Spontaneous formation of the B2 phase from a decagonal quasicrystal under reduced constraint

The relationship between the decagonal quasicrystal and B2 ordered phase transformation in diagonal quasicrystals is described. The B2 phase can be considered as an approximant phase of the icosahedral quasicrystal by going through a two stage process of obtaining approximant hyper crystal followed by the projection in the physical space. High resolution electron micrographs (HREM) and electron diffraction patterns of the single quasicrystal were taken with JEM 4000EX, JEM 3000F, and Philips CM20. It was observed that there were several B2 grains coexisting with icosahedral and decagonal grains in the interior partitions of the specimen. The transformation of the icosahedral and decagonal phases to the B2 phase is attributed to a change in concentration during thinning by ion bombardment and the resultant loss of aluminum atoms, and to the consequent shift of the alloy composition to the adjacent B2 phase phase field.