Electron-Microscope Study of Precipitation Sites in a Deformed Fe-Al-N Alloy

Abstract

The precipitation behaviour in a solution-treated and 5% deformed Fe-0.04% Al-0.005% N alloy has been studied at elevated temperatures by means of in situ observation of the foils in a high-voltage electron microscope. The operating voltages selected were 400 and 500 kV, which are, respectively, below and above the threshold voltage for the formation of Frenkel defects in α-Fe. Precipitates seen at the beginning of the heating experiment consisted of α″-Fe₁₆N₂ and were found to be much finer in deformed specimens than in undeformed ones. Following the reversion of α″ at ∼ 150° C, AlN precipitates were present in the temperature range between 520 and 560° C under irradiating conditions with 500 kV electrons, while under non-irradiating conditions they were observed above 7000° C. Prismatic dislocation loops induced by deformation were found to be preferred nucleation sites for the precipitation of both α″ and AlN.