Crystallisation in Al-ETM-LTM-La metallic glasses

Abstract

The addition of early and late transition metals to Al-La alloys has a strong influence on the glass forming ability and the subsequent devitrification route. Four quaternary alloys of nominal composition Al₈₇Fe₅Ni₅La₃, Al₈₈Fe₃Ni₃La₆, Al₈₂Fe₄Ni₄La₁₀, Al₇₅Ti₁₀Ni₁₀La₅ and a ternary alloy of nominal composition Al₇₅Ti₁₀Ni₁₅ have been melt spun at 10, 20, 30 and 40 m s^-1 wheel speed. Amorphous alloys thus secured have been annealed at the peak temperatures as indicated by the DSC thermograms from 10 min to 2 h. The Al₈₇Fe₅Ni₅La₃ alloy showed in the melt-spun state precipitates of α -Al, a FCC phase with 12.5 Å lattice parameter. The Al₈₈Fe₃Ni₃La₆ alloy in the melt-spun state shows nano-sized precipitate of α-Al in the amorphous matrix. The Al₈₂Fe₄Ni₄La₁₀ alloy after melt-spinning at 40, 30, 20 m s^-1 wheel speed becomes amorphous and shows precipitates of α-Al in the amorphous matrix when melt spun at 10 m s^-1 wheel speed. The amorphous phase in the Al₈₂Fe₄Ni₄La₁₀ alloy is stable up to 625 K and crystallises in three exothermic heat events. After heat treatment at the first crystallisation peak temperature and below the first crystallisation temperature precipitation of α-Al in the amorphous matrix can be observed. At the end of the crystallisation process very fine precipitates of Al₃La and LaNi can be seen at the α-Al grain boundaries. Activation energy of crystallisation has been calculated by Kissinger and Ozawa method. Al-Ti-Ni-La becomes partially amorphous after melt-spinning. Al-Ti-Ni alloy does not produce amorphous phase after melt-spinning. Precipitation of Al₃Ti phase can be observed in both the alloys. The development of different microstructures, effect of La on the glass forming ability and the stabilisation of the glassy matrix with enrichment of La and with the progress of crystallisation, establishes a possible link between Al based metallic glasses and La based bulk metallic glasses.