An ultra-micro indentation investigation of aspects of the fracture process in particulate reinforced metal matrix composites

Abstract

The technology now available for the control and precision measurement of force and displacement allows investigation of the micro-mechanical properties of materials using ultra-micro indentation. Ultra-micro indentation uses pyramidal or very small radius (typically 5--50 [mu]m) spherical diamond indentors, with indentation load vs penetration being accurately measured for loads to 1,000 mN and penetrations to 4,000 nm. Analysis of the contact response with both pyramid and spherical indentors provides considerably more information about a material than traditional microhardness testing; the hardness, elastic modules and (with spherical indentation) stress-strain response of a material can be determined. Such equipment is already used for fiber push-out investigations of the strength of the fiber/matrix interface in fiber reinforced composites. Ultra-micro indentation allows investigation of the response of the matrix, individual reinforcement particles and the interfacial region to indentation, providing information for prediction of the dominant fracture mode in a PR MMC system. The present article reports on an investigation of the fracture properties of two aluminium alloy based PR MMCs conducted using ultra-micro indentation. The experiments undertaken provided: (1) comparison of the hardness of the matrix in an Al 6061/Micral[trademark] PR MMC and that of monolithic Al 6061; (2) information on the response ofmore » particles in Al 359/SiC and Al 6061/Micral PR MMCs to indentation; and (3) information on the response of the particle/matrix interface in an Al359/SiC PR MMC to loading.« less