Effect of driving force of crystallization on critical cooling rate for Pd-based metallic glasses

The advent of bulk metallic glasses (BMG) has opened lot of scope of wide range of applications for this class of amorphous materials. Thermodynamics plays a very important role in glass formation in multicomponent metallic alloys. BMG's can be synthesized with relatively lower cooling rate with ease now. However, the glass formation in these systems seems to depend on quite a few parameters like enthalpy of melting, reduced glass transition temperature, under cooling. In present paper, we have studied the glass forming ability of Pd-based metallic glasses using theoretically determined Gibbs free energy difference (Delta G), between the supercooled liquid and the corresponding crystalline phase, and the critical cooling rate (R (c)). Time-temperature-transformation (TTT) diagrams were constructed to calculate R (c) using Uhlmann and Davies formulation. Different theoretical expressions of Delta G are incorporated in nucleation and growth equations to find R (c) from TTT diagram. The results obtained theoretically by Dhurandhar et al. expression of Delta G, assuming hyperbolic variation of specific heat difference (Delta C (p)), were found to be in excellent agreement with experimental data for different Pd-based systems.