Influence of Chemical Composition on the Room Temperature Plasticity of C15 Ca-Al-Mg Laves Phases

Abstract

The influence of chemical composition changes on the room temperature mechanical properties in the C15 CaAl2 Laves phase were investigated in two off-stoichiometric compositions with 5.7 at.-% Mg addition (Ca33Al61Mg6) and 10.8 at.-% Mg and 3.0 at.-% Ca addition (Ca36Al53Mg11) and compared to the stoichiometric (Ca33Al67) composition. Cubic Ca-Al-Mg Laves phases with multiple crystallographic orientations were characterised and deformed using nanoindentation. The hardness and indentation modulus were measured to be 4.1 ± 0.3 GPa and 71.3 ± 1.5 GPa for Ca36Al53Mg11, 4.6 ± 0.2 GPa and 80.4 ± 3.8 GPa for Ca33Al61Mg6 and 4.9 ± 0.3 GPa and 85.5 ± 4.0 GPa for Ca33Al67, respectively. The resulting surface traces as well as slip and crack planes, were distinguished on the indentation surfaces, revealing the activation of several different {11n} slip systems, as further confirmed by conventional transmission electron microscopic observations. Additionally, the deformation mechanisms and corresponding energy barriers of activated slip systems were evaluated by atomistic simulations.

Keywords: Laves phase plasticity, Off-stoichiometry, Electron microscopy, Nanoindentation, Atomistic simulation