Wear Analysis on 7075 Aluminium Metal matrix Composites with TiO 2 and Fly ash Particles

Transcription

1 Wear Analysis on 775 Aluminium Metal matrix Composites with TiO 2 and Fly ash Particles S.Sugumar * Assistant Professor, Dept. of Mechanical Engineering, IFET College of Engineering s.sugumar73@gmail.com K.Ainnar Assistant Professor, Dept. of Mechanical Engineering, Dr.Paul s Engineering College kmsainnar@gmail.com, B.Elamvazhudi Associate Professor, Dept. of Mechanical Engineering, IFET College of Engineeringelamvazhdib@yahoo.in Abstract: Composites as a class of engineering materials provide almost unlimited potential for higher strength, stiffness and corrosion resistance over pure material systems of metals, ceramics and polymers. Aluminum is the most attractive non-ferrous matrix material extensively used particularly in the aerospace industry where weight of structural components is crucial. The low density and high specific mechanical properties of aluminum metal matrix composites (MMC) make these alloys one of the most interesting material alternatives for the manufacture of lightweight parts for many types of vehicles. Wear is a process of removal of material from one or both of two solid surfaces in solid state contact. As the wear is a surface removal phenomenon and occurs mostly at outer surfaces, it is more appropriate and economical to make surface modification of existing alloys than using the wear resistant alloys. The objective of this research work is to fabricate the new hybrid metal matrix composites and analyse the tribological characteristics. In this work, 775 Aluminium alloy used as a matrix material and TiO 2, Fly ash particulates used as a reinforcement materials and this composite is manufactured by stir casting technique. In addition to that, the wear mechanism also analyzed using SEM images. Key words: strength, stiffness, corrosion resistance, wear, tribology. C 1 INTRODUCTION omposite materials are formed by combining two or more materials that have quite different properties. The different materials work together to give the composite unique properties, but within the composite the materials can be differentiated since they do not dissolve or blend into each other. In Metal Matrix Composites, ceramics or metals in form of fibers, whiskers or particles used to reinforce in a metal matrix. Most commonly used matrixes are aluminum, magnesium, copper, titanium and zinc. The commonly used reinforcements are silicon carbide, alumina, boron, graphite, Titanium-dioxide and fly ash. The strengthening effect of the reinforcements in composites depends on the orientation of the reinforcements to the direction of the loads. The majority of effort in aluminum matrix composites has been directed toward development of high performance composites, with very high strengths and module, for use in specialized aerospace applications. However, there are a number of other applications in aircraft engines and aerospace structures where these very high properties may not be required, and where it could be cost * Corresponding Author effective to use other metal matrix composites. For these reasons, efforts were initiated to assess the potential of applying low cost aluminum matrix composites to these structures, using low-cost reinforcements and low-cost composite fabrication processes, including powder metallurgy, direct casting, and hot molding techniques. The complex nature of wear has delayed its investigations and resulted in isolated studies towards specific wear mechanisms or processes. in this research wear characteristics of Aluminium alloy 775 is measured with effect of Titanium dioxide and fly ash particles reinforcements. 2 HYBRID COMPOSITES A. 775 Aluminium Alloy Aluminium alloy 775 is an alloy with zinc as the primary alloying element. It is strong, with strength comparable to many steels, and has good fatigue strength and average machinability, but has less resistance to corrosion than many other Al alloys. Its relatively high cost limits its use to applications where cheaper alloys are not suitable. The metal matrix selected for present investigation is Al 775. The chemical composition of the matrix material is as shown the Table.1

2 TABLE 1 CHEMICAL COMPOSITION OF 775Al Element Si Fe Cu Mn Mg Cr Zn Nominal Composi tion% (Weight).4 max max max Actual Composi tion% (Weight).55 < B. Titanium-Dioxide (TiO 2 ) Titanium dioxide, also known as titania is the naturally occurring oxide of titanium, with chemical formula s TiO 2. It is mainly extracted from limonite ore. Titanium dioxide nanoparticles appear in the form of black hexagonal crystals. TiO 2 has the excellent mechanical properties and is shown in Figure 1. Figure 2. Fly ash particles 3 MANUFACTURING METHODS A. Liquid State Processing In order to provide high level of mechanical properties of the composite, good interfacial bonding (wetting) between the dispersed phase and the liquid matrix should be obtained. Liquid state fabrication of Metal Matrix Composites involves incorporation of dispersed phase into a molten matrix metal, followed by its Solidification. Wetting improvement may be achieved by coating the dispersed phase particles. The techniques used for producing cast particulate composites using liquid metallurgy are Stir casting and Infiltration process. The simplest and the most cost effective method of liquid state fabrication is Stir Casting. (Fig.3) Figure 1. TiO 2 particles C. Fly Ash Fly ash, also known as flue-ash, is one of the residues obtained from combustion, and comprises the fine particles that rise with the flue gases. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys of coal-fired power plants. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO 2 ) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata. fly ash particles are shown in Fig.2 Figure. 3 Stir casting setup

