Critical cooling rates for glass formation in Zr-Al-Cu-Ni alloys

Critical cooling rates for glass formation in four Zr-based Zr-Al-Cu-Ni alloys, which exhibit a wide supercooled liquid region, are determined using three methods. The first method involves the construction of the time-temperature-transformation (TTT) curve. The second method considers continuous-cooling-transformation curves (CCT) which are constructed from various data. The last method involves the measurement of the offset temperature for fusion and the onset temperature of solidification upon cooling at different rates using differential thermal analysis (DTA). The critical cooling rates obtained from CCT curves were generally more than 50% less than those obtained from TTT curves. It was found that the critical cooling rates determined from CCT curves for a nucleation barrier of 50 to 55kT were similar to those determined from DTA results. These rates determined from TTT and CCT curves and DTA results for the present four Zr-Al-Cu-Ni alloys were found to decrease as the relative amount of Cu to Ni in the alloys was increased.