Evidence of kinetically controlled process in preparing supersaturated Al-Ti solid solutions

摘要

Recently, the synthesis of supersaturated solid solu-tion by mechanical alloying has been widely studied [1-9], It has been shown that mechanical alloying is a versatile tool to overcome the limitations imposed by the phase diagram such as immiscibility in the liquid and solid states. Nevertheless, the mechanism of the metastable phase formation has not been well determined. It has been suggested that the increased solid solubity can be explained by the metastable equilibrium between solid solution and the amor-phous phase [1,2], Yavari et al. [6] reported that fragments are introduced by intense deformation with tip radii of the order of nanometre scale, and that capillary pressures force the atoms on these fragments to dissolve, thus explaining the formation of fee FeCu solid solution which exhibits positive mixing enthalpy. Recent evidence from Mossbauer spectroscopy, extended X-ray absorption fine struc-ture (EXAFS) and thermal stability experiments assume that the solute atom may be associated with solute segregation in nanocrystalline grain bound-aries [7-9].