Motoko Yamada

Microstructure and Mechanical Properties of Ti-ZrO2 Composites Fabricated by Spark Plasma Sintering

This study aims to investigate the microstructure and mechanical properties of Ti-ZrO2 composites and ZrO2/Ti functionally graded materials (FGMs) fabricated by spark plasma sintering (SPS). SPS has been conducted in a vacuum at 1400 oC under the uniaxial pressure of 30 MPa. Mechanical properties such as hardness and elastic modulus of Ti-ZrO2 composites have been systematically investigated using micro-Vickers and nanoindentation. The experimental results demonstrate that the mechanical properties of Ti are dramatically improved by an addition of small amount of ZrO2. There is almost no effect from the presence of Y2O3 in ZrO2 on the hardness of Ti-ZrO2 composites. ZrO2/Ti FGMs have been successfully fabricated, and mechanical properties of the FGMs have been examined.

Fabrication of Metal-Based Functionally Graded Grinding Wheel by a Centrifugal Mixed-Powder Method

Metal-bonded diamond grinding wheel was fabricated by a centrifugal mixed-powder method. The centrifugal mixed-powder method is a novel and effective casting process to obtain functionally graded material (FGM). At the beginning, we performed fundamental experiments using Al-Si alloy system for the purpose of knowing the migration behavior of mixed-powder under centrifugal force. Al-Si hypereutectic alloyed-powder or mixed-powder of Al and Si particles was placed into the mold, and then Al molten metal was cast under a centrifugal force. Cross sectional microstructure observation and quantitative analysis of Si content were conducted using an electron probe microanalyzer. Amount of Si decreased with receding from a mixed-powder region. Si concentration gradient in the sample fabricated Al-Si powder was smaller than the one fabricated using mixed-powder of Al and Si particles. Subsequently, φ 20 mm Cu/diamond grinding wheel was fabricated by the casting method. Graded diamond distribution was successfully obtained.

Fabrication of Aluminum Alloy‐Based Diamond Grinding Wheel by the Centrifugal Mixed‐Powder Method for Novel Machining Technology of CFRP

The aim of this study is to investigate the fabrication process of aluminum alloy-based diamond grinding wheels for drilling carbon fiber reinforced plastic (CFRP) by the centrifugal mixed-powder method (CMPM). An Al-5.6mass%Zn-2.5mass%Mg-1.6mass%Cu alloy and an Al-4mass%Cu alloy have been chosen as base materials. Al-Zn-Mg-Cu alloyed-powder has been mixed with diamond powder. Afterwards, the mixed powder has been placed into the mold, and then molten Al-Cu alloy has been cast into the mold by the centrifugal force at various temperatures in vacuum. The microstructural observations of the fabricated aluminum alloy-based diamond composites have been carried out with a scanning electron microscope (SEM). Effects of fabrication conditions such as casting temperature on microstructure of the fabricated composites have been investigated. As a result, aluminum alloy-based diamond grinding wheels have been successfully fabricated by CMPM.

Effects of shot-peening and atmospheric-pressure plasma on aesthetic improvement of Ti–Nb–Ta–Zr alloy for dental applications

Ti and Ti alloys are widely used for biomedical applications such as artificial joints and dental devices because of their good mechanical properties and biochemical compatibility. However, dental devices made of Ti and Ti alloys do not have the same color as teeth, so they are inferior to ceramics and polymers in terms of aesthetic properties. In a previous study, Ti?29Nb?13Ta?4.6Zr was coated with a white Ti oxide layer by heat treatment to improve its aesthetic properties. Shot-peening is a severe plastic deformation process and can introduce a large shear strain on the peened surface. In this study, the effects of shot-peening and atmospheric-pressure plasma on Ti?29Nb?13Ta?4.6Zr were investigated to form a white layer on the surface for dental applications.

Effects of Particle Size on Fabrication of Al-TiO2 Functionally Graded Materials by Centrifugal Mixed-Powder Method

As one of processing methods of functionally graded materials (FGMs), centrifugal mixed-powder method has been proposed. The centrifugal mixed-powder method is the casting process combined of centrifugal casting and powder metallurgy. This processing method has advantage that fine ceramics-particles, whose wettability with matrix melt is low, can be compounded into metallic material. However, effects of particle size on microstructure and mechanical properties of the FGMs fabricated by the centrifugal mixed-powder method are unclear. In this study, two kinds of Al-TiO2 FGMs rings are fabricated by the centrifugal mixed-powder method. One contains TiO2 particles having similar diameter with Al matrix particles (hereafter, small different-size (SD) TiO2 particles), and the other one compounds TiO2 particles with much smaller diameter than Al matrix particles (hereafter, large different-size (LD) TiO2 particles). In case of the Al-TiO2 FGMs ring containing SD-TiO2 particles, the TiO2 particles are homogeneously dispersed in Al matrix on outer surface of the ring. On the other hand, the TiO2 particles in the Al-TiO2 FGMs ring with LD-TiO2 particles are distributed along grain boundary of Al matrix. Moreover, Vickers-hardness and wear resistance around outer surface of the Al-TiO2 FGMs ring containing the SD-TiO2 particles is higher than that of the Al-TiO2 FGMs ring with LD-TiO2 particles. Since Al particles in the mixed-powder with LD-TiO2 particles are surrounded by the TiO2 particles, the Al particles can be hardly melted by heat of molten Al at casting process. As a result, the Al-TiO2 FGMs ring with LD-TiO2 particles has low hardness and wear resistance. Therefore, it is found that TiO2 particles having similar diameter with Al matrix particles are more suitable for fabrication of the Al-TiO2 FGMs rings.

Fabrication of Self-Lubricating Cu-Based Composite Containing Graphite Particle by Centrifugal Mixed-Powder Casting

Reduction of frictional coefficient at sliding position can improve wear resistance of material. In previous studies, Cu-based composites containing graphite particles have been reported. Since graphite is better lubrication material, the Cu-based composites containing graphite particles have better wear property comparing with the pure Cu. However, these composites are mainly fabricated by sintering method and its strength is relatively low. In this study, Cu-based composites containing graphite particles are fabricated by centrifugal mixed-powder casting. The centrifugal mixed-powder casting is novel centrifugal casting method combined with powder metallurgy. Using this casting method, the Cu-based composites containing graphite particles are successfully obtained. The graphite particles are distributed in the Cu matrix and no casting defects are observed. Moreover, wear resistance of these Cu-based composites are much better than pure Cu, and the frictional coefficient between these composites and bearing steel as the counter part is reduced by dispersion of the graphite particles. Furthermore, it is found that the optimum area fraction of the graphite particles to improve the wear resistance of the present Cu-based composite is from 15% to 21%.