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 degrees C, 900 degrees C and 1100 degrees 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 degrees C treated coating, while they disappear in 900 degrees C and 1100 degrees C treated coatings. However, new FCC particles are formed instead near interface. In coating area, BCC single phase is acquired in untreated and 700 degrees C treated coatings. In 900 degrees C and 1100 degrees C treated coatings, lots of FCC and sigma (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 degrees C treated coating is slightly higher than that of untreated coating due to the age hardening effect, while the micro-hardness of 900 degrees C and 1100 degrees C treated coatings are much lower than that in untreated and 700 degrees C treated coatings due to the formation of soft FCC phase. Micro-hardness of 1100 degrees C treated coating is slightly lower than that of 900 degrees C treated coating due to the coarsening of sigma particles and spinodal decomposed structures.