Evolution of microstructure, mechanical and corrosion properties of AlCoCrFeNi high-entropy alloy prepared by direct laser fabrication

Abstract

High entropy alloy (HEA) is an emerging class of engineering materials that shows promising potential for high temperature applications. These multi-component alloys are mostly fabricated by arc melting. In this study, direct laser fabrication (DLF) is utilized to prepare AlCoCrFeNi high entropy alloy at optimized operation parameters. The phase, microstructure, mechanical and corrosion properties of as-deposited alloy as well as samples aged at temperatures of 600 °C, 800 °C, 1000 °C and 1200 °C for 168 h have been investigated. The results show that high cooling rate during deposition inhibits the formation of FCC phase, leading to a nearly single B2 solid solution structure for as-deposited sample. After ageing at 800 °C, 1000 °C and 1200 °C, the microstructures exhibit intergranular needle-like and plate-like FCC phase precipitates and wall shaped FCC phase precipitates along grain boundaries. As the FCC phase is softer than B2 phase, the formation of the FCC phase during ageing results in reduced compressive yield strength accompanied with enhanced ductility. The potential difference between Fe-Cr rich FCC phase and Al-Ni rich B2 matrix means the alloy is susceptible to galvanic corrosion, with the B2 matrix corroding preferentially.