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Dive into the research topics where C.M. Fernandes is active.

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Featured researches published by C.M. Fernandes.


Surface & Coatings Technology | 2003

Stainless steel coatings sputter-deposited on tungsten carbide powder particles

C.M. Fernandes; Victor M. Ferreira; A.M.R. Senos; M.T. Vieira

Abstract The aim of this work was to study the feasibility of a sputtering technique to coat WC powder particles, regarding it as an alternative to the conventional mixture of powders. For such purpose, a stainless steel 304 (AISI) coating was sputter deposited on WC powder particles using a magnetron sputtering equipment specially developed to coat powder particles. The morphology of the coated powder was characterized by scanning electron microscopy observations, Brunauer–Emmett–Teller and laser diffraction measurements. The crystallographic structure was determined by X-ray diffraction. Inductively coupled plasma–atomic emission spectrometer and electron microprobe analysis were used to characterize the amount, chemical composition and distribution of the sputtered coating. The characterization results indicated that all WC particles were coated and that all the steel constituent elements were deposited in the same original proportion. The coating had a ferrite b.c.c. structure and presented a columnar growth with some porosity. The compaction behavior of the coated powders was characterized by unidirectional pressing using pressures between 60 and 250 MPa. The maximum of relative density was attained for P ≥190 MPa, with values of 57–58% of relative density, comparable to that of non-coated powders, and without the need of any pressing binder to obtain green compacts resistant to handling. High sintered densities, of approximately 95%, were obtained at a relatively low temperature of 1325 °C with only ∼6 wt.% of binder phase in the coated powders.


Microscopy and Microanalysis | 2012

Interface Exploring of Tungsten Carbide-Stainless Steel Composites through HRTEM

C.M. Fernandes; Marc Georg Willinger; M.T. Vieira; A.M.R. Senos

Composites of tungsten carbide (WC) and stainless steel (SS) have been produced through an innovative powder coating technique using sputtering. These composites showed remarkable mechanical properties after vacuum sintering, in spite of significant amounts of brittle eta-phase, (M,W) 6 C. The formation of eta-phase is almost inevitable, because it is thermodynamically favoured for stoichiometric C in the WC-SS system and accelerated in the SS coated WC particles, due to the reduced diffusion distances between WC and SS and the nanocrystalline character of the metallic coating. Surprisingly, the mechanical properties are not seriously affected by the eta-phase. In fact, relatively tough and harder materials have been obtained compared to similar compositions of WC-Co. In order to understand the microscopic reason for the reported mechanical strength, in-depth structural analysis of grain boundaries and interfaces was performed by electron microscopy.


Microscopy and Microanalysis | 2008

Microscopic Characterization of the Thermal Evolution of Stainless Steel Coatings Sputter-deposited onto WC Particles

C.M. Fernandes; A.M.R. Senos; M.T. Vieira

The hardmetal composites are generally produced from powders of tungsten carbide (WC) and of metal elements, belonging to group 8-10 of the periodic table, which are mixed together by wet milling. News processes, alternatives to milling, have been developed, aiming a higher uniformity of the metallic binder distribution in WC based composites, together with other technological benefits. One of those methods consists of the sputter deposition of metal binder onto the WC powder leading to powder particles coated with the metallic elements. The particles coating showed to be chemically and morphologically very uniform and possesses a nanocrystalline structure and improved surface properties, such as powders flowability, pressing behaviour, sinterability and thermal reactivity.


Microscopy and Microanalysis | 2016

EBSD Microstructural Analysis of WC-AISI 304 Cemented Carbides with Carbon Addition

C.M. Fernandes; B.A. Almeida; E. Soares; J. Sacramento; A.M.R. Senos

WC-AISI 304 stainless steel (SS) composites have been developed aiming at replacing the WC based cemented carbides using cobalt or nickel binder. Interesting mechanical properties compatible with their applications as hard and wear resistant materials can be attained in such a composites and it was shown in previous work that the carbon content has an important role on the final microstructure features and, so, on the final properties [1]. For the stoichiometric carbon, correspondent to the WC, the (M,W)6C phase will be formed during heating up to the sintering temperatures, turning the composite fragile [2]. The content of (M,W)6C phase can be reduced or even eliminated through carbon addition to the powder. However, the “carbon window” to achieve microstructures free of undesirable phases, as (M,W)6C and graphite, in the WC-SS (Fe-Cr-Ni) system is narrow, turning the carbon control very critical to get composites with optimized properties [3,4]. Therefore, the objective of this work is to investigate the effect of the excess carbon on the microstructure, namely on the phase composition and grain size distribution.


Microscopy and Microanalysis | 2013

Morphological characterization by scanning electron microscopy of WC powder particles coated with Cu

J.B. Puga; C.M. Fernandes; M.T. Vieira; A.M.R. Senos

Cemented tungsten carbides (WC), are considered one of the oldest, most successful and commercialized powder metallurgy products [1]. These materials are commonly composites of WC powder particles bonded with transition metals such as Co or Ni via liquid-phase sintering. WC-based composites have been used for decades in wide engineering applications, as cutting tools, components for oil and gas drilling, metal forming, among others [2]. The conventional processing of the WC based composites initializes with powder preparation, performed by wet milling of all the powder components (WC and metallic binders) [2]. However, this process is high energy consuming, ecologically unfriendly and longstanding, thus new powder processing methods are welcome. In this work, copper (Cu) was selected as an alternative binder, due to its inability to form brittle carbides with WC at higher temperature, the superior ductility (compared with the traditional Co binder) and corrosion resistance. Nevertheless, melted Cu has low wettability on the WC surfaces, limiting the attained sintered density and, consequently, the final properties. Powder coating techniques, such as high energy ball milling (HEBM) and the sputter-coating technique (ST), improve the binder homogeneous distribution and nanostructuring enhancing the sinterability. WC-Cu composite powders (with 2 wt.% Cu) were prepared using the two methods mentioned above. The morphology of the particles was evaluated by scanning electron microscopy (SEMHitachi SU-70) and the distribution and chemical composition were assessed by energy dispersive spectroscopy (EDSBruker QUANTAX 400).


