elements were previously present. At a current of 150 A, the depth of the microcraters reached values of approximately 15 μm; however, microcrater depth reached 10 μm in the austenite matrix. Based on these investigations, an understanding of the mechanisms that result in the improvement of the resistance to erosion by cavitation of cast high-alloy steels whose surfaces were re-melted using the TIG technique is developed. • TIG surface re-melting of GX40CrNiSi25 - 20 cast stainless steel leads to improved cavitation erosion resistance. • Optimal TIG current was 150 A for a linear energy of 6300 J/cm. • More than six times improvement of the cavitation erosion resistance. • Micro-cracks initiated and developed on the austenite grain boundaries. [ABSTRACT FROM AUTHOR]

The paper analyses the effect of the surface microstructure effects on the cavitation erosion following rapid re-melting and solidification of gray cast iron parts with lamellar graphite and perlitic matrix. The heat source used was the electric arc generated between the tungsten electrode (via the TIG process) and the gray cast iron part. The local melting of the surface was performed at different linear energy values (E l = 3420–5400 J/cm) varying the current between 60 A and 90 A, at a constant voltage of 9.5–10 V. The results showed an increase of the surface hardness from 192 to 198 HV5 to 700–740 HV5 and an improvement of the cavitation erosion resistance, the mean penetration depth of the erosion decreasing by 2.4 times, and the erosion rate by 3.56 times. Optical and scanning electron microscope were used to characterize the microstructure and to identify the phases in the re-melted area. The results showed that the melting of the surface led to an almost complete dissolution of the graphite lamella; the fine microstructure after re-solidification was composed of dendrites of transformed austenite embedded in ledeburite, consisting of transformed austenite and cementite Fe 3 C. Austenite dendrites have a preferential orientation and martensite needles are formed inside some of them. • TIG surface re-melting of gray cast iron leads to a fine structure in the marginal layer. • Significant hardness increase observed as a function of TIG currents. • Two times improvement of the cavitation erosion resistance. • Cavitation localized at boundaries between acicular cementite and transformed austenite. [ABSTRACT FROM AUTHOR]

The cavitation erosion resistance of CuAl10Ni5Fe2.5Mn1 following plasma spraying with Al2O3· 30(Ni20Al) powder and laser re-melting was analyzed in view of possible improvements of the lifetime of components used in hydraulic environments. The cavitation erosion resistance was substantially improved compared with the one of the base material. The thickness of the re-melted layer was in the range of several hundred micrometers, with a surface microhardness increasing from 250 to 420 HV 0.2. Compositional, structural, and microstructural explorations showed that the microstructure of the re-melted and homogenized layer, consisting of a cubic Al2O3 matrix with dispersed Ni-based solid solution is associated with the hardness increase and consequently with the improvement of the cavitation erosion resistance. [ABSTRACT FROM AUTHOR]