Effects of electron irradiation on precipitation in Ni-Al alloys

Abstract

Binary Ni-Al alloys have been irradiatedin situ by high voltage electron microscopy (650 kV) in order to investigate the effects on precipitation. Nucleation and growth of dis-location loops are observed during irradiation in the temperature range 20 to 650°C. In solution-treated specimens, large faulted loops form during irradiation at 500°C. Con-trast analysis shows that loops are Frank-type with l/3 〈HI〉 Burgers vectors and in-terstitial in character. At 650°C and above, loop formation and growth are not observed once γ′ precipitates have formed. In preaged specimens, much smaller loops form dur-ing irradiations at below 500°C. At 500°C and above, no loops are observed in specimens containing large volume fractions of precipitates. The spatial distribution of loops ap-pears rather uniform regardless of the presence of γ′ precipitates except when large in-coherent precipitates exist. The growth of γ′ precipitates is enhanced by irradiation in the temperature range 300 to 750°C. Precipitate coarsening under irradiation follows radiation-enhanced diffusion kinetics. Quantitative analysis demonstrates that the radia-tion-enhanced diffusion coefficient responsible for coarsening of γ′ is independent of the temperature between 300 and 650°C. This result is in agreement with theoretical pre-dictions for the case in which irradiation-produced point defects are lost by their anneal-ing at fixed sinks.