Correlation between tensile and indentation behavior of particle-reinforced metal matrix composites: an experimental and numerical study

The correlation between tensile and indentation behavior in particle-reinforced metal matrix com- posites (MMCs) was examined. The model composite system consists of a Al-Cu-Mg alloy matrix reinforced with SiC particles. The effects of particle size, particle volume fraction, and matrix aging characteristics on the interrelationship between tensile strength and macro-hardness were investigated. Experimental data indi- cated that, contrary to what has been documented for a variety of monolithic metals and alloys, a simple relationship between hardness and tensile strength does not exist for MMCs. While processing-induced par- ticle fracture greatly reduces the tensile strength, it does not significantly affect the deformation under inden- tation loading. Even in composites where processing-induced fracture was nonexistent (due to relatively small particle size), no unique correspondence between tensile strength and hardness was observed. At very low matrix strengths, the composites exhibited similar tensile strengths but the hardness increased with increasing particle concentration. Fractographic analyses showed that particle fracture caused by tensile testing is inde- pendent of matrix strength. The lack of unique strength-hardness correlation is not due to the particle fracture- induced weakening during the tensile test. It is proposed that, under indentation loading, enhanced matrix flow that contributes to a localized increase in particle concentration directly below the indenter results in a significant overestimation of the overall composite strength by the hardness test. Micromechanical modeling using the finite element method was used to illustrate the proposed mechanisms under indentation loading and to justify the experimental findings.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.