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 La55Al25Cu20−xNix (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 thermodymics of these alloys was studied in the undercooled liquid and crystalline state by means of temperature-modulated DSC. Reduced glass transition temperature Trg given by Tg⁄Tl (Tg the glass transition temperature and Tl the offset melting point) is found to show a stronger correlation with critical cooling rate for glass formation than that given by Tg⁄Tm (Tm the onset melting point). The glass forming ability of these alloys is discussed in terms of microstructure selection and driving force for crystallization.