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<p>This study explores the synergistic effects of graphite nanoparticles (0.1 wt.%) and thermal annealing (100–600°C) on electroless Ni-B coatings for AISI 4140 steel. Graphite-enabled multifunctional performance—crystallization control, friction reduction, and antibacterial activity—are unlike conventional Ni-B systems. XRD showed amorphous-to-crystalline (Ni<sub>3</sub>B/Ni<sub>2</sub>B) transformation, with graphite acting as a nucleation agent below 300°C before degrading at 600°C. The 300°C-annealed composite achieved optimal properties: 0.2 friction coefficient (75% lower than uncoated steel), 60% higher wear resistance, and hardness of 777 HV (+&#xa0;3.6% over as-deposited), attributed to graphite lubrication and nanocrystalline Ni<sub>3</sub>B formation. Antibacterial tests revealed a 3.4-mm inhibition zone against <i>E. coli</i>, though efficacy declined at higher temperatures due to graphite oxidation. All composites maintained superhydrophilicity (contact angle ≈&#xa0;0°) without mechanical compromise. By correlating annealing temperature with microstructure, this work provides a design framework for Ni-B/graphite coatings combining low friction (<i>μ</i> = 0.2), high hardness (785 HV), and antibacterial functionality—addressing critical needs for wear-resistant, hygienic surfaces in biomedical and industrial applications.</p>

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Effects of Graphite Incorporation and Annealing on the Structural, Tribological, and Functional Properties of Electroless Ni-B Coatings

  • 期刊论文

  • 发表日期：

    2025年11月18日

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  • Ferhat Bülbül,
  • Adem Kara,
  • Leman Elif Bülbül,
  • Kübra Güneş

摘要

This study explores the synergistic effects of graphite nanoparticles (0.1 wt.%) and thermal annealing (100–600°C) on electroless Ni-B coatings for AISI 4140 steel. Graphite-enabled multifunctional performance—crystallization control, friction reduction, and antibacterial activity—are unlike conventional Ni-B systems. XRD showed amorphous-to-crystalline (Ni3B/Ni2B) transformation, with graphite acting as a nucleation agent below 300°C before degrading at 600°C. The 300°C-annealed composite achieved optimal properties: 0.2 friction coefficient (75% lower than uncoated steel), 60% higher wear resistance, and hardness of 777 HV (+ 3.6% over as-deposited), attributed to graphite lubrication and nanocrystalline Ni3B formation. Antibacterial tests revealed a 3.4-mm inhibition zone against E. coli, though efficacy declined at higher temperatures due to graphite oxidation. All composites maintained superhydrophilicity (contact angle ≈ 0°) without mechanical compromise. By correlating annealing temperature with microstructure, this work provides a design framework for Ni-B/graphite coatings combining low friction (μ = 0.2), high hardness (785 HV), and antibacterial functionality—addressing critical needs for wear-resistant, hygienic surfaces in biomedical and industrial applications.