Microstructure Evolution and Tribological Properties of WC-Reinforced Nickel-Based Alloy Cladding Layers Under Different Preheating Temperatures

Literature Overview

This research investigates the influence of preheating temperature on the microstructural evolution and tribological performance of tungsten carbide (WC)-reinforced nickel-based alloy cladding layers. The study is of significant practical importance as WC-reinforced nickel-based composites represent one of the most effective solutions for severe erosion-wear applications in pressure vessels, pumps, valves, and heat exchanger components operating in abrasive slurries or high-velocity gas-solid flows. Understanding how preheating temperature affects the microstructure-property relationship is essential for optimizing the cladding process and achieving the desired service life.

Core Technical Points

WC-Reinforced Nickel-Based Composite Cladding System

The study employs a commercially available WC-Ni composite powder with the following typical composition:

The microstructure of the as-deposited cladding layer consists of:

• WC particles (5-50 μm) dispersed in the nickel-based matrix
• η-carbide (Ni₃W) formed by the decomposition of WC at high temperatures
• ε-carbide (Ni₃WC) as an intermediate phase during WC decomposition
• γ-Ni solid solution matrix with Cr and Mo in solution
• Possible NbC or TiC if present as minor alloying additions

Preheating Temperature Effects on Microstructure

The study systematically varied the preheating temperature from 100°C to 600°C and examined the resulting microstructural changes. The key findings are summarized below:

The data clearly demonstrate an optimal preheating temperature range of 200-400°C where the balance between WC retention and matrix strengthening is maximized. Below 200°C, insufficient diffusion occurs to strengthen the matrix, while above 400°C, excessive WC decomposition reduces the effective volume fraction of the primary wear-resistant phase.

WC Decomposition Mechanism

The decomposition of WC in nickel-based matrices follows a well-established reaction pathway:

1. WC + 3Ni → Ni₃W + C (η-phase formation)
2. Ni₃W + 3Ni → 4Ni (complete decomposition)
3. WC + 3Ni → Ni₃WC + C (ε-phase formation, intermediate)

The decomposition rate is governed by:

• Temperature (Arrhenius-type dependence with activation energy of approximately 120-150 kJ/mol)
• Contact area between WC and Ni matrix
• Cooling rate (faster cooling preserves more WC)
• Preheating temperature (higher temperatures promote solid-state diffusion before melting)

The study reveals that preheating at 300°C achieves an optimal balance where approximately 10-15% of WC decomposes to form η-Ni₃W, which provides additional hardness contribution while retaining sufficient WC for primary wear resistance.

Process and Standards Analysis

Plasma Arc Cladding Process Parameters

The PTA process parameters used in the study are representative of industrial practice:

Tribological Performance Testing

The tribological properties were evaluated using a ball-on-disk tribometer under the following conditions:

The results demonstrate that the preheating temperature of 300°C yields the best tribological performance:

The optimal performance at 300°C is attributed to the synergistic effect of retained WC particles (providing abrasive resistance) and the η-Ni₃W phase (providing additional hardness and thermal stability). At higher temperatures, the excessive decomposition of WC into softer η-phase reduces the overall hardness and increases wear rate.

Standards Compliance for Wear-Resistant Cladding

For pressure vessel components requiring wear-resistant cladding, the following standards and specifications apply:

• ASME VIII Div.1 UW-13: General requirements for overlay welding
• API 934: Classification of corrosion and erosion resistant overlay weldings
• ASTM A240: Specifications for clad plate (for reference on cladding thickness requirements)
• ISO 14180: Welding consumables for plasma arc welding

The hardness requirements for wear-resistant cladding typically specify a minimum of 40 HRC (approximately 400 HV) for the cladding layer, which is readily achieved with WC-Ni composite cladding at all preheating temperatures tested. However, the tribological performance requirements are more demanding and require careful process optimization.

Integration with Engineering Practice

Application in Pressure Vessel Components

WC-reinforced nickel-based alloy cladding is extensively used in the following pressure vessel applications:

1. Slurry pumps and impellers: Subjected to severe erosion from abrasive particles in liquid media
2. Hydrocyclone internals: High-velocity slurry flow causes intense erosive wear
3. Valve seats and trim: Cyclic opening/closing with abrasive media causes erosion-corrosion
4. Heat exchanger tube sheets: Erosion from two-phase flow in the tube side
5. Pneumatic conveying system components: High-velocity gas-solid mixtures cause erosive wear

Engineering Case: Cement Industry Kiln Shell Cladding

A practical application from the cement industry illustrates the importance of preheating temperature control. A rotary kiln shell with a 25 mm carbon steel base plate required wear-resistant cladding to resist erosion from fly ash and cement particles at temperatures up to 400°C. The following PTA cladding procedure was developed:

• Substrate preheat: 300°C (optimal from the study findings)
• Powder: WC-Ni composite (65% WC, 25% Ni, 10% Cr)
• Cladding thickness: 3.0 mm (two passes)
• Dilution: 12% (measured by spectrographic analysis)
• Post-cladding heat treatment: 1100°C solution treatment, 2 hours, air cool

The resulting cladding layer achieved:

• Surface hardness: 820 HV (exceeding the 750 HV requirement)
• Bond strength: 280 MPa (exceeding the 200 MPa minimum)
• Service life: 18 months (compared to 6 months for unoptimized cladding at 500°C preheat)

This case demonstrates that proper preheating temperature selection can significantly extend the service life of wear-resistant cladding in demanding industrial applications.

Key Questions and Reflections

The Role of Residual Stress in Tribological Performance

One aspect that deserves further investigation is the influence of residual stress on the tribological performance of WC-reinforced cladding layers. Preheating temperature directly affects the residual stress state in the cladding layer, as higher preheat temperatures reduce thermal gradients and consequently reduce residual stresses. The study does not comprehensively address this interaction, but engineering experience suggests that compressive residual stresses at the cladding surface can improve fatigue resistance and reduce the propensity for spalling during wear.

Multi-Scale Characterization Needs

The current understanding of WC decomposition and its effects on tribological performance is primarily based on macroscopic and microscale observations. Future research should incorporate nanoscale characterization techniques such as transmission electron microscopy (TEM) and atom probe tomography (APT) to understand the atomic-level mechanisms of WC-Ni interaction and the evolution of carbide phases during solidification. This level of understanding would enable more precise control of the cladding process and prediction of long-term performance in service.

Study Insights and Implications

The systematic investigation of preheating temperature effects on WC-reinforced nickel-based alloy cladding layers provides clear guidelines for process optimization in industrial applications. The identification of 300°C as the optimal preheating temperature represents a practical and achievable process parameter that balances WC retention with matrix strengthening.

The study reinforces the fundamental principle that in composite cladding systems, the interaction between the hard phase and the binder matrix is governed by thermodynamic and kinetic factors that can be controlled through process parameter optimization. Engineers must understand these mechanisms to achieve consistent quality and predictable performance in production environments.

For the pressure vessel and cladding industry, the practical implication is that preheating temperature should be included as a critical process variable in welding procedure specifications for WC-reinforced composite cladding. The quality assurance system must include hardness testing, microstructural examination, and tribological testing to verify that the cladding layer meets the specified performance requirements. The transition from laboratory optimization to production implementation requires careful attention to process stability, operator training, and the development of robust quality control procedures that can detect deviations from the qualified parameters. Ultimately, the goal is to achieve maximum service life and minimum lifecycle cost for wear-resistant cladding in demanding pressure vessel applications.