Publications

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Conference Paper
A, Velhinho, Sequeira PD, Fernandes FB, Botas JD, and Rocha LA. "Al/SiCp functionally graded metal-matrix composites produced by centrifugal casting: Effect of particle grain size on reinforcement distribution." Functionally Graded Materials Vii. Vol. 423-4. FUNCTIONALLY GRADED MATERIALS VII, 423-4. 2003. 257-262. Abstract03_-_mater._sci._forum_423-425_2003_257-262.pdf

Functionally graded materials (FGM’s), particularly in the form of Al-Si metal matrix composites (MMC’s) selectively reinforced at the surface with SiC particles, are advanced materials, combining high wear resistance with high bulk toughness or even a thermal barrier at the surface. Centrifugal casting is one of the most effective methods for processing this type of MMC, but accurate control of the ceramic particles distribution/gradient in the metallic matrix has not yet been completely attained. In this work, precursor Al/SiC composites were prepared by rheocasting, using SiC particles and an Al-10Si–2.2 Mg alloy. Morphology of the SiC particles was previously characterized by laser interpherometry and SEM. Differing grain sizes were selected as reinforcing elements. The MMC’s were then molten and centrifugally cast in order to produce the FGM composites, whose structure and properties were investigated by XRD, quantitative image analysis of optical micrographs and longitudinal hardness profiles. Therefore, it was possible to evaluate the influence of the particle grain size on the structure and properties of the FGM. Apart from the evaluation of the effects of particle grain size per se, its influence when combined with differing casting conditions are reported as well.

N, Silva, and Velhinho A. "Assessment of particle clustering in MMCs by quantitative image analysis." Advanced Materials Forum Iii, Pts 1 and 2. Vol. 514-516. Advanced Materials Forum, 514-516. 2006. 779-783. Abstract
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JD, Botas, Velhinho A, and Silva RJC. "Elastic Behaviour of Spherical Particles Reinforced Metal-Matrix Composites." Advanced Materials Forum Iv. Ed. Baptista APM Sa Alves Malheiros LF Vieira C. F. M. Marques AT, Silva AF. Vol. 587-588. Materials Science Forum, 587-588. 2008. 202-206. Abstract

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A, Velhinho, Sequeira PD, Martins R, Vignoles G, Fernandes FB, Botas JD, and Rocha LA. "Evaluation of Al/SiC wetting characteristics in functionally graded metal-matrix composites by synchrotron radiation microtomography." Functionally Graded Materials Vii. Vol. 423-4. Functionally Graded Materials VII, 423-4. 2003. 263-268. Abstract04_-_mater._sci._forum_423-425_2003_263-268.pdf

The concept of functionally graded material (FGM), may be considered as a model particularly interesting to be applied in components for the automotive industry, if reliability and cost can be controlled in an advantageous way. In fact, coupling superior superficial wear resistance with a significant bulk toughness, without compromising important weight savings, by using Al-Si metal matrix composites (MMC’s) selectively reinforced at the surface with SiC particles, is likely to be considered as a innovative advance to that industrial field, if adequate production techniques are developed. Casting under a centrifugal force may well be considered as one of the most effective methods for processing Al-based FGM´s. A primary problem to be faced when producing MMC´s reinforced with ceramic particles is related with the imperfect wetting of the ceramic particles by the molten matrix alloy. A first consequence of defective wetting may be the formation of ceramic-ceramic, ceramic-gas and/or metal-gas interfaces, instead of the desired metal-ceramic interface. Secondly, wetting phenomena play an essential role regarding the physical, chemical and mechanical characteristics of the metal/ceramic interface. A general consequence of these aspects may be related with the degradation of the material properties, be it mechanical, chemical, or thermal in nature. The present work refers to an X-ray microtomography experiment aiming at the elucidation of some aspects regarding particle distribution in SiCp-reinforced functionally graded aluminium composites. Precursor composites were produced by rheocasting. These were then molten and centrifugally cast in order to produce the FGM composites. From these, small cylindrical samples were extracted and observed by X-ray microtomography at the European Synchrotron Radiation Facility (ESRF). The 3D tomographic images were obtained in edge-detection mode (phase-contrast mode), and an adequate segmentation procedure was employed to isolate the pores and SiC particles from the Al matrix. This has allowed a study of the relations between the matrix, the SiC particles, and locally intervening porosities of varying shapes, aiming at a better understanding of the mechanisms involved.

