Papers by Author: Akira Watazu

Abstract: Dense oxide coated AZ 31 magnesium alloy surfaces were uniformly formed using a radio frequency magnetron sputtering method. The magnesium oxide thin film thickness was about 240 nm. XRD results of the film indicated that film of magnesium oxide single phase was deposited. The surface of the film was uniform and no crack was observed. The Vickers hardness measured by the nanoindenter was about Hv80 and Hv200 for the AZ31 substrate and the sample coated with the thin film, respectively. The dynamic hardness of the AZ31 substrate and the sample coated with the thin film were almost the same. In the curve at the time of pressurization, a step was observed in the sample coated with the thin film. On the other hand, many steps were observed in the data curve for the thin film deposited on the glass substrate.

Abstract: Low Al single-phase magnesium alloy surfaces with dense magnesium oxide films were uniformly formed. The films were deposited with a radio frequency magnetron sputtering process with a planar magnetron sputtering system. The thickness of deposited magnesium oxide thin films was around 240 nm. According to the XRD results, a magnesium oxide phase film was formed on the substrate. The surface was uniform, and no cracks or exfoliation were observed. The deposited magnesium oxide film did not have any cracks or pores, and the surface of the sample was covered by magnesium oxide. The hardness of the magnesium oxide-coated magnesium alloy reached around Hv200, while that of the uncoated Mg-alloy was around Hv80. Moreover, the Vickers indenter under a 10-mN load indented the magnesium alloy substrate coated with the magnesium oxide film to a depth of around 640 nm, while that for the uncoated magnesium alloy substrate was around 620 nm. Meanwhile, the elasticity value for the magnesium alloy substrate coated with magnesium oxide film was around 5.3×10¹⁰ Pa, while that of the uncoated magnesium alloy substrate was around 4.2×10¹⁰ Pa.

Abstract: Titanium nitride (TiN) film on titanium film (Ti) was formed by magnetron sputtering method. Pure titanium substrates with TiN/Ti multi-layered films deposited using DC sputter-deposition machine in Ar gas atmosphere, in order to improve not only the blood compatibility of pure titanium but also the adhesion between the deposited TiN coating and the pure titanium substrate. The effects of the thickness of a pure titanium interlayer on adhesion of the TiN coating to the pure titanium substrate were investigated. And the effects of the TiN coating obtained in this study on blood compatibility were also investigated. The obtained multi-layered films looked yellow gold and appeared to be uniform and adhesive without any peel-offs. Based on the results of the platelet test, the ratio of the number of adhered platelets for the TiN/Ti film to that for the pure titanium substrate was estimated to be 0.54. Thus it was found that the platelet adhesion of the obtained TiN/Ti film was much smaller than the pure titanium, concluding that the TiN coating improved the blood compatibility.

Abstract: Calcium phosphate/ titanium oxide/ titanium/ plastic composite implants with 1.6-mm diameter and 7-mm length were successfully formed using a DC/ RF magnetron sputtering machine. The sample had no cracks and the surface of the sample was uniformly smooth. The chemical composition of the >10-nm-thick calcium phosphate layer was Ca: P: O=1.0: 0.79: 2.8. The sample was implanted into the tibia of an male 8-week-old SD rat for 28 days. When 0.70-μm sections of the tibia were prepared, the titanium layer with titanium oxide layer of the implant was not broken and the surfaces of the layer of the implant had not decomposed. The interaction between living bone and the implant could be clearly observed by light microscope and TEM.

Abstract: Grain refinements during hot compression of continuous casting AZ80 alloy bars and extrusive AZ61, AZ80 alloy bars were observed. The hot compression true stress-true strain curves of extrusive AZ61 and AZ80 alloy had similar tendencies, which were that the true stress increased and had a peak around 0.2 true strain, and then the stress decreased and was almost even from about 0.4 true strain. The stress peaks shifted to the high strain side as the compression speed, true strain speed, increased. However, the stress peaks did not shift at different compression temperatures. Fine grains were obtained under the condition of high strain speed and low temperature, but the grain sizes were uneven at low temperature compression. The stress peaks in the hot compression true stress-true strain curves of continuous casting AZ80 did not shift at different compression temperatures. AZ80 forging products with fine grains are expected to be formed under various conditions by using continuous casting AZ80.

Abstract: A new ECAP process method called rotary-die ECAP (RD-ECAP) was developed to form fine-grained bulk materials such as aluminium alloys, magnesium alloys, aluminium composites, and titanium, all of which can be processed under conditions of 573-773K, at an approximately 0.9-2.4 mm/s punch speed of 300MPa or lower. By the RD-ECAP method, ECAP processing of up to 2 passes can be done without sample removal and samples processed over 30 cycles were obtained.

Abstract: The AZ61 magnesium alloy was subjected to the differential speed rolling at different rolling conditions including reduction per pass, rotation speed ratio and rolling temperature, and the influences of the rolling conditions on microstructure, texture, mechanical properties and formability of the as-rolled sheets were investigated. Increasing the reduction per pass results in a more homogeneous microstructure and a relatively weaker basal texture. With increasing the rotation speed ratio, the inclination angle of basal pole toward the rolling direction increases and the stretch formability enhances correspondingly. Increasing the rolling temperature has an effect on weakening the basal texture intensity and leads to the enhancement of stretch formability.

Abstract: Titanium oxide/ titanium/ plastic composite implants were formed by coating commercially pure titanium thin films on the surfaces of plastic cylinders by DC magnetron sputtering method. The composite is uniformly formed and the surface of the composite implant is smooth. The implants in rat tibias were not broken and the films on the surfaces of the samples did not decompose. The samples with bone were able to cut by diamond knife and observations between bone and titanium oxide on titanium by TEM succeeded. Therefore, the composite is useful for implants or observations the interactions between titanium oxide and bone in detail.

Abstract: It was reported that the cold and warm press formability of the magnesium alloy was improved by the application of a differential speed rolling (DSR). However, it can be considered that the microstructure and the texture of the DSR processed sheets greatly change with the rolling conditions. In this study, commercial AZ31B magnesium alloy extrusions were processed by DSR at a differential speed ratio of 1.167 and a reduction per pass of 10% or less, and the effects of the rolling temperature, the number of rolling passes and reversal of the rolling direction on texture and mechanical properties were examined. As a result, it was found that the optimal rolling temperature in terms of the workability and formability of the material was 573 K. And the elongation and formability were maximal in sheets processed by 4–6 passes of DSR. Moreover, reversing the shear direction made the microstructure more homogeneous and finer than unidirectional shear, and improved the mechanical properties and formability. This improvement was greater in samples where the shear direction was reversed once in the middle than where it was reversed for each pass.

Abstract: The mechanical properties of the AZ31B alloy sheets processed by differential speed rolling (DSR) from the cast ingots homogenized at two different conditions were investigated. There still existed the uneven distribution of Al and Zn in the ingot homogenized at 673 K for 6 h, while it was homogeneous for the ingot homogenized at 723 K for 24 h. Compare with the sheet rolled from the ingot homogenized at 673 K for 6 h, the sheet rolled from the ingot homogenized at 723 K for 24 h exhibited a lower proof stress, a larger elongation, and a lager strain hardening exponent. The improvement in the ductility can be attributed to the elimination of the microsegregation of Al and Zn in the matrix.