3 For the synthesis of A1 DMMC by impeller stirring the reinforcement is added into the vortex created by stirring the melt with a mechanical device most often by a rotating stirrer, which causes the dispersions to more along with the fluids resulting in mixing. The dispersion added to the top of the stirrer liquid is drawn towards the center of the vortex and a larger velocity of rotation at a smaller radial distance form the center may impart sufficient centrifugal velocity to the dispersions for their entry into liquid melt. In the synthesis of DMMCs stirring, the parameter like type, diameter and width of impeller as well as angle and number of blades play a crucial role in the distribution of reinforcement in the composite. The mixture of preheated reinforcement particles is added inside the vortex of 775 Al alloy melt, during mixing a vigorous stirring is done to have complete wetting of particles and the matrix. After complete addition of the particle into the melt, the composite material is tilt poured into the preheated (25 C) permanent steel mould of size 3mm length and 5mm diameter and allowed to cool in atmospheric air. The billet is then removed from the mould for machining. B. Materials Composition The billet is then removed from the mould. The Al 775 hybrid composite with different volume fraction of reinforcement (Al % fly ash, Al fly ash + 2.5%TiO 2 and Al fly ash + 5%TiO2) are produced with nano size particles of TiO 2 and micron size particles of TiO 2 and wear specimen are prepared shown in Figure.4 for machining. Composition I (Al Nano size particles of TiO 2 +flyash) (i) 92.5% Al % fly ash + 2.5% TiO 2 (ii) 9% Al % fly ash + 5% TiO 2 (iii)87.5% Al % fly ash + 7.5% TiO 2 Composition II (Al micron size particles of TiO 2 +flyash) (i) 92.5% Al % fly ash + 2.5% TiO 2 (ii) 9% Al % fly ash + 5% TiO 2 (iii) 87.5% Al % fly ash + 7.5% TiO 2 Figure.4 Fabricated specimen C. Pin on disk setup Pin-on-Disk wear testing is a method of characterizing the coefficient of friction, frictional force, and rate of wear between two materials. During this tribological test, a stationary disk articulates against a rotating pin while under a constant applied load. Pin-on-disk wear testing machine in accordance with ASTM F732 shown in Figure 5. High capacity machines allow for the testing of several material combinations at a time, on a single test frame. Mass-loss evaluation and differential analysis of test fluids are typically performed post-test to characterize wear properties. In addition, a contact profilometer can be utilized to evaluate the changes in surface topography due to articulation. The sliding experiments were conducted at room temperature in a pin on disc wear testing machine. The pins are loaded against the disc by a dead weight loading system. The material of the disc is hardened steel. Wear test on composite specimen were carried out under dry sliding condition at different applied loads of 3Kgf, 4Kgf and 5Kgf and the testing conditions mentioned below. During the test the relative humidity and temperature of the surrounding atmosphere is about 5% and 25 C respectively. The test duration is 1 minutes and disc speed of 4 rpm for the entire test. Conditions of the setup: Room temperature : 27 c Wear and friction monitor : TR 21 Pin specimen diameter : 8mm Length : 2 mm Material of disc : OHNS Disk test piece diameter : 55 mm Thickness : 12 mm Time duration : 1 min Constant disc speed : 4 rpm