Velhinho, Alexandre, F. M. Braz Fernandes, and J. D. Botas. "Microstructural study of aluminium-matrix composites reinforced with SiC." Advanced Materials Forum I. Vol. 230-2. Key Engineering Materials, 230-2. 2002. 226-230. Abstract01_-_key_eng._mater._230-232_2002_226-230.pdf

Rheocasting, as a semi-solid process, allows the production of aluminium matrix composites at relatively low temperatures (ca. 580ºC), thus favouring a reduced reactivity at the reinforcement-metal matrix interface. When one considers the possibility of further processing (such as any treatment involving remelting, even if partial) of the material, this trait allows a more rigorous control of the interfaces. Composite samples have been produced using as matrix an Al-7Si-0.3Mg alloy reinforced with SiCp (granulometry: 120 μm; Vr = 0.30). These were rheocast at 583ºC, followed by forging and subsequent water-quenching. A structural characterisation (optical microscopy and XRD) of the as-received matrix material, as well as of the reinforced and non-reinforced rheocast material was performed. The phases identification will provide a basis for the understanding of the further processing where the rheocast material will be used as a raw material to produce functionally graded metal-matrix composites by centrifugal casting.

João, Gandra, Miranda Rosa M., Vilaça Pedro, and Velhinho Alexandre. "Production of functionally graded surface composites by friction surfacing." Mechanics of Nano, Micro and Macro Composite Structures. 2012. 1-2. Abstract
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A, Velhinho, Botas JD, Ariza E, Gomes JR, and Rocha LA. "Tribocorrosion studies in centrifugally cast Al-matrix SiCp-reinforced functionally graded composites." Advanced Materials Forum Ii. Vol. 455-456. Materials Science Forum, 455-456. 2004. 871-875. Abstract05_-_mater._sci._forum_455-456_2004_871-875.pdf

The present work reports results obtained from a series of preliminary experiments
aiming at complementing the current knowledge about the wear behaviour of centrifugally-cast
FGM Al/SiCp composites, through concurrent corrosion processes. Precursor MMC’s were
prepared by rheocasting, using 118.8 μm SiC particles and an Al-10Si–2.2 Mg alloy. Those MMC’s
were then molten and centrifugally cast in order to produce cylindrical FGMMC’s. Discs machined
from the top surface of each sample were tested against nodular cast iron pins, using an inverted
configuration pin-on-disc tribometer. Sliding tests took place at room temperature, over a 50000 m
sliding distance, with a sliding speed of 0.3 m s-1, under a 5 N normal load; both dry-sliding and
water-lubricated tests were performed. In order to elucidate the mechanisms involved, the wear
coefficients were calculated for each condition, and the samples were subjected to morphological
characterization via SEM/EDS. Concurrently, in the case of the water-lubrication tests, the
corrosion potential of the tribological pair was monitored. The results obtained show an increase in
material loss for the water-lubricated cases, although variations are registered depending on
reinforcing particle volume fraction. At the same time, the open circuit potential response of the
tribological pair may be correlated with the events of formation/destruction of the tribolayers.

Journal Article
S.C. Ferreira, A. Conde, Ángeles Arenas Rocha Velhinho M. L. A. A. "Anodization mechanism on SiC nanoparticle reinforced Al matrix composites." Materials. 7 (2014): 8151-8167.
Velhinho, A., and Ferreira Rocha Vignoles Cloetens S. C. L. A. Braz Fernandes, F.M. "Application of X-ray microtomography to the microstructural characterization of Al-based functionally graded materials." Adv. in Sci. & Technol.. 45 (2006): 1109-1116. Abstract

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Ferreira, SC, Velhinho, A, Silva, M. A. G., RJC, Rocha, and LA. "Corrosion behaviour of aluminium syntactic functionally graded composites." Int. J. Mater. & Product Technol.. 39 (2010): 122-135. Abstract

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A, Velhinho, Vignoles GL, Cloetens P, Thibault X, Boller E, Fernandes FB, Rocha LA, and Botas JD. "Evaluation of SiC-particle connectivity in functionally graded AI/SiCp composites by synchrotron radiation holographic microtomography." FUNCTIONALLY GRADED MATERIALS VIII. 492-493 (2005): 621-626. Abstract
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MB, Gawande, Velhinho A, Nogueira ID, Ghumman CAA, Teodoro OMND, and Branco PS. "A facile synthesis of cysteine-ferrite magnetic nanoparticles for application in multicomponent reactions-a sustainable protocol." RSC ADVANCES. 2 (2012): 6144-6149. Abstract
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J, Gandra, Miranda R, Vilaca P, Velhinho A, and Teixeira JP. "Functionally graded materials produced by friction stir processing." JOURNAL OF MATERIALS PROCESSING TECHNOLOGY. 211 (2011): 1659-1668. Abstract
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Tiago, Cadavez, Ferreira Sónia, Medeiros Pedro, Quaresma Paulo, Rocha Luís, Velhinho Alexandre, and Vignoles Gérard. "A Graphical Tool for the Tomographic Characterization of Microstructural Features on Metal Matrix Composites." Int. J. of Tomography. & Statistics. 14 (2010): 3-15. Abstract

