Glass formation in La-based La-Al-Ni-Cu-(Co) alloys by Bridgman solidification and their glass forming ability

Six La-based La-Al-Ni-Cu-(Co) alloys were subjected to a systematical study of glass formation by Bridgman unidirectional solidification at growth velocities between 0.1 and 4.82 mm/s at a temperature gradient of 15 K/mm. 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, indicating the largest glass forming ability for the La₅₅Al₂₅Ni₁₀Cu₁₀ alloy. However, replacement of Ni by Co leads to a further decrease in the critical cooling rate for the La₅₅Al₂₅Ni₅Cu₁₀Co₅ alloy. Critical cooling rates for glass formation in the present alloys were also obtained through a study of their melting and solidification behaviours by thermal analytical measurement. The effect of alloying addition and the significance of reduced glass transition temperature for the glass forming ability of these alloys is discussed.