Analysis and Characterization of Iron Doped Sintered Silicon Carbide without Binder in through Powder Metallurgy Route

Transcription

1 Analysis and Characterization of Iron Doped Sintered Silicon Carbide without Binder in through Powder Metallurgy Route Shiv Dayal Dhakad 1, Ankit Bansal 2, Harneet Saggu 3, Mayank Dwiedi 4 shivdhakad999@gmail.com Abstract The mechanism of sintering and particular of the structure formation in the liquid phase sintering of sintered abrasive magnetic powder that was silicon carbide as abrasive and carbonyl iron powder as magnetic were studied, and investigated the microstructural development at three different pressures and at constant sintering temperature. The specimens were prepared through powder metallurgy route. The weight percentage of silicon carbide and carbonyl iron powder was kept uniform that is 1:1 weight/volume respectively. During the preparation of specimens the holding time was investigated to keep green compact from deforming before sintering. Micro hardness testing was performed by Vickers hardness tester and density was calculated by Archimedes principle. The changes in microstructure and its morphology were studied by using scanning electron microscopy (SEM) at different magnification. The structure of silicon carbide was thoroughly studied and obtained the crystalline structure after sintering. There was exponential increase in the micro-hardness at 5 ton, 7 ton, and 9 ton respectively.as well as the density also increases with increasing compaction pressure. Particle size of pure CIP ranges from 1 4 µm, most of the particles are in the range of 3 ~ 4 µm. Keywords Sintering, SEM, CIP, Morphology, Grain size. Introduction Abrasive comes from the word abrade, which means to rub off. An abrasive substance is a very hard tough material.when crushed and ground into grains like sand; it has many Page 1

2 sharp cutting edges and points. Several common forms in which abrasive are used in metal working include the following. Abrasive compounds (in the form of paste, sticks or cakes) Grinding wheels, Sharpening stones Properties of abrasives. Abrasive must possess three common properties Hardness, Fracture resistance, Wearresistance. Hardness means the ability of the abrasive to cut the surface of the material being polished or ground. The fracture resistance of an abrasive is its toughness that is how well it resists breaking or crumbling during polishing or grinding when pressed against the work. The fracture resistance should be such that when the abrasive grains become dull they will break away when so broken, new sharp cutting edges are exposed. The fracture resistance of grinding wheels is related to the kind of bonding material that binds the grains together. The wear resistance of an abrasive is its ability to resist wear and stay sharp. This is related to the hardness of the abrasive material. Thus, harder abrasive materials generally are more wear resistant. Abrasives are classified as either natural or artificial. Natural abrasive are minerals that occur in nature. Artificial abrasive also known as synthetic or manufactured abrasive are manmade. With the exception of diamond, artificial abrasives are harder than the natural abrasives. Artificial abrasives have largely replaced natural abrasive in metal working because of their greater hardness and wear resistance like Silicon Carbide, Aluminium oxide, Boron Oxide, Zirconium Oxide. [1] Silicon carbide (SiC) is an artificial type of abrasive material with outstanding mechanical and physical properties, it possess high mechanical strength, low density,high hardness, high thermal conductivity, large bandgap, low thermal expansion coefficient, and excellent oxidation and corrosion resistances[2-4].due to its high thermal conductivity, it is a leading material for devices operating at high temperature, high power and severe environmental conditions.[5-6].micro-sized SiC particles and whiskers are commonly used as reinforcement materials for ceramics, metals and alloys for various structural and tribiological applications[7-8]. SiC belongs to a class of compounds with strong covalent bonds, which impedes mass transfer during sintering without the use of special additives. Ordinarily, dense SiC ceramics is obtained by means of liquid-phase sintering with oxide additives. The properties of the green compact are also importantto achieve an appropriate microstructure and hence a high quality product. Increasingly, attention is directed at processing methods that can produce a homogeneous green microstructure; colloidal techniques have been shown to be superior to dry pressing in achieving this[9]. Carbonyl iron is a highly pure (97.5% for grade S, 99.5+% for grade R) iron; prepared by chemical decomposition of purified iron penta carbonyl.it usually has the appearance of grey powder, composed of spherical micro-particles. Most of the impurities are carbon, oxygen, and nitrogen. Powdered cores made of carbonyl iron have high stability of parameters across a wide range of temperatures and magnetic flux levels, with excellent Q factors between 50 khz and 200 MHz. A popular application is in broadband inductors, especially in high-power applications. Particles of carbonyl iron (20-40%) suspended in a carrier fluid (60-80%) are used as a magnet or heological fluid. The molecular formula of carbonyl iron is Fe (Co)5, Manufactured using the carbonyl decomposition process. Experimental procedure The initial material was pure silicon carbide as abrasive and carbonyl iron powder as magnetic was taken in powder form. Next step was to mix the powders uniformly, the weight percentage of the silicon carbide and carbonyl iron powder were taken 1:1 weight/volume respectively. The starting powders were homogenized by ball milling for 1 Page 2

