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    Studies on newly developed hBN/graphene-based nano-fluids supported by cryogenic cooling conditions in improving the tribological performance of Ti6Al4V alloy
    (Elsevier, 2024) Korkmaz, Mehmet Erdi; Rai, Ritu; Demirsoz, Recep; Picak, Sezer; Vashishtha, Govind; Gunay, Mustafa
    Hexagonal Boron Nitride (hBN) is often referred to as a soft material due to its layered structure and properties that distinguish it from conventional hard materials like ceramics. The layered structure of hBN imparts lamellar lubrication characteristics and the weak van der Waals forces between adjacent layers allow for easy sliding, leading to low frictional resistance. The softness of hBN allows for ease of processing into various forms, facilitating its incorporation into lubricants, coatings, and composite materials. Therefore, the aim of this work is to enhance the lubricating capabilities of the nano-fluids and optimize the frictional behavior of Ti6Al4V alloy against tungsten carbide (WC) abrasive ball for potential biomedical applications, especially for combination of Ti6Al4V femoral stem and carbide femoral head. The newly formulated nano-fluids combine the unique properties of hBN and graphene to create a synergistic lubricating environment. The tribology and advanced characterization techniques were used to analyze the wear behavior of Ti6Al4V alloy surfaces. The results demonstrated that the applciaiton of cryogenically cooled lubricants with nanoparticles exhibited the lowest wear depth and friction forces, as a result of their increased viscosity.
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    The role of stair-rod dislocations on the twinning and martensitic transformation in single crystalline NiCoCr
    (Acta Materialia, 2025-03-15) Picak, Sezer
    High- and medium-entropy alloys are a sub-class of multi-principal element alloys with an exceptional combination of strength and toughness arising from twinning– and transformation–induced plasticity. The underlying mechanisms responsible for the nucleation of deformation twinning and ɛ-martensite transformation in multi-principal element alloys still remains under intense debate. In this work, high-resolution transmission-electron microscopy was used to reveal the complex dislocation reactions behind deformation twinning and ɛ-martensite in a model NiCoCr. The existence of stair-rod and Shockley partials under uniaxial loading was demonstrated. The stair-rods dislocations with multiple Lomer-Cottrell locks play a crucial role in the formation of deformation twinning and ɛ-martensite. Lomer-Cottrell locks significantly contribute to work hardening behavior by acting as both dislocation barriers and sources. The results herein offer clarity regarding the strengthening mechanisms in multi-principal element alloys.