Glass formation and glass forming ability of La based alloys

Glass formation and glass forming ability of six La-based La-Al-Ni-Cu-(Co) alloys have been studied systematically by Bridgman solidification and thermal analytical measurement. With increased Cu content the critical growth velocity for glass formation in La₅₅Al₂₅Cu_20-xNi_x (x = 0-20) alloys shows a steep minimum at 10 at%Cu, however, replacement of Ni by Co leads to a further decrease in the critical cooling rate for the La₅₅Al₂₅Ni₅Cu₁₀Co₅ alloy. The thermodynamics of these alloys was studied in the undercooled liquid and crystalline state by means of temperature-modulated DSC. Reduced glass transition temperature T_rg given by T_g/T₁ (T_g the glass transition temperature and T₁ the offset melting point) is found to show a stronger correlation with critical cooling rate for glass formation than that given by T_g/T_m (T_m the onset melting point). The glass forming ability of these alloys is discussed in terms of microstructure selection and driving force for crystallization.