Effect of tungsten matrix on the mechanical property of SiC fiber reinforced tungsten composites with foils fabricated at 1700 °C

The SiC fiber reinforced tungsten (W) composites were prepared by hot press process at 1700 °C for 1 h under a pressure of 20 MPa with W foils as matrix. The effect of thickness of W foils on the phases, microstructure, and mechanical properties of the composites were investigated in this work. In addition, the recrystallization temperature of W foil used in this work was confirmed. The results demonstrated that the composites with 0.08 mm foil exhibited better mechanical property with 197 MPa and high pseudo ductility than those of the 0.05 mm foil composites of 129 MPa. In addition, the used foils after sintering have recrystallized, and W can be identified by XRD. Therefore, SiC fiber can be an effective reinforcement to toughen W and dense foils as matrix can prevent the reaction partially

Densification behavior of monolithic SiC fabricated by pressureless liquid phase sintering method

As a preliminary investigation of process development for SiC fiber-reinforced SiC matrix composites (SiCf/SiC composites) via a pressureless liquid phase sintering (PLPS) method, the manufacturing process parameters of monolithic SiC fabricated with/without very low pressure during the sintering under high temperature (1850 and 1900 °C) were optimized. Two kinds of sintering additive system (only Al2O3 and Al2O3–Y2O3 mixtures) can be achieved full densification corresponding to 99% of the theoretical density without high pressure during the sintering. Monolithic SiCs of both sintering additive systems applied with prepressure of 20 or 40 MPa possessed the flexural strength and porosity comparable to those of conventional liquid-phase sintered SiC with high pressure during the sintering. The low pressure (0.63 MPa) during sintering reduced the densification in particular for the materials sintered with just Al2O3. The additions of BN particles led to a gradual decrease in mechanical strength with an increase in porosity

High temperature mechanical properties of BN particle dispersion SiC composites

Silicon carbide composites basically require weak fiber/matrix interphase like carbon or boron nitride (BN). The interphase material and its thickness are keys to determine mechanical properties. However precise control is the critical issue in terms of large scale production and material cost. The interphase is the weakest link for the environmental effects. The SiC composites were developed by applying BN particle dispersion in SiC matrix without the interphase. The objective is to understand the high temperature mechanical properties of the SiC composites. Please click Additional Files below to see the full abstract

Effect of Interfacial Shear Strength on Mechanical Property of SiC/SiC

In order to quantitatively evaluate mechanical properties of fibers, matrices and their interfaces in fiber reinforced SiC/SiC composites, nano-indentation tests have been carried out. Using the same technique, fiber push-out test was performed. The specimens were analyzed by means of scanning electron microscopy (SEM), before and after indentation tests. From the indentation load vs. displacement relations, the fiber pushed out process has been discussed and the initiation loads of interfacial debonding and those of interfacial sliding were defined and were discussed in comparison with the C/C composites. The load of interfacial debonding initiation was likely to increase in proportion to the fiber circumference. The initiation load of interfacial sliding increased with increment of contact area between fiber and matrix. The relation between bending strength and interfacial shear strength of SiC_/SiC_ is preliminary postulated together with crack initiation and propagation characteristics and microstructural characteristics of the composites

カク ユウゴウ ヨウ SiC / SiC フクゴウ ザイリョウ ノ キョウド トクセイ オヨビ ビサイ コウゾウ ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(エネルギー科学)甲第9050号エネ博第37号新制||エネ||10(附属図書館)UT51-2001-F380京都大学大学院エネルギー科学研究科エネルギー応用科学専攻(主査)教授 香山 晃, 教授 塩津 正博, 教授 木村 晃彦学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDA

