The Formation Kinetics of PdCusi-and PdNip-Metallic Glasses

Abstract

The critical cooling rate (Ṫ_c) required for glassy solidification of Pd₇₉ CU₄Si₁₇, Pd₇₇,₅Cu₆Si₁₆,₅ and Pd₄₀Ni₄₀P₂₀ alloys were measured by monitoring the critical velocity for the formation of amorphous structure during directional solidification, figure 1.The measured critical velocities (V_c,) and the critical cooling rates (T_c) for the three alloys are given in table 1. These results were compared with the T_c. values computed from CCT-diagram using the Uhlmann treatment considering only homogeneous nucleation. Influences of activation energy of nucleation (ΔG*) and Gibbs volume free energy difference between solid and liquid (ΔG_v)on the computed T_c were analysed. The computed T_c. are presented in figure 2. Computed T_c- values for both PdCuSi alloys are in satisfactory agreement with experimental data when the Thompson-Spaepen ΔG_v-approximation and ΔG* = 65 kT at 0.2 ΔT_r are used. For Pd₄₀ Ni₄₀ P₂₀ alloy none of the computed T_c agreed with experimental results in the ranges analysed.

on leave of absence from Federal University of Paraiba, CCT-DEM, Brazil