Probing the local strength and toughness of microscopic hard second phases in alloys and composites
Many engineering alloys and composites combine a ductile matrix with discrete microscopic reinforcing phases. It is known that the mechanical properties of such alloys and composites are strongly influenced by those of those reinforcing phases; however, surprisingly little is known of the toughness, or of strength-limiting flaws within those phases. To investigate the strength and fracture toughness of such microscopic particles directly, we have developed test methods that combine focused ion beam (FIB) milling with microtesting and bespoke finite element simulation. Local strength is measured using a nanoindenter probing micromachined samples carved into individual reinforcing particles in such a way that tensile stresses are produced in a volume of material that is free of FIB and polishing artifacts. Fracture toughness is measured using the chevron-notch fracture test technique adapted for microscopic samples. Testing methods are established using nanocrystalline alumina fibers as the testbench material, so as to compare data thus obtained with known fiber properties from tensile tests on long sections of the fibers. These test methods are now being transposed towards the microscopic testing of more irregularly shaped and anisotropic brittle second phases, while other tests are being developed to probe phases the shape of which enables the design of other tailored testing procedures.
This research is funded by the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Advanced Grant Agreement No. 291085.
Record created on 2016-04-28, modified on 2016-08-09