The effects of mechanochemical multifunction cavitation (MC-MFC) treatment, which generates cavitation bubbles containing a small amount of phosphoric acid during chemical conversion, on the surface characteristics of high-strength Mg alloys with various Al contents (AZ31, AZ61 and AZ91) were investigated to suppress the formation of pits on the surface of the alloys. Gold-colored films were formed on all of the investigated alloys, with darker coloration corresponding to a higher Al content. The surface roughness of AZ61 and AZ91 increased substantially after the treatment, and the formed films were thinner than those on AZ31. Analyses using scanning electron microscopy with electron-probe microanalysis revealed precipitates in regions where phosphate films were absent, and their size increased with increasing Al content. Fourier transform infrared analysis revealed a decrease in phosphate-related peak intensity, indicating nonuniform film formation. Surface wettability evaluated by contact angle measurements suggested increased susceptibility to localized surface degradation in chloride-containing environments after MC-MFC treatment. Observations of untreated alloys revealed network-like Mg-Al-Zn compounds whose fraction increased with increasing Al content, reducing the reactivity with phosphoric acid and hindering film formation. Consequently, alloys containing a larger amount of beta-Mg17Al12 phase exhibited limited phosphate film formation during MC-MFC treatment, resulting in deteriorated surface stability in chloride-containing environments.

Laser-textured oil-retaining surfaces are required to improve the tribological performance of Al alloy components. This study aimed to establish a laser-assisted chemical etching process to form controlled microgrooves on AA7075 Al surfaces. Laser irradiation generates a melt pool with a fine dendritic microstructure and induces redistribution of Cu, Mg, and Zn near the surface. These compositional variations are considered to influence local electrochemical behavior during hydrochloric acid etching, which may contribute to selective dissolution of the heat-affected zone. At 30 W and 10 mm/s, uniform grooves are obtained, and dissolution of the heat-affected zone is largely completed within about 10 min. Excessively low heat input results in shallow and irregular grooves, while excessively high heat input destabilizes the groove bottom. Multi-pass laser processing further enables the fabrication of asymmetric and herringbone-shaped grooves without apparent deterioration of the overall surface condition. The developed hybrid process provides a simple and robust route to create functional oil-retaining textures on Al alloy surfaces.

The effects of multifunction cavitation (MFC) on the fatigue characteristics of A6061-T6 aluminum alloy rods subjected to a T6 treatment and polished to a mirror finish were examined using rotating bending tests. The MFC technique was able to generate a surface-modified layer having a metallic luster while imparting compressive residual stress and high hardness. In contrast to conventional surface modification techniques using shot particles, such as fine particle peening (FPP), this process also limited the formation of relatively large dents on the rod surfaces. MFC processing was found to increase the fatigue strength and fatigue life of these rods after 107 bending cycles. The fatigue lives at low stress amplitudes for specimens treated using MFC were higher than those for materials processed using FPP. However, the latter technique provided a deeper surface-modified layer and more rapid increases in surface hardness. The effectiveness of the MFC process was confirmed by estimating the fatigue strength of the aluminum alloy rods based on assessing residual stress relaxation, surface morphology and surface hardness.

In this study, the effects of compressive residual stress and work hardening introduced by multifunction cavitation (MFC) treatment on the ductile-brittle transition for carburized steel were investigated. Prior to Charpy impact tests, variations in surface properties with processing time were evaluated. Both surface hardness and compressive residual stress increased rapidly and reached saturation at approximately 10 min, which was determined as the optimal treatment condition. Depth profile analysis under this condition revealed that the hardness and compressive stress increased to a depth of approximately 75 & micro;m from the surface. The Charpy impact test results showed that the absorbed energy and lateral expansion of the MFC-treated specimens were substantially higher than those of the untreated ones in the intermediate temperature range (473-573 K). A strong linear correlation (Delta h = kE) was observed between the absorbed energy (E) and the lateral expansion (Delta h), and the proportional coefficient k increased from 1.438 & times; 10- 2 cm/J for untreated steel to 1.544 & times; 10- 2 cm/J after the MFC treatment. These results indicate that the compressive residual stress induced by MFC treatment relaxes the stress concentration at crack tips and enhances plastic deformation. Consequently, MFC treatment was found to be an effective surface modification method for reducing the ductile-brittle transition temperature of carburized steel.

This study examined the effects of multifunction cavitation (MFC) and energy-intensive multifunction cavitation (EI-MFC) on residual stress and the hardness of carburized steel. Both treatments increased compressive residual stress and hardness due to plastic deformation, and EI-MFC tended to produce slightly higher residual stress and a deeper affected layer. The increase in hardness is considered to be associated with work hardening. Fatigue tests as stress ratio of −1 showed a tendency toward improved fatigue performance under low stress amplitude conditions. These results suggest that cavitation-based surface modification influences the mechanical properties under the present experimental conditions.

