Akira Kohyama

Tensile, Compressive and In-Plane/Inter-Laminar Shear Failure Behavior of CVI- and NITE-SiC/SiC Composites

A SiC/SiC composite is an attractive candidate material but it is a challenge to apply it to the practical components because of the inherent brittle-like failure and structural anisotropy. This study aims to evaluate the failure behavior of SiC/SiC composites by various test modes. Comparison between tensile and compressive strengths revealed the clear axial anisotropy of failure strength. The in-plane shear strength by the off-axial tensile method is invalid unless considering the mixed failure modes. Alternatively, it was demonstrated that the in-plane shear strength can successfully be obtained by the Iosipescu method. The true inter-laminar shear strength can be identified by the diametral compression method.

Multi-Faraday-cup-type beam profile monitoring system for a dual-beam irradiation facility

Abstract A multi-Faraday-cup-type ion beam profile monitor (BPM) with simplified readout circuit for use in dual-beam irradiation experiments is described.

EFFECT OF POROSITY ON PARTICLE EROSION WEAR BEHAVIOR OF LAB. SCALE SICF/SIC COMPOSITES

The use of silicon-based ceramics and composites as combustor liners and turbine vanes provides the potential of improving next-generation turbine engine performance, through lower emissions and higher cycle efficiency, relative to todays use of super alloy hot-section components. As a series of research for FOD resistant, a particle erosion wear test was carried out for continuous Pre-SiC fiber-reinforced SiC matrix composites with a new concept of lab. scale fabrication by LPS process. The result shows that aperture (some form of porosity) between fiber and interface has a deleterious effect on erosion resistance. Aperture along the fiber interfaces consequently causes a severe wear in the form of fiber detachment. Wear rate increase proportional as contents of open porosity increases. For nearly full dense composite materials of about 0.5 % porosity, are about 200 % more wear-resistant than about 5 % porous composites. Grain growth and consolidate condition of matrix which directly affects to FOD resistant are also discussed.

Processing and Properties of SIC and SIC/SIC Composite Materials by Melt Infiltration Process

This paper dealt with the microstructures and the mechanical properties of monolithic SiC and SiC/SiC composite materials fabricated by the melt infiltration process. The characterization of melt infiltrated SiC and SiC/SiC composite materials with different sizes of starting SiC particles was investigated by means of electron microscopies, three point bending tests and single-fiber push-out tests. Based on the mechanical property-microstructure correlation, process optimization methodology also was discussed. The flexural strength of melt infiltrated SiC material strongly depended on the content of residual silicon, which associated with the preparation route of C/SiC matrix slurry such as the composition ratio of C and SiC particles and the size of raw SiC particles. MI-SiC/SiC composites represented good flexural strength, even if the instability of matrix morphology and the interfacial debonding were occurred.

Industrialization of Advanced SiC/SiC Composites and SiC Based Composites; Intensive activities at Muroran Institute of Technology under OASIS

Organization of Advanced Sustainability Initiative for Energy System/Material (OASIS), at Muroran Institute of Technology is now intensively enforcing its efforts for industrialization of advanced SiC/SiC composites and SiC based composites by fabrication system integration of NITE method. This paper provides the brief review of the activities at OASIS, where prototype production line of green sheets and prepreg sheets are under installation. The near-net shaped preforms with the NITE green-sheets and prepreg-sheets are made into near-net shape components for potential applications under consideration by HIP and Pseudo-HIP. Aiming at the near term utilization, SiC/SiC hybrid structures with metallic materials, such as steels and other refractory metals, were fabricated with promising results. Trial to reduce the production cost has been continued.

Effects of Preform Densification on Near-Net Shaping of NITE-SiC/SiC Composites

Large volumetric shrinkage (~50 Vol%) occurs during ceramic matrix composites fabrication by hot-pressing due to infiltration and densification process of powder for matrix formation, resulting in unfortunately significant fiber-architecture and -strength damage. This study tries to explore damage-less near-net shaping technique by preform densification before hot-pressing in Nano-Infiltration and Transient Eutectic-phase (NITE) process. In particular, effects of preform densification for the damage-less near-net shaping, important influencing elements such as fiber-architecture, microstructural integrity and homogeneity, and composites mechanical properties were evaluated using simple shaped (plate) and complex shaped composites. The preform densification demonstrated protective fiber-architecture in complex shaped composites and enhanced composites density to 2.77/cm3 and ultimate bending strength to ~200 MPa in simple shaped composites, owing to significantly reduced volumetric shrinkage.

