Effects of Boron and Zirconium on the Microstructure and High-Temperature Strength of Cast Fe3Al-Based Alloys

In this study, the effects of boron (B) and zirconium (Zr) on the microstructure and high-temperature strength of Fe3Al-based alloys were investigated. Alloying was performed in a vacuum induction melting furnace (VIM) and, consequently, the melt then was poured into a cast iron mold. Microstructural investigation was conducted using optical and electron microscopy, X-ray diffraction, and differential thermal analysis. Addition of B and Zr to the alloys resulted in the formation of boride precipitates and Laves phases. Dendritic microstructures were found in as-cast alloys because of segregation of alloying elements into the interdendritic regions. To evaluate the high-temperature mechanical properties of the alloys, hot pressure test was performed. The results showed that, Zr exhibited the most pronounced effect on the high-temperature strength because of the formation of Laves phases. Boride phases tend to coarsen when increasing the temperature to 650°C, and they have no effect on the high-temperature strength of the alloy. In the temperature range of 450°C–550°C, an anomaly in the temperature-dependence of the yield strength was observed.