Addition Al and/or Ti Induced Modifications of Microstructures, Mechanical Properties, and Corrosion Properties in CoCrFeNi High-Entropy Alloy Coatings

The purpose of this work is to study the influences of Al and/or Ti addition on the microstructures, mechanical properties and corrosion properties of CoCrFeNi-(Al, Ti) high entropy alloy (HEA) coatings. Three coatings, AlCoCrFeNi (I), CoCrFeNiTi0.5 (II) and AlCoCrFeNiTi0.5 (III), were fabricated by laser cladding successfully. The AlCoCrFeNi (I) coating exhibited a simple body-centered cubic (BCC) solid-solution structure, whereas the CoCrFeNiTi0.5 (II) alloy exhibited a face-centered cubic (FCC) solid-solution and a small amount of Laves phase. The BCC phases in AlCoCrFeNiTi0.5 (III) coating were characterized as Fe–Cr rich disordered BCC phases (A2) and Al-Ni–Ti-rich ordered BCC phases (L21) separately. The AlCoCrFeNiTi0.5 (III) coating with dual-phase BCC structure showed the optimal performance of both mechanical and corrosion properties, which was superior to BCC-based AlCoCrFeNi (I) and FCC-based CoCrFeNiTi0.5 (II) coatings. Nanoindentation tests and quantitative investigations on the strengthening mechanisms of AlCoCrFeNiTi0.5 (III) coating were conducted, suggesting that the precipitation strengthening is the dominant strengthening mechanism. In short, the addition of moderate amount of Al and Ti in CoCrFeNi HEA shows potential for the development of a high strength and corrosion-resistant coating.