Interaction of dissolved atoms and relaxation due to interstitial atoms in hcp metals

The literature data on the mechanism of internal friction maxima induced by O, N, and C in alpha-Ti, alpha-Zr, and alpha-Hf, are contradictory. They do not answer the question which kind of complexes induces relaxation: interstitial atoms or interstitial atoms with substitutional atoms. To clarify this question, modeling of the short-range order and atomic displacement fields around the solute atom clusters was carried out by the Monte-Carlo technique for typical Ti-O-Zr alloys. The energies of strain-induced (elastic) O-O and O-Zr interactions and displacement fields of host atoms around the solute atoms were calculated and used in modelling. The concentration dependence of relaxation strength due to diffusion under stress of oxygen atoms was evaluated using the values of local displacement around the solute atom complexes. It is shown that the developing short-range order cannot be described by the single O-O or O-Zr pair and the associated relaxation, as simple reorientation of any specific atomic pairs. It seems likely that in many cases the internal friction is caused by more complicated clusters constituted by interstitial and substitutional atoms. (C) 2003 Published by Elsevier B.V.