Thermal stability of trapped interstitials in Al(Ag)

Abstract

The thermal stability of trapped interstitials in an irradiated Al-0.09 at.% Ag crystal was studied using the ion channeling technique. The fraction f〈lmn〉dAg of Ag atoms displaced from substitutional lattice sites into 〈lmn〉 channels was monitored, using backscattering of 1.0 MeV 4He ions, for 〈110〉 and 〈100〉 axial alignment as well as for an orientation 0.4° from the 〈110〉 axis. Irradiations at 70 K with 1.0 MeV 4He ions resulted in an appreciable fraction of the Ag atoms being displaced from lattice sites (particularly into 〈110〉 channels) when migrating interstitial atoms were trapped at the Ag atoms. For irradiation fluences up to ∼ 6 × 10 15ions cm −2, the 〈100〉 mixed dumbbell was the most prevalent trapping configuration. At higher ion fluences, however, the results indicated that there was a gradual change in the trapping configuration. The change in configuration was attributed to the trapping of more than one self-interstitial at each Ag atom.Annealing experiments were performed following 70 K irradiations with 1.0 MeV 4He ions to fluences ranging from 1.2 × 10 15 to 29.3 × 10 15 ions cm −2. At the lowest irradiation fluence of 1.2 × 10 15 ions cm −2 essentially no change in f〈lmn〉dAg (or in the trapping configuration) occurred during annealing from 70 to 170 K. However, f〈110〉dAg and f〈100〉dAg decreased in the temperature range 170 to 230 K; at 230 K nearly all of the Ag atoms returned to substitutional sites. The irradiation-induced dechanneling increment (a measure of the total defect concentration) also annealed out between 170 and 230 K. The results indicated that the trapping configuration was changing in the region 170 to 230 K, which suggested that the annealing mechanism involved more than simply the annihilation of a migrating monovacancy with the self-interstitial atom trapped in the mixed dumbbell configuration. As the irradiation fluence was increased, there was a downward temperature shift of the stage in which vacancies were annihilating with trapped interstitial atoms, presumably due to the higherconcentration of defects present. In addition, a noticeable recovery f〈110〉dAg occurred below ∼ 110 K, hence indicating a more complex annealing behaviour when multiple trapping of the self-interstitial atoms at Ag atoms occurred initially.