Ultrasonic characteristics of porous Pd42.5 Cu30 Ni7.5 P20 glassy alloys

Using ultrasonics, the acoustic characteristics of porous Pd42.5 Cu30 Ni7.5 P20 glassy alloys were examined in terms of complex elasticity. Bulk modulus (K) and Lam̀ parameter (λ) decrease in a parabolic manner as porosity increases, while Young (E) and shear (G) moduli decrease linearly. Consequently, the order of K>λ>E>G, which is monopolistically characterized by nonporous glassy alloys, changes to the order of E>K>λG at 58% porosity. The decrease in Poisson's ratio and the increase in GK ratio up to 58% porosity indicate crystallinelike characteristics that resist three-dimensional volume-nonpreserving deformation. An increase in porosity induces frequency convergence for longitudinal waves and an increment of the imaginary parts in the complex waves. The viscoelasticity of the porous glassy alloys is predominated by shear motion. In contrast to the continuous increment in dilational damping, the porosity-dependent increment in shear damping could be elucidated based on the accumulation of strains induced by the formation of pores.