4 material increased with the increment of reinforcements The effect of load and sliding distance on the coefficient of friction are plotted against sliding distance which are presented in Fig. 7(d) 7(f). From the Fig. 7(d), it has been asserted that the increase of sliding distance reduces the coefficient of friction. Composition I Composition II Figure 5 pin on disc setup 4 SEM ANALYSIS Metallurgical evaluation done with scanning electron microscope (SEM) and in electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that can be detected and that contain information about the sample's surface topography and composition. The electron beam is generally scanned in a raster scan pattern, and the beam's position is combined with the detected signal to produce an image. SEM can achieve resolution better than 1 nanometer. Specimens can be observed in high vacuum, in low vacuum, in dry conditions and at a wide range of cryogenic or elevated temperatures. The most common mode of detection is by secondary electrons emitted by atoms excited by the electron beam. By scanning the sample and detecting the secondary electrons, an image displaying the topography of the surface is created. A. Results 5 RESULTS AND CONCLUSIONS Fig. 6 (a) 92.5%Al %fly ash +2.5%TiO 2 Fig.6 (b) 9% Al % fly ash + 5% TiO 2 Fig. 6(d) 92.5%Al %fly ash +2.5%TiO 2 Fig.6 (e) 9% Al % fly ash + 5% TiO2 Characteristics were observed from pin on disc setup is shown in the Fig 7(a) - 7(c). Fig. 7(a) shows that the normalized wear rate 25 Micrometers during the contact time of 6 Sec. Fig 7(b) shows that wear rate of 15 microns and Fig 7(c) shows that wear rate of 2 microns. From these observations, addition of reinforcements 9% Al % fly ash + 5% TiO 2 in matrix material leads to decreases in wear rates (15 Micron). This is due to hardness of composite Fig.6(c)87.5% Al Fig.6(f) 87.5% Al 775 5% fly ash + 7.5% TiO 2 +5% fly ash +7.5% TiO 2 Figure 6(a) 6(f) SEM images of composition A& B

5 DISPLACEMENT CO-EFFICIENT DISPLACEMENT CO-EFFICIENT 5-5 Displacement Vs Time Fig. 7 (a) 92.5%Al % fly ash +2.5%TiO A1 5 1 B1 5 1 Fig.7 (b) 9% Al % fly ash + 5% TiO 2 Co-efficient of friction Vs Time Fig. 7(d) 92.5%Al %fly ash +2.5%TiO Fig.7 (e) 9% Al % fly ash + 5% TiO 2.6 The result obtained is almost similar to the result obtained earlier, Fig. 7(f) shows almost the same trend as observed earlier for N and 4 N load. The variations of coefficient of friction versus load for the hybrid metal matrix composites indicate a reduction in the value of coefficient of friction with incorporation of TiO 2 particles owing to the higher hardness of TiO 2 particles and fly ash particles. 6 CONCLUSIONS The wear rate of hybrid composites is analyzed by using wear performance graphs. The wear test results of the composition I & II hybrid composite specimen under dry sliding condition are presented in Fig.7 (a) - 7 (f). The graphs show that, the variation of wear rate and coefficient of friction with relation to the sliding distance at a room temperature. This indicates that wear resistance of the composite increases with increase in the percentage of silicon carbide and titanium oxide. The following things were concluded from the observations and graphs: wear rate is very low for 5% of TiO 2 and 5% flyash. wear rate is almost constant as compared to other materials. TiO 2 is best suited for high temperature, high load and medium speed applications. It has durability to withstand heat and pressure. TiO 2 and flyash hybrid metal matrix composites is suitable coating material for journal bearing applications because of its low wear rate, nofluctuation on wear rate. REFERENCES Fig.7(c)87.5% Al % fly ash + 7.5% TiO 2 Fig.7(f) 87.5% Al % fly ash +7.5% TiO 2 Figure 7(a) 7(f) Test results of composition A& B The reason being, the addition of different composition makes the composites into micro structural homogeneity, greater porosity and poor interfacial bonding between matrix and TiO 2 particles and fly ash particles. Fig. 7 (e) shows the variation of coefficient of friction varies from.4 to [1] Bharat Admile. Review on Mechanical & Wear Behavior of Aluminum-Fly Ash Metal Matrix Composite International Journal of Emerging Technology and Advanced Engineering Website: (ISSN , ISO 91:28 Certified Journal, Volume 4, Issue 5, May 214) [2] H.C. Anilkumar, H.S. Hebbarand K.S. Ravishankar, mechanical properties of fly ash reinforced aluminium alloy (al661)composites, IJMME, 211, vol.6. [3] Arun L. R, Dr. Suneel Kumar N. Kulkarni, Kuldeep B, Characteristic Studies on Aluminium Based Silicon Carbide and Fly Ash

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