The effect of interface diffusion and slip on the creep resistance of particulate composite materials

Reinforcements are known to increase the creep resistance of metal and intermetallic matrix composite materials. Experimental measurements at modest temperatures indicate that under a given applied strain rate the composite strength is higher than that of the matrix alone. However, at temperatures higher than approximately half of the melting temperature of the matrix, the composite strength is limited and in some cases the strengthening imparted by the reinforcements is completely lost. Diffusional relaxation and slip on the reinforcement-matrix interface are suggested as mechanisms responsible for the loss of strengthening. According to the proposed model, stress gradients caused by plastic constraint induce diffusional flow along the interface accompanied by slip of the matrix over the reinforcement. As a result the constraint tends to be relaxed and strengthening can be eliminated. The composite behavior is investigated by coupling the diffusion and slip along the interface with deformation of the matrix in the power law creep regime. A unit cell model is used in axial symmetry and the relevant boundary value problem is solved by the finite element method. Numerical results indicate that either diffusional relaxation or slip may knock down the creep resistance of the composite to levels even below the matrix strength.