Flexural strength of micron-scale plate-like silicon in aluminum
Mechanical properties of composite materials and alloys are strongly influenced by the intrinsic mechanical properties of the reinforcing phases they contain; however, due to the irregular shape and small size of particulate reinforcements, measuring their intrinsic properties is a substantial methodological challenge. Here we present a method with which we probe the local flexural strength of individual microscopic plate-like silicon particles, which constitute, together with aluminium, the eutectic microconstituent in AlSi alloys. Silicon particles are extracted from the cast and heat-treated alloy by deep-etching the aluminium matrix. The plates are then are dispersed on a steel substrate, where irregular plate- like particles rest lying on one of their large flat facets. A beam of well-defined dimensions is micro-machined out of individual particles using focused ion beam (FIB) milling perpendicular to the substrate. In this way, the particle surface which is in contact with the substrate and that will later on be subjected to tension upon beam bending, i.e. where strength will be measured, is not affected by the FIB nor by redeposition. The FIB is also used to produce a hole in the steel substrate nearby the micro-machined beam so that the silicon beam can be transported and placed on top of the hole using a micromanipulator. The beam is tested in 3- or 4-point bending until fracture by applying a force with a nanoindenter equipped with a diamond tip featuring one or two small rounded ridges that are longer than the width of the beam. Fractography is carried out after testing to locate and characterize the fracture initiation point. Test results are coupled with Finite Element simulations for interpretation. Error in the measurement, including the influence of possible misalignments, of the measured strength is evaluated.
Record created on 2015-07-16, modified on 2016-08-09