Abstract: Fracture behavior under multiaxial stress state of polycrystalline alumina was studied from the view point of an artificial crack propagation and fracture from a natural flaw. The former was studied by mixed-mode fracture toughness tests; asymmetric four-point bending and diametral compression techniques were carried out using precracked and notched specimens. The latter was studied by biaxial fracture tests in compression and torsion loading; multiaxial fracture statistics was applied to the measured fracture envelope. The ratio KIIC/KIC obtained from the biaxial tests was higher than that obtained by the mixed-mode fracture toughness tests. It revealed that the fracture from an artificial flaw does not simulate the fracture from a naturall flaw in polycrystalline ceramics.
Abstract: Three kinds of atmospheres (air, highly-pure Ar and ultra highly-pure Ar gas) with different oxygen partial pressures were applied to investigate the tensile properties and creep behavior of SiC fibers such as Hi-NicalonTM and TyrannoTM-SA. These fibers were annealed and crept at elevated temperatures ranging from1273-1773 K in such environments. After annealing at 1773 K, the room
temperature tensile strengths of SiC-based fibers decreased with decreasing the oxygen partial pressure and the near stoichiometric fiber TyrannoTM-SA shows excellent strength retention. At temperatures above the 1573 K, the creep resistance of SiC fibers evaluated by bending stress relaxation (BSR) method under high oxygen partial pressure was lower than that of in low oxygen partial pressure. The microstructural features on these fibers were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
Abstract: Conductive TiN/Si3N4 ceramic composites were processed by electrical discharge
machining (EDM) and their microstructure and conductivity investigated. A low electrical resistivity of 1.25×10-3Ω.cm was obtained in 40vol%TiN/Si3N4 composite. The whole process of tool electrode wear is evaluated by sinker-EDM. The machined surfaces of TiN/Si3N4 ceramic composites were examined by scanning electron microscopy (SEM) and profilometry to determine the surface finish. Micropores of 700µm in depth and 70µm in diameter were successfully machined in TiN/ Si3N4 composites by the micro-EDM method.
Abstract: Single crystal 4H-SiC was irradiated with 2 MeV Au ions at 165 K. Ion-induced defect
configurations and damage accumulation were studied by ion-channeling techniques along the <0001>, > < 3 40 4 and > < 1 20 2 directions. A nonlinear dependence of damage accumulation is observed for both the Si and C sublattices along all three directions, and the relative disorder observed along the > < 3 40 4 and > < 1 20 2 directions is much higher than that along the <0001> direction. The damage accumulation can be described by a disorder accumulation model, which indicates that defect-stimulated amorphization is the primary amorphization mechanism in SiC, and the high disorder level for the large off-axis angles is attributed to particular defect configurations. Molecular dynamics (MD) simulations demonstrate that most single interstitial configurations are shielded by Si and C atoms on the lattice sites along the <0001> direction, which significantly reduces their contribution to the backscattering/reaction yield along the <0001> direction.
Abstract: Atomic-level simulations are used to determine defect production, cascade-overlap
effects, and defect migration energies in SiC. Energetic C and Si collision cascades primarily produce single interstitials, mono-vacancies, antisite defects, and small defect clusters, while amorphous clusters are produced within 25% of Au cascades. Cascade overlap results in defect stimulated cluster growth that drives the amorphization process. The good agreement of disordering behavior and changes in volume and elastic modulus obtained computationally and experimentally
provides atomic-level interpretation of experimentally observed features. Simulations indicate that close-pair recombination activation energies range from 0.24 to 0.38 eV, and long-range migration energies for interstitials and vacancies are determined.
Abstract: The crystal structures of reduced-reoxidized ceria-zirconia solid solutions, Ce2Zr2O7+x, with an ordered arrangement of Ce and Zr ions were studied by transmission electron microscopy (TEM), X-ray powder diffraction and thermogravimetric analysis. The oxygen absorption of Ce2Zr2O7 with pyrochlore structure (space group m Fd 3 ) was revealed to proceed through two-step
reaction; reaction from Ce2Zr2O7 to b-Ce2Zr2O7.5 around 400K and reaction from b-Ce2Zr2O7.5 to Ce2Zr2O8 about 600K. b-Ce2Zr2O7.5 phase with space group m F 3 4 was thought to be formed by occupation of the half ordered oxygen vacancies with oxygen ions periodically. The oxidation from Ce2Zr2O7 to b-Ce2Zr2O7.5 was also occurred at room temperature by keeping for about 1 year or by irradiation of an electron beam in TEM. On the other hand, the crystal structure of Ce2Zr2O8,
completely oxidized state of Ce2Zr2O7, belongs to the space group of m P 3 4 or 23 P from the rule for possible diffractions and the symmetry of the ordering cations.
Abstract: In a global effort, the key players have combined their R&D forces to work jointly on the next generation thermonuclear fusion device. The development of structural, heat-sink and armor materials for plasma interactive components is focusing on neutron irradiation damage, and its impact on property retention and component integrity. Consequently, the processing of materials, realistic component testing methods as well as modeling are being optimized to suit the newest design concept(s). Nondestructive inspection of components is now available at an accuracy needed to ensure long service in a harsh, nuclear environment. The most promising materials and best established manufacturing processes are described; the proposed qualification techniques for fusion in-vessel and heat removal systems are reviewed.
Abstract: To evaluate the performance of plasma facing materials (PFM) and components for future thermonuclear fusion devices under the expected operation conditions, an in-depth material characterization and extensive high heat flux simulation tests are performed routinely in electron beam test facilities. These experiments cover both, thermal fatigue tests with power densities up to approx. 20 MWm-2 and thermal shock loads with deposited energy densities of several MJm-2. In addition, irradiation experiments have been performed in material test reactors to investigate the neutron induced material degradation.
Abstract: The behavior of thick SiC gradient coatings on different graphites under high power
electron beam irradiation, pulsed high energy laser impact, and HT-7 limiter plasma action was investigated. In the following tests at these facilities, the samples were examined using SIMS, EDAX, X-ray crystallography, profilometer and Auger spectroscopy. Thick SiC gradient coatings showed excellent durability under high heat flux and in real conditions of HT-7 limiter plasma irradiation. The primary results indicated that the use of multi-element doped graphite, GBST1308 (1%B4C, 2.5%Si, 7.5%Ti) with high thermal conductivity, as substrate will improve the durability
of thick SiC gradient coatings significantly.
Abstract: Tungsten has the highest sputtering threshold of all possible candidates and the highest melting point in metal. It will be the first candidate in selecting divertor materials. Great efforts are made on research and development on W/Cu functionally Graded Materials as high performance divertor material for next generation divertor-mounted Tokamak facilities in China recently. Four different processing technologies are used and compared and some results of evaluation of
plasma-relevant characteristics of these materials are reported.