Ryo Tsuboi

Lubricity and corrosiveness of ionic liquids for steel-on-steel sliding contacts

Ionic liquids are expected to be used as new high-performance lubricants because of their low volatility, high thermal stability, and high oxidation stability. It is well known that some ionic liquids exhibit excellent lubricity for metals. On the other hand, there is concern about the corrosiveness of ionic liquids caused by tribo-chemical reactions. In this study, the lubricating properties of seven kinds of commercially available ionic liquids were evaluated under steel-on-steel sliding contacts using an SRV oscillating sliding tester. The worn surfaces were analyzed by optical microscopy, confocal laser scanning microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The halogen-containing ionic liquids exhibited excellent lubricity for steel compared with the halogen-free ionic liquids. The X-ray photoelectron spectroscopy analytical results showed the formation of iron fluoride on sliding surfaces lubricated with the fluorine-containing ionic liquids. Formation of this iron-fluoride boundary layer reduced friction; however, corrosion occurred on the worn surfaces after the sliding. On the other hand, less corrosive damage was observed on the worn surfaces that slid under the dry-nitrogen atmospheric condition. These results suggested that the hydrofluoric acid, which was produced by the reaction between iron fluoride and contaminated water from the atmosphere, caused the corrosion on the worn surface. The halogen-free ionic liquids showed inferior lubricity compared with the halogen-containing ionic liquids, though they did not cause any remarkable corrosion. The corrosion-inhibition effect of the phosphorus element was shown in the halogen-containing ionic liquids composed of a phosphate anion or phosphonium cation. The friction-reduction effect was, however, inferior to that of the phosphorus-free ionic liquids. The tribo-chemical reaction of the phosphorus contained in the ionic liquids yielded a phosphate boundary layer that prevented the formation of iron halide on the sliding surface and enhanced the wear resistance.

Tribological Performance of Halogen-Free Ionic Liquids as Lubricants of Hard Coatings and Ceramics

Ionic liquids are expected to be used as new high-performance lubricants because of their low volatility, high thermal stability, and high oxidation stability. It is well known that halogen-containing ionic liquids exhibit excellent lubricity for metals. However, there is a concern about the corrosiveness of ionic liquids caused by the formation of halides. The lubricity of halogen-free ionic liquids for metals is inferior to that of halogen-containing ionic liquids; however, they do not cause any remarkable corrosion effects. In this study, the lubricity of halogen-free ionic liquids—1-butyl-3-methylimidazolium tricyanomethanide ([BMIM] [TCC]) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [DCN])—for hard coatings and ceramics was evaluated using an SRV oscillating sliding tester. Ionic liquids exhibited excellent lubricity for sintered ceramics. It is supposed that the lubricity of ceramics depends on the chemical interaction between the surface and the ionic liquids. Ionic liquids exhibited different lubricating properties with each nitride coating. [EMIM] [DCN] exhibited a better wear reduction than [BMIM] [TCC] on CrN, and its friction coefficient was higher than that of [BMIM] [TCC]. DLC coatings with [EMIM] [DCN] exhibited better lubricity than with [BMIM] [TCC], and the combination of H-free DLC and [EMIM] [DCN] particularly showed excellent lubricity. XPS analysis showed that two kinds of nitrogen compounds were on the sliding surface of H-free DLC lubricated with [EMIM] [DCN].

Modeling and Applications of Electrochemical Machining Process

Electrochemical Machining (below ECM) is one of advanced machining technologies and has been developed and applied in highly specialized fields, such as aerospace, aeronautics, defense and medical industries. In recent years, ECM is used in other industries such as automobile and turbo-machinery because of the following advantages. That is, it has no tool wear, and it can machine difficult-to-cut metals and complex geometries with relatively high accuracy. However, ECM still has some problems to be overcome. The efficient tool-design procedure, electrolyte processing, disposal of metal hydroxide sludge are the typical issues. In order to solve these problems, a numerical simulation is considered to be a powerful tool. However, the numerical code that can satisfactorily predict the flow field and the machining process has not been developed because of the complex flow natures such as the three-dimensionality, hydrogen bubble/metal sludge generation (i.e. three-phase effect), temperature increase and flow separation. In present paper, summery of my PhD works is mentioned, about modeling and applications. Modeling for ECM process takes into account metal dissolution, electrolyte flow, void fraction distribution of hydrogen bubbles generated from the tool cathode, thermal, electric potential, and electric conductivity. Especially, two types of method are used for the coupling between gas- and liquid-phase in electrolyte. One is one-way coupling method; only the electrolyte flow affects the void fraction distribution of hydrogen bubbles. The other is two-way coupling method; considering the interaction between the electrolyte flow and the void fraction distribution. In the two-way coupling method, considering bulk density distribution in the electrolyte flow path due to hydrogen bubble, Low-Mach-Number approximation is used for simulations. For applications with our numerical code, simulations for machining 3-D compressor blade are performed. Blade geometry is successfully predicted and we can obtain some guideline of ECM process.© 2009 ASME

Effect of surface roughness on friction behaviour of steel under boundary lubrication

The friction behaviour of grinded and polished surfaces was evaluated by using a reciprocal sliding tester under lubrication with PAO, PAO + ZnDTP and PAO + ZnDTP + MoDTC. Friction coefficients on the smooth surfaces showed higher values compared to those on the rough surfaces. For lubrication incorporating PAO and PAO + ZnDTP + MoDTC, friction coefficients on both the smoothest and the roughest surfaces decreased with sliding time. On the other hand, friction coefficients between these extremes decreased with sliding time. In this paper, the effects of surface roughness on friction behaviour are discussed.