Microscopy and Microanalysis | 2015

Microstructural inspection of the M6C phase in heat-treated WC-AISI 304 stainless steel powders

C.M. Fernandes; M.T. Vieira; A.M.R. Senos

Cemented carbides are two phase composite materials, in which hard refractory carbide phases, typically tungsten carbide, are bonded by an iron-group metal, usually cobalt. The attractive properties of such composites are related to the carbide hardness combined with the binder toughness. AISI 304 stainless steel (SS), an iron, chromium and nickel alloy has been investigated as an alternative binder to Co, aiming at applications needing higher oxidation/corrosion resistance with more competitive prices and using less toxic binders. To improve the binder distribution and the thermal reactivity in the composite powders an original powder coating process by a modified sputtering technique was applied [1]. Composites obtained by sintering of WC-SS sputter-coated powders showed the presence of large quantities of M6C phase, usually called eta-phase, which affects the mechanical performance [2]. The main objective of this work is to investigate the chemical and morphological characteristics of the eta-phase in WC sputter-coated powders with 16 wt.% AISI 304, heat-treated at different temperatures. For such purpose, heat treatments were performed in vacuum, at 1000 oC and 1400 oC, bellow and above the liquid phase formation, respectively, since the presence of eta-phase was detected at both temperatures using X-ray diffraction [3]. In order to explore the microstructure, scanning electron microscopy (SEM, Hitachi SU-70), energy dispersive spectroscopy (EDS, Bruker, QUANTAX 400) and electron microprobe microanalysis (EPMA-SX50, Cameca) were performed. WC particles present rough surfaces after sputtering, coming from the columnar growth of nanometric SS particles on the WC surfaces (as-coated in Fig. 1). The M6C phase is formed by reaction among SS and WC during heating and could be detected by XRD, from temperatures around 750 oC, far below the liquid phase appearance [2]. At 1000 oC, it can be observed that most of the WC particles surfaces are coated by the Ferich phase (SS), as shown in point Fig.1 and Table 1, but there are discrete regions where W and Fe can be detected (as in point Fig. 1 and Table 1). Those regions may correspond to the early M6C phase with the determined composition (Fe3.0Ni0.2)(Cr2.4W0.4)C. For temperatures higher than 1150oC a Fe-rich liquid phase is formed, dissolving M6C phase [3]. However, precipitation of M6C occurs during cooling and a secondary phase distributed among the WC grains can be observed in Fig. 1. The morphology of the eta-phase, surrounding the WC grains, is consistent with a reminiscent viscous matrix at sintering temperatures, being yet detectable small regions of Fe-rich phase, near the grains. The M6C composition at 1400 oC, determined by EDS (point Fig. 1 and Table 1), was (Fe2.5Ni0.3)(Cr0.7W2.5)C, while the composition achieved by EPMA is almost similar, (Fe2.6Ni0.2)(Cr0.6W2.6)C. Comparing with the composition at 1000oC, a huge increase of W in the (M,W)6C structure was observed, which may be a consequence of the significant WC decarburization occurring at high temperatures, together with a decrease of the Cr content, probably caused by the increased solubilization of this element in the Fe-rich binder with increasing temperature.


Journal of Physics D | 2014

Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films

D. A. Mota; Y. Romaguera Barcelay; A.M.R. Senos; C.M. Fernandes; P. B. Tavares; I. T. Gomes; P. Sá; L. Fernandes; B. G. Almeida; F. Figueiras; P. Mirzadeh Vaghefi; V. S. Amaral; A. Almeida; J. Pérez de la Cruz; J. Agostinho Moreira

Abstract Epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M ( T ) below the antiferrodistortive STO phase transition ( T STO ), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness ≤100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below T STO . However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the elastic energy stored in the film, which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour.Keywords: thin films, magnetic domain reconstruction, interface-mediated coupling, magnetoelasticity(Some figures may appear in colour only in the online journal)


International Journal of Refractory Metals & Hard Materials | 2011

Cemented carbide phase diagrams: A review

C.M. Fernandes; A.M.R. Senos


International Journal of Refractory Metals & Hard Materials | 2007

Control of eta carbide formation in tungsten carbide powders sputter-coated with (Fe/Ni/Cr)

C.M. Fernandes; A.M.R. Senos; M.T. Vieira


International Journal of Refractory Metals & Hard Materials | 2008

Mechanical characterization of composites prepared from WC powders coated with Ni rich binders

C.M. Fernandes; A.M.R. Senos; M.T. Vieira; Jorge M. Antunes

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M. Matos

University of Coimbra

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C.V. Gestel

École Polytechnique Fédérale de Lausanne

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