Microstructure, mechanical properties, and corrosion resistance of L21 phase-strengthened laser cladding CrFeNiTixAl1-x high-entropy alloy coatings

Abstract

In this study, CrFeNiTi_xAl_1-x (x=0.3, 0.7 in mole ratio) high-entropy alloy coatings (referred to as Ti_0.3Al_0.7, Ti_0.7Al_0.3 alloy coating, respectively) were prepared on AlSI1045 steel using the laser cladding (LC) method by adjusting the Al and Ti element contents. The phase constitutions, microstructures, mechanical properties, and corrosion resistance of the prepared coatings were comprehensively investigated and compared. Both Ti_0.3Al_0.7 and Ti_0.7Al_0.3 coatings exhibited rich Fe-Cr disordered BCC phase (A2) and NiAl ordered BCC phase (B2). The L2₁ phase in the Ti_0.7Al_0.3 coating accounted for as much as 47.7% when the Ti content was 0.7. The elevated Ti content significantly refined the internal structure of the coating, reducing the average grain size from 7.495 μm to 2.281 μm. With the combined effect of grain refinement and obstruction of dislocation motion by large angle grain boundaries, the microhardness of the Ti_0.7Al_0.3 alloy coatings increased from 685.12 HV_0.2 to 867.20 HV_0.2 compared to Ti_0.3Al_0.7. The precipitation strengthening effect of the noncoherent hard L2₁ phase, along with the protective role of the TiO₂ oxide film, resulted in the lowest friction coefficient of 0.171 for Ti_0.7Al_0.3. Ti_0.7Al_0.3 exhibits the dominant wear mechanisms of abrasive and oxidative wear. Meanwhile, these coatings also exhibited excellent resistance to Cl^- corrosion, with corrosion potentials shifted to -0.52 V and -0.46 V for Ti_0.3Al_0.7 and Ti_0.7Al_0.3, and corrosion current densities decreased to 1.26 ×10^-6 A/cm² and 4.35 ×10^-7 A/cm², respectively. These findings suggest that the replacement of equimolar Al with equimolar Ti in the CrFeNiTiAl high-entropy alloy compositions is a meaningful phenomenon that offers new perspectives for the design of novel high-performance HEAs.