Room temperature elastic properties of Rh-based alloys studied by surface Brillouin scattering

Platinum metal group alloys are promising materials for use in a new generation of gas turbine engines owing to their excellent high-temperature properties. In the present work, room temperature elastic properties of single crystals of Rh3Nb and Rh3Zr are investigated. Surface Brillouin scattering spectra for a range of wave vector directions on the (001) surface have been acquired in order to determine the angular variation of the velocities of the Rayleigh and pseudo-surface acoustic waves and that of the longitudinal lateral wave (LLW) threshold within the Lamb shoulder. The elastic stiffness constants C-11, C-12, and C-44 of these cubic crystal specimens have been derived using two approaches: the first involving the least-squares fit of the combined measured wave velocity data to calculated values and the second an analytical approach using the Rayleigh velocities in the [100] and [110] directions and LLW velocity in the [100] direction, and extracting the elastic stiffness constants from the secular equations for these velocities. Results from the two methods are in good agreement and are for Rh3Nb, C-11 = 368 +/- 3, C-12 = 186 +/- 5, and C-44 = 161 +/- 3 in GPa; and for Rh3Zr, C-11 = 329 +/- 4, C-12 = 185 +/- 6, and C-44 = 145 +/- 4 in GPa. (C) 2014 AIP Publishing LLC.