Effect of Laser Re-Melting on Electric Current Assistive Sintered CoCrFeNiAlxTiy High Entropy Alloys: Formation, Micro-Hardness and Wear Behaviors

Abstract

CoCrFeNiAlxTiy high entropy alloys were produced by electric current assistive sintering (ECAS) method and their surfaces were then subjected to laser re-melting. Microstructure, hardness, and wear behaviors were investigated using different parameters. While the CoCrFeNi alloy had FCC and oxide phases after ECAS treatment, only FCC phase was observed after laser re-melting. In addition to the FCC phase, also a BCC phase has been determined with the Al addition. FCC phases disappeared with the laser re-melting effect and the addition of Ti to the alloy. Mixing enthalpy values were found to be effective in microstructure and phase formation. Thanks to the rapid solidification provided by laser re-melting, the phases were distributed homogeneously and in much smaller particle size. Al and Ti elements have contributed positively to the hardness of the CoCrFeNi alloy. With additions of Al and Ti elements, a significant increase in the hardness of CoCrFeNi alloy was obtained. Significant increases in hardness values were observed after laser re-melting due to the smaller dispersion of the phases and the formation of hard phases (BCC/intermetallic). In the hardness values of all alloys, 1.5 times increase was observed by the effect of re-melting. The highest average hardness was determined as 859 Hv in laser re-melted CoCrFeNiAl0.5Ti0.5 alloy. The best wear resistance and the lowest friction coefficient was observed in the laser remelted CoCrFeNiAl0.5Ti0.5 alloy. Laser re-melted alloys exhibited lower volume losses compared to only ECAS-alloys.