Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Tungsten microstructural changes induced by ISTTOK plasma dischargesPublication . Mateus, R.; Carvalho, Patricia Almeida; Correia, J.B.; Nunes, D.; Gomes, R. B.; Duarte, P.; Fernandes, H.; Silva, C.; Alves, E.
- Multiscale Copper-uDiamond Nanostructured CompositesPublication . Nunes, D.; Livramento, Vanessa; Fernandes, H.; Silva, C.; Shohoji, Nobumitsu; Correia, J.B.; Carvalho, Patricia AlmeidaNanostructured copper-diamond composites can be tailored for thermal management applications at high temperature. A novel approach based on multiscale diamond dispersions is proposed for the production of this type of materials: a Cu-nDiamond composite produced by high-energy milling is used as a nanostructured matrix for further dispersion of micrometer sized diamond. The former offers strength and microstructural thermal stability while the latter provides high thermal conductivity. A series of Cu-nDiamond mixtures have been milled to define the minimum nanodiamond fraction suitable for matrix refinement and thermal stabilization. A refined matrix with homogenously dispersed nanoparticles could be obtained with 4 at.% nanodiamond for posterior mixture with ƒÝDiamond and subsequent consolidation. In order to define optimal processing parameters, consolidation by hot extrusion has been carried out for a Cu-nDiamond composite and, in parallel, for a mixture of pure copper and ÝDiamond. The materials produced were characterized by X-ray diffraction, scanning and transmission electron microscopy and microhardness measurements.
- Microstructure characterization of ODS-RAFM steelsPublication . Mateus, R.; Carvalho, P.; Nunes, D.; Alves, L. C.; Franco, N.; Correia, J.B.; Fernandes, H.; Silva, C.; Alves, E.; Lindau, R.Results of the microstructural characterization of four different RAFM ODS Eurofer 97 batches are presented and discussed. Analyses and observations were performed by nuclear microprobe and scanning and transmission electron microscopy. X-ray elemental distribution maps obtained with proton beam scans showed homogeneous composition within the proton beam spatial resolution and, in particular, pointed to a uniform distribution of ODS (yttria) nanoparticles in the Eurofer 97 matrix. This was confirmed by transmission electron microscopy. Scanning electron microscopy coupled with energy dispersive spectroscopy made evident the presence of chromium carbide precipitation. Precipitates occurred preferentially along grain boundaries (GB) in three of the batches and presented a discrete distribution in the other, as a result of different thermo-mechanical routes. Additional electron backscattered diffraction experiments revealed the crystalline textures in the ferritic polycrystalline structure of the ODS steel samples.
- Production of Cu/Diamond composites for first-wall heat sinksPublication . Nunes, D.; Correia, J.B.; Carvalho, Patricia Almeida; Shohoji, Nobumitsu; Silva, C.; Fernandes, H.; Alves, L. C.; Hanada, K.; Osawa, E.Due to their suitable thermal conductivity and strength copper-based materials have been considered appropriate heat sinks for first wall panels in nuclear fusion devices. However, increased thermal conductivity and mechanical strength are demanded and the concept of property tailoring involved in the design of metal matrix composites advocates for the potential of nanodiamond dispersions in copper. Copper-nanodiamond composite materials can be produced by mechanical alloying followed by a consolidation operation. Yet, this powder metallurgy route poses several challenges: nanodiamond presents intrinsically difficult bonding with copper; contamination by milling media must be closely monitored; and full densification and microstructural homogeneity should be obtained with consolidation. The present line of work is aimed at an optimization of the processing conditions of Cu-nanodiamond composites. The challenges mentioned above have been addressed, respectively, by incorporating chromium in the matrix to form a stable carbide interlayer binding the two components; by assessing the contamination originating from the milling operation through particle-induced X-ray emission spectroscopy; and by comparing the densification obtained by spark plasma sintering with hot-extrusion data from previous studies.
- Novel approach to plasma facing materials in nuclear fusion reactorsPublication . Livramento, Vanessa; Correia, J.B.; Nunes, D.; Carvalho, Patricia Almeida; Fernandes, H.; Silva, C.; Hanada, K.; Shohoji, Nobumitsu; Osawa, E.A novel material design in nuclear fusion reactors is proposed based on W-nDiamond nanostructured composites. Generally, a microstructure refined to the nanometer scale improves the mechanical strength due to modification of plasticity mechanisms. Moreover, highly specific grainboundary area raises the number of sites for annihilation of radiation induced defects. However, the low thermal stability of fine-grained and nanostructured materials demands the presence of particles at the grain boundaries that can delay coarsening by a pinning effect. As a result, the concept of a composite is promising in the field of nanostructured materials. The hardness of diamond renders nanodiamond dispersions excellent reinforcing and stabilization candidates and, in addition, diamond has extremely high thermal conductivity. Consequently, W-nDiamond nanocomposites are promising candidates for thermally stable first-wall materials. The proposed design involves the production of WAV-nDiamondAV-Cu/Cu layered castellations. The W, W-nDiamond and W-Cu layers are produced by mechanical alloying followed by a consolidation route that combines hot rolling with spark plasma sintering (SPS). Layer welding is achieved by spark plasma sintering. The present work describes the mechanical alloying processsing and consolidation route used to produce W-nDiamond composites, as well as microstructural features and mechanical properties of the material produced Long term plasma exposure experiments are planned at ISTTOK and at FTU (Frascati).