lubricants Article Tribological Evaluation of Turbostratic 2D Graphite as Oil Additive Halley Welther Jacques Dias 1,2 , Alessandra Batista Medeiros 1 , Cristiano Binder 1 , João Batista Rodrigue Neto 1 , Aloísio Nelmo Klein 1 and José Daniel Biasoli de Mello 1,2,3, *   Citation: Dias, H.W.J.; Medeiros, A.B.; Binder, C.; Rodrigue Neto, J.B.; Klein, A.N.; de Mello, J.D.B. Tribological Evaluation of Turbostratic 2D Graphite as Oil Additive. Lubricants 2021, 9, 43. https://doi.org/10.3390/ lubricants9040043 Received: 16 March 2021 Accepted: 13 April 2021 Published: 15 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Laboratório de Materiais, Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina, Florianópolis 88040-900, Brazil; halleydias@ifsc.edu.br (H.W.J.D.); alessandrabmedeiros@gmail.com (A.B.M.); cristiano.binder@labmat.ufsc.br (C.B.); joao.neto@labmat.ufsc.br (J.B.R.N.); a.n.klein@labmat.ufsc.br (A.N.K.) 2 Instituto Federal de Ciência e Tecnologia de Santa Catarina, Campus Araranguá, Araranguá 88905-112, Brazil 3 Laboratório de Tribologia e Materiais, Universidade Federal de Uberlândia, Uberlândia 38400-902, Brazil * Correspondence: ltm-demello@ufu.br or d.mello@labmat.ufsc.br; Tel.: +55-34-9-99293411 Abstract: In this study, powder technology was used to obtain Fe-SiC composites in which SiC particles act as precursors to generate a large amount of turbostratic graphite dispersed in the composite matrix. The selection of the alloy composition was studied employing Thermo-Calc ® software to obtain the temperature and composition range for the stabilization of the graphite phase in iron with a high yield. The extracted turbostratic 2D graphite particles were dispersed in mineral oil in order to evaluate the potential of these particles as a lubricating oil additive. The structure and morphology of the extracted graphite were examined by Raman spectroscopy and transmission electron microscopy (TEM), indicating the highly disordered nature of turbostratic graphite. Reductions in the friction coefficient and wear rate of a tribological pair were observed when compared to the pure mineral oil and mineral oil with commercial graphite particles added. The misorientation and increase in interplanar distances of turbostratic 2D graphite induce a low degree of interaction between these atomic planes, which contributes to the low-friction coefficient and the lower wear rate obtained for this system. Keywords: turbostratic graphite; lubricant additive; solid lubricant; friction; wear; nanoparticle 1. Introduction The severity of tribological contact imposes limits in controlling the energy-efficiency performance of modern systems [1]. In particular, severe operating conditions with higher speeds and smaller clearances of interfaces that are in contact require high strength of the tribological pair to achieve higher energy efficiency [2]. In this context, intense investigation and research has been directed toward the development of new contact materials [1,2]. The combination of solid and liquid lubrication may be one of the most promising choices for controlling friction and wear in sliding tribological pairs. Indeed, effective control of friction and wear contributes to increasing the energy efficiency of modern mechanical systems [1–5]. Several inorganic materials are lamellar solid lubricants (MoS 2 , WS 2 , HBN, H 3 O 3 , GaSe, GaS, SnSe), and the most important are carbon-based materials [6–8]. Graphite is a lamellar solid composed entirely of carbon, which under appropriate conditions provides low friction and high wear resistance to sliding surfaces. Furthermore, it is an abundant mineral in nature, with low cost, and is used in many industrial applications [9]. Interest in the study of carbon-based materials is motivated by their capacity to hybridize in sp, sp 2 and sp 3 [10]. Graphite, diamond, graphene, fullerene and carbon nanotubes, among other materials, are composed entirely of carbon, presenting different physical and chemical properties [11]. Graphite is organized in layers or lamellae with a hexagonal arrangement of covalent bonds, exhibiting van der Waals bonds between the lamellae or Lubricants 2021, 9, 43. https://doi.org/10.3390/lubricants9040043 https://www.mdpi.com/journal/lubricants