Tribo-Film Formation of Lubricant Additives on Cr-Plated Surface Sliding Against Nitrile–Butadiene Rubber

A Bowden and Leben type sliding tester was used with a base oil to evaluate four types of friction modifier additives—acid phosphate, hydrogen phosphite, acid phosphate amine salt, and amine—as a fundamental study on hydraulic fluid additives for sliding of nitrile–butadiene rubber on Cr-plated metal. Acid phosphate showed the lowest friction coefficient among the phosphorus acids. After the sliding test, the formation of tribo-films on the Cr-plated surface was investigated by Fourier transform infrared reflection absorption spectroscopy and a time-of-flight secondary ion mass spectrometer. The analytical results suggest that tribo-films formed by the phosphorus acids effectively reduced friction.

Erratum to: Tribological Performance of Halogen-Free Ionic Liquids as Lubricants of Hard Coatings and Ceramics

1. Second paragraph, L2 ‘‘On the other hand, the friction coefficient of Si3N4 lubricated with [EMIM] [DCN] was higher than that of SiC.’’ 2. Second paragraph, L5 ‘‘On the other hand, when [EMIM] [DCN] was used, a remarkable difference was observed between the friction behaviors of Si3N4 and the others.’’ 3. Second paragraph, L6 ‘‘Though Si3N4 had the smoothest surface of all ceramics, its friction coefficient showed the highest value.’’ 4. Second paragraph, L8 ‘‘However, the friction coefficient of Si3N4, which had the smoothest surface (Ra = 0.020), was higher than those of the others.’’

Development and Evaluation of Miniaturized 6-DOF Parallel Link Manipulator

Recently, compact machine tools have witnessed increased demand in the manufacture of small parts with high accuracy. However, miniaturization of these machines poses problems such as decrease in the accuracy and the range of motion. We focused on miniaturizing a parallel link manipulator, which is known to have high rigidity and accuracy. A non-cylindrical link was adopted in the designed manipulator for avoiding collisions among links with an impact drive actuator attached to their side. We confirmed through repeatability measurements that the developed manipulator had sufficient accuracy for handling small electronic parts.

Investigating Behavior of Hydrogen Bubbles in Electro-Chemical Machining

Electro-Chemical Machining (ECM) is an advanced machining technology and has been applied to highly specialized fields, such as aerospace, aeronautics, and medical industries. However, some problems remain to be solved. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are typical problems. To solve such problems, CFD is thought to have potential as a powerful tool. However, a numerical method that can satisfactorily predict the ECM process has not been established because of the complex flow natures. In a previous study, we presented a new model to simulate the flow fields in an ECM process. This model is based on a two-way coupling method, taking the interaction between gas and liquid phases into account. In this coupling method, we assumed that electrolyte and generated hydrogen bubbles over a cathode surface have the same velocity. Therefore, we could simplify the governing equations. Since the flow field had a non-uniform density distribution due to hydrogen bubbles, a low Mach number approximation was applied to solve the pressure Poisson equation. In the present study, we calculate hydrogen bubble trajectories and investigate the distribution and a behavior of hydrogen bubbles. Since hydrogen bubbles follow fluid well, they travel along the stream line. This is because hydrogen bubbles have small density. In the results, around the low velocity region, hydrogen bubbles remain there with making the spiral structure. Hydrogen particles remain more in the suction side than that in the pressure side of the blade.© 2008 ASME

Modeling of Multi-Phase Flow in Electro-Chemical Machining: One-Way Coupling Versus Two-Way Coupling

Electro-Chemical Machining (ECM) is an advanced machining technology. It has been applied to highly specialized fields such as aerospace, aeronautics and medical industries. However, it still has some problems to be overcome. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, CFD is considered to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict ECM process has not been established because of the complex flow natures. In the present study, we investigate the modeling of the two-phase flow (i.e. fluid and hydrogen bubbles) in ECM process. First, we present two models to calculate flow fields in ECM process. One is based on one-way coupling method, neglecting the effect from gas-phase to liquid-phase. The other takes account of the interaction between gas and liquid phases, namely two-way coupling method. In the later method, assuming that electrolyte and hydrogen bubbles have same velocity, we simplified the governing equations with Low Mach number approximation. We simulated ECM process for a flat plate channel configuration. And, we verified the present models by comparing the numerical result with the experimental data.Copyright

Modelling of Three-Phase Flow in Electro-Chemical Machining

Electro-Chemical Machining (ECM) is an advanced machining technology. It has been applied to highly specialized fields such as aerospace, aeronautics and medical industries. However, it still has some problems to be overcome. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, CFD is considered to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict the flow has not been established because of the complex flow natures. In the present study, we investigate the modelling of the three-phase flow (i.e. fluid, hydrogen bubble and metal sludge) in ECM process. First, the developed code is applied to the two-dimensional channel configuration. The interactions among three-phases and the dissolved wall are simulated, to verify the modelling and to determine the model parameters, Next, the sinusoidal channel is machined by our code. It is confirmed that hydrogen bubbles in the separation region suppress the dissolution of the wall, and make the final wall shape be wavy. Through this study, it is exhibited that our developed model and code are sound and useful for simulating ECM process.Copyright