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Study of the Wear and Friction Behavior of Immiscible As Cast-Al- Sn/Graphite Composite

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Study of the Wear and Friction Behavior of Immiscible As Cast-Al- Sn/Graphite Composite International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.2, Mar-Apr 2012 pp-025-042 ISSN: 2249-6645 Study of the wear and friction behavior of immiscible as cast-Al- Sn/Graphite composite S.Srivastava1*, S. Mohan2, Yogesh Srivastava1 and Aman J. Shukla3 1Materials Science & Metallurgical Engineering 1 Maulana Azad National Institute of Technology, Bhopal M.P. (India)-462051 2Institute of Technology, Banaras Hindu University, Varanasi-221005 3Research & Technology Development Centre Sharda University, G. Noida U.P. (India)-201306 Abstract: In this paper we investigate the tribological properties of Al- exhibit two immiscible liquid phases within a certain Sn-based alloy with different amount of graphite at different temperature range. However, the different densities of these normal loads and sliding speed. A modified impeller mixing liquid phases lead, to the formation of two different layers. coupled with chill casting technique was used for the This prevents the homogeneous distribution of particles in a preparation of immiscible alloys. In this paper Al-Sn binary matrix using simple and inexpensive casting processes. The alloys was chosen for this study. This binary system shows development of immiscible alloys has been largely the miscibility gap at different concentration and constrained by the conventional equilibrium processing, temperature. Graphite was chosen as reinforcing element which generally results in gross segregation due to the wide which was reinforced in the Al-Sn matrix. The graphite miscibility gap, and high disparity in the densities and content in the composite varied from 1.6 to 8.4 wt%. The melting temperatures between the immiscible elements [1, presence of graphite in the matrix not only improves the 2]. The idea is to obtain aluminum matrix with finely mechanical properties but also improve the tribological distributed particles of e.g. indium, bismuth or lead as a soft properties due to lubricating action. The ductility of phase or iron, nickel or cobalt as a hard phase with composite materials showed the adverse effect with increase lubricating function. However this is still far from the of the graphite content in the matrix. Pin-on-disc sliding practical application because the miscibility phenomenon wear tests were conducted in an ambient condition to poses problems during solidification [3-5]. A miscible gap in examine the tribological behavior of the aluminum-based the liquid state is found in metal-metal systems such as Al- graphite composite. The experiment was commenced at Bi, Al-Pb, Al-In, Al-Sn, Cu-Pb, and Zn-Pb, Ga-Pb etc. For different sliding distance, speed and using normal load. this study Al-Sn was selected as basic materials in which Having finished the tests, the weight losses of the specimen small amount of the graphite was added for improving the were measured, wear and friction characteristics were wear and seizure properties of the materials. A typical calculated with respect to time, depth of wear track, sliding equilibrium phase diagram is shown in Fig.1. The solid speed and bearing load. Friction coefficient and wear solubility is of the order of 0.10% Sn at approximately 900- volume have shown large sensitivity to the applied normal 0K, decreasing to reach a probable value of 0.05-0.07% Sn at load and the testing time (or sliding distance). The XRD and eutectic temperature, and much smaller values at lower SEM analysis were used to analyze the wear debris and temperatures. The density increased is approximately 0.06% track. for every 0.1% Sn added. Liquid gas surface tension and ratio solid-liquid /solid-solid surface tension decreases, and Key words: Aluminum alloy, Friction coefficient, Pin-on- this affect the shape of phase. Fluidity is greatly reduced, Disc, SEM, Sliding velocity, Tribometer, Wear, and XRD. and electric conductivity is decreased. There is practically no change in hardness, strength or elongation of commercial 1. Introduction aluminium, high purity aluminium is slightly strengthened. Aluminum alloys and other lightweight materials have Strength and especially elongation drop rapidly with o growing applications in the automotive industry, with temperature at 500 K the strength of a 10% tin alloy is respect to reducing the fuel utilization and shielding the halved and the elongation has dropped from 60% at room o environment, where they can successfully reinstate steel and temperature to less than 5% at 900 K the alloy are brittle. cast iron parts. There are a number of elements which have a Plastic deformation to break the tin network, followed by limited solubility in the aluminum matrix. Therefore they annealing to spheroidized the tin improve the properties [6]. www.ijmer.com 25 | P a g e International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.2, Mar-Apr 2012 pp-025-042 ISSN: 2249-6645 Fig. 1. Phase diagram of Al-Sn With solid lubricant particle like graphite or MoS2 volume and frictional coefficients to the presence of graphite dispersion in the matrix of aluminum alloy this material in the matrix, have been determined. exhibits good potential for resistant to wear and consequently becomes more suitable for tribological 2. Experimental investigation applications [7-9].Considerable efforts have been put into incorporating lubricating particles in aluminum alloy 2. 