The damping behavior in torsion of single phase beta-In3Sn has been evaluated at room temperature over a broad range of frequencies (10(-4) to 10(3) Hz) and as a function of various mechanical and thermal treatments. The results are consistent with a model for the power-law (tan delta proportional to f(-n)), high-temperature-background absorption being effected by diffusional processes on grain and, particularly, on subgrain boundaries. The results are compared/contrasted with those for damping in single-phase gamma-InSn4 and in the two-phase beta-gamma eutectic. Failure of the eutectic material to follow a composite model for damping, combined with a thermal aging effect that lowers damping only for certain frequencies, shows that the boundary-based absorption model for the high-temperature background applies, too, to phase boundaries. (C) 2003 Kluwer Academic Publishers.