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Densification and deformation behaviour of sintered powder metallurgy


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  • 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4 Issue 1 January- February (2013), pp. 01-07 IJMET© IAEME: Impact Factor (2012): 3.8071 (Calculated by GISI) ©IAEME DENSIFICATION AND DEFORMATION BEHAVIOUR OF SINTERED POWDER METALLURGY COPPER-7%TUNGSTEN COMPOSITE DURING COLD UPSETTING N.Vijay ponraj1, Dr.G.Kalivarathan2 1 Research Scholar, CMJ University, Meghalaya, Shillong, India 2 Principal/Dept of Mech. Engg, PSN Institute of Technology and Science, Tirunelveli, Tamilnadu, India, Supervisor CMJ University, Shillong, Meghalaya. Email:vijay_ponraj@yahoo.comABSTRACT Studies were conceded out to evaluate the initially preformed density and initialaspect ratio on the densification behavior of sintered Copper 7% Tungsten composite. Thepreform possessed 0.85 is the initial theoretical density. Aspect ratio varied from 0.4, 0.6 and0.8. Properties of Copper Tungsten composites with respect to linear strain, lateral strain andtrue stress were evaluated and plotted. Studies exposed that higher stress and higher strainvalues are obtained in composite when compared to the Tungsten powder. The composite ofCopper 7%W obtained at 750oC. The Composite obtained at lower aspect ratio acquired thehighest stress and strain when compared to the composites preforms obtained at other aspectratioKEYWORDS: Powder Metallurgy, Metal Matrix Composites, Preform, Sintered Copper-7%Tungsten Composite, Nano Structure.1. INTRODUCTION The term “composite” broadly refers to a material system which is tranquil of discreteconstituents (the reinforcement) distributed in a continuous phase (the matrix). It derives itsindividual characteristics from the properties of its ingredients, from the geometry andarchitecture, and also from the properties of the restrictions (interfaces) of its differentconstituents. Composite materials are usually classified on the basis of physical or chemicalnature of their matrix phase, like polymer matrix, metal-matrix and ceramic composites etc.Among the materials that are extended to an increasing scope of metal matrix composites.The space industry was the first sector captivated in the usage of these materials. Anotherfragment of even superior fiscal importance for the development of new metal matrixcomposites (MMC‟s) is the automotive industry. The suppleness allied with MMC’s in 1
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEtailoring their physical and mechanical properties as compulsory by the users have madethem suitable candidates for a gamut of applications related to automobile and aeronauticalsectors. The preface of fine dispersed particles into the metal matrix has crucial reinforcingeffects when maintained at prominent temperatures. Powder forging technique isconventional as the most inexpensive and efficient procedure leading to aperture eliminationand superior mechanical strength. Although a number of processes are available forproducing MMCs, the powder metallurgy technique was found to be the most appropriatebecause it yields better mechanical properties. Research on dispersion strengthened materialspoints out the implication of the properties of the starting metallic powders and also theimportance of the preliminary structure in preserving the structure of the concludingmanufactured goods. A very important aspect of scattering strengthening is the evenallotment of tungsten particles, their fine distribution, especially in nanometer scale, and theintroduction of a possible amount of dispersed particles into the volume of the base metal.The powder metallurgy sintered parts possesses 20-40% porosity which can beadvantageously used, but the mechanical properties of the component are adversely effectedby the presence of porosity. Therefore, the parts intended for dynamic applications, the finalcompaction should be close (up to about 1.5-2%) to that of fully dense material. Forging ofthe sintered preforms result in a precision component with the reduction or elimination ofporosity. The lessening in porosity during forging, results in a decrease in preform volume.The compliant of porous materials, thus, does not follow the laws of number constancy.Further, the “material parameters” (such as, modulus of elasticity and modulus of rigidity) arefunctions of density of the buckling body and as such the “material parameters” also feel avariation along with a change in porosity (density). Initially, there had been someexperimental, semi-experimental or analytical looms using slab method for obtaining thedensity of porous formed metal parts. Thereafter, several researchers studied the forging ofporous materials and garrison by using finite element method taking