abstract
In the definition of conceptual developments and design of new materials with singular or unique properties, characterisation takes a key role in clarifying the relationships of composition, properties and processing that define the new material. B4C has a rare combination of properties that makes it suitable for a wide range of applications in engineering: high refractoriness, thermal stability, high hardness and abrasion resistance coupled to low density. However, the low self-diffusion coefficient of B4C limits full densification by sintering. A way to overturn this constraint is by using an alloy, for example Al-Si, forming composites with B4C. Multi-carbide B4C-SiC/(Al, Si) composites were produced by the reactive melt infiltration technique at 1200 - 1350 degrees C with up to 1 hour of isothermal temperature holds. Pressed preforms made from C-containing B4C were spontaneously infiltrated with Al-Si alloys of composition varying from 25 to 50 wt% Si. The present study involves the characterisation of the microstructure and crystalline phases in the alloys and in the composites by X-ray diffraction and SEM/EDS with EBSD. Electron backscatter diffraction is used in detail to look for segregation and spatial distribution of Si and Al containing phases during solidification of the metallic infiltrate inside the channels of the ceramic matrix when the composite cools down to the eutectic temperature (577 degrees C). It complements elemental maps of the SEM/EDS. The production of a flat surface by polishing is intrinsically difficult and the problems inherent to the preparation of EBSD qualified finishing in polished samples of such type of composites are further discussed.
keywords
SCANNING-ELECTRON-MICROSCOPE; BORON-CARBIDE; MECHANICAL-PROPERTIES; B4C; DIFFRACTION; ALUMINUM; AL; PARTICLES
subject category
Materials Science; Physics
authors
Almeida, BA; Ferro, MC; Ravanan, A; Grave, PMF; Wu, HY; Gao, MX; Pan, Y; Oliveira, FJ; Lopes, AB; Vieira, JM
our authors
Augusto Luís Barros Lopes
Assistant Professor
Bruno Araújo de Almeida
Research Fellowship
Filipe José Alves de Oliveira
Principal Researcher
Joaquim Manuel Vieira
Retired Professor
Marta Ascenção Carmona Ferro
Laboratory OfficerGroups
G2 - Photonic, Electronic and Magnetic Materials
G3 - Electrochemical Materials, Interfaces and Coatings
acknowledgements
The authors would like to acknowledge the RNME - Pole University of Aveiro (FCT Project REDE/1509/RME/2005) for access to SEM microscopy, the scientific and technical assistance and one of the authors the EMMS consortium funded by the European Commission for the M. Sc.-scholarship.