LNEG - Laboratório Nacional de Energia e Geologia, I.P. Estrada do Paço do Lumiar, 22 1649-038 Lisboa Tel. +351 21 092 4600 (Ext. 4321)
filipe.neves@lneg.pt
1970.02.11 born in Lisbon (Portugal)
ACADEMIC DEGREES -PhD in Materials Engineering by the Faculty of Science and Technology of the University of Coimbra, Portugal, (2002 – 2005). -Graduation in Metallurgical and Materials Engineering by Instituto Superior Técnico (IST), Portugal, (1989 – 1994).
CURRENT AND PREVIOUS SCIENTIFIC AND/OR PROFESSIONAL ACTIVITIES 01/2012 – to present Post-Doctoral Research Fellowship at LNEG (National Laboratory of Energy and Geology), Lisbon, Portugal. 01/2008 – 12/2011 Post-Doctoral Research Fellowship (FCT-MCTES grant) at CENIMAT – Department of Materials Science, Faculty of Sciences and Technology, New University of Lisbon (FCT/UNL), Lisbon, Portugal. 01/2006 – 12/2007 Post-Doctoral Research Fellowship, Department of Materials and Production Technologies (DMPT) – INETI, Lisbon, Portugal. 01/1997 – 12/2005 Fellowship Researcher, DMP – INETI, Lisbon, Portugal. 06/1996 – 09/1996 Trainee at TAP-AIR PORTUGAL, S.A., Non-Destructive Testing Laboratory (NDT) (Responsible for Eddy Currents test lectures to the laboratory personal staff). 07/1995 – 12/1995 Trainee at OGMA - Indústria Aeronáutica de Portugal, S.A., Department of Engineering and Programs – Materials Technology Division (Identification of materials and production processes of composites for aeronautic structural applications). 11/1993 – 12/1994 Fellowship, INESC (Instituto de Engenharia de Sistemas e Computadores) (Application of the BET method in experimental studies of the superficial area and porosity of bulk and thin films gels produced by the “sol-gel” process).
Abstract: The phase transformation behaviour of bulk nanostructured NiTi shape memory alloys, produced by an innovative approach called MARES (mechanically activated reactive extrusion synthesis), was investigated using in situ x-ray diffraction and differential scanning calorimetry measurements. For the experimental conditions used, a suitable adjustment of the NiTi matrix composition was achieved after ageing at 500 degrees C for 7 h. The aged materials showed a homogeneous dispersion of Ni4Ti3 precipitates embedded in a B2-NiTi matrix. Under this condition the B2-NiTi matrix has undergone a B2 <-> R <-> B19' two-stage phase transformation. This was attributed to the complex microstructural evolution during MARES processing, i.e. formation of large-scale and small-scale heterogeneities. Transmission electron microscopy investigations of the solution-treated materials showed the existence of equiaxed nanocrystals in the nanocrystalline NiTi matrix.
Abstract: Mechanically activated reactive extrusion synthesis (MARES), as an innovation in powder sintering, was used for the first time to produce NiTi alloys. Equimolar powder mixtures of elemental Ni and Ti were firstly mechanically activated for 4 h and then extruded at relatively low temperatures (between 300 and 600 degrees C). No intermetallic phase formation was obtained after mechanical alloying. Instead, crystalline phases (Ni and Ti) and an amorphous phase were observed. The end product was constituted of agglomerated micrometer sized particles containing inhomogeneous areas of Ti and Ni. Differential thermal analysis of the as-milled powders showed two small exothermic peaks at about 460 and 540 degrees C, corresponding to the structure relaxation of the amorphous phase and to the synthesis of Ni-Ti intermetallics. The outcome of MARES trials was sensitive to the extrusion temperature, ram speed and to the total heating time prior to the application of load. The microstructure of the extruded material consisted of NiTi, NiTi2 and Ni3Ti besides Ni and Ti. MARES results are very encouraging for the formation of Ni-Ti intermetallics through a controlled synthesis reaction. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: Copper nitride films prepared by sputtering have applications such as optical data storage material. insulation barriers in micro electronic devices and coatings for mechanical applications. The present study examines nanocomposites prepared by mechanical alloying of copper with copper nitride under nitrogen atmosphere, at room temperature, in order to establish a comparison with properties of Cu-N sputtered films. The powders were consolidated into bulk samples via warm extrusion at temperatures ranging from 300 to 500 degrees C (0.42-0.64 T-f) after encapsulation without degassing. The as-milled powders and the extruded materials were studied using X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and microhardness measurements. Also, the TEM observation of the extruded sample indicates a mean train sire of about 50 nm. This evidences a higher thermal stability of the as-milled powders and the advantage of using a fast consolidation process, at a relatively low temperature. Therefore, the consolidated material did not show the dramatic softening associated with recrystallization. The consolidation of nanostructured copper-copper nitride composite powders via warm extrusion. without major grain coarsening. was demonstrated.