material to be rigidlyplastic. A challenge to use numerical method for the analysis of powder metal forgingoperation has also been studied by various researchers using a unyielding plastic approach.Rigid plastic approach could be adequate for large deformation by excluding the effect ofresilient behaviour of the material. Subsequently, there have been some attempts to developelastic-plastic approach to study the deformation of porous materials. The aim of the presentwork is to study the mechanics of cold forging of powder metal preforms taking into accountits plastic strains as the work material which undergoes deformation. The model developedwas applied to study the forging of an axis symmetric short frozen cylindrical part undersimple upsetting. The analysis was carried out for the press forging with slow rates ofdeformation where inertia and temperature effects were negligible. The total results predictedthe densification pattern of the work material and the loads required to produce the desireddeformation.2. PROBLEM FORMULATION Present exploration focused on the densification behavior of sintered copper 7%tungsten powders when taken in varying quantities. Frictionless compression tests are used tofind out the fundamental plastic flow characteristics of porous metals. Studies expose that thedeformation was uniform with barreling of cylindrical surfaces. The proposed study alsocarries out to evaluate the initial preformed density and initial aspect ratio on thedensification behavior of sintered copper 7% tungsten composites. The preform obsessed0.85 as initial density and three aspect ratio varied from 0.4, 0.6, and 0.8. Four performs, each 2
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEof different aspect ratio were taken for each temperature. A critical literature survey revealsthat several attempts has been made in producing components through powder metallurgyroute, which may contain one or the other type of impurifier. These perhaps could not beverified during the course of several investigations as the fine dispersion of self oxidizedmaterial in the component perchance induced enhanced properties. A wide variety of researchin the area of elemental powder and its own oxide composite has been carried out. But earlierinvestigations have shown that extruding the sintered preform containing the self oxidizeddispersions in different proportions on extrusion may encourage improved mechanicalproperties. It is well established that in the metal forming operations the deformation is neversternly homogeneous and therefore pores present on the surface of the component can neverbe closed either due to the predominance of tensile forces or due to hydrostatic forces presentin the dead metal zones. Therefore, it is more likely that the particulate structure will becustomary at the surface of the component irrespective of preform design for any upsettingtest. For studying the behavior of copper 7% tungsten composite during cold upsetting,mechanical properties should be given precedence. In most of the methods adapted forstudying the strengthening of the composite, strengthening metal must have higher meltingpoint than matrix metal. In this method, we have developed tungsten as a strengtheningcomponent, but it possesses higher melting temperature than Copper (matrix metal). Thebasic advantage of dispersion strengthened materials is that it does not improve yield strengthat ambient temperature or work hardening rate. The present investigation on compositecarried out at temperatures of 7500c with three aspect ratios of 0.4, 0.6 and 0.8.3. EXPERIMENTAL PROCEDURE3.1. Materials Required:The materials required for this investigation are: Copper and Tungsten powder for compositepreparation, graphite for using as lubricant, high carbon die steel punch and die, two flatplates heat treated to Rc 53 to 56 and tempered to Rc 46 to 49, a stainless steel tray, and anelectric muffle furnace.3.2. Preparation of Copper-7% Tungsten Composite:Copper and Tungsten powders were used in the present investigation. These powders werepurchased from M/s. Metal Powder Company (P) Ltd., Tirumangalam, Madurai, Tamilnadu,India. Electrolytic copper and atomised tungsten were obtained with 100% and 99.73% purityrespectively. The individual powders were pulverized in a high energy ball mill (Fritsch,Germany - Pulverisette - 6) for four hours after that it was mixed on weight basis with 7%Tungsten and rest Copper powder. These composite powders were pulverized in a highenergy ball mill and after 10 hours milling, the obtained particle size was approximatelybelow 400nm. SEM was used for evaluation of morphological changes of the particles aftermilling and is shown in Fig. 1(a-c). Fig. 1(a) shows the SEM image of the Cu particles at9500X magnification and has a structure of a cluster of tiny particles and like small flattenedflake particles due to severe plastic deformation of copper, micro-welding and fracture of thelarge flakes due to typical mechanical milling. Fig. 1(b - c) shows the SEM image of the Wpowders at 6000X and 2000X magnification respectively, It is in the formation of flattenedparticles with pancake structure. Fig. 1(d) shows the SEM image of the Cu-7%W PowderComposite at 8000X particles. It shows the morphological changes of Cu-7%W powdermixture after 10 hours milling. No significant difference between the Cu morphology in thecomposite and the monolithic W powder is observed at low milling times; that means the fine 3
