Mitsuji Hirohashi

Influence of oxygen partial pressure on transparency and conductivity of RF sputtered Al-doped ZnO thin films

Abstract Transparent conductive Al-doped ZnO thin films were prepared on glass substrates by radio frequency (RF) diode sputtering with Ar+O2 gas at an Al2O3-mixed ZnO ceramic target. The samples, with constant thickness of 0.5 μm, were prepared under various O2 partial pressure ratios in the range of 0% to 3%, and then annealed at 400°C for 4 h in a vacuum furnace. Their electrical, optical, and X-ray diffraction properties were evaluated. The resistivity of transparent films was in the range of 5×10−3 to 1×10−2 Ω·cm, the carrier concentration was 2×1020 cm−3, Hall mobility was 3–6 cm2/V s, and the property of infrared wavelength cutoff was confirmed. Introducing O2 gas prevented the films from yellow coloration caused by lack of oxygen atoms, and improved the durability with respect to cracking and peeling caused by residual stress. Atomic force microscopy and X-ray diffraction measurements showed that the lateral grain size was 100–150 nm and vertical grain size was about 12 nm.

Formation of TiO2/Ti Composite Photocatalyst Film by 2-Step Mechanical Coating Technique

In the present work, 2-step mechanical coating technique (2-step MCT), an advanced MCT, was proposed and carried out to form TiO2/Ti composite photocatalyst film with anatase TiO2. The microstructures and photocatalytic activity of the composite film were investigated. The results show that the proposed 2-step MCT is a simple process for forming TiO2/Ti composite film. The composite film has a microstructure with a nonuniform thickness, like random distribution islands. The TiO2/Ti composite film has high photocatalytic activity, which is related with crystallinity and volume of the TiO2 in the composite film.

Deformation Behavior of Mg-Ni-Y Alloy with Long Period Stacking Ordered Phase

Microstructures of the long period stacking ordered (LPSO) phase deformed by compression test or rolling at room temperature were investigated. The Mg85Ni6Y9 (at.%) alloy was composed mostly of plate-type phase with 10H-type LPSO structure. The Mg85Ni6Y9 alloy exhibited compression yield stress of 365 MPa and fracture strain of 30 % at room temperature. After compression test with applied stress of 25 %, a bend, delamination between basal planes and crack initiation at boundary of the LPSO phase were observed. From these microstructural features, it was considered that the deformation of the LPSO phase significantly influenced by a kink deformation. The Mg85Ni6Y9 alloy could be rolled with 30 % reduction at room temperature. The kink deformation was frequently observed in the LPSO phase of the alloy sheet. The basal plane texture was formed in plane sheet of the alloy sheet. However, it was more difficult to form basal plane texture in the LPSO phase than in the pure-Mg due to introduce the kink deformation. Therefore, it was considered that better rollability of the Mg85Ni6Y9 alloy compared with the pure-Mg was brought for the kink deformation.

Thermal behavior during combustion synthesis on intermetallic compound of Ni-Al system

It is to be expected that intermetallic compounds synthesized by aluminum or silicon with transition metals such as Ti, Ni, Fe and Nb are used as structural materials. Because of their properties such as light weight, ability to resist corrosion and excellent mechanical properties at elevated temperatures, Ti±Al system intermetallic compounds have been practically applied as structural materials [1, 2]. Unfortunately, it is dif®cult to develop intermetallic compounds: They are neither easy nor inexpensive to fabricate using the usual processes, such as the melting method, because intermetallic compound is brittle and dif®cult for machining and forming. Combustion synthesis, using a huge enthalpy during synthesis, is anticipated as a useful powder metallurgy process [3]. The synthesis conditions and reaction rate have been studied experimentally and analyzed using the thermodynamic method [3±8]. It has been observed that the maximum temperature during the combustion synthesis was over the melting point of Al, for example, reaching 1367 8C [5]. In analyzing the combustion synthesis, Al is usually considered to be in a liquid state [3, 5]. However, the combustion synthesis process is completed in a very short period (in a few seconds), so it is very dif®cult to control. Therefore, it is important to clarify thermal behavior during the combustion synthesis. In this study, thermal behavior during the combustion synthesis of the Ni±Al system was examined by differential thermal analysis (DTA). The effects of the composition and heating rate on the thermal behavior are discussed. Gas-atomized aluminum powder 99.5% pure and with a diameter under 100 im and nickel powder 99.8% pure and with a diameter under 7 im were used as source powders. To mix the powders thoroughly, the mixing was carried out using a ball mill for 7.2 ks to obtain the stoichiometric composition (atomic ratio) of Ni:Al with 1:1, 2:1 and 3:1. The powder mixtures were pressed into green compacts with a diameter of 20 mm at a compacting pressure of 800 MPa for 900 s after pre-pressing at 80 MPa for 300 s. Stearic acid was used as a diewall lubricant. Atomic ratio, the weight percentage of Al, density, calculated density and Vickers hardness for the green compacts are given in Table I. A sample component micrograph by scanning electron microscopy (SEM) of a green compact of (Ni±33 at %Al) is given in Fig. 1. The black and white phases are Al and Ni, respectively. The production conditions described above yielded green compacts with a high density (about 0.9 of the calculated density) and a microstructure with a good distribution. Thermal behavior during the combustion synthesis was analyzed with a differential thermal analysis processor (TG-DTA2000-s) produced by the Mac Science Company. To examine the effect of the heating rate on the thermal behavior, the heating rate was set at 5, 10 and 40 8C miny1. Samples of about 50 mg with a cylinder for DTA were cut from the green compacts. Al2O3 powder was used as the standard sample. To prevent oxidization, high-purity (99.9999%) Ar gas was owed into the processor at

