Phase boundary sliding of a reticular-structured Mg-O-9Al alloy

In a Mg-9Al alloy containing O atoms (Mg-O-9Al alloy) supplied from the decomposition of TiO2 nanoparticles in a Mg-9Al melt, the O atoms are mostly located in the eutectic β-phase after solidification. During homogenization treatment, the β-phase decomposes and the α′′-phase (hard) surrounded by thick α′-phase (soft) gradually develops by the spinodal decomposition of the homogenized α-phase. That is, when the compositions of both Al and O atoms are reached at near 5 at% in the α-phase, the spinodal decomposition activates in the range of the homogenization temperatures. The core-mantle structured (i.e., reticular-structured) Mg-O-9Al alloy shows high hardness and elastic modulus, and yield stress of 129 MPa and elongation to failure of 15.7%, much higher than those obtained in the homogenized Mg-9Al alloy (87 MPa and 8.7%). Because the hard α′′-phase is wrapped by the soft α′-phase, the α′′-phase undergoes phase boundary sliding during plastic deformation at room and high temperatures, exhibiting the α′′-phase rotation and shear deformation of the α′-phase. The alloy shows a strain rate sensitivity in the range of 0 (dislocation activity) to 1 (diffusion flow), depending on the plastic deformation mechanism of the α′-phase.