Diffusion mechanism of internal friction in a niobium–titanium alloy

Abstract

An NT50 alloy of the composition Nb–(48.5 ± 1.5)% Ti is studied after severe plastic deformation and subsequent 100-h annealing. During heating at a rate of 2 K/min, the NT50 alloy subjected to this thermomechanical treatment demonstrates two internal friction peaks at 493 K and 573 K. As the heating rate increases by a factor of three, both peaks shift to higher temperatures and the peak height at 573 K increases. A diffusion mechanism of the temperature-dependent internal friction in the strongly deformed NT50 alloy is proposed. Using this mechanism, the effect of the heating rate on the internal friction in this alloy is explained as the volume titanium diffusion due to the diffusion growth of α-Ti precipitates in subgrains in the alloy. In this case, the first peak is related to the bulk diffusion that accompanies grain-boundary diffusion in subgrains, and the second peak, to usual bulk diffusion in subgrains.