Deformation behavior of Mg-Zn-Y icosahedral quasicrystal phase in a magnesium matrix by high pressure torsion at room temperature

Complex physical and mathematical concepts of quasicrystals have been applied, for the first time, to an engineering processing of an alloy containing a quasicrystalline phase. Icosahedral quasicrystals (i-phase), which are quasiperiodic and possess fivefold symmetry, are often found as stable phase in aluminum and magnesium alloys. They are known to be hard and brittle at room temperature, therefore their deformation behavior at lower temperatures is not well understood yet. High pressure torsion (HPT) gives an opportunity to study deformation of brittle materials due to confinement of the dies. Here, we report on deformation behavior of 27 vol% eutectic i-phase present in a magnesium alloy Mg-12Zn-2Y (at%) subjected to HPT under 5 GPa pressure at RT with a number of rotations N. The matrix \(\alpha\) $\alpha$ -Mg phase deformed by twinning and dislocation slip, leading to full recrystallization. Consequently, diffraction peaks showed broadening, followed by sharpening. The peaks of i-phase continued to broaden. Fivefold symmetry diffraction peaks broadened disproportionately to the others. Peak broadening analysis showed that deformation occurs predominantly by changes in fivefold symmetry planes, as observed to be by twinning and formation of narrow planar faults. No evidence of new random phason strains was detected. Introduction of localized phonon strain was detected at high strains, which could be correlated with creation of interfaces and surfaces by fragmentation of i-phase into nanoparticles and dispersion into the matrix. Vickers microhardness of the alloy increased from 118 Hv to over 175 Hv after N = 40.