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME )W elements distributed throughout the Cu matrix and represents the particle size in the range thebetween 200-400nm. (a) (b) Fig. 1 SEM micrograph after ball milling (a) Cu powder 9,500 X (b) W powder 6,000X3.3. Characteristics of Oxidized Powder:The characteristic of the copper and Tungsten powder is shown in Table 1 (a (a-b). Theindividual powders were pulverized in a high energy ball mill (Fritsch, Germany -Pulverisette - 6) for four hours after that it was mixed on weight basis with 7% Tungsten and %rest Copper powder. Table 1 Characteristics of powder (a) Copper Powder Test IS 5461 ASTM B-417 ASTM B- ASTM E- Standard 213 194 Property Sieve analysis, % Apparent Flow rate Acid +75µm +45µm -45µm density (g/cc) Sec(50g-1) Insoluble EC/86 0.42 5.43 94.24 1.58 Nil Nil Grade (b) Tungsten Powder Characteristics Test Standard Value Sieve analysis : - 45 µm ASTM D-185 99.00 Average Particle Size, Fisher ASTM B-330 3.92 Number Oxygen Content (Hydrogen Loss) ASTM E-159 1.85 Other Impurities AAS 0.21 Purity 97.93 4
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME3.4. Compaction of Zinc-Zinc Oxide Powder:Cylindrical compacts of 20 mm diameter with an aspect ratio of 0.40, 0.60 and 0.80 wereprepared. The compacts were prepared using ball milled Cu-7% W composite. The compositepowders were compacted by using suitable punch and die set assembly on a UniversalTesting machine having 1 MN capacity. Compacting pressure was applied gradually and itwas 1.2 GPa for three aspect ratios. Graphite was used to lubricate the punch, die and thebutt. When preparing the compacts, the initial density and aspect ratio were maintained byprecisely controlling the mass and accurately monitoring the compacting pressure employed3.5 SinteringAfter the compaction, the compacts were immediately taken out from die set assembly andloaded into the furnace for sintering. To prevent oxidization, the green compacts wereinitially covered with inert argon atmosphere in the furnace. The sintering was carried out inan inert gas circulated electric muffle furnace at 750°C for a holding period of one hour. Assoon as the sintering schedule was over, the sintered preforms were cooled inside the furnaceitself to the room temperature. After the completion of sintering, the preforms were cleanedby using a fine wire brush.3.6 Cold Deformation ExperimentsDeformation experiments were carried out by using flat faced dies and a hydraulicallyoperated compression testing machine of having 1MN capacity. The flat dies were machinedand tempered. Flat faces of the dies were ground after heat treatment in a grinding machine,in order to obtain the final dimensions and surface quality and its hardness was measured as90 HRB after tempering. Graphite was well applied as lubricant on the ends of preforms andcontacting surfaces of flat dies, which created a situation for almost frictionless idealdeformation. In general, each compact was subjected to an incremental compressive loadingin steps of 50kN until the appearance of visible cracks on the free surface. Immediately, afterthe completion of each step of loading, the height, the contact diameters at the top andbottom, the bulged diameter and the density were measured for each of the deformedpreforms. The density measurements were carried out using Archimedes principle.Experimental measurements were also used to calculate the various parameters namely thestresses, the Poisson’s ratio, density ratio and the strain.4. RESULTS AND DISCUSSIONS The sintered P/M Copper-7% W composite was made under the temperatures of7500c. Cylindrical preforms of three different aspect ratios were employed in the compressiontests. Plots were drawn for copper-7% W between the hoop strain and the axial strain tocompare with different aspect ratios. The rate of change of hoop strain with respect to axialstrain was not the same for all aspect ratios. This indicates that each aspect ratio had differentslope and the hoop strain increased with axial strain. Among the three aspect ratios, sinteredpreforms oxidized at aspect ratio of 0.8 had more strain values. Similarly, the aspect ratio of0.8 also had high strain values when compared with others. From the plots it was also evidentthat the strain increased with higher aspect ratios. The deformation of the composites underlower aspect ratio is less. Due to the low value of hoop and axial strain, composites have thelow ductile property .This composite is more suitable for the compressive load applications.Plots between the true stress and true strain are shown in figure 3. It is observed that the trueaxial stress increases rapidly as the true axial strain is increased, followed by a gradual 5
