Key Engineering Materials Vols. 373-374

Abstract: The microarc oxidation (MAO) films on AZ31 magnesium alloy were modified by high-intensity pulsed ion beam (HIPIB) at an ion current density of 200 A/cm2 with 1-5 shots. The modified MAO films presented a corrosion resistance superior to that of the original films. Scanning electron microscopy (SEM) observation revealed that a sealing layer was formed on the MAO films by HIPIB irradiation. The corrosion behaviors of the MAO films in 3.5 % NaCl solution were characterized by using electrochemical impedance spectroscopy (EIS). The noticeable improvement in the corrosion resistance of MAO films is attributed to the blocking effect of the sealing layer that hinders the process of electrolyte penetrating the MAO films to the magnesium alloy.

Abstract: This paper discusses the design and development of sulphidation resistant coatings. The first section discusses the rationale for designing and developing such coatings. The rationale for selecting the coating systems has been derived from our work on the HT sulphidation behaviour of MCrAlYX (M=Co, or Co-Fe and X=V, Nb, Mo and W) type of coating alloys. This work has allowed the establishment of the mechanisms of sulphidation and led to the choice of the coating systems discussed here. The second section describes the sulphidation performance of several selected coatings, single and multilayer, deposited on Ti, TiAl and Ni-based alloys at 750-850oC in environments of low oxygen and high sulphur potentials.

Abstract: Two type of ceramic composite coatings of Fe-Cr-B alloy reinforced with cobalt-coated tungsten carbide (WC-Co) particles or nickel-coated tungsten carbide (WC-Ni) particles were deposited on a mild steel substrate by arc spraying, respectively. The microstructure of the coating was investigated by optical microscopy. X-ray diffraction analysis was used to study the phase composition in the coating. The microhardness of the coating was determined. The wear behavior of the coating was evaluated. The results showed that the WC-Co/FeCrB coating has the excellent abrasive wear resistance which is about 11 times higher than that of Q235 mild steel. The main wear mechanism of both coatings was silica scratching and micro-cutting of the matrix and the resultant pulling out of WC particles.

Abstract: In this work, the self-assembled monolayers of γ-aminopropyltrimethoxysilane and octadecyltrichlorosilane were prepared on titanium films, radiated and solidified by ultraviolet radiation/ozone photochemical process. The characterization and friction properties of titanium film, APS SAMs, OTS SAMs and the radiated APS SAMs, OTS SAMs were explored by atomic force microscopy and friction force microscopy. The effects of functional groups, sliding velocity, load and ultraviolet radiation/ozone photochemical process on friction properties of SAMs were analyzed. The experimental results show that the titanium film coated with SAMs, especially under ultraviolet radiation/ozone, is exhibited with a good friction property. The friction property of APS SAMs is better than OTS SAMs under or no ultraviolet radiation/ozone. The friction force increases with the increasing of sliding velocity and decreases with the increasing of load.

Abstract: A new technology, duplex ion nitrocarburizing and sulphurizing technology (DINS), for friction reduction and anti-scuffing applications of diesel engine cylinder was studied. Duplex ion nitrocarburized-sulphurized layer was prepared on the surface of CrMoCu alloy cast iron by using the DINS process. The morphology, phase structure and tribological behaviors under sulphur contained additive lubrication were investigated. Results show that the sulphide surface layer of the duplex layer is mainly composed of close-packed hexagonal structured FeS phase and cubic structured FeS2 phase. The nitrocarburized sub-surface layer of the duplex layer is mainly composed of Fe2C and Fe3N phases. The harder nitrocarburized layer can provide effective support to the softer sulphide layer and avoid its lamellar tear. The synergistic effect between the duplex layer and the sulphur contained additive lubricant, resulted in 10% and 33.3% reduction in coefficient of friction and wear volume, respectively, compared with those of the sulphurized surface, and 25% and 50.1% reduction, respectively, compared with those of the plain surface. Bench test of diesel engine further demonstrated that the DINS process can provide the treated cylinder with superior properties in anti-scuffing and friction reduction, so that it can be used to prolong the service life of the cylinder.

Abstract: The growth behaviors of intermetallic compound (IMC) layers in soldered and diffusion bonding Sn/Cu joints and the effects of magnetic field have been investigated. The results indicate that, without high magnetic field, the growth behaviors of these two IMC layers are similar in the aging except the initial morphologies. However, the morphologies and crystal orientations of these two IMC layers have changed after being aged in high magnetic field.

Abstract: Development and optimizing of friction material formula, oriented to improve the service life and security of brake disk, is largely based on advanced measurement method to accurately provide the friction coefficient. In this study, virtual instrumentation technique was used to design an automation measurement system of friction coefficient. With proper sensors, data of four measured variables such as temperature, rotation speed, pressure and friction torque are acquired by the computer combined with a plug-in data acquisition board. The system work principle, selection of sensors, multi-channel sampling, signal processing and anti-jamming measures have been presented in detail. Those functions of the software such as real-time data acquisition, dynamic wave displaying, high-speed report saving and inquiry, and so on, have been realized by LabWindows/CVI 7.1. The system works safely with high accuracy and friendly user interface in practical operation.

Abstract: The tribological behavior and the mechanism of nano-silicate mineral powder as lubrication oil additive were researched in the article. The tribological behavior of nano-silicate mineral powder with mass ratio 0.6% in lubrication oil 50CC was tested and compared with the lubrication oil 50CC’s by friction wear testing machine. The surface morphologies and elementary compositions of grinding cracks were analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS).The results showed that the friction coefficient is decreased 37.5%, and the lost mass of the upper proof sample reduces 68.75%, the down’s reduces 86.7%, after adding nano-silicate mineral as lubrication oil additive, by comparison to lubrication oil 50CC’s. Under the lubrication oil which has been putted nano-silicate mineral as additive, there is a repairing layer whose material is different from basal body material on the grinding cracks; in addition, Si, Mg and other elements are deposited on the repairing layer. These state that nano-silicate mineral as lubrication oil additive possesses superior behavior of wear resistance, antiwear and self-repairing effects.

Abstract: (Ti(1-x)AlxN) coated drill is a new product of Mitsubishi Co. Its superior cutting performances in strengthened wearbility, reduced cutting force, and elongated tool-life have been reported. Aimed at providing enough information for in-process measurement and control, drilling tests on steel workpiece are performed to investigate cutting behavior and chemical stability of the coating material. The experiments are as follows: measurement of cutting force and torque, hole quality, and flank and cutting edge wear under dry and wet drilling; SEM characterization of the coated surface. Experiment results reveal that the coating material exhibits solid lubricant effect to improve the tribological interaction between the drill and the workpiece and to facilitate chip evacuation. Excellent chemical stability of the coating material is demonstrated by the material’s microstructure.

Abstract: Surface modification mechanism on scratch of ion implanted p-Si (100) is investigated by scanning electric microscopy and micro-Raman spectroscopy. Raman experimental results reveal that the amorphous Si appears near the scratch during the scratching process, while the ion implantation adjusts the structural parameters of the amorphous Si and changes the residual stress state of the surface scratch from tension to compression. Moreover, Raman experimental results reveal that the laser power synchronously decreases Raman shift and full width of half maximum intensity (FWHM). The laser heating effect can be neglected because a lower laser power is selected in our measurements.