Effect of cobalt addition on Fe-20Cr-5Al-1Y₂O₃ ODS alloy fabricated by arc plasma sintering (APS) process

In this research, microstructure, phases and hardness of Fe-Cr-Al based Oxide Dispersion Strengthened (ODS) alloy with addition of cobalt (Co) produced using arc plasma sintering (APS) method were investigated. ODS alloy has an important role particularly in high temperature applications, since it has the ability to maintain their strength at high service temperature. On the other hand Co is well known to increase creep resistance of many alloys, which could in turn increases their lifetime in high temperature environment. To produce ODS alloy, usually high cost and long processing time are required. To overcome these problems, a new sintering method based on arc plasma was used in this study, which has been successfully applied in previous works. The alloys composed of Fe-20Cr-5Al-1Y₂O₃ with addition of 0.5, 1, 1.5 and 2 wt% cobalt were first prepared by mechanical alloying (MA) comprising high-energy milling for 8 hours and subsequent isostatic pressing at 20 ton-force/in² prior to sintering by APS method up to 28 minutes. The sintered samples then characterized by means of Scanning Electron Microscopy (SEM) equipped with an Energy Dispersive X-Ray Spectrometer (EDX) to observe the microstructure, the X-Ray Diffraction Technique (XRD) to investigate the formed phases, and Vickers microhardness test to examine hardness value of the alloys. The results show that APS method is technically and economically feasible for fabricating ODS alloys since this process significantly reduces time and energy required. Variation of cobalt in the alloy obviously does not cause observable microstructure difference. However, the alloy with 0.5 wt% cobalt exhibited single FeCrAl matrix phase, while at higher cobalt concentration additional AlCo phases were found in the FeCrAl matrix, which can be assumed to improve the high temperature usage of the alloy. Cobalt addition also increased hardness value of these alloys.