Key Takeaways & Executive Findings
- •• Low-energy laser shock peening (LE-LSP) significantly enhances the surface hardness of CrN coatings, with a maximum increase of 2.35 times at 150 mJ laser energy. • LE-LSP treatment disrupts the columnar crystal structure of CrN coatings, fragmenting grains into finer sizes, which contributes to improved mechanical properties. • The fretting wear resistance of CrN coatings is optimized at 150 mJ laser energy, achieving a 76.32% reduction in wear volume compared to untreated coatings. • The study introduces a novel post-treatment methodology for PVD coatings, providing theoretical support for PVD/LSP composite strengthening techniques.
Abstract
CrN coatings are also employed to protect structural materials in nuclear power plants. It should be noted that the preparation process utilizing physical vapor deposition (PVD) techniques inevitably entails certain defects. Such a phenomenon will affect the protective properties of CrN coatings. In this study, low-energy laser shock peening (LE-LSP) with varying energies was employed for the post-treatment of CrN coatings. The effects of different laser energy LE-LSP treatments on the surface morphology, crystal structure and fretting wear properties of CrN coatings were investigated. The results revealed that the surface of the CrN coatings subjected to LE-LSP underwent significant plastic deformation and displayed a regular texture structure. The surface roughness and Vickers hardness of the CrN coatings exhibit a significant increase. Under a laser energy of 150 mJ, the surface hardness exhibits a maximum increase of 2.35 times. The residual stress of CrN coatings diminishes with the augmentation of laser energy due to the formation of surface cracks. Following LE-LSP treatment, the columnar crystal structure of the CrN coating was disrupted and fragmented into fine grains due to the impact force. As the laser energy augments, the fragmented CrN grains undergo further compaction. During fretting wear, all specimens were in the gross slip regime. The wear mechanism of the CrN coating, 120 and 150 mJ specimens are primarily dominated by abrasive wear, and accompanied by oxidative wear. For specimens treated with 30, 60 and 90 mJ, the predominant wear mechanisms are mainly peeling and abrasive wear, and accompanied by oxidative wear. Both the wear area and wear volume initially increase and then decrease as the laser energy increases. The 150 mJ specimen exhibited the smallest wear area and wear volume of all tested specimens. The wear volume was reduced by 76.32% when compared to that of the CrN coating. This study complements the existing research on PVD/LSP composite strengthening techniques. Introduces a novel post-treatment methodology for PVD coatings. Provides certain theoretical support for subsequent PVD/LSP composite strengthening.
1. Introduction
Stainless steel, being one of the structural materials employed in nuclear power reactors, frequently encounters structural failures induced by wear, corrosion, irradiation, and other factors during its service [1–6]. This phenomenon will significantly impact the safe and reliable operation of the nuclear power reactor. The application of coatings on the surface of a material can effectively enhance its wear resistance and corrosion resistance [7–10].
CrN coatings exhibit high hardness, excellent wear and oxidation resistance, which has sparked significant interest [11–13]. CrN coatings have been deposited on the surfaces of nuclear reactor structural materials, and extensive investigations have been conducted on their wear and oxidation resistance [9, 14–17]. These research results also demonstrate that CrN coating exhibits excellent wear and oxidation resistance. However, inherent microstructural defects, including pinholes and cracks, are inevitably present in coatings fabricated via PVD technology [18–20]. This may lead to premature failure of the coating during service. Incorporating additives into the coating preparation process or applying specific post-treatments can effectively enhance the performance of the coating. For example, graphene is commonly utilized as an additive due to its excellent lubricating properties [21, 22]. Cui et al. [23, 24] further enhanced the wear and corrosion resistance of the coating through post-treatment processing.
Laser shock peening (LSP) has rapidly emerged as a surface modification technology in recent years, characterized by short-pulse duration, high power density and ultrahigh strain rate [25–27]. When the material surface is subjected to laser irradiation, it undergoes rapid melting and vaporization, resulting in the f
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Chuangming Ning, Ke Li, Guocan Tang, Yujie Xie, Lunlin Shang, Guangan Zhang, Zhenbing Cai (2025). Fretting Wear Performance of CrN Coating after Laser Shock Peening. Chinese Journal of Mechanical Engineering. https://doi.org/10.1186/s10033-025-01256-0
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Frequently Asked Questions
What is the effect of laser shock peening on CrN coatings?
Laser shock peening (LSP) induces plastic deformation and grain refinement in CrN coatings, increasing surface hardness and altering residual stress, which can improve wear resistance.
How does laser energy affect the fretting wear performance of CrN coatings?
The study found that as laser energy increases, wear area and volume initially increase then decrease. The best wear resistance was achieved at 150 mJ, with a 76.32% reduction in wear volume compared to untreated coatings.
What are the main wear mechanisms of CrN coatings after LSP treatment?
For untreated and high-energy (120, 150 mJ) specimens, abrasive wear dominates, accompanied by oxidative wear. For lower energies (30, 60, 90 mJ), peeling and abrasive wear are predominant, also with oxidative wear.
Why is post-treatment of CrN coatings necessary?
CrN coatings deposited by PVD often contain defects like pinholes and cracks, which can lead to premature failure. Post-treatments like LSP can enhance coating performance by modifying surface structure and properties.
What is the significance of this study for nuclear power applications?
The study provides a novel post-treatment method to improve the wear resistance of CrN coatings used in nuclear reactors, potentially extending component lifespan and ensuring safer operation.
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