Zhuojin Pipe Fitting Co., LtdMicrostructure and Wear Resistance of WC-Reinforced Nickel-Based Overlay Deposited by Plasma Arc Surfacing
Literature Overview
Published in Hot Working Technology (Vol. 52, No. 17, pp. 27–31, 2023) by Liu Zhiyu, Wang Zhenyu, Liu Zhengjun, and Liu Zheng from Shenyang Institute of Technology, this paper systematically investigates the influence of tungsten carbide (WC) addition content on the microstructure and tribological behavior of nickel-based overlay layers deposited by plasma arc surfacing onto Q235 carbon steel substrates.
Nickel-based overlays are widely used in high-temperature and corrosion-wear applications due to their excellent thermal stability and oxidation resistance. The addition of WC as a reinforcement phase is a well-established strategy to enhance wear resistance, but the optimal WC content and its effect on phase evolution remain subjects of ongoing investigation.
Experimental Methodology
The researchers prepared plasma arc surfaced specimens with varying WC addition levels (expressed in weight percentage) onto Q235 steel plates. The specimens were characterized through:
- X-ray diffraction (XRD) for phase identification
- Scanning electron microscopy (SEM) for microstructural analysis
- Vickers hardness testing (HV0.5) for mechanical property evaluation
- Room-temperature abrasion wear testing for tribological assessment
| WC Content (wt%) | Primary Phases Identified | Average Hardness (HV0.5) | Wear Loss (mg) |
|---|---|---|---|
| 0 | γ-Ni, M₂₃C₆, M₆C | ~580 | ~12.5 |
| 10 | γ-Ni, M₂₃C₆, M₆C, Cr₇C₃, FeNi₃ | ~650 | ~8.2 |
| 20 | γ-Ni, M₂₃C₆, M₆C, Cr₇C₃, WC, W₂C, FeNi₃ | ~720 | ~5.8 |
| 30 | γ-Ni, M₂₃C₆, M₆C, Cr₇C₃, WC, W₂C, FeNi₃ | 767.2 | 3.9 |
| 40 | γ-Ni, M₂₃C₆, M₆C, Cr₇C₃, WC, W₂C, FeNi₃ | ~750 | ~5.1 |
Phase Evolution and Microstructural Analysis
The phase analysis reveals a complex multi-phase system that evolves with increasing WC content:
- Matrix phase: γ-Ni (ferritic nickel matrix) remains the dominant continuous phase throughout all compositions, providing ductility and thermal stability.
- Carbide phases: M₂₃C₆ and M₆C form from the Cr and Mo content in the nickel-based alloy. Cr₇C₃ appears as a secondary carbide phase, contributing to hardness.
- Tungsten carbides: WC and W₂C are identified as discrete hard phases. WC is the thermodynamically stable phase, while W₂C may form through the reaction of WC with the molten pool carbon during the rapid solidification of plasma arc surfacing.
- Intermetallic compounds: FeNi₃ forms at the interface between the base metal and overlay, influenced by dilution from the Q235 substrate.
A critical microstructural transition occurs at 30 wt% WC addition: the eutectic microstructure in the mid-section of the overlay layer transitions from a lamellar (plate-like) morphology to a blocky (equiaxed) morphology. This transition is significant because blocky eutectic structures generally provide better resistance to crack propagation and delamination during wear.
Wear Mechanism Analysis
At room temperature, the dominant wear mechanism across all compositions is delamination wear (剥层磨损). However, the 30 wt% WC specimen exhibits the smallest delamination damage, indicating superior resistance to subsurface crack initiation and propagation. The mechanism can be understood as follows:
- The hard WC and W₂C particles act as load-bearing asperities, reducing plastic deformation during sliding contact.
- The blocky eutectic structure at 30 wt% provides a more uniform stress distribution, reducing localized stress concentrations that initiate delamination.
- The γ-Ni matrix provides sufficient ductility to accommodate plastic deformation without catastrophic failure.
Optimal WC Content Determination
The results clearly identify 30 wt% as the optimal WC addition level for this nickel-based alloy system, based on the combined criteria of maximum hardness (767.2 HV0.5), minimum wear loss (3.9 mg), and favorable microstructural morphology. Beyond 30 wt%, the wear performance degrades, likely due to:
- Excessive carbide clustering leading to brittle regions
- Reduced matrix continuity compromising the load-bearing capacity of the overlay
- Potential for microcracking at carbide-matrix interfaces during cooling
Engineering Application Considerations
For pipeline and equipment applications where nickel-based overlays are employed — such as high-temperature gas path components, chemical pump impellers, and erosion-prone pipeline sections — this study provides a quantitative basis for WC content selection. The 30 wt% recommendation is specific to the alloy system and surfacing process investigated and should be validated for other nickel-based alloy compositions.
In the context of pipeline repair, where plasma arc surfacing is often used due to its precision and low dilution characteristics, the findings suggest that incorporating WC into the surfacing powder can dramatically improve wear life. The blocky eutectic transition at 30 wt% is particularly relevant for ensuring long-term structural integrity of the overlay under cyclic loading conditions typical in pipeline service.
The study demonstrates that plasma arc surfacing is a viable process for depositing WC-reinforced nickel-based overlays with controlled microstructure and predictable wear performance, supporting its adoption in industrial repair and manufacturing applications.