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

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.

AtıfScopus1·WoS1

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Gültekin, Çağrı; Çolak, Murat; Tabak, Yasemin; Şensoy, Abdullah Tahir

There are many studies on improving the properties of aluminum alloys, but the addition of rare earth elements occupies a particularly important place among them. In this study, the effect of erbium (Er) addition on the microstructure and mechanical properties of A380 aluminum casting alloy was systematically investigated. A series of alloys with varying Er contents (0.03%, 0.05% and 0.1 wt.%) was fabricated using the conventional casting method. The addition of Er led to significant grain refinement, primarily due to the formation of Al3Er intermetallic particles, which acted as potent nucleation sites during solidification. Optical microscopy and SEM analyses confirmed the morphological transformation of the eutectic silicon phase into a finer and more fibrous structure. Mechanical testing revealed that the alloy containing 0.1 wt.% Er exhibited the highest ultimate tensile strength (236 MPa), elongation (4.56%), and hardness (87.6 HB), indicating an optimal balance between strength and ductility. The improvement is attributed to both microstructural refinement and dispersion strengthening mechanisms. These results suggest that controlled Er addition can be an effective strategy for enhancing the performance of cast Al–Si alloys, making them promising candidates for demanding structural applications in the automotive and aerospace industries.

AtıfScopus3·WoS1

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