Naoki Miyano

Preferred orientation relationship of intra- and inter-granular precipitates in titanium alloys

Abstract In a previous study by one of the authors, it had been reported that intra-granular α (HCP) precipitates have a Burgers orientation relationship (O.R.) with the β (BCC) matrix in Ti–22V–4Al and Ti–15V–3Cr–3Sn–3Al alloys. On the other hand, grain boundary α precipitates were shown to have a tendency for parallelism of the {110} β //{1 1 01} α planes, i.e. they display a Potter O.R. with one of the conjugate β grains. A three-dimensional near-coincidence site lattice (3-D-NCS) model, coupled with transmission electron microscope (TEM) observations, has been developed to explain these observations. The shape of an embryo predicted by the 3-D-NCS analysis is compared for the Burgers and Potter O.R., assuming the morphology is only determined by the anisotropy of the structural part of the interfacial energy. An intra-granular precipitate with Burgers O.R. has a lower free energy of formation for the critical nucleus than one with the Potter O.R., in agreement with the observations. However, α precipitates with the Potter O.R. are preferred at grain boundaries, again in agreement with the experimental observations.

Gene transfer device utilizing micron-spiked electrodes produced by the self-organization phenomenon of Fe-alloy

In the diffusional phase transformation of two-phase alloys, the new phase precipitates form the matrix phase at specific temperatures, followed by the formation of a mixed microstructure comprising the precipitate and the matrix. It has been found that by specific chemical-etching treatment, the precipitate in Fe-25Cr-6Ni alloy projects substantially and clusters at the surface. The configuration of the precipitate has an extremely high aspect ratio: it is several microns in width and several tens of microns in length (known as micron-spiked). This study targets the development of a gene transfer device with a micro-spike produced based on the self-organization phenomenon of the Fe-25Cr-6Ni alloy. With this spike-projected device, we tried to efficiently transfer plasmid DNA into adherent cells by electric pulse-triggered gene transfer using a plasmid-loaded electrode (electroporation-based reverse transfection). The spiked structure was applied to a substrate of the device to allow efficient gene transfer into adherent cells, although the general substrate was flat and had a smooth surface. The results suggest that this unique spike-projected device has potential applications in gene transfer devices for the analysis of the human genome in the post-genome period.

Future Relations between Humans and Artificial Intelligence: A Stakeholder Opinion Survey in Japan

Concern about the potential benefits and risks of artificial intelligence (AI) has given impetus to the establishment of AI research. AI requires responsible research and innovation (RRI) with the collaboration of various stakeholders, including the public, from the early stages. However, stakeholders may have different opinions about AI and human-machine relations. We aim to discuss these viewpoints by conducting a questionnaire survey, and to suggest perspectives on future collaborations among stakeholders.

Temperature Dependence of Austenite Nucleation Site on Reversion of Lath Martensite

The temperature dependence of austenite nucleation behavior within lath martensitic structure was investigated in an ultralow carbon 13%Cr-6%Ni martensitic stainless steel partially reversed at (austenite + ferrite) two phase region. The shape and nucleation site of the reversed austenite grains were varied depending on the reversion temperature; fine acicular austenite grains frequently formed along the lath boundaries at a temperature lower than 915 K, while the granular ones tended to nucleate mainly on the prior austenite grain boundaries at a higher temperature. In order to explain the temperature dependence of nucleation site transition, the difference in energetics of austenite nucleation between the lath boundary and the prior austenite grain boundary was discussed on the basis of the classical nucleation theory and FEM analysis. The calculation of the changes in interfacial energy and elastic strain for austenite nucleation suggested that the lath boundary acts as more preferential nucleation sites for austenite rather than the prior austenite grain boundary to reduce the increment of elastic strain when the reversion temperature is low.

Fabrication of TiNi shape memory alloy micro-structures and ceramic micro-mold by LIGA-MA-SPS process

Metals and ceramics are becoming increasing of importance to microsystem in reproduction and molding techniques because of the mechanical and physical properties. In the study, we have developed a new process using LIGA mold which is able to cast a microstructure of alloys or ceramics using spark plasma sintering (SPS) machine. In addition, the alloys are made by mechanical alloying (MA) method using a combination of different metal powder. A micro spring structure of Ti-Ni-Cu shape memory alloy powder was produced by way of trial. Finally, it was found that the LIGA-MA-SPS process is an effective technique.

