Enhanced plasticity in metal matrix composites during thermal cycling under load

The deformation behaviour of a SiC particle reinforced 2009 Aluminium alloy is studied during thermal cycling between 305 and 443 K superimposed on a tensile load of 150 MPa. After several cycles, the strain rate observed under these conditions is found constant and higher than the strain rate observed under pure creep conditions. An Arrhenius law and a power law are found for dependencies of the strain rate on the upper temperature of the cycles and the mechanical applied stress, respectively. Calculations of stress fields during thermal cycling based on Eshelby theory show that the enhanced deformation is likely to be due to emission and punching out of dislocations from the matrix-particle interface in relation with the relaxation of the thermal local stress fields arising on the cooling of the sample.