INFLUENCE OF MICROSTRUCTURAL SCALE ON PLASTIC-FLOW BEHAVIOR OF METAL-MATRIX COMPOSITES

Metal matrix composites fabricated from pure aluminum metal and cerami c particles of magnesium aluminate spinel were deformed in uniaxial co mpression. The flow stress of the composites ranged from about 70 to 7 00 MPa, and broadly followed an inverse square root relationship with metal ligament size. The composites had excellent ductility. The chang e in the dislocation substructure with increasing plastic deformation was examined by TEM. Random dislocation tangles observed in the undefo rmed specimens were found to have been replaced by low angle sub-bound aries in the deformed specimens. This observation is explained by invo king compatibility between crystal slip in metal ligaments and sliding accommodated by dislocation glide parallel to metal-ceramic interface s. A model based on this mechanism is developed and compared to the ex perimental results, The analysis successfully predicts the inverse squ are root dependence of the how stress on the metal ligament size, and gives fair agreement with the magnitude of the measured flow stresses. (C) 1997 Acta Metallurgica Inc.