QUASI-CRYSTALLINE GA-PD-M (M = CR, MN OR FE) ALLOYS PREPARED BY RAPID SOLIDIFICATION

New icosahedral alloys were found to form at Ga70Pd20M10 (M = Cr, Mn or Fe) in a rapidly solidified state. The icosahedral phase has the simple P-type quasicrystalline structure and its grain size is in the range from 1 to 3 mum. The icosahedral phase (I) in these alloys is in a metastable state, and the subsequent heating causes the decomposition into crystalline phases (Cryst.) through two-stage reactions of I --> I + Cryst. -->Cryst., the total exothermic heat (DELTAH(x)) being 2.3 kJ/mol for M = Cr, 1.5 kJ/mol for M = Mn, and 0.76 kJ/mol for M = Fe. The onset temperature of the decomposition (T(x)) increases in the range of 470 to 550 K in the order of Cr < Mn < Fe. There is a tendency for T(x) to increase with decreasing DELTAH(x). The finding of the Ga-based quasicrystalline alloys indicates the possibility that a new quasicrystalline alloy may be obtained in other alloy systems except Al-based alloys.