低合金钢上激光熔覆 AlCoCrFeNi2.1 基高熵合金涂层在 650 °C 长期时效过程中的界面微观结构转变与力学性能演变

The evolution of metallurgically bonded interfaces has a major influence on the long-term reliability of laser-cladded high-entropy alloy coatings on low-alloy steels. Here, AlCoCrFeNi 2.1 and Mo 7 (AlCoCrFeNi 2.1 ) 93 coatings on 15CrMo steel were aged at 650 °C for up to 1000 h. Carbon migration from the substrate produced a 142–167 μm carbide-rich zone and drove a common phase-transformation sequence. Carbide precipitation depleted Cr and Fe from the adjacent matrix and additionally consumed Mo in the Mo-containing coating. The resulting compositional changes shifted the local phase stability from FCC toward BCC. Mo modified the extent of this transformation by altering the carbide type and distribution. Compared with the coarse M 7 C 3 carbides in AlCoCrFeNi 2.1 , the M 23 C 6 carbides in the Mo 7 (AlCoCrFeNi 2.1 ) 93 coating incorporated more metallic elements from the adjacent matrix per unit carbon because of their higher metal-to-carbon ratio. Their finer and more dispersed distribution further extended the compositionally modified matrix region, producing a broader and more continuous BCC-dominated zone. This transformation raised the interface-side microhardness maxima to approximately 510 and 540 HV 0.2 , respectively. Meanwhile, substrate decarburization, grain coarsening, and softening reduced the nominal shear strengths by 36% and 32%, respectively, and all specimens fractured within the 15CrMo substrate. These findings provide a mechanistic basis for tailoring interfacial phase evolution and improving the long-term reliability of laser-cladded HEA coatings.