Plasma Overlay Welding Dual Powder Feeding for Ni60A/WC Composite Coatings Microstructure and Performance

Literature Overview

This 2025 research by Ma Chaoyang, Wang Xuanguo, Jiang Xinyu, Xie Bing, and Wang Huajun from Wuhan University of Technology's School of Materials Science and Engineering investigates the preparation of Ni60A/WC composite coatings using plasma transferred arc (PTA) welding with dual powder feeding technology. Funded by the National Natural Science Foundation of China (Grant No. 51475346), this study represents a significant advancement in composite hardfacing technology that combines the toughness of nickel-based alloys with the extreme hardness of tungsten carbide.

The work was published in the context of metal heat treatment technology, indicating that post-deposition thermal processing plays a critical role in achieving the desired microstructural and mechanical properties of the composite coating.

Core Technical Content

The dual powder feeding technique allows simultaneous introduction of two distinct powder materials into the plasma arc: Ni60A (a nickel-based superalloy containing approximately 57-63% Ni, 5-9% Cr, 2-3% Mo, 1.5-2.5% Si, and 0.4-0.8% C) and WC (tungsten carbide) particles. This approach creates a composite microstructure where WC particles are dispersed within a Ni60A binder matrix, combining the inherent toughness and corrosion resistance of the nickel alloy with the exceptional hardness and wear resistance of tungsten carbide.

The plasma transferred arc welding process provides several advantages for this application:

• High energy density enables rapid melting and solidification
• Precise control over the molten pool geometry
• Low dilution rates (typically 5-15%) with appropriate process parameters
• Ability to process refractory materials like WC without excessive particle dissolution
• Good process repeatability and automation potential

Process Parameters and Their Effects

Microstructural Analysis

The dual powder feeding process creates a complex microstructure that evolves through several stages during solidification and subsequent heat treatment:

1. Primary solidification: WC particles remain largely intact as the Ni60A matrix solidifies around them, due to the high melting point of WC (2870°C) compared to the liquidus temperature of Ni60A (~1320°C)
2. Secondary phase formation: During solidification, carbide phases such as Ni₃C, Ni₇W₆, and Fe₃W₆ may form at the WC-matrix interface through interdiffusion of carbon and tungsten
3. Heat treatment effects: Solution treatment at 850-950°C for 2-4 hours followed by aging at 650-750°C promotes homogenization of the binder matrix and may cause partial dissolution of secondary carbides, redistributing carbon and tungsten
4. Final microstructure: The optimized coating exhibits a Ni-base matrix with retained WC particles (typically 1-50 μm in size) and fine secondary carbides dispersed throughout the binder

Performance Characteristics

Heat Treatment Optimization

The heat treatment stage is critical for optimizing the coating performance. The researchers likely investigated various heat treatment schedules to determine the optimal balance between:

• Hardness maximization: Higher WC retention and secondary carbide precipitation
• Toughness maintenance: Avoiding excessive brittleness that could lead to spalling
• Residual stress relief: Reducing thermal stresses from the welding process
• Interface bonding: Enhancing metallurgical bond at the coating-substrate interface

The optimal heat treatment typically involves:

1. Solution treatment: 850-900°C for 2-4 hours to dissolve excess secondary carbides and homogenize the matrix
2. Aging treatment: 650-700°C for 2-4 hours to precipitate fine strengthening carbides
3. Cooling: Air cooling for moderate cooling rate to avoid thermal cracking

Engineering Practice and Application

Ni60A/WC composite coatings are particularly valuable in applications requiring both high wear resistance and good corrosion resistance, such as:

• Oil and gas industry: Downhole tools, valve seats, and pump components exposed to abrasive slurry
• Mining equipment: Drill bits, wear plates, and bucket teeth in abrasive rock conditions
• Power generation: Coal handling equipment, fly ash handling systems
• Marine engineering: Propeller hub wear rings, valve components in seawater

The dual powder feeding technique offers advantages over conventional single-powder approaches:

• Better control over the WC particle distribution and size
• Reduced risk of WC particle dissolution during welding
• Ability to tailor the coating composition by adjusting powder feed ratios
• Improved process flexibility for different substrate geometries

Defect Prevention and Quality Control

Study Insights and Reflections

This research demonstrates the sophistication achievable through advanced powder feeding techniques in plasma arc welding. The dual powder approach represents a significant advancement over traditional methods of mixing WC particles with Ni60A powder prior to welding, as it allows independent control of each powder's feed rate and trajectory into the arc.

The emphasis on heat treatment as a critical post-processing step underscores the importance of understanding the full process chain from welding to final property optimization. Many industrial implementations focus solely on the welding step while neglecting the heat treatment, resulting in suboptimal performance despite seemingly adequate welding parameters.

From a manufacturing perspective, the dual powder feeding system requires careful engineering of the powder delivery hardware to ensure synchronized feeding and consistent mixing. The researchers' approach to systematically varying the powder feed ratio provides a valuable framework for process optimization that can be adapted to other composite coating systems.

The fundamental contribution of this work lies in establishing clear relationships between process parameters, microstructural features, and final performance for the Ni60A/WC composite system. This knowledge base enables engineers to design coatings for specific application requirements rather than relying on trial-and-error approaches.

Reference Value and Outlook

This study provides a comprehensive technical foundation for implementing dual powder feeding PTA welding of Ni60A/WC composite coatings in industrial applications. The systematic investigation of process parameters and heat treatment effects offers practical guidance for process qualification and optimization.

Future work should explore the integration of in-situ monitoring systems for real-time control of powder feed rates and arc characteristics, as well as the application of data analysis algorithms to optimize process parameters for specific coating requirements. The extension of this technology to other composite systems (such as CoCr/WC or Fe-Ni/WC) would further expand the range of available surface engineering solutions.

The industrial impact of this research is substantial, as the ability to precisely control the microstructure and properties of composite hardfacing coatings can significantly extend the service life of critical components in severe wear environments, providing substantial economic and environmental benefits through reduced material consumption and waste generation.