Section of a metal matrix composite (MMC)

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