Nickel-based superalloy blades cause cracks, thermal fatigue, and wear problems during service, whereas their effective repair can extend the life cycle of an engine. Currently, studies pertaining to the laser deposition of CoCrW and T800 alloy claddings on superalloys are limited, and the development of wear-resistant coatings for DZ125 alloys is necessitated. In this study, CoCrW and T800 alloys were used for laser-deposition repair on DZ125 directionally solidified substrate to provide a basis for the laser-deposition repair of service defects in nickel-based superalloy blades.

An aqueous ethanol ultrasonic cleaning machine was used to clean a DZ125 nickel-based high-temperature plate at low power for 15 min. After drying, the substrate was polished with sandpapers. The roughness of the plate surface after rough grinding reduces the reflection of the sample on the laser during the cladding process. CoCrW and T800 alloy coatings were prepared on a DZ125 alloy matrix, and the system platform was protected by a six-axis industrial robot, a fiber laser, a wire feeder, and an inert gas. The optimized laser cladding parameters are as follows: laser power levels, 100?1200 W and 800?1000 W; defocusing quantity, +2?+5 mm; protective gas flow rate, 15?20 L/min; and wire feed speed, 0.1?0.2 m/min. The microstructures of the CoCrW and T800 coatings were analyzed via scanning electron microscope (SEM). The distributions of grains, intercrystalline carbides, and intermetallic compounds in the CoCrW and T800 coatings were analyzed using energy-dispersive spectrometry (EDS). A vertical universal-friction machine and a wear-testing machine were used to determine the microhardness distribution in the deposition direction of the coating layer. GCr15 steel ball was selected as the friction pair material, a 4.7 N load was applied, and a friction track with a radius of 3 mm was adopted. Wear resistance was tested at room temperature for 20 min at a rotation speed of 200 r/min.

CoCrW and T800 cladding layers were successfully prepared on the surface of DZ125 alloy using laser cladding technology. The microstructures of the CoCrW and T800 cladding layers are similar; the interface zone is the fusion zone between the wire and base material, the near-interface zone is the columnar crystal zone, and the surface zone is the equiaxial crystal zone (Fig. 3). As the distance to the surface of the cladding layer decreases, the columnar and equiaxed crystals become refined gradually (Figs. 4 and 5). The CoCrW cladding layer contains γ-Co and enhanced phases of Cr₇C₃ and MC carbides (Fig. 7 and Table 3). Additionally, the layer contains numerous Co and Cr elements, among which Ni, Co, W, Cr, and C are enriched and distributed in the solid solution state (Fig. 8). In the T800 cladding layer, MC and Cr₇C₃ carbide strengthening phases are generated, whereas γ-Co solid solution and Ni-Cr-Co-Mo solid solution exist (Fig. 10 and Table 4). The strengthening phase in the CoCrW cladding layer is evenly distributed, whereas the strengthening phase in the T800 cladding layer is more dispersed; among them, the strengthening phase in the CoCrW cladding layer is smaller and more abundant (Figs. 6 and 9).

Under the optimized parameters, CoCrW and T800 wires can be uniformly coated on DZ125 alloy, thus providing a foundation for the subsequent laser-deposition repair of nickel-based superalloy blades. The microstructures of the CoCrW and T800 cladding layers are epitaxial columnar and chaotic equiaxed crystals, respectively, and the columnar and equiaxed crystals refine gradually as the distance to the surface of the cladding layer decreases. The CoCrW cladding layer is evenly distributed with γ-Co, Cr₂₃C₆, and MC, which are smaller and more abundant. The strengthening phases in the T800 cladding layer are relatively dispersed and primarily comprises petal-like Cr₇C₃ and MC phases. The CoCrW cladding layer is strengthened to a greater extent than the T800 cladding layer, and the strengthening phase is smaller and more evenly distributed. The hardness of the CoCrW cladding layer is 50 HV higher than that of the T800 cladding layer, the near-interface hardness is 450?600 HV, and the surface-area hardness is 600?650 HV. The hardness of the equiaxed crystals in the cladding layer is higher than that of the columnar crystals, all of which are higher than that of the substrate. The average friction coefficients of the CoCrW and T800 cladding layers are 0.6903 and 0.7282, respectively, and the wear resistance of the CoCrW cladding layer is 5.2% higher than that of the T800 cladding layer. As the average hardness increases, the wear loss of the cladding layer decreases and the wear resistance of the CoCrW cladding layer improves.