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A, Velhinho, and Rocha LA. "Longitudinal centrifugal casting of metal-matrix functionally graded composites: an assessment of modelling issues." JOURNAL OF MATERIALS SCIENCE. 46 (2011): 3753-3765. Abstract
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Sá, Sofia, Manoj B. Gawande, Alexandre Velhinho, João Pedro Veiga, Nenad Bundaleski, João Trigueiro, Alexander Tolstogouzov, Orlando M. N. D. Teodoro, Radek Zboril, Rajender S. Varma, and Paula S. Branco. "Magnetically recyclable magnetite-palladium (Nanocat-Fe-Pd) nanocatalyst for the Buchwald-Hartwig reaction." 16 (2014): 3494-3500. Abstract

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MB, Gawande, Rathi AK, Branco PS, Potewar TM, Velhinho A, Nogueira ID, Tolstogouzov A, Ghumman CAA, and Teodoro OMND. "Nano-MgO-ZrO2 Mixed Metal oxides: Extensive characterization by SIMS and application in the reduction of carbonyl compounds and in multicomponent reactions." 3 (2013): 3611-3617. Abstract
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MB, Gawande, Rathi AK, Branco PS, Nogueira ID, Velhinho A, Shrikhande JJ, Indulkar UU, Jayaram RV, Ghumman CAA, Bundaleski N, and Teodoro OMND. "Regio- and Chemoselective Reduction of Nitroarenes and Carbonyl Compounds over Recyclable Magnetic Ferrite-Nickel Nanoparticles (Fe3O4-Ni) by Using Glycerol as a Hydrogen Source." CHEMISTRY-A EUROPEAN JOURNAL. 18 (2012): 12628-12632. Abstract
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Savita, Singh, Kale Sandip, Gawande Manoj, Velhinho Alexandre, and Jayarama Radha. "A synthesis of copper based metal-organic framework for O-acetylation of alcohols." 44 (2014): 24-28. Abstract
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Botas, JD, Velhinho, A, Silva, M. A. G., and RJC. "A theoretical approach to the elastic behaviour of compact and hollow spherical particles reinforced metal-matrix composites." Int. J. of Mater. Research. 101 (2010): 752-757. Abstract

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Paulo, Quaresma, Lopes Adriano, Medeiros Pedro, Preto Bruno, and Velhinho Alexandre. "Tomo-GPU: Um Ambiente de Resolução de Problemas Destinado à Análise de Dados Tomográficos Relativos à Caracterização Estrutural de Materiais." 5 (2010): NONE. Abstract
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João, Gandra, Vigarinho Pablo, Pereira Diogo, Miranda Rosa, Vilaça Pedro, and Velhinho Alexandre. "Wear characterization of Functionally Graded Surface composites produced by Friction Surfacing." 52 (2013): 373-383. Abstract
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A, Velhinho, Sequeira PD, Martins R, Vignoles G, Fernandes FB, Botas JD, and Rocha LA. "X-ray tomographic imaging of Al/SiCp functionally graded composites fabricated by centrifugal casting." Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms. 200 (2003): 295-302. Abstract02_-_nuclear_instr._and_methods_b_200_2003_295-302.pdf

The present work refers to an X-ray microtomography experiment aiming at the elucidation of some aspects regarding particle distribution in SiC-particle-reinforced functionally graded aluminium composites.
Precursor composites were produced by rheocasting. These were then molten and centrifugally cast to obtain the
functionally graded composites. From these, cylindrical samples, around 1 mm in diameter, were extracted, which were then irradiated with a X-ray beam produced at the European Synchrotron Radiation Facility.
The 3-D images were obtained in edge-detection mode. A segmentation procedure has been adapted in order to
separate the pores and SiC particles from the Al matrix. Preliminary results on the particle and pore distributions are presented.

Miscellaneous