Acoustic attenuation of longitudinal and shear waves in Ni–X (X = Al, Cu, Pd) alloys due to phonon–phonon interactions

In this theoretical study, the acoustic attenuation coefficients per unit frequency square have been calculated for both longitudinal and shear waves propagating along the ⟨100⟩ crystallographic axis of Ni-X (X = Al, Cu, Pd) alloys, within the temperature range 300-700 K. Three different alloy compositions Ni80X20, Ni50X50 and Ni25X75 were considered for each alloy.Initially, the nonlinearity parameter D, which takes into account the anharmonic behavior of the materials, was calculated using the second order and third order elastic constants of material.Mason's theory of phonon-phonon interactions, based on the temperature dependent non-linearity parameter, was used to obtain the attenuation coefficients per unit frequency square α f 2 for each of the alloys.The α f 2 values are found to be temperature dependent and increase with it.It is observed that the α f 2 for pure nickel metal is greater than that for the Ni-X alloys.As the percentage of added metal X in the alloys increases, the attenuation coefficient values slightly decrease within the range of 10 to 25 percent.The study also shows that, as the molecular weight of metal X added to pure nickel increases, the attenuation coefficient per unit frequency square decreases.For the investigated nickel alloys, α f 2 is found to have the maximum value for NiAl alloy and the lowest for NiPd alloy.Mason's theory of wave attenuation due to phonon-phonon interaction can successfully explain the attenuation of both longitudinal and shear waves propagating through the Ni-X alloys.