Hardness and flow strength in particulate metal matrix composites

Strain hardening and damage by particle cracking effects on the correlation between hardness and tensile/compressive flow stress have been assessed for several metal matrix composites. The Vickers hardness value (in kg mm−2) is equivalent to 0.3 times the compressive flow stress (in MPa) at an applied strain which is small (1–2%) for composites with high strength matrices or large (4–7%) for composites with low strength matrices. The strain at which the parameters correlate increases with the materialʹs strain hardening exponent. A similar correlation is observed in tension only when damage has little effect on the strain hardening rate of the material. Damage introduced during fabrication may have a deleterious effect on the hardness/tensile flow stress correlation while the effect of damage developed during the tensile deformation is more limited. For most cases the use of hardness to predict the tensile flow stress is likely to lead to significant over-estimates.