Stacking faults in high-temperature-deformed Al-Pd-Mn icosahedral quasicrystals

Stacking-fault contrasts were observed by transmission electron microscopy in high-temperature, plastically deformed Al-Pd-Mn icosahedral quasicrystals. Bright- and dark-field contrast and trace analysis experiments show that there are two types of stacking-fault contrast. One has a fault plane perpendicular to a twofold axis and a displacement vector parallel to the fault plane normal, while the other has a fault plane perpendicular to a fivefold axis and a displacement vector parallel to the fault plane normal. High-resolution electron microscopy reveals that these stacking-fault contrasts are not conventional planar defects. They are found to be broadened, forming wavily bounded stacking-fault platelets of about 2.5-10 nm thickness. Systematic investigations of stacking-fault contrasts in several samples subjected to deformation under different conditions are consistent with the hypothesis that moving dislocations in quasicrystalline materials leave phason-type stacking faults behind which broaden and then disappear owing to intensive diffusion at high temperatures.