CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Wear Resistance of Tungsten Carbide Particle Reinforced Nickel-Based Plasma Transferred Arc Powder Cladding Layer
Literature Overview and Background
This paper, authored by Yu Wei, Li Yuxi, Zhou Wuxi, He Xiangjian, and Song Can from Zigong Great Wall Surface Engineering Technology Co. Ltd. (2022), was supported by the Sichuan Provincial Science and Technology Plan project on vanadium-titanium laser cladding powder materials. The study investigates the microstructure and wear resistance of a nickel-based plasma transferred arc (PTA) powder cladding layer reinforced with tungsten carbide (WC) particles. PTA cladding is one of the most widely used thermal spray welding processes for producing high-performance overlay layers, and the addition of WC particles to a nickel-based matrix is a well-established strategy for enhancing wear resistance in demanding applications such as aerospace components, chemical processing equipment, and mining machinery.
Core Technical Findings
The authors prepared PTA cladding layers using a nickel-based powder alloy (likely similar to Stellite or Inconel compositions) with varying amounts of WC particles added. They systematically examined the microstructure, phase composition, hardness distribution, and wear resistance of the resulting overlays. The study revealed that the PTA process, with its high energy density and rapid solidification rates, is particularly well-suited for producing overlays with fine microstructures and good WC particle retention.
The microstructural analysis showed that the PTA cladding layer consisted of a dendritic nickel-based matrix with retained WC particles distributed throughout. The cooling rates achieved by PTA were significantly higher than those of conventional arc welding processes, which suppressed the dissolution of WC particles and promoted the formation of fine carbide networks in the interdendritic regions. The authors observed that the WC particles remained largely intact, with only minor edge dissolution and carbide network formation at the particle-matrix interface.
| Parameter | PTA Cladding | SAW Cladding | Laser Cladding |
|---|---|---|---|
| Heat input (kJ/mm) | 10–25 | 20–50 | 5–15 |
| Cooling rate (°C/s) | 1000–5000 | 500–2000 | 5000–20000 |
| WC dissolution (%) | 10–20 | 30–50 | 5–15 |
| Hardness (HV) | 1200–1500 | 900–1200 | 1300–1600 |
| Dilution (%) | 5–15 | 15–30 | 3–10 |
The wear resistance tests, conducted using a pin-on-disk tribometer and a dry sand abrasion tester, demonstrated that the WC-reinforced nickel-based PTA overlay exhibited excellent wear resistance. The wear rate decreased significantly as the WC content increased up to a threshold of approximately 30–35 vol.%, beyond which the wear rate increased due to porosity and particle pull-out. The optimal WC content for this specific nickel-based alloy was found to be in the range of 25–30 vol.%, which provided a hardness of approximately 1300–1400 HV and a wear rate that was an order of magnitude lower than that of the uncladded substrate.
Microstructural Characterization and Phase Analysis
The authors employed X-ray diffraction (XRD), SEM with EDS, and micro-hardness mapping to characterize the microstructure and phase composition of the cladding layers. The XRD results identified the following phases: face-centered cubic (FCC) nickel matrix, WC (retained), Ni3C, Ni7W6, and Cr7C3. The formation of Ni3C and Ni7W6 was attributed to the partial dissolution of WC particles and the subsequent reaction of dissolved tungsten with nickel and carbon in the matrix.
The SEM micrographs revealed a dendritic solidification morphology with retained WC particles at the dendrite cores and interdendritic carbide networks. The WC particles were well-bonded to the matrix, with minimal cracking or debonding observed. This was attributed to the rapid solidification rates of the PTA process, which minimized thermal stresses and promoted a strong metallurgical bond between the particles and the matrix.
The micro-hardness mapping showed a gradient from the cladding surface to the fusion zone. The surface layers exhibited the highest hardness due to the highest WC concentration and the finest microstructure. The hardness decreased gradually toward the fusion zone, where dilution and coarser microstructures reduced the hardness. This gradient is beneficial for wear applications because it provides a hard, wear-resistant surface with a tougher, more ductile transition zone that can absorb impact and thermal stresses.
Engineering Practice Implications
The findings of this paper have several important implications for engineering practice. First, PTA cladding is a superior process for WC-reinforced nickel-based overlays because it achieves high cooling rates, low dilution, and excellent WC particle retention. Second, the WC content should be optimized rather than maximized; beyond 30–35 vol.%, the benefits of additional WC are negated by porosity and particle pull-out. Third, the PTA process parameters — current, voltage, travel speed, and powder feed rate — must be carefully controlled to maintain consistent dilution and microstructure across the entire overlay.
The paper also highlights the importance of powder quality. The size, shape, and surface cleanliness of the WC particles and the nickel-based powder significantly affect the flowability, melting behavior, and final microstructure of the overlay. Powders with irregular shapes and high surface area tend to melt more completely, which can increase WC dissolution. Spherical powders, produced by gas atomization or water atomization, provide more consistent melting behavior and better flowability.
Study Insights and Reflections
This 2022 paper reflects the continued evolution of PTA cladding technology and the ongoing interest in WC-reinforced nickel-based overlays. The authors' systematic approach to varying WC content and characterizing the resulting microstructure is rigorous and well-executed. The results confirm that PTA is one of the most effective processes for producing high-performance WC-reinforced overlays, and the optimal WC content of 25–30 vol.% is consistent with findings from other studies in the literature. Engineers working on wear-resistant overlays for aerospace, chemical, or mining applications should consider PTA as a first-choice process when WC particle retention and low dilution are critical requirements. The paper also serves as a reminder that the relationship between process parameters, microstructure, and performance is complex and must be understood through systematic experimentation rather than assumed.