Abstract: The production of NiTi alloys through mechanically activated reactive forging synthesis (MARFOS) of elemental powder mixtures with equiatomic composition has been investigated for the first time. The short duration of mechanical activation (4 h) successfully produced powder mixtures capable of being hot deformed at relatively low temperatures. As a consequence, a bulk product constituted by intermetallic and metallic nanocrystalline phases was effectively obtained at 700 degrees C. An additional heat treatment at 950 degrees C/24 h removed almost all the undesired phases and maintained the nanocrystalline structure, resulting in an Ni-rich NiTi matrix containing some Ti2Ni/Ti4Ni2Ox and having a microhardness of 708 H(V)0.3. The formation of such microstructure may be attributed to the presence of oxygen and nitrogen impurities in the materials. After ageing at 500 degrees C/48 h, some degree of compositional rectification was achieved in the NiTi matrix due to the formation of Ni4Ti3 precipitates. (c) 2008 Elsevier Ltd. All rights reserved.
Abstract: Thin layers of silver and titanium were deposited onto commercial Ti-Al-48 particles by magnetron sputtering prior to their consolidation by hot isostatic pressing and subsequent heat treatment. Based on picnometry and electron probe microanalysis results, average values of 1.5 and 2.5 at.%, respectively, were obtained for the silver and titanium contents in the coated particles. The surface modified Ti-Al-48 particles exhibited improved sintering ability than the unmodified ones. The consolidated samples have duplex microstructures formed by gamma-TiAl and gamma-TiAl 1 + alpha(2)-Ti3Al grains. Ag-rich nanoprecipitates were detected in the microstructure of the compacted Ti-Al-48 + Ag. sample. The coatings are no longer visible at the grains boundaries after a subsequent homogenization heat treatment at 1200 degrees C. The highest values of hardness and Young's modulus were obtained for the Ti-Al-48 + Ag sample, associated with a higher density and a lower percentage of pores.
Abstract: In the present Study, an alternative approach to the synthesis of TiNi alloys through powder metallurgy was successfully conducted by mechanically activated reactive extrusion synthesis (MARES) using elemental powders. The production of dense bodies was essentially dependent on the amount of intermetallic phases formed prior to reactive extrusion and on the densification temperature. The mechanically activated powders yielded a well controlled synthetic reaction during heating up to 900 degrees C with formation of multiphase products. This was possible due to the powder structure developed during mechanical activation. The best densified products were obtained at 700 degrees C although without a complete conversion into NiTi phase. More homogeneous microstructures and an effective reduction in the amount of secondary intermetallic phases were achieved after heat treatment at 950 degrees C/24 h followed by water quenching, yielding TiNi as the predominant phase, a relative density of 97%, and a Vickers micro-hardness of 682 H-V. (c) 2007 Elsevier Ltd. All rights reserved.
