Changchun Ge

Fabrication and evaluation of SiC/Cu functionally graded material used for plasma facing components in a fusion reactor

Abstract A new SiC/Cu functionally graded material that contains a spectrum of 0–100% compositional distributions of SiC used for plasma facing component was proposed and fabricated by a novel process termed graded sintering under ultra-high pressure, by which a near dense graded composite has been successfully obtained. Tests on plasma relevant performances showed that in SiC/Cu graded composite the CD4 production due to chemical sputtering is 85% lower than that of SMF800 nuclear graphite, while its thermal desorption is about 10% of that graphite; fatigue cracks and chemical decomposition were found on the surface of SiC/Cu FGM after 300 cyclic impacts of laser pulse with power density of 398 MW/m2; slight damage was also observed on the material surface after in situ plasma irradiation in a Tokamak facility.

Development of functionally graded plasma-facing materials

Abstract Three different processing technologies are described for the fabrication of SiC/C functionally graded material (FGM), B 4 C/Cu coating FGM and W/Cu FGM. The microstructure and physical properties of the FGMs are evaluated. Some plasma-relevant performances of these three FGMs show their prospect as plasma-facing materials in fusion reactors.

Frontal polymerization synthesis and characterization of temperature- and pH-sensitive hydrogels

The temperature- and pH-sensitive hydrogels, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)), were synthesized via frontal polymerization (FP). The reaction components have been varied in order to find their influences on frontal parameters and copolymer features. The results showed that front velocity and front temperature were dependent on the initiator concentration, reactant dilution, and NIPMA/AAc molar ratio. In addition, the morphology and sensitive behavior of the FP hydrogels were mainly affected by monomers’ ratio. Namely, the pore size, swelling abilities, LCST, and response kinetics of copolymer hydrogels obviously increased with the increasing acrylic acid concentration; however, they slightly changed with varying of amounts of initiator and solvent. Finally, in comparison with the hydrogels prepared by conventional batch polymerization, the ones synthesized by frontal polymerization exhibited more homogeneous chain composition and improved microstructure and response ability.

Recrystallization temperature of tungsten with different deformation degrees

Pure tungsten (PW) and W-1 wt% La2O3 (WL10) were prepared by powder metallurgical route followed by the swagingxa0+xa0rolling process. The logarithmic strains are 0, 0.37, 0.58, and 0.98 for WL10 and 0, 0.58 for PW. Heat treatments were performed at temperatures varied from 1,573 to 2,173xa0K to determine the recrystallization temperature. Recrystallization temperatures are 1,973 and 2,173xa0K for WL1 (logarithmic strain of 0.37) and WL3 (logarithmic strain of 0.98), respectively. But in the case of WL2 (logarithmic strain of 0.58), full recrystallization is not achieved at temperature of above 2,173xa0K. Furthermore, the recrystallization temperature of PW with logarithmic strain of 0.58 is at least 300xa0K lower than that of the equivalent WL10 sample. Moreover, the increase of recrystallization temperature inhibits the strength degradation of WL2: samples lose 4 % and 22xa0% strength when annealed at 1,573 and 1,973xa0K compared with room temperature (RT) sample. Finally, the texture evolution for the swagedxa0+xa0rolled WL10 is significantly related to the deformation degree: the dominated orientation is 〈001〉 for WL2 while 〈110〉 for WL3.

Design and fabrication of TiC-based symmetrically compositional functional graded materials

Abstract TiC-based cermets with Ni–Mo alloys are now increasingly used in industry. For further improving the properties of TiC-based cermets with the aim to replace more kinds of WC-based cemented carbides, TiC(Mo, Ni) x /TiC(Mo, Ni) y /TiC(Mo, Ni) x symmetrically compositionally functional graded materials (SCFGM) are proposed and fabricated, which have the following advantages: (1) more wear resistant surface layers composed of less Ni–Mo alloying in combination with tougher mid-layer(s) composed of more Ni–Mo alloying; and (2) artificial residual compressive stress created on both surfaces of the specimen due to the difference in the thermal expansion coefficient between surface layers and mid-layer(s), which remarkably increases the bending strength and the fracture toughness of the SCFGM. The analytical model for SCFGM is established based on elasticity mechanics, mechanics of composite materials and computing mathematics. Triangle series are employed to describe distributions of residual thermal stress on both surfaces of the FGM caused by the difference in thermal expansion coefficients between surface layers and central layers. As an example, TiC-based SCFGM is successfully fabricated based on calculated thermal stress distribution by the self-developed SCFGM CAD system.

Corrosion Resistance of Chromium-Coated Ferritic-Martensitic Steel in Supercritical Water

CNS-I (9Cr) and modified CNS-II (12Cr) were specifically designed for supercritical water reactors. Chromium (Cr) coatings with thicknesses of about 1 μm were deposited on the CNS-I and modified CNS-II substrates by magnetron sputtering to improve their corrosion resistances. Corrosion behavior was investigated in supercritical water at 823 K and 25 MPa with an oxygen concentration of 200 ppb for 200, 400, 600, 800, and 1,000 h. The coated CNS-I and coated modified CNS-II showed negligible weight gains of 0.542 mg/dm2 and −13.351 mg/dm2, respectively, considerably lower than those of the corresponding bare samples (602.17 mg/dm2 and 459.42 mg/dm2, respectively) after 1,000 h of exposure. The remarkable improvement in corrosion resistance could be attributed to the formation of dense chromium oxide (Cr2O3) layers on the Cr coatings. Interestingly, the Cr-coated CNS-I consisting of 9 wt% Cr displayed an equally excellent corrosion resistance to the coated modified CNS-II consisting of 12 wt% Cr due to the b...

Tunable carbon nanotube-tungsten carbide nanoparticles heterostructures by vapor deposition

A simple, versatile route for the synthesis of carbon nanotube (CNT)-tungsten carbide nanoparticles heterostructures was set up via vapor deposition process. For the first time, amorphous CNTs (α-CNTs) were used to immobilized tungsten carbide nanoparticles. By adjusting the synthesis and annealing temperature, α-CNTs/amorphous tungsten carbide, α-CNTs/W2C, and CNTs/W2C/WC heterostructures were prepared. This approach provides an efficient method to attach other metal carbides and other nanoparticles to carbon nanotubes with tunable properties.

Fabrication of solid-phase-sintered SiC-based composites with short carbon fibers

Solid-phase-sintered SiC-based composites with short carbon fibers (Csf/SSiC) in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSiC matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSiC because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

Design and joining of graphite to copper by a simple direct casting technology

A simple low-cost direct casting technology has been developed for joining graphite and copper. The direct casting of copper on graphite was possible through mixing transition metal (Cr) powders with Cu powders to decrease the contact angle between graphite and copper and form a carbide layer at high temperature (>1100°C) in a vacuum furnace for 20–80 min. For decreasing the coefficient of thermal expansion of copper alloy, refractory metal W powders were also added into the mixed powders. The reaction between the transition metal and graphite determined the formation of a thin carbide layer on the graphite surface, as detected by X-ray diffraction analysis. The cross-section of the joined samples was observed by SEM. The shear strength of the C-Cu joints was measured at room temperature with a compression machine.

Author Correction: Nanostructured laminar tungsten alloy with improved ductility by surface mechanical attrition treatment

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