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEincrease in the true axial stress with further increase in the axial strain. Further, it is foundthat the 0.80 preform improved load bearing capacity compared to that for other aspect ratios,while the initial fractional density remains constant. Cu - 7%W Initial Theoretical Density 0.85 1.6 1.4 1.2 Hoop Strain 1 0.8 Aspect Ratio 0.4 0.6 Aspect Ratio 0.6 0.4 Aspect Ratio 0.8 0.2 0 0 200 400 600 800 Axial Strain Fig.2 Axial Strain Vs Hoop Strain for different aspect ratio of 0.4, 0.6 and 0.8 Cu - 7% W Initial Theoretical Density 0.85 1.6 1.4 1.2 Axial Strain 1 0.8 Aspect Ratio 0.4 0.6 Aspect Ratio 0.6 0.4 Aspect Ratio 0.8 0.2 0 0 200 400 600 800 Axial Stress Fig.3 Axial Strain Vs Axial Stress for different aspect ratio 0.4, 0.6 and 0.85. CONCLUSION The major findings of this investigation include the rate of change of hoop strain withrespect to the axial strain indicated high values for higher aspect ratios. The rate of change oftrue stress with respect to true strain was different for different aspect ratios. Higher aspectratio had the maximum value of both true stress and true strain than lower aspect ratio. 6
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEREFERENCES[1] J. Eliasson, R. Sandström, “Application of aluminium matrix composites”. KeyEngineering Materials, 104-107, 1995, 3-36.[2] P.S. Gilman, Journal Metallurgy, Vol. 43, No. 8, 1991, 7.[3] Y. Wu, Y. Zhang, X. Huang, J. Guo Ceram. Int., Vol. 27, 2001, 265-268.[4] P.K. Jena, E.A. Brocchi, M.S. Motta, “In-situ formation of Cu–Al2O3 nano-scalecomposites by chemical routes and studies on their microstructures”. Materials Science andEngineering: A, Vol. 313, Issues 1-2, 2001, 180-186.[5] D.W. Lee, G.H. Ha, B.K. Kim, “Synthesis of Cu-Al2O3 nano composite powder”. ScriptaMaterialia, Vol. 44, Issue 8, 2001, 2137-2140.[6] P.K. Jena, E.A. Brocchi, I.G. Solórzano, M.S. Motta, “Identification of a third phase inCu–Al2O3 nanocomposites prepared by chemical routes”. Materials Science andEngineering: A, Vol. 371, Issues 1-2, 25, 2004, 72-78.[7] C. Skoufadis, D. Panias, I. Paspaliaris, “Kinetics of boehmite precipitation fromsupersaturated sodium aluminate solutions”. Hydrometallurgy, Vol. 68, No. 1, February,2003, 57-68.[8] M.S. Motta, E.A. Brocchi, I.G. Solórzano and P.K. Jena, “Complementary microscopytechniques applied to the characterization of Cu-Al2O3 nanocomposites”. FORMATEXMicroscopy Book Series No. 2 - Current Issues on Multidisciplinary Microscopy Researchand Education [ISBN (13): 978-84-609-6605- 4/ (10): 84-609-6605-4] 2004, 215-223.[9] P. Ramakrishana, “Powder metallurgy-progress and opportunities”. Proceedings ofNational Seminar on Powder Metallurgy-Opportunities for Engineering Industries, IITBombay, Vol. 1, 1985.[10] P.K. Jhonson, “P/M industry, trends, new technologies propel P/M growth”.International Journal of Powder Metallurgy, Vol. 32, No. 2, 1996, 145-154.[11] R.J. Green, “A plasticity theory for porous solids”. International Journal of MechanicalScience, Vol. 14, 1972, 205-224.[12] S. Shima, M. Oyane, “Plasticity theory of porous metals”. International Journal ofMechanical Science, Vol. 18, 1976, 285-291.[13] T. Tabata, S. Maski, K. Hosokawa, “A yield function for forging of porous metals”.International Journal of Powder Metallurgy, Powder Technology, Vol. 16, 1980, 149.[14] S.M. Doraivelu, H.L. Gegel, J.C. Malas, J.S. Gunasekera and J.F. Thomas, “A NewYield Function for Compressible P/M Materials”. International Journal of MechanicalScience, Vol. 26, No. 9/10, 1984, 527-535.[15] H.K. Cho, J. Suh, K.T. Kim, “Densification of porous alloy steel preforms at hightemperature”. International Journal of Mechanical Science, Vol. 36, 1994, 317-328.[16] H.K. Cho, K.T. Kim, J.S. Kim, “Cold compaction of composite powders”. Transactionson ASME, Journal of Engineering Materials and Technology, Vol. 122, 2000, 119-128.[17] K. Mori, S. Shima, K. Oskada, “Finite element method for the analysis of plasticdeformation in porous metals”. Bulletin of JSME, Vol. 23, No. 178, 1980, 516-522. [18] B. Selvam, A. P. Singh, Densification and Deformation Behavior of Sintered P/M Zinc-Zinc Oxide Composite during Cold Upsetting”. Jordan Journal of Mechanical and IndustrialEngineering.Vol.5, 2011,Pg447-450. 7