Photonic crystals in biology - NanoTR-VI

PP,PP*PPoster Session, Thursday, June 17Theme F686 - N1123Tribological Properties of Al/AlR2ROR3R Nano-composite Surface Layer on Al-based Substrate111Aziz Shafiei ZarghaniPPSeyed Farshid Kashani-BozorgPPand Abbas Zareie-HanzakiP1PSchool of Metallurgy and Materials Engineering, University of Tehran, Tehran, IranAbstract-Friction stir processing technique was employed for the production of Al/AlR2ROR3R nano-composite surface layer on Al-based substrate;Nano-size AlR2ROR3R particulates were introduced into the stir zone and dispersed uniformly within it by optimizing the process parameters. Microhardness value and wear resistance of the fabricated layer and the untreated substrate were evaluated. The micro hardness value of the surfacenano-composite layer was found to be improved by almost three times of that of the as-received Al alloy. Also, significant improvement in wearresistance was exhibited by surface nano-composite layer as compared to the as-received substrate. The improved wear resistance of surfacenano-composite layer is attributed to its greater micro hardness value (due to grain refinement of the Al matrix and uniform dispersion of nanosizeAlR2ROR3R particulates).Metal matrix composites reinforced with hard ceramicparticulates can offer relatively higher strength, stiffness, andsuperior wear resistance than those of the un-reinforced matrixmaterial. Surface modification processes can provide hardsurface with enhanced wear properties while the materialretains its internal ductility and toughness. Friction stirprocessing (FSP) is a solid state processing technique to obtainsurface modified/composite layers with fine-grainedmicrostructure [1-2]. The aim of the present investigation wasevaluation of wear performance of surface nano-compositelayer produced using FSP.An A6082 aluminium substrate with a thickness of 7 mmwas used. A groove was machined through the center of thesubstrate. Nano-size AlR2ROR3R powder with an average particlesize of ~50nm was filled in groove. The FSP unit was amodified form of a conventional miller machine. A hardenedH-13 tool steel pin was used. A tool rotation rate of 1250 rpmwas used, and the rotating tool was traversed at a speed of 135mm/min along the long axis of the work piece. Samples weresubjected to various numbers of FSP passes from one to four.Fig. 1 shows that uniform dispersion of AlR2ROR3R was achievedusing four FSP passes. The dark regions in images are AlR2ROR3RFigure 1. Secondary electron image of the surface nanocompositelayer fabricated using four FSP passes at fixed toolrotation rate and travel speed.particles which have been verified using energy dispersivespectroscopy, and the white particles are strengtheningprecipitates of A6082 alloy which are dispersed in the Almatrix. The grain size of Al matrix was refined by the FSP. Itseems that the grain refinement was caused due to dynamicrecrystallization during the FSP. However, the FSP with thenano-size AlR2ROR3R particles more effectively reduced the grainsize of the A6082 alloy matrix. For example, some matrixgrains of the surface nano-composite layer produced by fourFSP passes were less than 300 nm while the grain size ofA6082 extruded bar was 120m. The surface nano-compositelayer produced using four FSP passes exhibited almost a threetimes increment of the hardness value of the parent Al alloy(312 compared to 110 Hv).Figure 2. The wear loss weight of the as-received substrate andsurface nano-composite layer fabricated using four FSP passesas a function of sliding distance.The wear loss of as-received Al and surface nano-compositelayer fabricated using four FSP passes were measured by apin-on-disc wear testing machine against hardened GCr15steel disc with hardness of about 60 HRC under 40N appliedload. It may be noted that wear loss is considerably reduced(to almost two or three orders of magnitude) due to FSPcomposite surfacing (Fig. 2). The superior wear behavior isattributed to improved micro hardness in the surface layerbecause of the presence of hard ceramic particles and grainrefinement.In this investigation, Al/AlR2ROR3R surface nano-compositelayer was successfully fabricated by the FSP and tribologicalbehavior was studied. Hardness and wear resistance of thesurface nano-composite layer produced by four passes issuperior to those of the matrix alloy; this is attributed toimproved micro hardness in the surface layer because of thepresence of hard ceramic particles and grain refinement.*Corresponding author: fkashani@ut.ac.ir[1] R.S. Mishra and Z.Y. Ma, Mat. Sci. and Engine. R 50, 1(2005).[2] R.S. Mishra et al. Mat. Sci. and Engine. A 341, 307 (2003).[3] Y. Morisada et al. Mat. Sci. and Engine. A 419, 344 (2006).[4] A. Shafiei-Zarghani et al. Mat. Sci. and Engine. A 500, (2009).6th Nanoscience and Nanotechnology Conference, zmir, 2010 747