Effect of TiC precipitates on the kinetics of static recrystallisation has been studied by using a Fe-26Al-5Cr (at%) single-phase (α:A2/B2/D03) alloy and two-phase (α+TiC) alloys with different amounts of TiC precipitates. Based on the results, a desirable thermo-mechanical processing is proposed for the development of wrought Fe3Al-based alloys with strengthening MG carbides.
In the alloys with a high amount of TiC, needle-like TiC precipitates with 1–10 µm in length formed during air-cooling after homogenisation. Hot deformations with such large precipitates cause inhomogeneous deformation around the particles, leading to particle stimulated nucleation (PSN) and hence accelerate recrystallisation.
The occurrence of PSN is harmful for the embrittlement problem, i.e. ductility drastically decreases when recrystallisation occurs, but useful for grain refinement. The following process is proposed to accomplish grain refinement, strengthening by precipitates and avoidance of the embrittlement: hot deformation with a large amount of precipitates to make grain refinement possible by using PSN, followed by hot deformation with a small amount of precipitates near α single-phase region and a subsequent heat treatment to obtain fine precipitates. The fine particles would also act to pin the boundaries of growing grains, thus leading to extended recovery rather than recrystallisation. This process is difficult to carry out in the (Fe-26Al-5Cr)-TiC system because the temperature necessary to enable precipitation is very high and the kinetics is quick. The precipitation temperature is significantly decreased by replacing TiC by VC or MoC.
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Kobayashi, S., Zaefferer, S. & Schneider, A. Optimisation of Precipitation for the Development of Improved Wrought Fe3Al-based Alloys. MRS Online Proceedings Library 842, 263–268 (2004). https://doi.org/10.1557/PROC-842-S5.19