Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNbx Medium-entropy Alloy Coatings

MA Minghao; MA Xinghua; WANG Yongzhe; MU Yongkun; YIN Zihao; LI Haozhen; MA Xingyi; GAO Bo; ZHANG Shuling; GUO Feng

doi:10.16490/j.cnki.issn.1001-3660.2026.08.008

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Surface Technology ›› 2026, Vol. 55 ›› Issue (8) : 95-108. DOI: 10.16490/j.cnki.issn.1001-3660.2026.08.008

Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNb_x Medium-entropy Alloy Coatings

MA Minghao¹, MA Xinghua^1,*, WANG Yongzhe², MU Yongkun³, YIN Zihao¹, LI Haozhen⁴, MA Xingyi⁴, GAO Bo¹, ZHANG Shuling¹, GUO Feng¹

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Abstract

Cavitation erosion and wear failure critically limit the service life of flow-passing components such as pump impellers, turbine blades, and propeller systems which are frequently subjected to high-speed liquid impact and cyclic flow-induced stresses. To address this challenge, the work aims to design a high-performance surface coating with enhanced hardness, wear resistance, and cavitation erosion resistance by tailoring the Nb content in a CoCrNi medium-entropy alloy (MEA) system. CoCrNiNb_x (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) coatings were fabricated on 316L stainless-steel substrates with an FL020 fiber laser under identical processing parameters. The effect of Nb addition on the phase constitution, microstructure, mechanical properties, tribological behavior, and cavitation performance of the coatings was comprehensively investigated to determine the optimal composition for balanced mechanical and anti-erosion properties. Phase analysis by X-ray diffraction (XRD) showed that increasing Nb content promoted a transition from a single face-centered cubic (FCC) solid solution to a dual FCC + hexagonal close-packed (HCP) phase structure. The emergence and growth of the Nb-rich HCP phase were accompanied by pronounced lattice distortion and precipitation strengthening. Microstructural characterization using field-emission scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) revealed that Nb preferentially segregated along interdendritic regions, where fine HCP-phase precipitates gradually formed a semi-continuous strengthening network. Electron backscatter diffraction (EBSD) analysis further confirmed that Nb addition significantly refined the grain structure and altered the phase distribution, providing quantitative evidence for the heterogeneous dual-phase microstructure. Mechanical tests demonstrated that the coatings exhibited a non-monotonic hardness evolution with the increasing Nb content. The average Vickers microhardness firstly increased and then decreased, reaching a maximum of 689HV0.1 at x = 0.6, approximately 3.7 times that of the 316L substrate. This improvement was attributed to the combined effects of solid-solution strengthening induced by Nb addition and precipitation hardening associated with Nb-rich HCP phases. However, excessive Nb addition (e.g., x = 1.2) resulted in brittle phase aggregation and a slight reduction in hardness. Nanoindentation measurements were further conducted to evaluate the localized mechanical response of the coatings, revealing that Nb-containing coatings, particularly Nb_1.0 exhibited a favorable combination of hardness and elastic compliance, indicative of enhanced energy absorption capability under concentrated loading. Tribological experiments using a reciprocating wear tester against Si₃N₄ balls in deionized water showed that the specific wear rate decreased initially and then increased slightly with the increasing Nb content. The Nb_0.6 coating achieved the lowest wear rate (8.665 × 10^-5 mm³·(N·m)^-1), which was consistent with its high hardness and refined microstructure. In contrast, cavitation erosion tests performed for 12 h revealed that the Nb_1.0 coating exhibited the best cavitation resistance, with a cumulative mass loss of only 2.8 mg and an average erosion rate of 0.233 3 mg/h representing an improvement of approximately 26 times over the 316L substrate and 20 times over the Nb₀ coating. Surface morphology analyses confirmed that appropriate Nb incorporation effectively suppressed cavitation pit formation, mitigated fatigue crack initiation, and prevented large-area material spalling. The enhanced cavitation erosion resistance was attributed to the synergistic effects of solid-solution strengthening, refined dual-phase microstructure, and the semi-continuous distribution of Nb-rich HCP phases, which facilitated load redistribution and impact energy dissipation under high-frequency cavitation loading. Moderate Nb addition (x = 0.6-1.0) enabled an effective balance between strength and toughness, whereas excessive Nb content led to phase continuity and localized stress concentration, resulting in increased brittleness and degradation of erosion resistance. In summary, Nb alloying effectively enhances the microstructural stability and mechanical integrity of CoCrNi MEA laser-cladded coatings. An Nb content of x = 1.0 provides the optimal overall performance by combining high hardness, good wear resistance, and superior cavitation erosion resistance. These findings confirm the feasibility of Nb-alloying strategies for developing high-durability MEA laser-cladded coatings and provide valuable guidance for the design of long-life protective layers in flow-bearing and high-impact engineering components.

Key words

laser cladding / CoCrNi medium-entropy alloy / Nb alloying / HCP phase / coating / hardness and wear resistance / cavitation erosion

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MA Minghao, MA Xinghua, WANG Yongzhe, MU Yongkun, YIN Zihao, LI Haozhen, MA Xingyi, GAO Bo, ZHANG Shuling, GUO Feng. Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNb_x Medium-entropy Alloy Coatings[J]. Surface Technology. 2026, 55(8): 95-108

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