ME - Comunicações em actas de encontros científicos internacionais
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Browsing ME - Comunicações em actas de encontros científicos internacionais by Author "Alves, L. C."
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- Microstructural characterization of the ODS Eurofer 97 EU-batchPublication . Mateus, R.; Carvalho, Patricia Almeida; Nunes, D.; Alves, L. C.; Franco, N.; Correia, J.B.; Alves, E.Four as-processed forms (Plate 16, Plate 6, Rod 20 and Rod 12.5) of the ODS Eurofer 97 EU-batch produced under different thermomechanical conditions have been investigated by scanning nuclear microprobe, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, electron backscattered diffraction, hightemperature X-ray diffraction and microhardness measurements. The materials presented a ferritic microstructure with a homogeneous distribution of Y. The thicker plate presented a fine carbide dispersion while the other forms showed carbide morphologies corresponding to pseudo-pearlitic and pseudo-bainitic transformations with wellmatched hardness values. Hot rolling induced crystallographic textures of the {101}<101> type, rotary swaging resulted in a complex texture, and extrusion produced a strong <101> fiber texture. X-ray diffraction experiments at high temperature showed that at a cooling rate of 5 ºC/min the complete austenite-to-ferrite transformation occurs between 760 and 750 ºC compromising the material quenchability.
- 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.