This study investigated pit formation on the surface of AZ31 magnesium alloy under multifunction cavitation generated by a high-pressure water jet with ultrasonic superposition. Processing was conducted at injection pressures (Pi) of 20-35 MPa and stand-off distances (Ds) of 55-75 mm. At Ds = 65 mm, increasing Pi reduced the severity of pitting and surface roughness; however, relatively pronounced pitting was still observed. When the Ds was varied, the severity of pitting decreased in the downstream region at all Pi values due to jet attenuation and an increase in cavitation number. Evaluation of the cavitation number showed that it increased downstream, indicating that a more spatially uniform distribution of collapse impacts contributed to improved suppression of pit formation.

We investigated the electrochemical properties of compounds and chlorides in the films formed on the surfaces of Mg alloys using cavitation for phosphating. The compounds formed by this treatment were Mg3(PO4)2 and Mg (OH)2. In addition, electrochemical measurements and combined cycle tests were carried out to investigate the chloride corrosion resistance of the films formed after surface treatment. Regarding the anodic polarization curves, each surface-treated sample exhibited passivation-depassivation behavior. In cathode polarization curves, the corrosion rate for each surface-treated sample was approximately 1/10 that of the corresponding untreated sample. In the combined cycle test, the amount of surface oxidation caused by chlorides was less for each treated sample than for the corresponding untreated sample. In addition, when droplets containing chlorides were dropped onto a surface and the angle of the droplets that adhered to the surface was measured, the angle for the untreated sample remained constant even after the droplets were dropped several times. However, when several droplets were dropped onto each of the cavitation-treated samples, some areas were highly hydrophobic and some areas were less hydrophobic than the untreated samples. The results revealed that, although the coating formed on Mg alloys by phosphating using cavitation showed a protective effect in the early stages when chlorides were attached, the protective effect decreased over time.

This study proposes using multifunction cavitation (MFC) to strengthen the surface of helical gears used in transmissions. In addition, because the steel used for helical gears exhibits poor corrosion resistance in water, samples plated with electroless nickel and iron tetroxide were also investigated. In addition to using samples with modified surfaces, we used samples strengthened by carburizing and nitriding. The noncoated and plated samples showed a slight increase in surface roughness and increased compressive residual stress and hardness. The plating method that did not cause red rust during the MFC treatment was iron tetroxide plating. In the samples strengthened by carburizing and nitriding, red rust did not occur on the surface after MFC treatment, the surface roughness was suppressed, and compressive residual stress and hardness increased. The results show that the MFC treatment effectively improved the fatigue properties of gear surfaces with complex shapes.

This work developed an energy-intensive multifunction cavitation technology involving ionic liquids (ILs). This technology was used to process a single crystal of the Ni-based superalloy SC610, employing a mixture of the IL 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and pure water. The intensity of this process was found to result in the formation of surface cracks and new chemical compounds that were deposited on the alloy surface. The application of this treatment to a columnar crystal of the Ni-based superalloy CM186LC provided a more uniform surface structure than that obtained from the same process without the IL. Incorporating the IL also reduced the processing time and increased the hardness that could be obtained. The ions comprising the IL were found to be incorporated into the cavitation bubbles. Multiphoton ionization was promoted by laser irradiation and collisions between bubbles were made more forceful by the Lorentz force associated with a magnetic field. These factors increased the number of bubbles available for processing.

The effect of multifunction cavitation (MFC) processing on the fatigue properties of carburized low-alloy steel rods was examined under rotating bending. MFC was conducted for electrochemically polished steel rods pretreated with gas carburizing and tempering. In contrast to conventional surface modification techniques that use a cavitation jet, MFC can generate compressive residual stress and suppress the formation of surface dents on the surface of carburized rods during rotation. High compressive residual stress (similar to 800 MPa) was generated on the surface of carburized rods by MFC because of a martensitic transformation; however, MFC did not increase the fatigue limit of the carburized rods because the compressive residual stress generated by MFC was released during fatigue tests and the surface roughness value was slightly increased by MFC due to the formation of surface pits with red rust. By contrast, the compressive residual stress for the carburized specimens without MFC increased because of the stress induced martensitic transformation during fatigue tests, which is one of the reasons why the fatigue limit of the carburized rods subjected to MFC did not increase. The fatigue limit estimation based on a modified Goodman diagram and mechanism of subsurface fatigue fracture in carburized steel rods were also examined.

The effect of natural aging by multifunction cavitation (MFC) on the fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys was examined. Surface observation and plane bending fatigue tests were conducted for the MFC-treated aluminum alloys at a stress ratio, R, of -1. The hardness of aluminum alloy without T6 treatment was significantly increased by MFC due to both the work hardening and natural aging. MFC treatment improved the fatigue lives and the fatigue strength at N = 107 cycles of aluminum alloys due to the generation of compressive residual stress and increasing the surface hardness; however, surface pits were large enough to easily nucleate an initial fatigue crack. In addition, the fatigue strength at N = 107 cycles of MFC-treated aluminum alloys can be estimated considering the residual stress, pit size and surface hardness.