A modeling of radiation induced microstructural evolution under applied stress in austenitic alloys

Abstract Effects of applied stress on interstitial type Frank loop evolution at early stages of irradiation were investigated by both numerical calculation and irradiation experiments. In the experimental part of this work, microstructural inspection has been made by transmission electron microscopy with a special emphasis on Frank loops and perfect loops on every {111} plane. The results of the TEM observation revealed that Frank loop concentration on a {111} plane increased as the resolved normal stress to a {111} plane increased and that small perfect loops were more likely produced on {111} planes where larger resolved shear stress was applied. The model of a stress effect on Frank loop unfolding was provided, which is triggered by nucleation of a Shockley partial dislocation loop in a Frank loop, was proposed. The results of the numerical calculation was successful to predict the strong dependence of Frank loop concentration on the resolved normal stress to {111} plane, which was the characteristic feature seen in the irradiation experiments.

Diffusion Bonding Technology of Tungsten and SiC/SiC Composites for Nuclear Applications

Silicon carbide (SiC) is a candidate for the structural material in the next generation nuclear plants. Use of SiC/SiC composites is expected to increase the operation temperature of system over 1000 °C. For the high temperature system, refractory metals are planned to be used for several components. Tungsten is a candidate of armor on the divertor component in fusion, and is planned to be used for an upper-end plug of SiC/SiC fuel pin in a Gas cooled Fast Reactor (GFR). Joining technique of the SiC/SiC composites and tungsten is an important issue for nuclear systems in future. Nano-Infiltration and Transient Eutectoid (NITE) method is able to provide dense stable and high strength SiC/SiC composites having high resistance against pressure at elevated temperature, a diffusion bonding technique is usable to join the materials. Present research produces a NITE-SiC/SiC composite and tungsten as the similar dimension as a projected cladding tube of fuel pin for GFR using diffusion bonding, and investigated microstructure and mechanical properties.

SiC/SiC and W/SiC/SiC Composite Heater by NITE-method for IFMIF and Fission Reactor Irradiation Rigs

For nuclear and fusion materials R&D, high dose neutron irradiation at very high temperature is one of the most important and challenging techniques. As the part of Japan/EU Broader Approach (BA) program for fusion, International Fusion Materials Irradiation Facility/Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) project is on-going. Where, High Flux Test Module (HFTM) design aiming up to 1000°C has been intensively investigated. Innovative SiC/SiC and tungsten embedded SiC/SiC (W/SiC/SiC) heaters have been recognized potential and promising candidates. These heaters were fabricated successfully by NITE method and were evaluated. The SiC/SiC heater showed weak temperature dependence up to 1000°C on in-plane electrical conductivity. Irradiation capsule for heater performance evaluation under neutron irradiation in Belgian Reactor 2 (BR2) is also under preparation. The results of heater performance and basic properties evaluation and of underlying microstructure behavior analysis are provided.

Microstructure and Property Changes of SiC Fiber under Thermal and Ion Irradiation Environments

Although, SiC/SiC composites are very attractive for applications at high-temperature including advanced nuclear fusion/fission plants, their high material cost has been one of biggest issues to be utilized. In the neutron irradiation environments, high crystallinity of SiC fibers and matrix is essential to stabilize the mechanical properties, but the expensive crystallized SiC fibers may enhance the cost of material. As a potential option from the cost down aspect, utilization of amorphous SiC fibers was planned. This paper concerns about the radiation damage tolerance of SiC/SiC with amorphous SiC fibers as starting reinforcing fibers. The crystallization procedure of amorphous SiC fibers was investigated during thermal treatments, and a new NITE-SiC/SiC, called as IC-NITE (IC stands for in-situ crystallized), composite was produced. Its radiation damage behaviour and microstructural stability were examined by a heavy ion irradiation experiment and TEM.