Reasons for Formation of Twin-Precipitates in Two Phase Stainless Steel

This study focuses on the entire shape of the  twin-precipitate in two phase stainless steel, Fe-25Cr-6Ni in terms of the interphase and elastic strain energies generated between the precipitate and matrix. An investigation of this precipitation is important not only in terms of microstructure control but also for improving the mechanical properties of materials. Firstly, the three-dimensional near-coincidence site lattice (3D-NCS) model, which is based on the atomic matching model, is applied for estimating the preferred habit planes by evaluating the result of geometrical atomic matching. Subsequently, the precipitate shape is determined from candidates of the preferred habit plane produced by the 3D-NCS model, and the elastic strain surrounding and within the precipitate is investigated by FEM analysis, which can calculate the anisotropic elastic strain depending on the shape of the precipitate. The results are compared with observed precipitate by TEM.

Fabrication of a TiC/Ti5Si3 Nano-Grained Composite for Micro-Parts Using Pseudo-Superplastic Deformation by Non-Equilibrium PM Process

Ceramics composites are suitable as the materials for a micro electro mechanical system (MEMS) parts in terms of its mechanical and physical properties. We apply the PM process in combination with mechanical alloying (MA) and Spark Plasma Sintering (SPS) to produce micro-parts using a ceramic composite, TiC/Ti5Si3. Powders of elements Ti and SiC whose composition is Ti-20 mass%SiC are blended for MA. After the alloying, the MA powder whose average particle size is 20� 30 mm, has amorphous-like structures. Results of compression-tests and TEM observations indicate the occurrence of unusual high-temperature deformation behaviors such as low flow stress at the lower deformation temperature. The deformation is attributed to a pseudo-superplasticity in which the phase transition of metastable microstructure occurs during the deformation. The pseudo-superplasticity observed in the SPS compact improves the formability in fabrication of the microparts. The MA powder is filled into a micro-size mold produced by LIGA process, and casts together by SPS in order to fabricate a new microparts using TiC/Ti5Si3. Optimization of the pseudo-superplasticity enables the fabrication of the micro-parts using TiC/Ti5Si3.

Application of Pseudo-Superplasticity to Produce TiN/Ti5Si3 and TiC/Ti5Si3 Nano Grain Composites for Micro Molding

The requirement and importance of metals and ceramics are increasing to microsystem in reproduction and molding techniques because of the mechanical and physical properties. In this study, a non-equilibrium PM processing such as an MA/SPS process is examined in a Ti-20 mass% SiC as well as in a Ti-20 mass% Si3N4 materials systems. We also apply the MA/SPS PM process to produce micro-parts made of ceramic composites. As a result of compression-test and TEM observations, unusual high temperature deformation effects such as low flow stress at low deformation temperatures or at the high initial strain rates were observed in the SPS compacts. Such an unusual deformation behavior is attributed to a pseud-superplasticity in the material, in which the phase transition of metastable microstructure occurs during the deformation. The MA/SPS process was able to apply to a Ni mold LIGA process. Optimization of the pseud-superplasticity enables to fabricate molds made of fine ceramics composites such as TiN/Ti5Si3 or TiC/Ti5Si3. Introduction Structural ceramics hardly deforms because of its poor ductility and toughness. Usually it requires high temperature sintering process as well as high temperature deformation for the ceramics parts production. However, one of the authors proposed a non-equilibrium powder metallurgy (PM) process, which enables to fabricate a near net-shape product made of the ceramics composites [1-3]. The non-equilibrium PM process combined with mechanical alloying (MA) [4] and sintering, such as hot pressing (HP) or spark plasma sintering (SPS), improves a formability and productivity of ceramics composites due to the phase transformation during high temperature deformation. The concept of the process is shown in Fig. 1. For example, a mixture of Ti and SiC or Si3N4 powders were processed by MA and the mixed powders resulted in formation of amorphous and nano alphaTi phases [1-3]. The powders were then sintered at elevated temperatures and became TiC/Ti5Si3 or TiN/Ti5Si3 ceramics composites. These composites kept an equiaxial grain structure and indicated an extremely low stress deformation due to the grain boundary sliding and/or the stress relaxation by nucleation of new phases, under some specific condition of temperatures and strain rates. Thus, it can be expressed as a pseud-superplasticity. In the present study, we apply the non-equilibrium PM (MA/SPS) process to fabricate TiC/Ti5Si3 or TiN/Ti5Si3 ceramics composites for micro size parts (called micro-parts). Recently, although Materials Science Forum Online: 2004-02-15 ISSN: 1662-9752, Vols. 447-448, pp 311-316 doi:10.4028/www.scientific.net/MSF.447-448.311