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- 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.
- 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.