CONTINUOUS-COOLING-TRANSFORMATION (CCT) CURVES FOR ZR-AL-NI-CU SUPERCOOLED LIQUIDS TO AMORPHOUS OR CRYSTALLINE PHASE

The continuous-cooling-transformation (CCT) curves from supercooled liquid to the amorphous or crystalline phase were measured by conventional thermal analysis for Zr60Al10Ni10Cu20 and Zr55Al10Ni10Cu25 alloys. Based on the CCT curves, the critical cooling rate for glass formation is determined to be as low as 16 K/s for the former alloy and 14 K/s for the latter alloy. These low critical cooling rates demonstrate clearly that these Zr-based amorphous alloys have extremely large glass-forming ability. The onset temperature of structural relaxation (T-r), the heat of structural relaxation (Delta H-r) and glass transition temperature (T-g) are dependent on cooling rate and the increase of cooling rate causes the decrease in T-r and the increase in Delta H-r and T-g. On the other hand, the onset temperature of crystallization from supercooled liquid is independent of cooling rate. The accumulation of the information on the CCT curves for these amorphous alloys is extremely important for the subsequent development of amorphous alloys.