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Prediction of behaviour in forming of sintered copper 10%tungsten nano powder composite

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  • 1. INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp. 387-393© IAEME: www.iaeme.com/ijmet.asp ©IAEMEJournal Impact Factor (2012): 3.8071 (Calculated by GISI)www.jifactor.com PREDICTION OF BEHAVIOUR IN FORMING OF SINTERED COPPER-10%TUNGSTEN NANO POWDER COMPOSITE N.Vijayponraj1, Dr.G.Kalivarthan2, Vetrivel.S.C3 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. 3 Asso.Prof/Dept. of Mech. Engg, PET Engineering College, Tirunelveli, Tami nadu, India, E mail: vijay_ponraj@yahoo.com ABSTRACT Experimental investigations are performed in order to predict the mechanism of deformation and densification behaviour during cold upset forming operation on sintered Cu- 10%W Nano composite. High-energy mechanical milling was used to produce Cu and W Nano powder composites. Cylindrical preforms with initial theoretical density of 85% possessing three different aspect ratios of 0.40, 0.60 and 0.80 were prepared using a die and punch assembly with a hydraulic press. The preforms are sintered in an electric muffle furnace at 650°C, and subsequently the furnace was cooled. Cold deformation experiments are conducted in incremental deformation steps. The relationships between various parameters are evaluated Keywords: Metal-Matrix Composites (MMCs), Nano-structures, Preform, Mechanical properties, Sintered copper-10% Tungsten 1. INTRODUCTION Composite material is the combination of two or more materials which are having different phases and the properties superior to the base materials. Composite materials are produced by casting and powder metallurgy methods. By means of casting methods, composite materials reinforced by dispersion particles [1, 2], platelets [3], non-continuous (short) fibres and continuous (long) fibres [4-5] as well as composite materials with hybrid reinforcement composed of particles and fibres [6] are produced by powder metallurgy methods, composite materials reinforced by dispersion particles [7-9], platelets [13], non- continuous fibres [10-11] and continuous fibres [12] are manufactured. High-energy mechanical ball milling can be used to produce nano powders from micron size. When mechanical milling is used in the traditional sense, the process does not generate a new material, since the microstructure of the powder does not change. Particulate 387
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEcomposites are prepared by mixing reinforcement and matrix material in powder form andcold pressing to near theoretical density. An important aspect of composites is theirfabricability to near-net shapes. To develop and improve near-net shape forming process thestudy on analyzing the fabrication process is necessary as well as experimental study onfabrication of composites. Most of the authors were reported the deformation behaviour of various powdercomposites in micro and nano particle sizes except Cu-W. The material properties of thesintered compacts were ascertained from the uniaxial compression test with 10% Tungstenwith copper three aspect ratios 0.40, 0.60 and 0.80. Graphite was used as surface preformlubricant. From this study, it was also attempted to establish the relationship between thefractional theoretical density, the Poisson’s ratio and other parameters namely the stress,strain and strain factor under Cu-10%W preform compositions.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) InsolubleEC/86 Grade 0.40 5.40 94.20 1.56 Nil Nil (b) Tungsten Powder Characteristics Test Standard Value Sieve analysis : - 45 µm ASTM D-185 99.00 Average Particle Size, Fisher ASTM B-330 3.90 Number Oxygen Content (Hydrogen Loss) ASTM E-159 1.87 Other Impurities AAS 0.22 Purity 97.902. EXPERIMENTAL DETAILS2.1 Materials and characteristics Copper and Tungsten powders were used in the present investigation. These powderswere purchased from M/s. Metal Powder Company (P) Ltd., Tirumangalam, Madurai,Tamilnadu, India. Electrolytic copper and atomised tungsten were obtained with 100% and99.00% purity respectively. The characteristic of the copper and Tungsten powder is shownin Table 1 (a-b). 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 5%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 flattened 388
