Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 610

Full Record for Micrograph 610

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Micrograph no
Brief description
Section of a metal matrix composite (MMC)
annealing Link to MATTER Glossary entry for annealing, cold swaging, composite material Link to MATTER Glossary entry for composite material, extrusion Link to MATTER Glossary entry for extrusion, MMC, particle, SiC, silicon carbide
Commercial purity (99.5%) + 15 micron angular silicon carbide particles
Standard codes
Commercial purity (99.5%) aluminium has been atomised, mixed with SiC reinforcement particles, tumbled for 12 hours, cold compacted (20MPa) into an evacuated can, extruded, annealed, cold swaged (strain=0.75) and then heat treated (1h 350 degrees C)
Metal matrix composites (MMCs) offer high specific stiffness which can be retained to high temperatures. This makes them suitable for applications in the aerospace industry. They also offer controlled (or zero) thermal expansion coefficients, good wear resistance and good impact properties.
Sample preparation
The sample has been oxidised to provide colour contrast for different grain orientations.
Reflected light microscopy, polarised
Length bar
40 μm
Further information
The extrusion and cold swaging processes lead to the elongation of grains. This micrograph shows a longitudinal section with the working direction lying horizontal. Since the material has only been annealed for 1h at 350 degrees C, recrystallisation has only just started. Nucleation occurs at the reinforcement particles but there is no clear preference for nucleation at highly angular particles or particles with high aspect ratios. It was also noted that recrystallisation occurs preferentially at the surface of cold swaged specimens, probably due to strain localisation.
Prof T W Clyne
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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