EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The influence of grain and coherent precipitates sizes on the ductile-brittle transition temperature (BDTT) are studied in the Fe$_{78}$Al$_{10}$V$_{12}$ (A2 + L2$_1$) alloy. The alloy was produced by induction casting and followed by thermomechanical processes to obtain different precipitate and grain sizes. Further, considering the composition of the matrix phase, a single-phase (Fe$_8$Al$_8$V$_8$) alloy was also produced to analyse in isolation the BDTT of the A2 solid solution. Tensile tests were carried out at different temperatures and strain rates to assess the variation of the yield stress with temperature. The BDTT in the single-phase alloy and in the two-phase alloy with two grain sizes (d) and three precipitate radii (r) was measured by hot impact Charpy tests. The results show that grain refinement reduced the BDTT at the peak hardening condition (t = 0.37 h) from 509 °C (d = 75 µm) to 485 °C (d = 38 µm). Furthermore, increasing the aging time (at 700 °C) in the latter case reduces sharply the BDTT to 409 °C (t = 5 h) and 341 °C (t = 72 h), approaching the BDTT of 154 °C registered for the A2 single-phase alloy. In addition, the experimental data in combination with a physical-based model lead to novel results. For the first time, an inversely linear dependence between cleavage resistance and the size of coherent precipitates is evidenced. The present work provides new insights of microstructural variables affecting the BDTT of bcc-superalloys.