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To strengthen face-centered cubic structured high entropy alloys, this paper explores a new method of ceramic reinforced CoCrFeNiMo 0.2 high entropy alloy composite gradient coating. In this study, four sets of gradients were created by first preparing a pristine alloy coating without silicon carbide content on the substrate, followed by preparing composite coatings with varying silicon carbide mass fractions (8 %, 16 %, 24 %) on the pristine coatings. The coatings were then analyzed for their phase composition, microstructure, microstructure evolution process, and friction wear properties. The study reveals that the microstructure of the initial alloy coating consists of a single-phase face-centered cubic solid solution. It is observed that intragranular segregation occurs in the coating, resulting in the boundary enrichment of Mo and Cr elements. As the silicon carbide addition increases, the segregation behavior becomes more pronounced, and the generation of body-centered cubic phase is observed. The second, third, and fourth layers exhibit significantly higher average hardness, measuring at 594 HV, 722 HV, and 788 HV respectively. This can be attributed to the presence of body-centered cubic structure, carbide, and grain boundary strengthening effects. On average, the hardness of these layers is three to four times higher than that of the first layer. With an increase in the number of layers, the wear mechanism changes from adhesive wear to abrasive wear. The wear rates of the second, third, and fourth layers were all reduced by at least 87 % compared to the first layer. However, there were different forms of abrasive wear observed between these layers. The findings of this study have significant engineering implications. • The microstructural evolution of columnar grains to equiaxed dendrites was studied. • The high-density of dislocations enhances the diffusion of Mo and Cr elements. • The tissue shows phase separation act containing the BCC structure. • The shift behavior of the wear mechanism of the gradient structure was studied. [ABSTRACT FROM AUTHOR]

Solid-solution agglomerated ZrO 2 -based powders co-doped with Gd 2 O 3 , Yb 2 O 3 and Y 2 O 3 rare earth oxides were synthesized by solid-phase sintering and spray drying. The corresponding GYYZO coating was prepared by using atmospheric plasma spraying, while the 8YSZ coating was also prepared as a control group for the high temperature performance investigation. The high temperature structure and phase stability as well as the sintering resistance of both coatings were investigated by SEM, XRD, DSC, EPMA and TEM observations. The results showed that the 8YSZ coating began to undergo a phase transition of tetragonal (t) phase to monoclinic (m) after 50 h heat treatment at 1400 °C, while the GYYZO coating remained free of phase transition even heat-treated for up to 200 h, demonstrating a better phase stability. In addition, as an indicator of sintering resistance of the coating, the porosity of the 8YSZ coating decreased up to 90.1 % after 200 h heat treatment, while that of the GYYZO coating decreased only 20.6 %. The superior high temperature performance of GYYZO coating can be explained by the pinning effect of nano-pores on grain boundaries. The formation of nano-pores was associated with the evolution of defect clusters in the coating, which were facilitated by the substitution defects and oxygen vacancies created by the Gd Yb co-doping. During the heating process, these clusters migrated along with the grain boundaries and formed pearl-string-like nano-pores at the grain boundaries. The eventual formation of nanopores not only further inhibits grain boundary migration to reduce sintering, but also prevents the segregation of Y elements to hinder t-phase to m-phase transition. • GYYZO coating has excellent phase stability and sintering resistance at high temperature. • The nanopores of GYYZO coating have pinning effect on grain boundaries. • The pinning effect of nanopores can inhibit grain boundaries migration and Y elements segregation. [ABSTRACT FROM AUTHOR]