TEM study of Ti-N and Cr-N precipitate formation in iron alloys

The formation of precipitates of Ti and Cr nitrides in cold-rolled Fe + Ni( 4at%) Ti(2at%) and Fe + Ni(4at%) + Cr(3at%) after a pre-nitriding step was investigated by Mossbauer spectroscopy (MS) and transmission electron micro scopy (TEM). From MS data we conclude that initially most of the Ti and Cr were atomically dispersed. Using TEM and high-resolution TEM (HRTEM), we fo und that the Baker-Nutting (B-N) orientation relationship (OR) holds for pl atelets one to two interatomic distances thick, producing streaking around the (200) reflections, while for thicker precipitates the Nishiyama-Wasserm an (N-W) OR is more favorable. We also observed a transient phase, Cr2N, th e formation of which was possible due to the relatively low nitriding tempe rature, a low nitriding potential, and the presence of Cr inclusions of rel atively large initial size.