Modification on near-surface precipitation in AlGE alloy by ion irradiation

A model including precipitate dissolution and solute segregation is used to explain the changes in precipitate distribution during 100 keV Al⁺ ion irradiation of AlGe alloy. It is found by TEM that Ge precipitates in the peak damage region i.e. <100 nm from the surface are destroyed by prolonged irradiation to doses greater than 28 dpa, whereas precipitates near the tail of the damage profile i.e. 100–250 nm from the surface, continue to grow. SIMS has shown that the dissolution of near-surface precipitates is accompanied by segregation of Ge to depths below the damage peak, indicating that Ge segregates down defect gradients.

The results show that solute segregation is an important factor in determining precipitate stability. It is thought that the reversal in precipitate behaviour from growth to dissolution occurs because the solute depletion in the matrix near the surface reduces the solute arrival rate at the precipitate sufficiently for recoil dissolution to determine the precipitate behaviour. A preliminary study on low temperature irradiation of AlGe shows that Ge solute re-distribution rate is limited by the concentration and mobility of vacancy-solute complexes, and not by the rate of precipitate dissolution.