| Research Abstract |
The main aim of this research is to study the quasicrystal-quasicrystal phase transformation of Al-Pd-Mn icosahedral phase. It have been reported that an Al_<71>Pd_<21>Mn_8 icosahedral phase is not only an F-type icosahedral phase, but can be F2-type and F2M-type icosahedral phases. We have added to study F2M-type phase. On the alloy composition near Al_<71>Pd_<21>Mn_8, the F-type icosahedral phase is stable at about 800ﾟC,whose name is originated as the 6-dim supercubic lattice based on the idea is face centered cubic. The F2-type is understood and F2M-type icosahedral phases. We have added to study F2M-type phase. It is easy to understood the F2M-type as the 6-dim diamond lattice of F2-type icosahedral phase. We have tryed to study the feature of unknown F2M-type icosahedral phase, we called medium phase, and the growing conditions of F2-type and F2M-type icosahedral phases. And We have got the knowledge for the quasicrystal stability.
Feature of unknown F2M-type icosahedral phase : F
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2M-type is not truely icosahedral phase, but has trigonal or cubic symmetry. It has usual crystal symmety, but quasiperiodic.
Growing conditions of F2-type and F2M-type icosahedral phases : We searched it under such conditions ; we fixed the higher temperature annealing condition as T=803-806ﾟC and 50 hours and we controlled the second annealing conditions, cooling it by 2-300ﾟC/h after it. (1) As the result of the second stage condition as 602ﾟC and 100h, we got F2-type as the higher cooling rate than 200ﾟC/h and F2M-type as slower. (2) As the result of the 200ﾟC/h cooling rate and no second stage, we got F2-type as the higher quenching temperature than 728ﾟC and F2M-type as lower than 676ﾟC.As the result of the second stage condition as 708-728ﾟC and 5-282h, we got F2-type. (3) As the result of the 200ﾟC/h cooling rate and the second stage condition as 739ﾟC and 41h, we got F2M-type.
We have the temporary following experimental results. It seems to be true from such experimental results that the F2M-type is a lower phase. It is thought that the realization of F2M-type icosahedral phase needss to two processe : The first process is F-type to F2-type phase transformation and this finishes for a short time ; The second is F2-type to F2M-type phase transformation and this is thought to be a diffusion process as this needs for a long time. Now we are going to make mm single F2M-type icosahedral phase quasicrystals as we have x-ray diffraction experiments. Less
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