Spherical Cast Tungsten Carbide Particles in Overlay Layer Microstructure and Wear Performance

Literature Overview and Research Significance

Published in 2017 in the journal Materials and Design for Mechanical Engineering, this study by researchers from the Guangdong Institute of Materials and Processing Technology addresses a critical challenge in hardfacing technology: the incorporation of ceramic particles into weld overlay deposits to enhance wear resistance. The research was supported by multiple funding programs including the National International Science and Technology Cooperation Program (2011DFR50740) and the Guangdong Provincial Strategic Emerging Industry Core Technology Program (2011A091102007).

The use of tungsten carbide (WC) particles as reinforcement in weld overlay deposits is a well-established approach to achieving extreme wear resistance, particularly for applications involving severe abrasive and erosive wear. However, the morphology and distribution of WC particles significantly influence the mechanical performance of the resulting composite overlay. This study specifically investigates the effect of using spherical cast WC particles, as opposed to irregularly shaped commercial WC powder, on the microstructure and wear behavior of the overlay layer.

Core Technical Findings

Particle Morphology and Its Influence on Overlay Properties

The spherical cast WC particles used in this study were produced through a specialized casting process that yields particles with high roundness, narrow size distribution, and minimal surface defects. Compared to irregularly shaped WC particles produced by grinding or milling, spherical particles offer several potential advantages:

• More uniform distribution within the weld pool due to reduced tendency for agglomeration
• Better bonding with the metallic matrix due to increased surface area-to-volume ratio and smoother surfaces
• Reduced stress concentration at particle-matrix interfaces due to absence of sharp edges and corners
• More predictable melting and dissolution behavior during welding

The study compared overlays produced with spherical cast WC particles against those produced with conventional irregular WC powder, examining both microstructural and mechanical performance differences.

Microstructural Analysis

The microstructural observations reveal that spherical WC particles integrate more effectively into the weld matrix, resulting in a more homogeneous composite structure. The reduced interfacial porosity and improved particle-matrix bonding contribute to enhanced mechanical integrity of the overlay deposit.

Wear Performance Evaluation

Wear testing was conducted using standardized dry sliding wear tests against alumina (Al2O3) counterfaces under multiple normal loads. The results demonstrated clear advantages of the spherical WC particle reinforced overlay:

• At a normal load of 20 N, the spherical WC overlay exhibited a wear rate reduction of 35% to 45% compared to the irregular WC overlay.
• At higher loads of 50 N and 100 N, the improvement remained significant, with wear rate reductions of 25% to 35%.
• The spherical WC overlay maintained more stable wear behavior across the entire load range, indicating better resistance to progressive material degradation.
• Fractographic analysis revealed that failure in the spherical WC overlay occurred primarily through matrix deformation and particle pullout, while the irregular WC overlay exhibited additional failure through interfacial debonding and particle fracture.

Hardness and Toughness Balance

The hardness measurements confirmed that both overlay types achieved high hardness values, with the spherical WC overlay reaching 1200 to 1400 HV and the irregular WC overlay reaching 1100 to 1300 HV. However, the more critical finding was the improved fracture toughness of the spherical WC overlay, which was measured to be 20% to 30% higher than the irregular WC counterpart. This improvement in toughness is particularly important for applications involving impact loading, where brittle failure of the overlay deposit can lead to catastrophic component failure.

Engineering Applications and Process Considerations

The research findings have direct implications for the design and fabrication of wear-resistant components in several industrial sectors:

1. Mining equipment: Shovel buckets, dragline buckets, and conveyor idlers benefit from the improved wear resistance and toughness of spherical WC reinforced overlays.
2. Cement industry: Mill liners, chutes, and hoppers experience severe abrasive wear from cement clinker and raw materials, making WC reinforced overlays an ideal solution.
3. Oil and gas industry: Drill collars, stabilizers, and valve components exposed to erosive drilling fluids and sand-laden streams require the extreme wear resistance provided by WC composites.
4. Power generation: Ash handling equipment, fly ash chutes, and boiler tube protectors benefit from the enhanced wear performance.

For process implementation, the following considerations are important:

• The spherical WC particles should be incorporated into the overlay using flux-cored wire, self-shielded wire, or submerged arc welding with pre-placed particle layers.
• Welding parameters should be optimized to minimize WC dissolution while ensuring adequate particle-matrix bonding. Lower heat input and faster travel speeds generally favor particle retention.
• Multi-pass overlaying with controlled interpass temperature provides the best combination of wear resistance and mechanical integrity.
• Post-weld heat treatment may be necessary to relieve residual stresses without compromising the WC particle distribution.

Study Insights and Future Directions

This research demonstrates that particle morphology is a critical but often overlooked factor in the design of particle-reinforced weld overlay composites. The systematic comparison between spherical and irregular WC particles provides clear evidence that spherical morphology offers significant advantages in terms of microstructural homogeneity, mechanical performance, and wear resistance. The improved particle retention rate and reduced interfacial porosity translate directly into more reliable overlay performance in demanding service conditions.

For future research, the following areas deserve investigation: the effect of WC particle size on overlay performance, the development of hybrid particle systems combining WC with other ceramic phases such as TiC or SiC, and the optimization of welding parameters for maximum particle retention. Additionally, the development of cost-effective manufacturing methods for spherical WC particles would enhance the economic viability of this technology for widespread industrial adoption. The principles established in this study provide a solid foundation for advancing the technology of particle-reinforced weld overlay composites in the coming years.