Microstructure and Properties of Wear-Resistant Electrode Overlay Layer for Hydraulic Gate Additive Repair

Technical Context and Application Background

The research by Zhu Sisi, Hu Xing, and colleagues from China Yangtze Power Corporation, the National Engineering Research Center for Water Resources Efficient Utilization and Engineering Safety, and Hohai University, published in Materials for Mechanical Engineering in 2025 and funded by the National Engineering Research Center Open Research Fund (Grant No. GJGCZX-JJ-202408), focuses on the additive repair of hydraulic gates using wear-resistant welding electrodes. Hydraulic gates, particularly those used in large-scale water conservancy projects such as the Three Gorges Dam, are subjected to severe abrasive wear from sand-laden water flow, biological fouling, and corrosion. When wear reaches critical limits, the gates must be restored to their original dimensions and surface integrity. Traditional machining and replacement are expensive and time-consuming, making weld overlay repair an economically attractive alternative.

Overlay Microstructure and Wear Performance

The study examines the microstructure and mechanical properties of the overlay layer deposited using wear-resistant welding electrodes on hydraulic gate surfaces. Wear-resistant electrodes typically contain high concentrations of alloying elements such as chromium, molybdenum, tungsten, and vanadium, which form hard carbides (Cr7C3, WC, VC) in the overlay microstructure. The overlay microstructure generally consists of a matrix phase (austenite, ferrite, or martensite, depending on composition) embedded with hard carbide particles. The hardness of the overlay layer is a primary indicator of wear resistance; for hydraulic gate applications, overlay hardness in the range of 50–65 HRC is typically targeted to provide adequate resistance to abrasive wear from sand-laden water.

The microstructure is strongly influenced by welding parameters including current, voltage, travel speed, and layer thickness. Higher heat inputs promote grain growth and carbide coarsening, which can reduce hardness and wear resistance. Conversely, excessive cooling rates may lead to the formation of brittle phases and microcracks. The optimal process window balances hardness, toughness, and resistance to thermal fatigue. The study likely demonstrates that a multi-pass overlay strategy with controlled interpass temperatures can achieve a uniform microstructure with fine, evenly distributed carbides, providing both high hardness and acceptable toughness.

Engineering Practice and Quality Control Considerations

In practice, the repair of hydraulic gates requires careful surface preparation, including the removal of existing wear marks, corrosion products, and loose material. The overlay must be deposited in a manner that restores the gate's original geometry while ensuring adequate bond strength with the base metal. Post-overlay machining is often necessary to achieve dimensional accuracy and surface finish requirements. Non-destructive testing, including magnetic particle inspection (MT) or ultrasonic testing (UT), is essential to detect surface cracks and lack of fusion defects. The study's findings provide a basis for establishing qualified welding procedures and acceptance criteria for hydraulic gate overlay repairs, ensuring that repaired gates meet safety and performance standards throughout their remaining service life.

Summary and Key Takeaways

This research contributes practical knowledge to the field of additive repair of large-scale hydraulic structures. The selection of appropriate wear-resistant electrode compositions, combined with optimized welding parameters, can produce overlay layers with excellent abrasive wear resistance suitable for hydraulic gate applications. The study underscores the importance of microstructure-property relationships in overlay repair and provides a foundation for developing standardized repair procedures that balance economic efficiency with long-term reliability.