Effect of Tungsten Carbide Particles and Cladding Substrate on Wear Resistance of Cladding Layer

Literature Overview and Research Significance

The incorporation of tungsten carbide (WC) particles into weld overlay cladding layers represents one of the most effective approaches to achieving extreme wear resistance in industrial components. The literature reviewed here investigates the systematic influence of WC particle characteristics (size, shape, volume fraction) and the substrate material composition on the overall wear performance of the cladding layer. This research is particularly relevant for applications involving severe abrasive wear, such as mining equipment, cement mill liners, and paper mill rollers.

Fundamental Mechanisms of Wear Resistance Enhancement

WC particles enhance wear resistance through several mechanisms that operate simultaneously:

1. Load-bearing capacity: WC particles (hardness ~2400 HV) bear a disproportionate share of the applied load due to their high hardness relative to the metallic matrix, reducing the contact area available for wear.
2. Ploughing resistance: The high hardness of WC particles resists penetration by abrasive asperities, preventing material removal through micro-ploughing.
3. Matrix strengthening: The presence of WC particles restricts dislocation movement in the metallic matrix through Orowan bowing, increasing the matrix flow stress.
4. Crack deflection: WC particles act as obstacles to crack propagation, forcing cracks to deflect or branch, thereby increasing fracture energy.

The effectiveness of these mechanisms depends critically on the particle size, distribution uniformity, and the strength of the particle-matrix interface.

Influence of WC Particle Size

The literature presents systematic studies on the effect of WC particle size on wear resistance, with results summarized as follows:

The data clearly demonstrates that smaller WC particles provide superior wear resistance at equivalent volume fractions. This is attributed to the larger total particle-matrix interfacial area, which more effectively restricts matrix deformation, and the reduced risk of particle debonding under load. However, very fine particles (<5 μm) may suffer from excessive oxidation during the welding process, leading to WC degradation and reduced effectiveness.

The optimal particle size range identified in the literature is 10-50 μm, with a volume fraction of 30-40% providing the best balance of wear resistance and mechanical integrity. Above 40% volume fraction, the risk of particle clustering and matrix discontinuity increases, leading to reduced toughness and potential delamination.

Influence of Substrate Material on Cladding Performance

The substrate material exerts a significant influence on cladding layer properties through two primary mechanisms: dilution during welding and thermal stress development.

Dilution Effects

Different substrates contribute varying amounts of alloying elements to the fusion zone, affecting the cladding layer composition:

The literature emphasizes that for WC-composite cladding, the dilution effect is generally manageable because the WC particles provide such high intrinsic hardness that moderate compositional changes in the metallic matrix do not dramatically affect overall wear resistance. However, excessive dilution from high-carbon substrates can lead to carbide network formation at grain boundaries, reducing toughness.

Thermal Stress and Residual Stress

The coefficient of thermal expansion mismatch between the cladding layer and substrate generates residual stresses that can either enhance or detract from wear performance:

• Compressive residual stresses (achieved by using substrates with higher thermal expansion than the cladding) improve fatigue resistance and can enhance wear resistance by 10-20%.
• Tensile residual stresses (from high thermal expansion mismatch or excessive cooling rates) reduce fatigue life and may promote crack initiation at particle-matrix interfaces.

The literature recommends using substrates with thermal expansion coefficients matching or slightly exceeding that of the cladding layer. For WC-Co-NiCrMo composites (CTE ≈ 13-14 × 10⁻⁶/K), carbon steel substrates (CTE ≈ 12 × 10⁻⁶/K) provide an acceptable match, while austenitic stainless steels (CTE ≈ 17 × 10⁻⁶/K) generate compressive stresses beneficial for fatigue resistance.

Microstructural Analysis and Phase Evolution

Metallographic examination of WC-composite cladding layers reveals several critical microstructural features:

Particle-matrix interface: High-quality cladding layers show a clean, well-bonded interface between WC particles and the metallic matrix. Poor interfaces (characterized by gaps, oxide films, or reaction layers) significantly reduce wear performance. The interface quality depends on:

• Powder preheating temperature (optimal: 200-400°C to remove surface oxides)
• Arc temperature and power density (sufficient to achieve intimate contact)
• Cooling rate (rapid cooling preserves the interface; slow cooling allows reaction layer growth)

Matrix microstructure: The metallic matrix typically consists of martensite (for high-Cr steels) or austenite (for Ni-Cr-Mo alloys) with dissolved carbide-forming elements. The matrix hardness should be at least 50% of the WC particle hardness to ensure effective load transfer. A too-soft matrix (< 400 HV) leads to matrix-dominated wear, while an excessively hard matrix (> 900 HV) may be too brittle to support the WC particles effectively.

Porosity and inclusions: WC particles can act as nucleation sites for gas pores if insufficiently wetted by the molten metal. The literature recommends using a flux or surfactant to improve wetting, and ensuring adequate arc energy to achieve complete melting and intimate contact.

Process Optimization for WC-Composite Cladding

The welding process parameters must be carefully optimized to preserve WC particle integrity while achieving good fusion:

A critical process consideration is the avoidance of WC particle degradation. WC decomposes at temperatures above approximately 1200°C, forming W₂C and free carbon. This decomposition reduces the effective hardness of the particle and creates brittle carbide networks. Process parameters should be selected to minimize the time the powder spends at temperatures exceeding 1200°C.

Wear Testing Results and Performance Comparison

The literature presents comparative wear testing results using standard pin-on-disk and dry sand rubber wheel methods:

The data confirms that WC addition provides dramatic improvements in wear resistance, with 30-40% volume fraction providing optimal performance. The substrate material effect is secondary to the WC content and particle size effects, though it influences the practical feasibility of achieving the target volume fraction through dilution control.

Engineering Applications and Practical Considerations

In mining applications, WC-composite cladding of excavator bucket teeth has demonstrated 5-8× life improvement over conventional manganese steel teeth. The cladding is typically applied using submerged arc welding with a wire-powder combination, followed by machining to achieve the final geometry. The economic analysis typically shows payback within 2-3 replacement cycles despite the higher initial cladding cost.

For cement mill roller cladding, the challenge lies in maintaining WC integrity during the severe impact and sliding conditions of mill operation. The literature recommends using WC particles in the 25-50 μm size range with a Ni-Cr-Mo binder matrix, applied as 3-4 layers of 2-3 mm each, with the final surface layer containing the highest WC fraction.

Study Insights and Conclusions

The systematic investigation of WC particle and substrate effects on cladding wear resistance reveals that particle size and volume fraction are the dominant factors, with substrate composition playing a secondary but not negligible role. The optimal design combines WC particles in the 10-50 μm range at 30-40% volume fraction, applied to a compatible substrate using process parameters that minimize particle degradation.

The key practical insight is that achieving consistent WC distribution and particle integrity requires careful process control at every stage, from powder preparation through final machining. Engineers should invest in process development and qualification rather than simply selecting a consumable and applying it without optimization. The performance potential of WC-composite cladding is substantial, but realizing this potential demands systematic attention to process details that may seem minor but have outsized effects on final performance.