Microstructure evolution of a multi-track AlCoCrFeNi high entropy alloy coating fabricated by laser cladding

In order to understand the microstructure evolution characteristics of AlCoCrFeNi high entropy alloy (HEA) coating at high environmental temperatures, a laser cladded AlCoCrFeNi HEA coating is heated to 700 °C, 900 °C and 1100 °C respectively, holding for 30 min and cooled in air. Microstructure and micro-hardness of the treated coatings are investigated, in both interface and coating areas. In interface area, FCC blocks exist on the boundary of interface and coating in untreated specimen, besides the BCC single phase in coating. The primary FCC blocks remain in 700 °C treated coating, while they disappear in 900 °C and 1100 °C treated coatings. However, new FCC particles are formed instead near interface. In coating area, BCC single phase is acquired in untreated and 700 °C treated coatings. In 900 °C and 1100 °C treated coatings, lots of FCC and σ (Cr-rich carbide) particles are distributed mainly on grain boundaries of BCC phase matrix and spinodal decomposition occurs to BCC phase. Micro-hardness of 700 °C treated coating is slightly higher than that of untreated coating due to the age hardening effect, while the micro-hardness of 900 °C and 1100 °C treated coatings are much lower than that in untreated and 700 °C treated coatings due to the formation of soft FCC phase. Micro-hardness of 1100 °C treated coating is slightly lower than that of 900 °C treated coating due to the coarsening of σ particles and spinodal decomposed structures.