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Sepparticles with pancake structure. Fig. 1(d) shows the SEM image of the Cu 10%W Powder Cu-10%WComposite at 8000X particles. It shows the morphological changes of Cu 10%W powder Cu-10%Wmixture after 10 hours milling. No significant difference between the Cu morphology in the morphologycomposite and the monolithic W powder is observed at low milling times; that means the fineW elements distributed throughout the Cu matrix and represents the particle size in the rangebetween 200-400nm. (a) (b) Fig. 1 SEM micrograph after ball milling (a) Cu powder 9,500 X (b) W powder 6,000X2.2. Compacting Cylindrical compacts of 20 mm diameter with an aspect ratio of 0.40, 0.60 and 0.80were prepared. The compacts were prepared using ball milled Cu 10% W composite. The Cu-10%composite powders were compacted by using suitable punch and die set assembly on a owdersUniversal Testing machine having 1 MN capacity. Compacting pressure was appliedgradually and it was 1.2 GPa for three aspect ratios. Graphite was used to lubricate the punch,die and the butt. When preparing the compacts, the initial density and aspect ratio weremaintained by precisely controlling the mass and accurately monitoring the compactingpressure employed.2.3 Sintering After the compaction, the compacts were immediately taken out from die set takenassembly and loaded into the furnace for sintering. To prevent oxidization, the greencompacts were initially covered with inert argon atmosphere in the furnace. The sintering wascarried out in an inert gas circulated electric muffle furnace at 650°C for a holding period ofone hour. As soon as the sintering schedule was over, the sintered preforms were cooledinside the furnace itself to the room temperature. After the completion of sintering, thepreforms were cleaned by using a fine wire brush.2.4 Cold Deformation Experiments Deformation 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 as91 HRB after tempering. Graphite was well applied as lubricant on the ends of preforms and 389
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEcontacting 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. The Theoretical approach tocalculate the above parameters are discussed in detail under ref. [13].3. RESULTS AND DISCUSSION3.1. Deformation Behaviour of Preforms The results of deformation behaviour of 85% initial fractional density, Cu-10%Wcomposite preforms are discussed in this section. The following stress strain relationshipconcerning the plastic deformation is discussed in detail for the various aspect ratios withgraphite lubricants3.1.1. Various stresses and axial strain Using the simple theory of plasticity, the axial stress (σz), the hoop stress (σθ) and thehydrostatic stress (σm) were calculated and plotted against the axial strain (εz) for differentaspect ratios in Figures 2(a –c) for the Cu-10%W composite preforms. The hoop stress istensile in nature because during compressive loading the bulged diameter expands.Meanwhile, for any deformation level, the increase in the hoop stress due to loading is verylow compared to that of the axial stress. However, the value of the hydrostatic stress is muchless than the other stresses, namely the axial stress (σz) and the hoop stress (σθ) and it is alsocompressive in nature, at different strain level. For all preforms, the axial and the hoop stresslevel also increases for a given aspect ratio. The values of the axial stress, the hoop stress andthe hydrostatic stress are high for the lower aspect ratio (0.40) than higher aspect ratios(0.60and 0.80) preforms. 800 Initial Fractional Density 0.85 600 Cu 10%W Aspect Ratio 0.8 400 Lubricator:Graphite STRESS,Mpa 200 Axial Stress 0 Hoop Stress -200 0 0.2 0.4 0.6 0.8 1 Hydro Static Stress -400 -600 (a) -800 AXIAL STRAIN 390
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 600 Initial Fractional Density 0.85 400 Cu 10%W Aspect Ratio 0.6 Lubricator:Graphite 200 STRESS,Mpa 0 Axial Stress 0 0.5 1 -200 Hoop Stress -400 Hydro Static Stress -600 (b) -800 Axial Strain 1000 Initial Fractional Density 0.85 Cu 10%W Aspect Ratio 0.4 Lubricator:Graphite 500 STRESS,Mpa Axial Stress 0 Hoop Stress 0 0.2 0.4 0.6 Hydro Static Stress -500 (C) -1000 Axial Strain Fig. 2.The Variation of stresses with respect to axial strain for various aspect ratios (a) 0.80 (b) 0.60 (c) 0.403.1.2 Axial stress and axial strain Fig.3 shows the effect of aspect ratio on the characteristic features of the axial stress(σz) against the axial strain (εz) for a given initial fractional density of 0.85 of Cu-10%Wcomposite. These plots are similar in nature irrespective of the aspect ratio values. It isobserved that the true axial stress increases rapidly as the true axial strain is increased,followed by a gradual increase in the true axial stress with further increase in the axial strain.Further, it is found that the 0.80 preform improved load bearing capacity compared to that forother aspect ratios, while the initial fractional density remains constant. 391
