Ultrasonic investigation of Pd39Ni10Cu30P21 bulk metallic glass upon crystallization

Acoustic velocities of ${\mathrm{Pd}}_{\mathrm{39}}{\mathrm{Ni}}_{\mathrm{10}}{\mathrm{Cu}}_{\mathrm{30}}{\mathrm{P}}_{\mathrm{21}}$ bulk metallic glass (BMG) are measured by an ultrasonic technique upon annealing. The elastic constants and the Debye temperature are obtained. A large softening of the transverse phonon is exhibited in the as-quenched BMG relative to its crystallized state. Upon crystallization, the shear modulus and the Debye temperature increase by $\text{∼30\%}$ and $\text{∼12\%,}$ respectively; however, the density increases by only $\text{∼0.6\%.}$ Some anomalous acoustic and elastic behaviors are observed near the glass transition temperature and in the supercooled liquid region of the BMG. The anomalies are explained with regard to the structural changes.