Effect of the boriding environment on the wear response of laser-clad AlCoCrFeNi high entropy alloy coatings

Abstract

Laser-clad AlCrFeCoNi high entropy alloy (HEA) coatings, produced on the surface of AISI 316 L stainless steel, were pack-borided at 1000 ?C for 4 h in open air, high-purity Ar and vacuum environments. The HEA, which had an initial hardness of 6.14 +/- 2.06 GPa, formed a complex boride layer consisting of (CoFe)B-2, (CrFe)B(2 )and Cr(2)Ni(3)B(6 )phases on its surface, with hardness ranging from 15.95 +/- 0.7 to 20.15 +/- 4.50 GPa as a result of the boriding process. While the greatest boride layer thickness was obtained in the sample borided in vacuum, the highest surface hardness was obtained in the sample borided in air. The borided coatings showed improved wear resistance and lower friction values compared to the untreated control samples, both at 25 ?C and 650 ?C. The borided coatings also showed reduced coefficients of friction at 650 ?C. The wear losses at 650 ?C significantly exceeded those at 25 ?C.