ALPDMN PHASE-DIAGRAM IN THE REGION OF QUASI-CRYSTALLINE PHASES

We report results on a metallurgical investigation of the Al-Pd-Mn Pha se diagram in the region of the quasicrystalline phase field. Liquidus phase fields have been determined for icosahedral, decagonal and seve ral periodic compounds which are approximant crystals of the quasicrys tals. Structure analyses of these phases have been carried out by tran smission electron microscopy. As defined from the linear phason strain field theory, the different crystal approximants can be distinguished as belonging either to the icosahedral phase or to the decagonal phas e. An equilibrium between icosahedral and modulated icosahedral phases has also been identified. The modulations occur along the threefold i cosahedral axes.