Effect of interfacial shear strength on reliability of strength and fracture process of SiC–Al composite

Abstract A unidirectional SiC fibre reinforced pure aluminium composite was fabricated by the hot press method. Tensile testing of the SiC–Al was carried out to determine composite and interfacial shear strengths. A Monte Carlo procedure based on the elastic–plastic finite element method, involving the interfacial layer around the fibres, was constructed to simulate the tensile testing and to calculate the strength and Weibull parameters for the SiC–Al composite. The effect of the interfacial shear strength on the composite strength and its reliability is discussed. The results show that the composite strength and the Weibull shape parameter increase with increasing interfacial shear strength. The contribution of the interfacial shear strength to the composite strength and reliability is efficient when the interfacial shear strength is lower than the matrix shear strength. It is concluded that both composite strength and reliability are closely related to the fibre fracture process.

Effect of Grain Size and Microstructure on Appearance of Low Temperature Superplasticity in Al-Mg Alloy

The deformation mechanism and the role of grain boundary sliding (GBS) and intragranular deformation characteristic of low temperature superplasticity (LTSP) were investigated in ultrafine-grained (UFG) Al-Mg alloy using a multi-axial alternative forging technique. In UFG materials, it was shown that elongation and strain rate sensitivity were 340 % and 0.39 respectively at 473 K under a strain rate of 2.8 x 10 -3 s -1 . On the other hand, when grain size exceeded 3 5m, superplasticity did not appear under the same conditions. The main factors affecting the deformation mechanism were investigated based on observations of the microstructure using SEM and TEM. The intragranular deformation contribution, estimated from the aspect ratio of the grains after deformation, was observed to be about 43 %. The appearance of LTSP indicates that the role of intragranular deformation and grain size, together with GBS, were the most important factor.

Simple Evaluation of Superplastic Characteristic by Tensile Test Using R-Type Specimen

Superplastic elongation is correlated positively with a value of strain-rate sensitivity index m. The measurement method of the value and the shape of specimen for uniaxial tensile test are various. Therefore, a special technique is required to measure the m-value. In this study, R-type specimens having no smoothed region were employed instead of smoothed test-pieces. A series of tests for various aluminum alloys sheets were carried out at elevated temperatures to evaluate superplasticity. It was difficult to measure the m-value using a single R-type specimen. However, the obtained value using more than three test-pieces was fairly in good agreement with the value of smoothed test-pieces. Furthermore, the total elongation of the gage length of 6mm in the bottom of R-part could replace that of the smoothed test-pieces. The obtained value was less scattered in comparison with the value of smoothed specimen. In conclusion, R-type specimen can be useful for simple evaluation of superplasticity.

Performance Improvement of TiO2/Ti Composite Photocatalyst Film by Heat Oxidation Treatment

In the present work, heat oxidation treatment was carried out for improving the photocatalyst activity of TiO2/Ti composite film. The microstructures and photocatalytic activity of the composite film were investigated. Effect of heat oxidation treatment was discussed. The results show that crystallinity of TiO2 in the composite film was improved by heat oxidation treatment. The photocatalyst activity was increased owing to the improvement of TiO2 crystallinity by heat oxidation treatment.

Fabrication of fiber-reinforced aluminum smart composites with optical fiber by the interphase forming/bonding method

In order to reduce costs and develop new functionalities of continuous fiber reinforced metals, fiber/matrix interphase is developed by the original low cost fabrication method. Optical fiber can be embedded in stainless steel fiber or SiC fiber reinforced aluminum composites by the interphase forming/bonding method. Deterioration of optical fiber during composite fabrication by this method is small enough to connect it to external fibers leading to LD light source and power meter with rubber joints. The composites can be bent without fiber fracture as secondary forming by local melting of the interphase. At lower temperatures, if the SiC fiber/matrix interface adhesion is improved, fracture of SiC fiber is considered to become earlier than that of optical fiber, where it will work as health monitor.

A study of the residual stress and its influence on tensile behaviors of fiber- reinforced SiC/Al composite

Unidirectional fiber-reinforced SiC/Al composite was fabricated by hot pressing. The residual stress in the composite generated by heated treatment, sub-zero treatment, or pre-loading was measured by X-ray diffraction. In addition, tensile tests were carried out for the composite, and the effect of the residual stress on the tensile behaviors was evaluated by both the experimental investigation and the calculation analysis based on the the rule of mixture (ROM) taking the residual stress into account. The experimental results showed that the residual stress had great influence on the tensile stress when the tensile stress was small; while the influence became weaker and weaker with the increase in tensile stress and almost disappeared when the tensile stress reached the ultimate tensile strength. Furthermore, the residual stress almost had no effect on Young’s modulus of the SiC/Al composite. The calculation analysis based on the ROM taking the residual stress into account was found to be a simple and effective way to evaluate the effect of residual stress on the tensile behaviors of the SiC/Al composite.