Erosive Wear Mechanism of New SiC/SiC Composites by Solid Particles

A solid-particle erosive wear test by impinging silicon carbide (SiC) powders was carried out at room temperature over a range of median particle sizes of 425–600 μm, speed of 100 m/s and impact angle of 90° and assessed by wear measurements and scanning electron microscopy. Erosive wear behaviour was examined on newly fabricated nano-powder infiltration and transient eutectoid (NITE) SiC/SiC composites and two commercial composites by the chemical vapour infiltration (CVI) and NITE fabrication route. Microstructural observation was performed to examine the correlation between erosive wear behaviours and fabrication impurities. Conspicuous defects were observed in the prototype materials as the forms of porosity, fibre deformation, residual oxide, pyrolytic carbon (PyC) deformation, PyC cleavage, among others. Erosive wear behaviour was rather serious in the prototype of fabricated composites, which employ pre-SiC fibre and phenolic resin. Two dominant erosive wear mechanisms were observed: delamination of constituents, mainly caused by erosive crack propagation, and fragmentation and detachment of constituents, which usually resulted from erosive impact. A unit size of delamination was the most decisive factor affecting wear volume. The bonding strength of each constituent was mostly affected by various forms of porosities. Therefore, the fundamental cause and subsequent results must be carefully elucidated. The correlation of microstructural defect and wear behaviour was investigated with the aim of reducing dominant wear by improving fabrication conditions. The final product of the cost-effective composite had a 2.5-fold higher resistance than the commercial CVI composite. Consequently, by controlling fabrication impurities, we have been successful in developing and improving a new fabrication technique; consequently, the known defects are rarely observed in final product. A schematic wear model of erosive wear mechanisms is proposed for the newly fabricated SiC/SiC composites under particle erosion

Fabrication of SiC/SiC composites by means of in situ Crystallization of SiC Fibers

A novel challenge, the in situ crystallization of Pre-SiC reinforced-fiber during the fabrication of SiC/SiC composites, has been made for cost effectiveness. Constituent parts of each fabricated material with various manufacturing conditions were assessed by microscopic observation. The depending issues of a prototype process were rather serious that the unwanted areas were conspicuously observed in several places, such as a residual oxide area, unsintered area, course matrix, porosity along the fiber-tows, and a huge scale of deformation on fiber-tows. Crystallization process of Pre-SiC fiber itself caused volume contraction about 24.5%, which result in formation of a gap between the fiber-tow and pyrolytic carbon (PyC) interface. The optimization has been successfully made for a new fabrication technique by controlling most of the known defects. As a result, defects are rarely observed in final product of composite material

Effect of joining temperature on the microstructure and strength of tungsten/ferritic steel joints diffusion bonded with a nickel interlayer

A diffusion bonding process, for joining of tungsten to ferritic steel using nickel as an interlayer, was developed for nuclear component application. The effect of joining temperature on the microstructure and tensile strength of the joint was investigated in this work. Metallographic analysis revealed that a good bonding was obtained at both the tungsten/nickel and nickel/steel interfaces, and the diffusion products were identified in the diffusion zone. Nano-indentation test across the joining interfaces demonstrated the effect of solid solution hardening in the diffusion zone. Tensile test showed that the maximum average tensile strength of not, vert, similar200 MPa was obtained for the joint diffusion bonded at 900 °C. The results were discussed in terms of the joining temperature and of the residual stress generated during joining process

Microstructure and mechanical properties of diffusion bonded joints between tungsten and F82H steel using a titanium interlayer

Diffusion bonding between W and ferritic/martensitic steel F82H using a Ti interlayer was carried out in vacuum at temperature range of 850–950 °C for 1 h with 10 MPa. Metallographic analysis with field-emission scanning electron microscopy revealed excellent bonding at both W/Ti and Ti/F82H interfaces. The chemical compositions of the reaction products were analyzed by energy dispersive spectroscopy and their existence were confirmed by X-ray diffraction technique. α–β Ti solid solution was detected at W/Ti interface, while the reaction phases at Ti/F82H interface are dependent on the joining temperature. Joint strength was evaluated and the variations in strength of the joints were significantly related to the microstructural evolution of the diffusion zone. All the joints fractured at Ti/F82H interface during shear testing. The hardness distribution across the joining interfaces was also determined