Al_xCrFeCoNi High-Entropy Alloys: Surface Modification by Electron Beam Bead-on-Plate Melting

Two five-component Al_xCrFeCoNi high-entropy alloys, x-0.6 and 0.8, were prepared by vacuum arc-melting. Electron beam surface re-melting was employed to modify the surface properties of the two high-entropy alloys. The effects of electron beam surface re-melting on the structure and mechanical properties of the alloys were investigated using scanning electron microscopy and the Vickers hardness test. Regions of Al_0.6CrFeCoNi (P3 alloy) subjected to multi-pass electron beam surface re-melting showed an average value of 374 HV, an increase of 28% when compared to base metal values, while Al_0.8CrFeCoNi (P2 alloy) welds exhibited a much higher increase to 530 HV, corresponding to a 34% increase relative to the values obtained with the base metals. In the P2 alloy subjected to multi-pass surface re-melting, significant temper softening caused by overlapping tracks was detected, in contrast to the hardening of the surface induced by a single-pass. It is noteworthy that the significant increase in hardness realized in the P2 multi-pass fusion zones resulted in a microstructure with a high tendency to crack. The increased hardness of that region subjected to electron beam surface re-melting for both alloys is likely associated with a superposition of several factors related to the high cooling rates of solidification in the electron beam re-melted areas.