Electron-ion-plasma boriding of a multilayer nanostructural high-entropy alloy

The structure and properties of a high-entropy alloy (HEA) subjected to saturation with boron atoms by a combined electron-ion-plasma method are characterized. On a HEA film of 5 μm thickness deposited on AISI 304 steel, a film (boron + chromium) with a thickness of 1 μm was deposited and then the system “(Cr + B) film / (HEA film deposited on AISI 304 steel) substrate” was irradiated with a pulsed electron beam. It is shown that the wear resistance of the resulting alloy is more than 30 times higher than that of the original HEA film. The microhardness of the alloy is 10.5 % higher than that of HEA in the initial state. It has been revealed that irradiation of the system with a pulsed electron beam leads to the formation of a multi-element surface alloy of composition (at.%) 5.8Al-11.6Ti-12.9Cr-13.0Fe-2.4Ni-13.1Cu-10.4Zr-8.8Nb, the rest (22 at.%) is oxygen and boron. Thus, seven-element HEA of non-stoichiometric composition, the concentration of metal elements of which varies within (5.8 –13.0) at.%, and additionally containing atoms of nickel, oxygen and boron was formed. It has been established that the high tribological and strength properties of the surface alloy are due to the formation of a multiphase submicron-nanocrystalline structure of high-speed cellular crystallization in the modified layer 6 µm thick. High-speed crystallization is accompanied by alloy delamination with the formation of extended interlayers enriched with copper atoms located along the boundaries of crystallization cells.