With the growing demands for advanced materials in harsh operating conditions, such as high mechanical loads, severe wear, and repeated impacts, this research focuses on enhancing the surface performance of critical components by incorporating WC particles into Co-based alloy coatings with the primary goal to optimize the WC particle content to achieve a favorable balance between hardness, wear resistance, and toughness, and thus provide a theoretical and technical foundation for the development of high-performance composite coatings.
In this study, WC/Co-based composite coatings were fabricated via laser directed energy deposition (LDED) according to the variable-process discontinuous overlapping multi-track strategy, with WC particle contents ranging from 0% to 50%. The effects of WC particle content on the coatings' forming quality, microstructure, phase composition, mechanical properties, and strength-toughness behavior were comprehensively evaluated. Advanced characterization techniques, including optical microscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were employed. Additionally, hardness tests (Rockwell, Vickers, and nano-indentation), impact testing, and friction-wear experiments were conducted to assess the coatings' macroscopic and microscale mechanical properties, as well as their resistance to deformation and wear.
The results revealed that the addition of WC particles significantly enhanced the coatings’ hardness and wear resistance, primarily through mechanisms such as hard particle strengthening, grain refinement, dispersion strengthening, and the pinning effect. However, excessive WC particles led to increased porosity, surface roughness, and internal defects, which negatively impacted the coatings' toughness and load-bearing capacity. Key findings are as follows: as WC particle content increased, the coatings exhibited finer grains and a higher density of hard phases (e.g., Co6W6C and W2C). Nevertheless, excessive WC particles caused agglomeration and uneven distribution, resulting in defects such as cracks and pores. The coatings' hardness and wear resistance increased with the WC particle content, reaching optimal values at a 40% WC content; beyond this threshold, toughness decreased due to the formation of internal cracks and reduced ductility. Coatings with 40% WC displayed the lowest wear rate (62.3 μm³/(N·m)) and friction coefficient (0.28), which was attributed to the synergistic effects of WC particles in disrupting wear mechanisms and enhancing the coatings' resistance to plastic deformation. While the coatings' resistance to deformation improved with increasing WC content, excessive WC particles raised the risk of cracking under impact loads. These findings demonstrated that the optimal WC particle content for achieving a favorable balance between hardness, wear resistance, and toughness was 40%. Beyond this point, the coatings' performance deteriorated due to increased defects and reduced ductility. The results provided valuable insights into the optimization of WC/Co composite coatings for applications requiring high durability and resistance to wear and impact.
These findings demonstrate that the optimal WC particle content for achieving a favorable balance between hardness, wear resistance, and toughness is 40%. Beyond this point, the coatings' performance deteriorates due to increased defects and reduced ductility. The results provide valuable insights into the optimization of WC/Co composite coatings for applications requiring high durability and resistance to wear and impact, and offer a theoretical basis and practical guidance for the development of advanced composite coatings with enhanced mechanical properties.
Key words
laser directed energy deposition /
WC particle /
composite coating /
microstructure /
mechanical property /
strength-toughness behavior
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Funding
National Natural Science Foundation of China (52404124); China Postdoctoral Science Foundation (2023M73148)
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