Papers by Author: Filipe J. Oliveira

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Authors: Filipe J. Oliveira, Rui F. Silva, José Maria F. Ferreira, Joaquim M. Vieira
1989
Authors: J.M. Carrapichano, A. Taillaire, Filipe J. Oliveira, Rui F. Silva
225
Authors: Filipe J. Oliveira, Rui F. Silva, Joaquim M. Vieira
377
Authors: Filipe J. Oliveira, Rui F. Silva, Joaquim M. Vieira
2068
Authors: Flávia A. Almeida, Helena Bóia, Catarina Santos, Jorge Monteiro, Filipe J. Oliveira, Rui F. Silva
Abstract: The addition of titanium nitride (TiN) particles to a Si3N4 matrix reduces the intrinsic electric resistivity of this ceramic allowing it to be machined by EDM in cutting tools manufacturing. Gains can be expected given the cost reduction by the increase of productivity when shaping these hard to machine ceramic materials. Si3N4 ceramic matrix composites (CMC’s) with 0- 30vol.% of TiN sub-micrometric particles were produced by uniaxial hot pressing (HP) and pressureless sintering (PS). For the PS samples, EDM tests showed that machining of the composites is possible when they contain at least 23vol.% TiN particles what corresponds to a resistivity of 7.5cm. For HP samples at least 30vol.% of TiN is required to get an electroconductive material for EDM machining. This difference is due to the lower temperatures used in the HP process that delay the formation of a conductive network between the TiN particles.
638
Authors: C.S. Abreu, Filipe J. Oliveira, J.R. Gomes, Manuel Belmonte, A.J.S. Fernandes, Rui F. Silva
Abstract: In-situ measurements of acoustic emission (AE) in self-mated tribological pairs of CVD diamond coated silicon nitride (Si3N4) were made with the purpose of investigating the relationship between AE signal and friction events. A good correlation is found between the energy dissipation/emission processes, therefore enabling the possibility of monitoring the different friction regimes occurring during the sliding contact of microcrystalline diamond (MCD) coatings. Deposition of MCD on flat and ball-shaped Si3N4 samples was accomplished using microwave plasma assisted chemical vapour deposition (MPCVD) with H2/CH4 gas mixtures. The friction behaviour of self-mated MCD coatings was assessed using a reciprocating ball-on-flat geometry. The tests were run in ambient atmosphere without lubrication, the frequency (1Hz) and stroke (6mm) were kept constant while the applied normal load varied in the range 10-80N. The microstructure, surface topography and roughness of the MCD coatings were characterised by SEM and AFM techniques. The diamond quality was assessed from micro-Raman spectroscopy. The friction evolution was characterised by a short running-in period where the main feature is a sharp peak reaching values as high as approximately 0.6 followed by a steady-state regime with very low values in the range 0.03-0.04.
749
Authors: Rui F. Silva, J.M. Carrapichano, Filipe J. Oliveira
323
Authors: Ming Xia Gao, Filipe J. Oliveira, Y. Pan, J.L. Baptista, Joaquim M. Vieira
239
Authors: D. Marinha, Filipe J. Oliveira, Mário S. Reis, Florinda M. Costa, Maria Fátima Carrasco, João P. Araújo, João Bessa Sousa, Joaquim M. Vieira, Vitor S. Amaral
Abstract: Bulk MgB2 samples were synthesized by hot isostatic pressing under pressures up to 200MPa at 950°C. In these conditions, full densification of samples was obtained (~98% of theoretical density). SEM, EDS and XRD analysis on final dense bodies were used to evaluate samples, and show increasingly better control over the amounts of secondary MgO (down to ~10%) and complete prevention of formation of MgB4 by using simple glass encapsulation techniques and addition of Mg(s) to the capsule. The samples display superconducting properties, including a narrow critical transition in electrical properties (Tc ~36-38K). Magnetic studies were performed, allowing the determination of the superconducting fraction and critical current density Jc of the materials. Contrary to the Tc, the Jc is quite sensitive to the processing and microstructure and values from 0.3 to 0.6x106 A/cm2 are obtained at 10K. The reduction of Jc with the applied magnetic field requires further improvements to reduce weak links.
333
Authors: Joaquim M. Vieira, Y. Zheng, Filipe J. Oliveira
263
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