Multifunction cavitation (MFC) has potential as an environmentally friendly surface-modification method. In the present study, the modified surface layer and the fatigue properties for MFC-processed low-alloy steel were investigated. When the processing time was longer than 2 min, the surface roughness increased and the surface potential decreased. The maximum compressive residual stress was induced after a processing time of 2 min, and decreased for longer processing times. Electron backscatter diffraction analysis of a cross section of a sample subjected to MFC for 30 min showed that the modified layer was thicker than that for samples processed for shorter times. The fatigue life at high cycle numbers increased for the specimens processed by MFC under the conditions corresponding to the greatest compressive residual stress. MFC processing was shown to be effective in improving the fatigue properties of steel, and therefore has potential as a next-generation surface-modification method.

In this study, multifunction cavitation (MFC) was performed on low-alloy steel (AISI 4140 steel) rods with different hardnesses to increase their fatigue limit. It was found that a high compressive residual stress was generated on the surface of steel rods by MFC and that the magnitude of the compressive residual stress tended to increase with increasing specimen hardness, which resulted in a higher fatigue limit. However, fatigue cracks are known to be initiated from the pits and red rust that form on the surface during MFC treatment in water. Furthermore, relaxation of the compressive residual stress was also investigated during the fatigue test to elucidate the mechanism for improving the fatigue properties. The results showed that the fatigue limit for MFC-treated steel rods was accurately estimated by considering residual stress relaxation, hardness, and pit formation. Validation of the fatigue limit estimation was also conducted through comparison with Murakami's equation. MFC generated compressive residual stress on the surface of steel rods. MFC increased the fatigue limit for steel rods. The fatigue limit of MFC-treated steel rods with different hardnesses was estimated. Fatigue cracks were initiated at surface pits formed by MFC.

The effect of multifunction cavitation (MFC) on the rotating bending fatigue properties of low-alloy steel rods was examined. MFC generates compressive residual stress on the surface of steel rods, in contrast to conventional water jet peening, which improves the fatigue limit of steel rods. The fatigue limit of MFC-treated steel rods can be estimated using a modified Goodman diagram. The proposed equation gives the maximum value of the fatigue limit of MFC-treated steel rods (227.7 MPa) and the maximum value of the compressive residual stress contributing to the increased fatigue limit (-117.9 MPa).

This work developed a novel metal processing technique referred to as laser-assisted magnetic energy-intensive multifunction cavitation. This technology employs a strong magnetic field to focus bubble energy while applying sonic radiation around a waterjet cavitation jet. Individual bubbles in the cavitation cloud undergo repeated isothermal expansion and adiabatic compression, raising the temperature and pressure of the bubbles. In addition, the presence of a magnetic field over the region between the nozzle exit and the cavitation cloud in which cavitation primarily occurs greatly increases the number and energy density of charged bubble collisions based on the Lorentz force acting between the bubbles. The application of laser light to the charged bubble cloud provides multiphoton excitation that increases the charges of the ions within each bubble, leading to more active collisions. This enhanced cavitation treatment technology was applied to AZ31B magnesium alloy and was found to improve the functionality of the metal.

In this study, we will report the efficiency of hybrid filler for the mechanical properties and the thermal conductivity of Polyamide-6 (PA6) composite. One of the ways to improve the thermal conductivity of the composite is to add fillers to the matrix, but the excessive filler causes the composite to form aggregation and void. They make the mechanical properties and thermal conductivity decline. As the solution to this problem, to use of hybrid filler is expected to realize the lower filler content of composite with keeping the properties. However, the most efficient ratio of hybrid filler is unclear. In this study, PA6 and filler were composited using a twin-shaft melt-mixing machine. A manual injection molding machine was then used to produce test specimens for thermal conductivity measurement and tensile test specimens. Thermal conductivity was measured based on the laser flash method. The structure of the composite was also investigated by fracture surface observation after tensile testing. It is revealed that two types of fillers were composited with PA6 to obtain higher thermal conductivity than that of a single filler with the same filler content. This is because the different shapes of the two fillers made the thermally conductive path.

Magnesium alloy is attractive for lightweight construction but often suffers from poor corrosion resistance and low strength. Cavitation processing with chemicals, i.e., multifunction cavitation (MFC), was introduced to form a high-corrosion film and improve the fatigue properties of an AZ31 magnesium alloy. Surface analysis and plane bending fatigue tests were conducted for the MFC-treated magnesium alloy at a stress ratio, R, of ̶1. The mechanical action of cavitation bubbles improved the fatigue life of magnesium alloys due to increasing the surface hardness and generating compressive residual stress. However, the combined mechanical and electrochemical action during MFC formed pits on the surface. These pits were large enough to easily nucleate an initial fatigue crack. In addition, the magnesium alloys without pit formation, for which a coating process using phosphoric acid was conducted after MFC using water, showed superior fatigue properties.

In the present work, a strong magnetic field was applied near the outlet of the water jet nozzle to promote the generation of multifunction cavitation bubbles. Because these bubbles contained charged species, the bubbles experienced a Lorentz force due to the magnetic field and collided with greater force. As such, the internal bubble pressure exceeded the threshold value required for fusion to occur. The expansion of these charged bubbles in response to ultrasonic irradiation affected adjacent charged bubbles so that the energy density of the atoms in the bubbles was greater than the fusion threshold. The results of this work strongly suggest that the formation of bubbles via the UTPC process in conjunction with a strong magnetic field may result in bubble fusion.