Ji Chen

To investigate the influence mechanisms of Ti addition on inclusions in FeCrAl alloys, a series of experiments and thermodynamic calculations are carried out by controlling Ti additions. In FeCrAl alloys without Ti, inclusions are mainly AlN, and a tiny amount of Al ₂ O ₃ is surrounded by AlN inclusions. In the sample containing 0.025 wt%Ti, AlN inclusions occupy a dominant position, and no TiN inclusions are detected; as the Ti content increases to 0.127 wt%, AlN inclusions are the main component and begin to transform into TiN, with single‐phase TiN and TiN‐AlN complex inclusions appearing; when the Ti content reaches 0.277 wt%, AlN inclusions completely disappear, while inclusions are mainly single‐phase TiN and Al ₂ O ₃ ‐TiN complex inclusions. The number density of AlN inclusions decreases with Ti addition, indicating that the addition of Ti inhibits the formation of AlN inclusions. Based on the Clyne‐Kurz model, a coupling model is established to calculate the precipitation behavior of AlN and TiN inclusions in FeCrAl alloys during solidification. The results show that the precipitation of AlN is completely inhibited when the Ti content reaches the critical threshold of 0.176 wt%. The experimental results are consistent with the calculation results of FactSage 8.0 and the coupling model.

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.

To investigate the effect of yttrium (Y) addition on nonmetallic inclusions in FeCrAl alloys, a series of laboratory experiments and thermodynamic calculations are carried out as a function of reaction time and Y addition amount. Without Y addition, the main inclusion in FeCrAl alloys is AlN, and only a small amount of Al₂O₃ inclusions is evident. The higher content of Cr in FeCrAl alloy promotes the formation of Al₂O₃. Y addition can effectively modify Al₂O₃ inclusions to YAlO₃ or YS inclusions. With the addition of 0.0046 wt% Y, the evolution route of inclusions in FeCrAl alloys with reaction time is Al₂O₃ → YAlO₃‐Al₂O₃ → YAlO₃. The variation in Al₂O₃ inclusions with increasing Y content is Al₂O₃ →YAlO₃ → YS. The experimental results are consistent well with the thermodynamic calculation results.