Cracking mechanism of brittle FeCoNiCrAl HEA coating using extreme high-speed laser cladding

Abstract

FeCoNiCrAl high entropy alloys (HEAs) are regarded as promising coating materials for traditional steel. However, the brittle nature always contributes to the cracking of the equiatomic FeCoNiCrAl HEA coating. In this work, FeCoNiCrAl coatings on C45 carbon steel and 304 stainless steel (304SS) pipes were fabricated using extreme high-speed laser cladding (EHLA) with a cladding speed of 50 m/min. The results showed the high-hardness character of the two coatings on C45 and 304SS substrates. The C45 substrate showed a remarkable effect on the cracking of the coating. The martensitic transformation of the heat-affected zone (HAZ) of the C45 substrate was considered the main factor contributing to cracking of the coating. The finite element method showed that the martensite transformation of C45 expanded the volume and increased the hardness of the HAZ. This restricted the plastic deformation of the substrate and increased the tensile stress and cracking tendency of the coating. As a martensitic transformation did not occur in 304SS, the low-hardness substrate effectively relieved the tensile stress in the coating and avoided cracking. • The MT of HAZ of C45 contributed the cracking of EHLA HEA coating • MT increased the volume and hardness of HAZ of C45 substrate. • Volume expansion and hardening of HAZ restricted the interfacial plastic deformation. • High interfacial stress of coating resulted in the crack initiation.