Materials Science Forum Vols. 561-565

Abstract: Titanium foils were subjected to soaking in NaOH aqueous solutions in the concentration range 0.1 M to 10.0 M, followed by oxidation in the range 400°C to 800°C. The samples were characterised by glancing angle X-ray diffraction and Raman microspectroscopy. The results showed that the corrosion by NaOH solution resulted in: • Partial dissolution of the anatase passive oxidation layer • Partial dissolution of the underlying titanium foil • Formation of a TiO2-rich sodium titanate hydrogel (Na2O·mTiO2·nH2O) The subsequent oxidation of the hydrogel on the titanium substrate resulted in: • Recrystallisation of sodium titanate (Na2O·5TiO2) • Recrystallisation of the rutile polymorph of TiO2 The concentration of the NaOH solution was important in that it affected the dissolution or retention of the anatase passive oxidation layer, where lower concentrations (0.5 M and 1.0 M NaOH) resulted in a lower degree of dissolution in comparison to where higher concentrations (5.0 M and 10.0 M NaOH) were used.

Abstract: This research adopts modified Submerged Arc Nanoparticle Synthesis System to produce TiO2 nanoparticle which has good roundness and consistence in size. The TiO2 nanoparticle produced is coated on conductive glass by electrophoresis, and then combined with dyes, electrolyte (I-/I3 -), carbon film and conductive glass to produce dye sensitized solar cells; its electro-optical conversion efficiency is measured. As the results of experiment show, the average roundness of those TiO2 nanoparticle is 1.29 nm and their average diameter is 26.5 nm. In the process electric current, electric voltage, and time to finish the film are controlled to obtain TiO2 film with thickness of 0.5~1.3μm . To make TiO2 nanofilm by electrophoresis has the advantages of high flatness and high roughness, and can increase the effects of dye coating. In addition, the dye sensitized solar cells produced are exposed to Metal Halide Lamp, and their electro-optical conversion efficiency is measured. The results show that the electro-optical conversion efficiency is higher than commercial ones.

Abstract: In this paper investigates the dynamic stability of Fe3O4 magnetorheological fluid produced by Submerged Arc Nanoparticle Synthesis System which our team has modified, that is, the dynamic stability of magnetic microparticle in Brownian motion. Through this modified system, parameters such as the exact peak current, the time of discharge and off time, and voltage can be preset. The results of the experiment show that the Fe3O4 magnetorheological fluid produced by the modified submerged arc nanoparticle synthesis system has wt 20% and vol 1% surfactants after being mixed with water. After being placed aside for one day and 15 days respectively, the average diameters of the two nanofluid measured with particle size analyzer and TEM are both 40nm. Furthermore, after analyzed through Brookhaven ZetaPlus the zeta potential of the two nanofluid both reach 40mv, which proves that the magnetic nanofluid show superior performance of suspension.

Abstract: In this study, the effect of thermal oxidation on the high cycle rotating bending fatigue behavior of Ti6Al4V alloy was investigated. Oxidation, which was performed at 600°C for 60 h in air, considerably improved the surface hardness and particularly the yield strength of the alloy without scarifying the tensile ductility. Unfortunately, the rotating bending fatigue strength at 5x106 cycles decreased from about 610 MPa to about 400 MPa upon oxidation. Thus, thermal oxidation leaded a reduction in the fatigue strength of around 34%, while improving the surface hardness (HV0.1) and yield strength 85 % and 36 %, respectively.

Abstract: Spectroscopic ellipsometry is the technique of choice to characterize thickness and refractive indices of transparent and semi-transparent thin layers with thickness ranging from few Angstroms to few micrometers. However, in case of porous thin film, traditional EMA (Effective Medium Approximation) fails to provide qualitative information on porosity. However, Spectroscopic Ellipsometry can benefit elaborated hardware and software set-up involving the adsorption/desorption of an adsorbate in the porous thin film, we call it, Ellipsometry Porosimetry Atmospheric (EPA) and the adsorbate is water. The change in refractive index induced by the introduction of water is measured and thanks to Lorentz Lorenz effective medium model, the volume of water adsorbed by the material is calculated. EPA becomes an effective method for characterization of porosity volume, pore size distribution (PSD), average pore size, cumulative surface area and Young’s modulus of porous films. EPA is also suitable to evaluate the sealing of a porous layer. An example of study is carried on for TiO2 mesoporous prepared by Evaporation Induced Self-Assembly with various calcinations treatment. Plots results are characteristic of mesoporous medium with well defined pore dimensions. Upon calcinations, EP-A allows to follow a significant pores enlargement from 3 to 10 nm. In this paper, the instrument as well as TiO2 porous thin film study will be presented.

Abstract: A crack size-dependence crack growth model was used to characterise the fatigue crack growth in AL 7075-T6 and AL 2024-T351 alloys. It is shown that the crack growth parameters %K and a can be used to linearise the crack growth in regions I (elastic) and II (plastic) by plotting fatigue data linear-linear da/dN×√a versus %K3, where cubic stress dependency is assumed. A theoretical attempt was made to relate this crack size-dependence fatigue crack growth parameters to the strain-life relationship constants. A reasonably good agreement was achieved when comparing between the theoretical predicted and experimental determined material constants.

Abstract: This article summarizes the efforts done for using acoustic emission as wear mechanisms monitoring technique for wear testing in a pin-on-disc setup. The basic characteristics of the mechanisms were previously determined via controlled tensile testing (fiber breakage, debonding …). The knowledge of these basic characteristics then resulted in an easier classification of wear mechanisms related to wear testing of pultruded glass fiber reinforced polyester.

Abstract: WC-Co based cemented carbides are widely used in technical applications, in which they are exposed to complex thermo-mechanical loadings. Previous research work has demonstrated that these materials exhibit a lifetime-limiting fatigue sensitivity at room temperature. This investigation is focused on the influence of heating as a result of friction of pin-on-plate tribocouples. WC-Co samples have been manufactured and surface finished by wire-EDM and grinding. Reciprocative dry friction experiments are performed under various loading conditions and sliding velocities. Correlations are established between the bulk temperature rise of the test samples and the imposed test conditions, material properties, surface conditions and coefficient of friction. Topographies and cross-section views of the tested samples were examined by SEM, revealing temperature dependent wear mechanisms, including binder phase modification.

Abstract: The contents of the paper point out the necessity of combining the theoretical and experimental approaches in the investigation of tyre load in vehicles. The models are planar and they model the cross-section of the tyre enabling the consideration of the bottom load and the internal pressure in the tyre, as well as the influence of the lateral force. The paper presents the findings, the formulations necessary for solving the task obtained in the experimental model tests and serving as a basis for comparison with the results obtained from purely theoretical approaches, e.g. by the method of finite elements, with identical load conditions. The steel cords reinforcing motor vehicle tyres are unevenly loaded in time as the tyre is in operation and in contact with the road surface. The conditions for conducting and evaluating experimental tests that would model the considered loading of the steel-cord-reinforced tyre have been defined. To be able to conduct these experimental tests, it was necessary to design simple test equipment for cyclic loading of the test specimens.

Abstract: There are close relations between stress concentration factor of notch and stress intensity factor of crack when the boundary conditions and geometrical conditions are in the same. The transition method of geometrically similar element to calculate the stress concentration factor of notch is proposed and some examples are computed by this method. There are some advantages for this method such as no limit of structural dimension, good adaptability, high precision and use convenience.