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    Effects of Graphite Incorporation and Annealing on the Structural, Tribological, and Functional Properties of Electroless Ni-B Coatings
    (Springer, 2026) Bulbul, Ferhat; Kara, Adem; Bulbul, Leman Elif; Gunes, Kubra
    This study explores the synergistic effects of graphite nanoparticles (0.1 wt.%) and thermal annealing (100-600 degrees 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 degrees C before degrading at 600 degrees C. The 300 degrees 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 approximate to 0 degrees) without mechanical compromise. By correlating annealing temperature with microstructure, this work provides a design framework for Ni-B/graphite coatings combining low friction (mu = 0.2), high hardness (785 HV), and antibacterial functionality-addressing critical needs for wear-resistant, hygienic surfaces in biomedical and industrial applications.
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    Multifunctional electroless nickel boron composite coatings incorporated by magnesium diboride ceramic particles
    (Wiley, 2024) Bulbul, Ferhat; Kara, Adem
    In this study, the role of MgB2 in composite coatings is pivotal. Electroless Ni-B plating, a current-free chemical reduction process, deposits nickel-boron coatings. Other than MgB2, reinforcements like SiC, B4C, and so forth are used with Ni-B coatings for improved properties. The research focuses on Ni-B/MgB2 coatings on AISI 4140 steel using electroless deposition and annealing at different temperatures. Initially, the coating appears dense and amorphous, transforming into worm-like structures through crystallization with MgB2. Higher annealing temperatures lead to brush-like, feathery, and oyster mushroom structures, forming crystalline nickel boron compounds and oxide phases due to synergy. Interestingly, the newly introduced phases disrupt friction patterns nonlinearly, which is linked to MgB2's ceramic nature and reinforcement quantity. Conversely, incorporating MgB2 and annealing-induced intermetallic phases notably enhances hardness (up to 6) and improves hydrophilicity and antibacterial traits in the coating.