Fracture of aluminium reinforced with densely packed ceramic particles: influence of matrix hardening

Increasing the Strength/Toughness Combination of High Volume Fraction Particulate Metal Matrix Composites using an Al‐Ag Matrix Alloy

“…Broken alumina particles, on the other hand, cover a large fraction of the fracture surface, more so than with an as-cast matrix. As shown in, [1] in such composites containing about 60 vol. %.…”

“…Referring to the toughening mechanisms proposed earlier for these composites, [1,2] if particle fracture remains the main crack advance mechanism, the local peak stress of the cohesive law must be roughly the same in both composites. The "amplification" factor by which the local (cohesive) fracture energy is increased cannot then be higher in the present composites than with Al-4.5 %Cu composites, since this factor is mainly governed by the ratio of peak cohesive stress to composite yield stress.…”

“…It was shown by alloying the aluminium matrix of these composites with copper that, when the above conditions are met, the fracture toughness and the tensile strength of these composites can be increased simultaneously by increasing the matrix flow stress r y , all else being constant. [1] We demonstrate here further simultaneous improvements in composite tensile strength and toughness, using a somewhat exotic matrix alloy, namely an alloy of aluminium with silver; we justify this choice in the next section. Matrix Selection: There are, as mentioned above, several factors that practically limit the choice of the matrix alloy in high-performance metal matrix composites.…”

“…If their microstructure is adequately designed and optimized, these materials can be made to exhibit strength/ toughness combinations that match those of unreinforced high-strength engineering aluminium alloys. [1,2] The potential of these composites in energy-intensive structural applications is thus clearly high. The elevated toughness of these composites is achieved by meeting certain critical microstructural conditions, defined and explained in.…”

“…The elevated toughness of these composites is achieved by meeting certain critical microstructural conditions, defined and explained in. [1][2][3][4] To summarize, these include: (i) the initial (high) quality of the stiff ceramic particles used, which must be free of stress concentration sites and internal defects, (ii) the presence of a ductile matrix free of brittle second phases, (iii) a capacity for composite bulk plastic deformation, made possible in spite of the high ceramic loadings by the fact that only the metal is continuous in their microstructure. These characteristics combined produce, in the composite, a local fracture cohesive law, [5,6] that features both (i) an elevated peak stress and (ii) a high local fracture energy.…”