Friction and wear behavior of a PMMA-SiO 2 coating on hardened steel
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Friction and wear behavior of a PMMA-SiO2 coating on hardened steel Luis E. Torres-Parga, Carolina Hernández-Navarro, Karla J. Moreno-Bello, J.S. García-Miranda, Luis D. Aguilera-Camacho, Raúl Lesso-Arroyo, Benjamín Arroyo-Ramírez and Álvaro SánchezRodríguez Department of Mechanical Engineering, Technological Institute of Celaya, Celaya, Guanajuato, Mexico ABSTRACT Sol-gel coatings show an excellent chemical stability, oxidation control and enhanced corrosion resistance for metal substrates. An organic-inorganic hybrid consisting of poly (methyl methacrylate) (PMMA) and silica (SiO2) was successfully synthesized in the form of solution, by using 3-(trimethoxysilyl) propyl methacrylate (TMSPM) as a coupling agent and cohydrolyzed with tetraethyl orthosilicate (TEOS) to afford chemical bondings to the forming silica networks by a sol-gel method. The as-synthesized hybrid material was subsequently characterized by Fourier Transformation infrared (FTIR) spectroscopy. PMMA-SiO2 was applied as a protective film on hardness steel substrates by dip-coating. The thickness of the coating was 25 μm, while the roughness Ra = 0.6 μm. The wear and friction behavior of the coating on hardened steel (HS) was evaluated by a ball-on-disk test in dry conditions with a AISI steel ball as counterface applying 2, 4, 6, 8 and 10 N normal loads. Friction coefficient values (μk) were in the range of 0.76 to 0.99, whereas the lowest wear rate (k) was observed at 6N with a value of 1.30x10-4 (mm3(Nm)-1). INTRODUCTION Hardened steels (HS) are widely used in the automotive, gear, bearing, tools and die industry [1]. Sol–gel coatings improve the chemical and physical properties of the metal surfaces relative to corrosion, friction and wear without altering the original properties of strength and toughness of the substrate [2]. Further, the sol–gel method is an environmentally friendly technique of surface protection and had showed the potential for the replacement of toxic pretreatments and coatings, which have traditionally been used for increasing corrosion resistance of metals [3]. Recent work on PMMA/SiO2 hybrids has been reported on the synthesis by a sol-gel procedure [4-7], as an anticorrosively coating on steel substrates [2,4] and the study of mechanical properties [6,810], among others. Tribological behavior of hybrid materials prepared by the sol-gel method and deposited by dip-coating had been reported for hybrid thin films on glass slides [5,11] and acrylic substrates [6,11], however, less information is available on their tribological properties as coating on metal, specifically on hardened steels (HS) substrates. Protective coatings for wear and corrosion protection are of interest to induce significant changes in the performance of HS applied as engineering components. Moreover, PMMA-SiO2 coatings are flexible, a property conferred by the organic component, and thus they can undergo higher deformations before cracking if applied on steel substrates. In this work, PMMA/SiO2 hybrid material was simple synthesized in the form of sol
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