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.
AbstractThe 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.
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