1 Selection of materials matrices to improve resistant to wear. Earlier researcher [9- Commercially pure aluminium (99.8%) and tin-metal were 12] has reported graphite as a suitable solid lubricating selected for the preparation of Al-Sn composites with material for the preferred applications. Aluminum alloy– different content of graphite. Graphite particulate composite exhibits its potential to act as a self lubricating material with improved resistance to wear, 2.2 Procedure for preparation machinability, delayed on set of severe wear and seizure. The experimental set-up used for mixing and casting of P.R. Gibson et al [13, 14] and S. Das et al [15] investigated composites is shown in Fig 2. It comprises of a cylindrical that a solid lubricating film can be formed on the wearing sillimanite crucible of 150mm diameter and 250mm depth surface with addition of graphite particulate in the aluminum with attachment of four baffles to its sidewalls for proper alloy. It helps in reducing the friction coefficient and to dispersion of second phase in melt during stirring. The increase the anti seizing quality and also improve crucible was placed in an electric heated muffle furnace. It tribological behavior of the base alloy. Jha et al [7] have was also equipped with a bottom pouring attachment, which observed that the porosity encountered during the production could be closed or opened by graphite stopper with a lever of aluminum-graphite composite material embrittles the system. A steel mould was placed beneath the furnace to cast material with crack nucleation and reduction in fracture the molten metal. In the top cover suitable opening was toughness and elongation of the matrix alloy leading to provided to charge materials and insert thermocouples. The increased wear. However addition of appropriate level of temperature of the furnace could be controlled with an graphite particulate can reduce it. Also at increased sliding accuracy of about ±50C. Metallic bath temperature was speeds the wear rate decreases with addition of graphite measured continuously by chromel/alumel thermocouple. content [16-20]. The agitator system could be raised or lowered with the help of the hanger and steel frame structure. After adjusting the The present article aims to contribute to a better mixer in a central position and required height from the understanding of the interrelation between presence of the bottom of the crucible, the motor was bolted and locked graphite particles in the matrix and the corresponding while mixing of melt. Three-blade impeller was used for mechanical properties and wear behavior. In the present effective mixing. This design provides very high rates of work, Al-Sn composite with different amount of graphite are shear and only axial and radial flow currents are utilized for being produced by liquid metallurgical route. Experimental mixing without any significant vortex formation due to the quantitative expressions, which correlate the ultimate tensile presence of baffles. The Al-Sn-graphite composites were strength (UTS), yield tensile strength, elongation, wear prepared employing liquid metallurgical route. The required www.ijmer.com 26 | P a g e International Journal of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.2, Mar-Apr 2012 pp-025-042 ISSN: 2249-6645 amount of commercial pure aluminum was charged into the by stirring action. Mixing was done for a period of 60 crucible and aluminum was heated to a temperature 2000C seconds. The emulsion was poured into the chilled above its melting point i.e. 6620C. A mechanical stirrer was cylindrical mould placed beneath the crucible. The same inserted into the melt, and agitation was started at a speed of procedure was adopted for different compositions. 35 s-1. The 50-μm-size electrolytic grade graphite powder Cylindrical casting of length 20cm and dia.2cm were was charged into the melt during stirring and the addition of obtained. the particulate into the melt was facilitated by vortex created 2.4 Wear test Pin-on-disc machine was used for evaluating the wear 2.3 Evaluation of as-cast Properties of the Composite properties under dry sliding condition. The cylindrical test The wet chemical analysis was used to determine the pin of 8mm diameter and 40mm length were used against a percentage of iron in the bulk .The metallographic hardened steel disc of 120 mm diameter. Wear tests were specimens were prepared using standard technique and conducted with variable applied pressure 3.9x10-1 Mpa and a studied under SEM for different feature present. The sliding speed of 0.5 m/s with a constant sliding distance of densities of the composite were determined using 10000 meters.
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