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Initial Fractional Density 0.85 Cu-10%W 1000 800 Axial Stress 600 Aspect Ratio 0.8 400 Aspect Ratio 0.4 200 Aspect Ratio 0.6 0 0 0.5 1 Axial Strain Fig.3 The relationship between σz and εz3.2 Densification Behaviour of preforms In densification behaviour of preforms the following relationships are discussed indetail by varying the initial aspect ratio provided the initial fractional density value is keptconstant for Cu-5%W composites.  ρf  (ε z − ε θ ) • Fractional density ρ   and strain parameter e  th 3.2.1. Fractional density and strain parameter Figure 4 has been drawn to establish the relationship between the fractional densityvalue  f  of the deforming preform and the value of e (ε ρ   z −εθ ) in accordance with the    ρ th theoretically-derived relationship [16] for sintered P/M preforms during cold axialdeformation. The plots show the existence of power law relationship between the fractionaltheoretical density  ρ f  and e (ε z   −ε θ ) . However the lower aspect ratio shows better ρ   th fractional density values because it has lesser porosity. 0.96 Fractional Density 0.92 Cu-5% W Composite 0.88 Lubricant:Graphite Aspect ratio: 0.4 0.6 0.84 1.0 1.1 1.2 1.3 Strain parameter Fig.4 The relationship between Fractional Density and Strain parameter 392
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME4. CONCLUSION The study has been carried out of cold upset forming of sintered Cu-5%W nanocomposites performs. The basic conclusions that can be drawn from the presentinvestigations are as follows. The axial stress has an increased trend with higher level of deformation till failure. This isbecause, at the time of increasing the load, the pores in the preforms are flattened and contactsurfaces are increased. So the load –bearing capacity increasing steeply by increase of strain. Lower aspect ratio exhibits improved densification and load –bearing capacity comparedto that of higher aspect ratio performs densify uniformly and quite easily due to rapid loadtransfer resulting in extensive work-hardening.REFERENCES[1] Corbin S F, Wilkonson D S. The tensile properties of a particulate reinforced Al alloy inthe temperature range 196-300°C. Canad Metall 1996; 35:189-198.[2] Gupta M, Lai M O, Soo C Y, Effect of type of processing on the microstructural featuresand mechanical properties of Al-Cu/Si metal matrix composites. Mater Sci Eng 1996; A210:114-122.[3] Kainer K U. Cast magnesium alloys reinforced by short fibre. In: Proceedings of theInternational Conference on Magnesium Alloys and their Applications. Garmisch-Partenkirchen 1992; p. 415-422.[4] Bowman R R, Misra A K, Arnold S M. Processing and mechanical properties of Al2O3fiber-reinforced NiAl composites. Metall Mater Trans 1995; 615-628.[5] SchroÈder J, Kainer K U. Magnesium base hybrid composites prepared by liquidinfiltration. Mater Sci Eng 1991; 243-246.[6] Abkowitz S, Weihrauh P F, Abkowitz S M. Particulate-reinforced titanium alloycomposites economically formed by combined cold and hot isostatic pressing. Ind Heating1993; 32-37.[7] Doel T J A, Bowen P. Tensile properties of particulate-reinforced metal matrixcomposites. Composites A 27 1996; 655-665. [8] Mordike B L, Kaczmr J, Kielbinski M, Kainer K U. Effect of tungsten content on theproperties and structure of cold extruded Cu-W composite materials. Powder Metall Int 1991;[9] Kainer K , SchroÈder J, Mordike B L. Influence of various P/M production methods onthe properties of magnesium-SiC-Composites. In: Proceedings of the InternationalConference on Advanced Composites 1993; p.1061-1065.[10] Kaczmar J W, Kainer K U, Effect of alumina fibre content on properties of PM 6061aluminium alloys based composite materials, Powder Metall 1992; 35:133-135. [11] Kuhn H A, Downey C L, How flow and fracture affect design of preforms of powderforging. Powder Metal Powder Technol 1974; 10 (1): 59–66.[12] Kuhn H A. Deformation processing of sintered powder materials. In: Powder MetallurgyProcessing Academic Press. New York 1978; p.99–138.[13] Selvakumar N, Narayanasamy R. Deformation Behavior of Cold Upset Forming ofSintered Al-Fe Composite Preforms. J Eng Mater Technol 2005; 127: 241-246. 393

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