Solidification Analyses of Bulky Zr60Al10Ni10Cu15Pd5 Glass Produced by Casting into Wedge-Shape Copper Mold

Abstract

The liquid-crystalline transformation behavior during continuous cooling and the transformation-induced structure were examined for a Zr₆₀Al₁₀Ni₁₀Cu₁₅Pd₅ molten alloy which was ejected into a wedge-shape cavity in a copper mold. The wedge-shape cavity has a constant depth of 50 mm and different vertical angles (θ) ranging from 5 to 15 degrees. The ejection temperature of the molten alloy was also changed in the range of 1273 to 1573 K. The cast structure consists only of a glassy phase in the θ range smaller than 10 degrees and changes to a mixed structure consisting of glassy and nonequilibrium crystalline Zr₂Ni and Zr₂Cu phases in the higher θ range. The glass transition temperature and crystallization temperature of the cast metal glass are 683 and 778 K, respectively, which agree with those for the melt-spun glassy ribbon. The start (Cs) and termination (Ct) points for the transformation from the supercooled liquid to crystalline phases during continuous cooling were determined from the thermal analytical data obtained at different sites in the wedge-shape cavity and the continuous-cooling-transformation (C.C.T.) curves were constructed. The nose temperature (T_n) and the time (t_n) up to the nose point in the C.C.T. curves were 1018 K and 0.93 s respectively. The critical cooling rate for glass formation defined by (T_m−T_n)⁄t_n is evaluated to be 110 K/s. Further, the time interval between Cs and Ct is as short as 0.2 s and the fast growth reaction is attributed to the easy formation of the nonequilibrium crystalline phases and the increase in temperature caused by the precipitation-induced recalescence.