Enhancing high-temperature stability of Fe–12Cr–6Al–1Ti–0.25Y2O3 via in-situ nitride and oxide synthesis in laser powder bed fusion

In this study, the effects of high-temperature thermal exposure at 1200 °C for 1 h and 10 h on the microstructure and mechanical properties of Fe–12Cr–6Al–1Ti–0.25Y2O3 alloys fabricated by Laser Powder Bed Fusion (L-PBF) were investigated, with particular focus on the evolution of various in situ synthesized nitride and oxide precipitates. The average grain size of the Fe–12Cr–6Al–1Ti–0.25Y2O3 alloy was 9 µm, which increased to 13 µm after 1 h of thermal exposure and further to 16 µm after 10 h. With increasing thermal exposure duration, the alloys underwent recrystallization and grain growth. Despite this growth, the grain sizes remained significantly smaller than that of the Fe–12Cr–6Al alloy, which exhibited an average grain size of 71 µm. After 1 h of thermal exposure test, TiN precipitates remained present, accompanied by the formation of Al2O3 and Y2O3 precipitates. Following 10 h of thermal exposure, the formation of complex precipitates, such as Al–Y–O and Y–O–N, was observed alongside the stable TiN precipitates, while other oxides disappeared. Furthermore, progressive coarsening of these precipitates was observed with the extended thermal exposure test. After 1 h of thermal exposure, the yield strength (YS) and ultimate tensile strength (UTS) decreased, while elongation improved. Following 10 h of thermal exposure test, the mechanical properties continued to degrade; however, they remained superior to those of the base Fe–12Cr–6Al alloy.