High temperature oxidation study of direct laser deposited AlXCoCrFeNi (X=0.3,0.7) high entropy alloys

Abstract

High entropy alloys (HEAs) are being explored as prospective substitutes for high temperature structural components. These HEAs are typically fabricated using conventional techniques like arc melting, mechanical alloying etc., but these routes exhibit a wide range of limitations. Direct laser deposition (DLD) process (an additive manufacturing technique) generates complex products from metal powder by selectively melting alloy powder in successive layers. The present study shows the development of HEAs namely Al0.3CoCrFeNi, Al0.7CoCrFeNi possessing crystal structures face-centered cubic (FCC) and FCC plus body-centered cubic (BCC) respectively using direct laser deposition (DLD) technique. HEA plates of the above-mentioned alloys were fabricated using DLD technique. In the present work, microstructures, mechanical (mainly hardness) and cyclic oxidation behaviors at 1100 ̊Cof developed HEAs have been investigated. Microstructural studies revealed FCC and FCC + BCC structures respectively, for Al0.3CoCrFeNi and Al0.7CoCrFeNi alloys with corresponding hardness of 170HV and 380HV. Cyclic oxidation studies were performed on the HEAs at a temperature of 1100 ̊°C for 200 h. Both the HEAs displayed quasi parabolic oxide growth after an initial sharp growth slope. Over the studied oxidation period, the mass gain for HEA Al0.3CoCrFeNi was greater than for Al0.7CoCrFeNi. Each oxidized HEAs forms an external Cr2O3 scale with Al2O3 subscale formed beneath, but the thickness and continuity of oxide layers vary according to Al content. Increased Al content enhanced the oxidation resistance of the HEA.