Solidification precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys

Abstract

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys.