A neutron diffraction study of creep and damage occurrence in an A359/SiC composite

Neutron diffraction is used to measure lattice strains in an A359 aluminium alloy/SiC composite during creep at 300 degreesC and during subsequent room temperature mechanical tests. The stress exponent of creep rate is 8 when analyzed in terms of the overall applied stress. If the rate is examined in terms of the phase stress acting in the matrix. as determined by neutron diffraction lattice strain measurements, the exponent is approximate to 3. The large overall stress exponent is ascribed to the progress of damage, decohesion and cracking of particles during creep. The damage is confirmed by changes in Young's modulus and the relationship of lattice strain versus stress, both measured at room temperature after creep. The kinetics of stress relaxation by interfacial diffusion is used to account for the occurrence of damage. Experimentally, the SiC particles (14 pm in size) are found to be damaged during creep, while Si particles (2.1 mum) a constituent in A359, are not found to be damaged. (C) 2002 Elsevier Science B.V. All rights reserved.