The present study was undertaken to investigate precipitation and growth of aluminum nitride precipitates in the Fe-Al-N alloy. Especially, the emphasis is placed on the precipitation behavior of face-centered cubic aluminum nitride, the morphological change of the aluminum nitride precipitates, and the relation between residual aluminum nitride and austenitic grain size. Direct observations of aluminum nitride precipitates were made by means of transmission electron microscopy for the first time so far as the author knows.
The main results obtained are as follows;
(1) In the furnace cooled specimen, unlikely in the water guenched specimen, electron microscopic examinations revealed the existence of facecentered cubic aluminum nitride even at the high annealing temperature.
(2) The influence of the holding temperature on the size of the precipitate follows the Arrhenius type equation. At a definite annealing temperature, the diameter of the rod-like precipitate is proportional to the square root of the holding time and the length is to the holding time.
(3) The size of the aluminum nitride precipitate is related to aluminum and nitrogen contents of the specimen. The mean volume ratio of the precipitate is nearly coincided with the square root of the concentration product of aluminum and nitrogen.
(4) The ratio of the length to the diameter of the rod-like particle changes after the Arrhenius type equation for the holding temperature and parabolically for the holding time.
(5) The growth direction of the aluminum nitride precipitate is [001]p, and the orientation relationship between the aluminum nitride precipitate and the iron matrix is (010)p//(001)m and [001]p // $[\bar{2}10]$ m.
