Micrograph 611 and full record

Micrograph no

611

Brief description

Section of a metal matrix composite (MMC) after extrusion and annealing

Keywords

alumina

, annealing

, coincidence site lattice (CSL), composite material

, extrusion

, island grains, MMC, nucleation

, particle, stringers

Categories

Composite

System

Composition

Commercial purity (99.5%) + 13 micron alumina spheroids

Standard codes

Reaction

N/A

Processing

Commercial purity (99.5%) aluminium has been atomised, thoroughly mixed with alumina reinforcement particles and then extruded.

Applications

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.

Technique

Reflected light microscopy, polarised

Length bar

40 μm

Further information

Commercial purity aluminium has atomised, mixed with 13 micron spherical alumina particles, ball milled, tumbled, cold compacted (20MPa) and then extruded (with the working direction vertical in the image). It has then been annealed at 630 degrees C. Vertical stringers of fine oxide particles are visible. Note the small yellow 'island' grain which has formed within one of the recrystallised grains and is likely to have nucleated on the adjacent reinforcement particle. Note also the boundary facets of some grains. These indicate a preferred habit plane and are probably coincidence site lattice (CSL) boundaries.

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