Abstract: (Ti-48Al)-based intermetallics were synthesized by a combination of mechanical alloying, sputtering and hot isostatic pressure techniques. Blended elemental powders of TiH2 and Al with nominal composition TiH2-48Al were mechanically alloyed for different periods of time. The powders were then coated with Ti and Ag and subsequently hot isostatically pressed at 900 degrees C with a maximum pressure of 150 MPa for 2 h. Finally they were heat treated at 1200 degrees C for 4h. After processing, the compacts obtained from the TiH2-48Al coated powders had a lower hardness but a higher Young's modulus and fracture-toughness than the uncoated compacts. Therefore, the combined used of mechanical alloying, sputtering and compaction techniques might be an alternative method for the synthesis of compacts with non-conventional microstructures, formed by surface modified intermetallic particles. (C) 2006 Elsevier B.V. All rights reserved.
Abstract: The present paper describes part of the work that is being carried out to investigate the formation of Ti-Al-Ag nanostructured intermetallic compounds using Mechanical Alloying (MA). Mixtures of elemental powders with nominal compositions 52TiH(2)-(48-x)AlxAg (x = 0, 2 and 4 at. %) were milled for 25h at 500rpm in a planetary ball mill. The MA led to the formation of a TiH2 (Al) solid solution coexisting with Ll(2)-TiAl3 phase. In all cases, Hot Isostatic Pressing (HIP) at 900degreesC/150MPa/2h and the subsequent heat-treatment at 1200degreesC/4h resulted mainly in gamma-TiAl phase formation. When compared with similar alloys produced in previous work by MA at 200rpm for 50h and consolidated in the same conditions more homogeneous microstructures were obtained. Addition of Ag led to a formation of Ag-rich phases preferential located at the grain boundaries.
Abstract: The Mechanical alloying (MA) of the Ni-Ti system has been the subject of a considerable number of investigations since the late 1980s. Although it is known that careful milling practice can reduce the overall level of contamination to well within acceptable limits, relatively little attention has been paid to the effects that different levels of contamination (mainly the one arising from oxygen and nitrogen from the atmosphere) might cause in the MA process and in what is called the Critical Milling Behavior (CMB). This behavior is related with the sticking of powder to the milling media due to the ductile behavior of Ni and Ti. So, the remaining question is: âIs the CMB dependent on the level of oxygen and nitrogen present in the milling atmosphere?â. To our knowledge, such systematic investigation was not yet carried out.
To solve this issue, several MA experiments were conducted in a planetary PM100 mill (Retsch) using mixtures of pure elemental Ni and Ti powders in the stoichiometric ratio of 50at.%Ni. The different levels of contaminants were achieved by varying the milling atmosphere (air, Ar and Ar+5%H2), by carrying some experiments with (5wt.% of ethanol) and without adding a process control agent and by improving the sealing of the vials with a few layers of Parafilm in-between the vial and the cover. The vials and the powder mixtures were always handled in a glove box filled with Ar. Moreover, the milling speed and the ball-to-powder weight ratio ranged between a minimum and a maximum of 150 rpm to 300 rpm and 5:1 to 10:1, respectively. Stainless steel vials (250 ml) and balls (10 mm) were used, while the milling time went up to a maximum of 32 h. To avoid temperature increase during milling, milling periods of 10 min were alternated with 5 min periods of rest. At selected milling time, a small amount of mixed powder was removed for analysis. In all stages of the process the mixtures were characterized by electron microscopy, x-ray diffraction, differential thermal analysis, Vickers micro-hardness tests and by chemical analyses of oxygen and nitrogen contents.
