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This paper analytically investigates the flow as well as the chemically reactive solute transfer problem in a viscous fluid. The motion equations are reduced to a nonlinear ordinary differential equations system using the similarity transformations. The obtained nonlinear differential system is for the first time approximately solved by means of the Optimal Homotopy Asymptotic Method (OHAM). The effects of the partial slip and suction/blowing parameters are analytically analyzed. Some examples are given; the obtained results provides us with a good agreement with the numerical results and reveal that our procedure is effective, accurate and easy to use.

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]

The effect of the gas-nitriding thermochemical treatment on the cavitation erosion resistance of a Cr-Ni-Mo alloy is analyzed using a piezoceramic vibrating equipment and following the ASTM G32-2010 standard. The evaluation of the cavitation erosion behavior was made based on the analysis of the mean depth of erosion (MDE) and mean depth of erosion rate (MDER), for samples subjected to the cavitation erosion for different times. The surface topography and the structural changes in the marginal layer were analyzed through optical and scanning electron microscopy. Following nitriding the cavitation erosion resistance was about 9.6 times higher compared to the annealed state and about 8.2 times higher compared to the hardened and tempered state. [ABSTRACT FROM AUTHOR]

During processing or use, duplex steels can be subjected to heating at high temperatures that can affect their behavior. This work aims to correlate the influence of the sensitization treatment on the ultrasonic cavitation erosion behavior of a UNS S31803 (X2CrNiMoN22-5-3) duplex stainless steel. Duplex stainless steels, formed as a result of rapid cooling after solution annealing, are sensitized at temperatures of 475 and 850 °C, respectively, leading to hardening and embrittlement due to the spinodal decomposition of the ferrite and the precipitation of secondary phases. The ultrasonic cavitation erosion experiments showed that the sensitization at 850 °C reduced the mean depth of erosion by about 11% and the mean depth of erosion rate by 28%. By contrast, the sensitization at 475 °C deteriorates the cavitation erosion resistance, increasing the erosion parameters by up to 22%, compared to the solution annealed state. [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]

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 paper analyzes the microstructural changes occurring in two-phase alloy Ti-6Al-4V by changing solution treatment temperature between 810 ° C and 1050 ° C with cooling water or air, followed by aging at 550 ° C. The micrographic investigations and sclerometry examinations highlighted features of martensitic transformation hardening mechanism and the precipitation of secondary phases during the aging treatment. [ABSTRACT FROM AUTHOR]

Samples of the martensitic stainless steel GX4CrNi13-4 have been thermally treated and tested under cavitation erosion. Were obtained cavitation erosion resistance increases due to structural changes. There were hardness and microstructure analysis. Showed how steel structure influence on mass loss by cavitation. The thermal treatment of quenching, high tempered followed by nitrating give a high cavitational erosion resistance to martensitic stainless steel GX4CrNi13-4. In conclusion, the mechanisms resulting in cavitation and destruction that has significant impact on the structural state on the cavitation behavior of martensitic steel. [ABSTRACT FROM AUTHOR]

This paper presents the results of cavitation erosion tests on the deposited Iayers of austenitic manganese steel on the surface parts allow alloy ferrite-pearlite steels by welding technique by melting archery equipment. Metallographic examinations by alloy electron microscopy had shown the structural changes in the cavitational affected portion of the material and the propagation mechanism of cracks. Comparison of characteristic curves of cavitation erosion of austenitic manganese layer, made by welding with the referable standard steel 41Cr4, shows excellent resistance to cavitation which it has. [ABSTRACT FROM AUTHOR]

The paper makes the analysis of damages produced by vibratory cavitation at four types of austenitic stainless steels (with 100% austenite, 98% austenite + 2% ferrite, 90% austenite + 10% ferrite and 65% austenite and 35% ferrite). The quantity of structural constituents was established in according with Schäffer diagram [1). These steels were created for runner blades of Hydraulic Machinery. The maximum depth penetration (MDPmax) at erosion was considered as comparison parameter, measured after 165 minutes of cavitation attack. Remarks and conclusions were based both on chemical effects (especially of manganese and silicon contents) and an simultaneously influence of microstructure and chemical composition on cavitation attack behavior of the steel. So, steels with ferritic structures may be created in order to resist to cavitation attack better than completely austenitic structure steels. The tests were realized in accordance with ASTM G 32-85, in a magnetostrictive vibrator device with nickel tube in the Laboratory of Hydraulic Machines from Timisoara. [ABSTRACT FROM AUTHOR]