Ge Changchun

High Heat Flux Testing of B4C/Cu and SiC/Cu Functionally Graded Materials Simulated by Laser and Electron Beam

B4C, SiC and C, Cu functionally graded-materials (FGMs) have been developed by plasma spraying and hot pressing. Their high-heat flux properties have been investigated by high energy laser and electron beam for the simulation of plasma disruption process of the future fusion reactors, And a study on eroded products of B4C/Cu FGM under transient thermal load of electron beam was performed. In the experiment, SEM and EDS analysis indicated that B4C and SiC were decomposed, carbon was preferentially evaporated under high thermal load, and a part of Si and Cu were melted, in addition, the splash of melted metal and the particle emission of brittle destruction were also found. Different erosive behaviors of carbon-based materials (CBMs) caused by laser and electron beam were also discussed.

Effect of helium implantation on SiC and graphite

Effects of helium implantation on silicon carbide (SiC) and graphite were studied to reveal the possibility of SiC replacing graphite as plasma facing materials. Pressureless sintered SiC and graphite SMF-800 were implanted with He+ ions of 20 keV and 100 keV at different temperatures and different fluences. The He+ irradiation induced microstructure changes were studied by field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Comparison of Characteristics of Gd2BaCuO5 Powders Prepared by Different Processes

Abstract Ultra-fine Gd 2 BaCuO 5 (Gd211) powders were prepared by three different routes including low temperature combustion synthesis (LCS), coprecipitation and solid state reaction. The powders were characterized in terms of morphology, chemical purity, specific surface area and particle size. The results show that LCS process yields the most weakly agglomerated powder with smallest average particle size. The microstructure and superconductor property of GdBa 2 Cu 3 O 5 (Gd123) bulk material fabricated from the precursor of Gd211 powders were also studied. It is found that the employment of fine Gd211 starting powder is effective for the size reduction of Gd211 particles in the bulk samples. Gd123 bulk produced from LCS powder achieved the largest critical current density ( J c ) value compared with those from other two powders.

The influence of ablation products on the ablation resistance of C/C–SiC composites and the growth mechanism of SiO2 nanowires*

Ablation under oxyacetylene torch with heat flux of 4186.8 (10% kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C?SiC composites fabricated by chemical vapor infiltration (CVI) combined with liquid silicon infiltration (LSI) process. The results indicated that C/C?SiC composites present a better ablation resistance than C/C composites without doped SiC. The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process. Bulk quantities of SiO2 nanowires with diameter of 80 nm?150 nm and length of tens microns were observed on the surface of specimens after ablation. The growth mechanism of the SiO2 nanowires was interpreted with a developed vapor?liquid?solid (VLS) driven by the temperature gradient.

Erosion and Modifications of Tungsten-Coated Carbon and Copper Under High Heat Flux

Tungsten-coated carbon and copper was prepared by vacuum plasma spraying (VPS) and inert gas plasma spraying (IPS), respectively. W/CFC (Tungsten/Carbon Fiber-Enhanced material) coating has a diffusion barrier that consists of W and Re multi-layers pre-deposited by physical vapor deposition on carbon fiber-enhanced materials, while W/Cu coating has a graded transition interface. Different grain growth processes of tungsten coatings under stable and transient heat loads were observed, their experimental results indicated that the recrystallizing temperature of VPS-W coating was about 1400 °C and a recrystallized columnar layer of about 30 μm thickness was formed by cyclic heat loads of 4 ms pulse duration. Erosion and modifications of W/CFC and W/Cu coatings under high heat load, such as microstructure changes of interface, surface plastic deformations and cracks, were investigated, and the erosion mechanism (erosion products) of these two kinds of tungsten coatings under high heat flux was also studied.

Effect of additives on thermal-shock resistance of W/Cu FGMs

W/Cu functionally graded materials (FGMs) comprised of 1% La2O3, 1% TiC and 25% Ta, respectively, were prepared using an ultra‐high pressure (GSUHP) graded sintering method. This method produced high sintered densities (90.23%, 91.57% and 93.33% respectively) as confirmed by measurement. Further, the graded materials demonstrated good performance in thermal‐shock resistance tests based on laser power density of 200 MW/m2. In particular, after 1000 thermal‐shock resistance tests, the W/Cu specimens containing 1% La2O3 were not damaged, those which contained 1% TiC began to crack, and only those which contained 25% Ta began to spatter after being tested 100 times. Finally, preliminary discussion of the effect of additives on the heat‐shock resistance is also was also preliminarily discussed.