During the MA process, the levels of oxygen and nitrogen contents were found to be dependent on the milling conditions. Those contents ranged between a minimum and a maximum of 0.25 â 0.79 wt.% for oxygen and 0.02 â 0.90 wt.% for nitrogen, with the lowest values obtained when the most protective milling conditions were used. Nevertheless, those values represented a systematic increase if we take into account the initial values of the pristine powders (0.19 wt.% for oxygen and 0.01 wt.% for nitrogen). The increase in the nitrogen content was always higher than that measured for the oxygen. A very interesting result, within the experimental conditions used, is the fact that not only oxygen gas has been found to react with the MA powders but also nitrogen. When comparing experiments carried out with the same milling intensity, the lowest powder yields corresponds to the lowest increase in the contaminants contents. Whatever the milling conditions no intermetallic phase was formed during MA. Also, an intimate mixture between the Ni and Ti elements was observed. The most effective mixing occurred for the mixtures with the highest contaminants contents. It was shown that both gases (oxygen and nitrogen) play an important role in the CMB as well as in the alloying process.
Acknowledgements
F. Neves is supported by an FCT/MCTES Grant (SFRH/BPD/38354/2007).
Notes: Accepted for publication in Powder Metallurgy.
Abstract: In the present study, structural characterization of NiTi smart shape memory alloys (SMAs), produced by an alternative powder metallurgy approach named mechanically activated reactive forging (MARFOS), was carried out by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that MARFOS materials had a multiphase nanocrystalline structure. In addition, the transformation behaviour associated with the shape memory effect of the MARFOS aged materials was studied with differential scanning calorimetry (DSC). Multiple-step martensitic transformations could be observed in aged materials.
Abstract: The objective of this work was to study a new methodology of production for gamma-TiAl based titanium aluminides. Two routes were selected: in the first one, mixtures of elemental powders with nominal compositions TiH2â(48-x)AlxAg (x=0, 2 and 4 at %) were mechanically alloyed in a planetary ball mill under different rotation speeds and total milling times, followed by consolidation through Hot Isostatic Pressing at 900ºC/ 150 MPa/ 2 h and subsequent homogenization heat treatment at 1200ºC for 4 h; the second route consisted in the deposition of Ag and of Ti thin layers (coatings) by magnetron sputtering on TiH2-48Al mixtures milled in optimized conditions as well as in commercial Ti-48Al powder, which were then submitted to the same consolidation and heat treatment cycles. The Ti-48Al powder specific purpose was to provide a comparison to the deposition process of the mechanically alloyed mixtures.
Several characterization techniques were used: X-ray diffraction for evaluation of the formed phases; scanning electron microscopy associated with energy dispersive spectrometry for morphological and microstructural analysis and for localized chemical compositions, X-ray elemental maps and X-ray line profiles; laser diffraction for particle size distribution analysis; differential thermal analysis for thermal stability studies of the processed materials; elementary analysis techniques for gases content determinations; helium pycnometry technique for density determinations; and hardness measurements with different loads for hardness, Young´s modulus and fracture toughness determinations.
The results presentation and discussion cover the effect of using TiH2 powder as raw material, the influence of milling conditions (speed and time) in the quality and evolution of the milled powder, the conditions for gamma-TiAl phase formation, the effect of Ag additions in the mechanically alloyed materials and in the microstructure and properties of the final materials, the milled and commercial powders ability for the coating process. The influence of the coating in the consolidation process, the microstructures and the properties of the produced materials were also evaluated.
With the experimental conditions used, the use of TiH2 increased the efficiency of the milling process, the 300 rpm/ 50 h mechanical alloying was shown to be the more efficient one and the addition of Ag did not have a significant influence in the mechanical alloying process. The gamma-TiAl phase was not formed during the mechanical alloying process but only after consolidation at 900 ºC. After heat treatment this phase remained as the main constituent for the processed materials.
After consolidation and subsequent heat treatment, in all materials containing Ag, added in the mechanical alloying process or introduced as a coating, the formation of Ag-based nano-precipitates were detected.
After heat treatment the hardness values obtained were slightly higher and the Young´s moduli either equal or higher than the ones expected for the gamma-TiAl based materials. The coatings improved the Youngâs modulus of the studied materials. Moreover, it was also beneficial for the fracture toughness of the mechanically alloyed mixtures.
