A Comparative Study on the Surface Degradation Mechanisms of Arc Melted and Laser Remelted CoCrFeNiAl0.5Nb0.5 HEA

Abstract

In the current study, a CoCrFeNiAl0.5Nb0.5 high entropy alloy was manufactured via arc melting and exposed to laser surface remelting. The presence of Nb and Al was limited to the formation of single simple cubic phase formations. Both alloys are composed of four phases. Laser remelting did not change current phases, but it affected the microstructure. Hardness increased from 475 HV to 785 HV thanks to the change in phase ratios and grain refinement resulting from laser remelting. Wear resistance improved due to the increase in hardness, and volume losses decreased by 28 %. In short-term high-temperature oxidation, laser remelting enabled better oxidation resistance in alloy since it provided more paths for the diffusion of aluminum, which forms an alumina oxide scale. Interestingly, such a trend was not observed in the increased oxidation period. In the final oxidation stage, the depletion of B2 phases and the formation of inner oxides significantly worsened the oxidation resis-tance of LR alloy. Although Icorr, which expresses the corrosion resistance of the laser-melted alloy, was higher than before the laser-remelting process, the changes in the alloy's microstructure with rapid cooling caused a decrease in the passivation resistance of laser-remelted CoCrFeNiAl0.5Nb0.5 HEA.