Effect of Zr content on microstructure and hardness of ODS-FeCrAl alloys

Abstract

Oxide dispersion strengthened (ODS) Fe-12Cr-5Al-2 W-xZr (x = 0, 0.3, 0.6, 1.0 wt%) alloys were produced by mechanically alloying and spark plasma sintering. The size and distribution of grain, number density, size distribution and types of nanoscale oxides as well as hardness of the ODS alloys were analyzed by EBSD, TEM, HRTEM and an indentation experiment, respectively. The results showed that the grain size is not sensitive to Zr content, but the increase of Zr content is helpful for the homogenization of grain size. With the increase of Zr content from 0 to 0.6 wt%, the number density of oxides is increased from 1.66 × 1021 m−3 to 9.94 × 1022 m−3, while the mean size of oxides is decreased from 21.2 nm to 11.1 nm. The coarsening of oxides occurs when Zr is up to 1 wt%. In Zr-free alloy, nano-oxides are YAlO3 with perovskite structure (YAP) and α-Al2O3. In Zr-containing ODS alloys, the trigonal δ-phase Y4Zr3O12, YAP and α-Al2O3 are observed. An appendage oxide, Y4Zr3O12/YAP/α-Al2O3, is found in the alloy with 1.0 wt% Zr and the possible formation mechanism is briefly analyzed. The hardness of 6.03 GPa is achieved in the 0.6 wt% Zr alloy.