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Abstract: In this paper, we report some new progress on plasma facing materials in University of Science and Technology Beijing (USTB), China. They include fabrication of tungsten coating with ultra-fine grain size by atmosphere plasma spraying; fabrication of tungsten with ultra-fine grain size by a newly developed method named as resistance sintering under ultra-high pressure; using the concept of functionally graded materials to join tungsten to copper based heat sink; joining silicon doped carbon to copper by brazing using a Ti based amorphous filler and direct casting. [Copyright &y& Elsevier]

Solid helium bubbles were directly observed in the helium ion implanted tungsten (W), by different transmission electron microscopy (TEM) techniques at room temperature. The diameters of these solid helium bubbles range from 1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction (SAED) and fast Fourier transform (FFT) images revealed that solid helium bubbles possess body-centered cubic (bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials. [ABSTRACT FROM AUTHOR]

A nanostructured surface layer was fabricated on commercial pure tungsten using the method of surface mechanical attrition treatment (SMAT). The microstructure evolution of the surface layer was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and its formation mechanism was discussed as well. Both refinement and elongation of the brittle W grains were confirmed. The elongated SMATed W was heavily strained, the maximum value of the strain at the grain boundaries reaches as high as 3–5%. Dislocation density in the SMATed W nanograins was found to be 5 × 10 12 cm −2 . The formation of the nanograins in the top surface layer of the W was ascribed to the extremely high strain and strain rate, as well as the multidirectional repetitive loading. Bending strength of commercial W could be improved from 825 MPa to 1850 MPa by SMAT process. Microhardness results indicated the strain range in SMATed W can reach up to 220 μm beneath the top surface. The notched Charpy testing results demonstrated that SMATed W possess higher ductility than that of commercial W. The top surface of the W plates with and without SMATe processing possesses residual compressive stress of about −881 MPa and −234 MPa in y direction, and −872 MPa and −879 MPa in x direction respectively. The improvement of toughness (DBTT shift) of SMATed W may be the synergistic effect of residual compressive stress, dislocation density improvement and microstructure refinement induced by SMAT processing. SMAT processing could be a complementary method to further decrease the DBTT value of tungsten based materials. [ABSTRACT FROM AUTHOR]

Abstract: Both tungsten with a microstructure of ultra-fine grain size (sub-micron grain size) and functionally graded W/Cu materials have been fabricated by a newly developed technology named resistance sintering under ultra-high pressure. It is found that when decreasing the grain size of tungsten (from 7μm to 0.5μm), the micro-hardness and bend strength of tungsten will increase significantly. Thermal shock resistance by water quenching shows that the concept of functionally graded materials is effective at reducing the thermal stress between tungsten and copper. High heat flux testing using a laser beam shows that tungsten with sub-micron grain size can endure a higher heat load than that of tungsten with a grain size of larger than 1μm, and functionally graded W/Cu materials can endure a higher heat load than that of pure tungsten. [Copyright &y& Elsevier]

Abstract: Three different methods, plasma spraying, infiltration-welding method and resistance sintering under ultra-high pressure, have been developed to fabricate W/Cu FGM based plasma facing components. SEM analysis showed that good grading composition of all FGM samples had been obtained. Water quenching and electron, or laser beam test facilities have been utilized to investigate and compare thermal shock behavior and performance under high heat load. It is found that the grading at the interface between W and Cu is very effective for the reduction of thermal stress. W/Cu FGM fabricated by infiltration-welding method has the best thermal shock resistance among these three kinds of W/Cu FGM. [Copyright &y& Elsevier]

Abstract: A novel one-step method, named “resistance sintering under ultra-high pressure”, has been developed to fabricate W/Cu functionally graded materials (FGM) without the addition of any sintering additive. A W/Cu FGM with more than 97% theoretical density has been successfully fabricated. The designed composition distribution of the FGM can be preserved very well. The densification effect and microstructure of the W/Cu FGM are investigated. [Copyright &y& Elsevier]

• A shape-controllable preparation mechanism for nanomaterials has been specified. • The preparation is catalyst-free and inside of mesoporous carbon nanotube (mCNT). • Mesoporous in mCNT sidewall is the key to make the mechanism possible. • The mesoporous can maintain a dynamic equilibrium for gaseous substances in mCNT. • W nanowire and nanodot have been shape-controllable prepared without catalyst. Owing to its unique structure of mesoporous carbon shell and hollow tubular core, mesoporous carbon nanotubes (mCNT) are highly regarded as one of the most intrinsic adsorbing materials. Based on its significant property, a catalyst-free and shape-controllable reduction mechanism of ammonium metatungstate (AMT) in mCNT (AMT@mCNT) has been investigated. Reactions in mCNT are distinct because the mesoporous nanotubes can adsorb and release substances during the process. Using a field emission scanning electron microscope, X-ray diffraction, thermogravimetry and mass-spectrometric, the mechanism is determined. Finally, referring to the mechanism, tungsten nanowires and nanodots have undergone shape-controllable preparation via reduction of AMT@mCNT. [ABSTRACT FROM AUTHOR]