The formation of AIN crystals in an Fe-Mn-Al-C alloy during the nitriding process

We observed the formation of AIN crystals in an Fe-Mn-Al-C alloy during a nitriding process. The composition of the alloy was Fe-30.4 wt pct Mn-8.7 wt pct Al-1.0 wt pct C. The nitriding process consisted of heating the Fe-Mn-Al alloy in pure nitrogen at 1000 °C for 1 hour. During nitriding, AIN crystals formed in the regions near the surface layer of the alloy. The aluminum nitride formed along specifically preferred orientations of the metal matrix. We discovered that the formation of the secondary arms of the AIN crystals was related to the direction of flux of the nitrogen, and we proposed a growth mechanism for the formation of secondary arms on the primary AIN plates. As the supply of nitrogen continued from the surface, the AIN Widmanstätten side plates formed the secondary arms growing on the leeward side of the primary AIN plates.