A new method to study the composition dependence of mechanical properties of intermetallic phases
Wei Luo, Max-Planck-Institut für Eisenforschung, Düsseldorf, GermanyChristoph Kirchlechner, Max-Planck-Institut für Eisenforschung, Düsseldorf, GermanyGerhard Dehm, Max-Planck-Institut für Eisenforschung, Düsseldorf, GermanyFrank Stein, Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany
High temperature intermetallic phases like transition-metal-based Laves phases and Fe aluminides show excellent strength properties at high temperature, but their brittleness at low temperature is a great drawback. Our knowledge about the plasticity of these intermetallic phases and the way mechanical deformation proceeds is quite incomplete. The problem becomes even more complex as the existing literature indicates that their mechanical properties strongly depend on composition.
A severe challenge for a systematic study of the mechanical behaviour of these intermetallic phases is the preparation of appropriate samples. Their distinct brittleness makes it difficult to prepare flawless bulk samples for mechanical tests. Moreover, grain size, second phases and impurities influence the mechanical behavior of bulk samples, which may mask the composition and crystal structure dependence of their mechanical properties. Therefore, we propose a new method for a comprehensive and precise study of the composition dependence of mechanical properties of intermetallic phases. With the diffusion couple technique we can grow diffusion layers of target intermetallic phases covering the whole homogeneity range. The idea is to get thick diffusion layers of the intermetallic phases with coarse grains to cut a series of micro-sized, single-phase and single-crystalline samples with the same orientation and different compositions using focused ion beam (FIB) cutting and then to study their mechanical properties with micro- or nanomechanical testing.
In this presentation, we show some results obtained for the NbCo2 Laves phases and for Fe aluminides using the new method. We prepared several diffusion couples to get diffusion layers of C36, C15 and C14 NbCo2 Laves phases. And with a Fe-20 at.% Al / Fe-53 at.% Al diffusion couple we get a large diffusion zone including A2 Fe(Al), D03 Fe3Al and B2 FeAl phases. The composition dependence of nanohardness was measured by nanoindentation. In the case of NbCo2 Laves phases, single-phase and single-crystalline micropillars were cut along the composition gradient by FIB with the aim to study the deformation behavior of the C36, C15 and C14 NbCo2 Laves phases by micropillar compression test.