Time–temperature–transformation diagram and microstructures of bulk glass forming Pd40Cu30Ni10P20

Isothermal crystallization studies were performed on the bulk glass forming alloy ${\mathrm{Pd}}_{\mathrm{40}}{\mathrm{Cu}}_{\mathrm{30}}{\mathrm{Ni}}_{\mathrm{10}}{\mathrm{P}}_{\mathrm{20}}$ in the undercooled liquid region between the glass transition and liquidus temperature, resulting in a complete time–temperature–transformation (TTT) diagram for crystallization. The TTT diagram shows a typical “C” shape with the nose at 50 s and 680 K. Assuming steady state nucleation and a diffusion-controlled growth rate, the TTT diagram was successfully fit over the entire range of the measurement. The microstructure after isothermal crystallization shows a modulation in Cu and P for all degrees of undercooling. The primary solidified phase is ${\mathrm{Cu}}_{\mathrm{3}}\mathrm{Pd},$ which forms distinct dendrites at low undercooling. From additional constant cooling experiments, the critical cooling rate to bypass crystallization was determined to be 0.33 K/s.