3 hour with stainless steel milling balls and, subsequently dried in a rotation evaporator and sieved. Powder batches were consolidated by hydraulic press at three different pressures that is at 5 ton, 7 ton and 9 ton of to cylindrical green compacts with a height and diameter of 10 mm respectively. The circular green compacts for the measurement of different mechanical properties had dimensions of 30 mm internal diameter while 50 mm external diameter. Sintering experiments were performed in a graphite resistance furnace in a constant temperature of 1200 degree centigrade under various atmosphere conditions. There were no binders or additives were used in sintered abrasive magnetic powder, so its green compact stability mostly depends on holding time after compression of the powders. The loss depends upon sintering condition and varies between 2 and 5wt%.The final density is measured by using Archimedes method with water as the immersion medium. The sintered samples were prepared at a temperature of 1200 C and three different pressure of 5 ton, 7 ton, and 9 ton respectively. Fracture and micro hardness were determined by Vickers hardness tester by indentation method of 10kg.Microstructral development and morphology were investigated by spectrum electron microscopy(sem) and the results are compared. Result and discussion Micro-hardness The micro hardness testing was done on Vickers hardness tester of pyramid indentor,the specimen is of disc type with diameter of 30mm and thickness with 10mm respectively. There is exponential increase in micro hardness with increase in compaction load, the following values obtained during micro hardness testing. S.No Compaction load(ton) Micro hardness (kgf/mm2) Table 1: Micro hardness at 5, 7, 9 ton pressure respectively. Graph showing the micro hardness value Page 3

4 The investigation through this test is compaction load is directly proportional to the hardness. Density of sintered magnetic abrasive S.No Compaction load Density gm/cm3 (ton) Table 2: Densities at 5, 7, 9 ton pressure. Density gm/mm density gm/mm density compaction load in ton Graph showing the densities value Density of sintered abrasive magnetic was calculated by Archimedes principle through water immersion method and obtained that the value of density increasing with increase in compaction load. In above graph the subscript 1, 2, 3 represents the compaction load at 5 ton, 7 ton, 9ton respectively. Morphology of carbonyl iron powder Characterization of powders was done by using scanning electron microscopy (SEM).The SEM topography of carbonyl iron particles shows that carbonyl iron is of spherical morphology (figure 1 (a)).it had been investigated that the particle size of carbonyl iron powder ranges from 1 4 µm, most of the particles are in the range of 3 ~ 4 µm. Page 4

5 Fig 1 scanning electron microscopy (a) SEM image of carbonyl iron powder pure (b) SEM image of un-bonded abrasive magnetic. (b) Morphology of un-bonded abrasive magnetic powder The SEM topography of un-bonded abrasive magnetic shows that, the spherical morphology was carbonyl iron and the sharp edges were of silicon carbide powder respectively. The particles were un-bonded there were no bond between the particles and the particle size was not uniform. Morphology of silicon carbide The SEM topography of silicon carbide show that,the sharp edges of silicon carbide can be seen of crystalline structure, the particle size was not uniform ranges from 4-12um respectively. Page 5

6 Fig (a) SEM image of silicon carbide Morphology of sintered abrasive magnetic powder at 5, 7, 9 ton respectively Page 6

7 (a) SEM image of sintered Abrasive magnetic, compaction pressure at 5 ton (b) SEM image showing grain boundaries of sintered abrasive magnetic. (c) SEM image of sintered Abrasive magnetic, compaction pressure at 7 ton Page 7

8 (d) SEM image of sintered Abrasive magnetic,compaction pressure 9 ton The morphology of abrasive has been investigated by SEM,The sharp edges of sintered abrasive magnetic can be seen after crushing the sintered specimen in ball mill and shapes sizes of different abrasive magnetic grains. The CIP is diffused on the surface of abrasives particles due to high compaction pressure and become magnetic abrasivesin fig (a) The SEM image of sintered abrasive magnetic compacted at a pressure of 5 ton and sintered at an increasing temperature from C up to the total densification was achieved during the complete sintering cycle. The particle size ranges from 2um um and the average size of particles was 6.2 um respectively. The size of the particles were not uniform and it was investigated that the abrasive and magnetic particle formed bond between grains as compared to un-bonded abrasive magnetic powder and the grains comes closer due to increase in compaction pressure.in fig (c) SEM image of sintered abrasive magnetic powder at a compaction pressure of 7 ton and on constant temperature,the grain particles comes much closer as compared to the grains of powder compacted at 5 tons, The size of the particles was not uniform and particle size ranges from 3um -15um.In fig (d) the abrasive and magnetic powder particles comes much closer and form a strong bond as compare to other two images and due to which increases its hardness. Conclusion 1. The micro hardness of the green compact increased with increasing compaction pressure by 4% and 7% as compare to 5 ton on 7 ton and 9 ton repectyively. 2. The density of the green compact also increased with increasing compaction pressure 3. Porosity of the green compact decreased with increasing compaction pressure. 4. SEM images of carbonyl iron powder, silicon carbide and un-bonded abrasive magnetic explained the topography clearly. 5. SEM images of sintered abrasive magnetic powder at three different pressure shows the variation in microstructure that is in particle size,grains boundaries etc. Acknowledgement SEM testing was conducted at central facility IIT-ROORKEE. Page 8

9 References 1- M. W. Barsoum, Fundamentals of ceramics, Boca Raton, FL Taylor & Francis, T. Narushima, T. Goto, T. Hirai, Y. Iguchi, Mater. Trans. JIM 38,821 (1997) 3- S.Z. Wang, L.Y. Xu, B.Y. Shu, B. Xiao, J.Y. Zhuang, E.W. Shi,J. Inorg. Mater. 14, 527 (1999) 4- K. Watari, J. Ceram. Soc. Japan 109, S7 (2001) 5- M. Mehregany, C.A. Zorman, S. Roy, A.J. Fleischman, C.H. Wu,N. Rajan, Int. Mater. Rev. 45, 85 (2000) 6- M. Willander, M. Friesel, Q.U. Wahab, B. Straumal, J. Mater.Sci. Mater.Electron. 17, 1 (2006) 7- D.Z. Wang, H.X. Peng, J. Liu, C.K. Yao, H. Han, Comp. Sci.Technol. 53, 21 (1995) 8- I. Garcia, J. Fransaer, J.P. Celis, Surf. Coat. Technol. 148, 171(2001) 9- I. A. Aksay, F. F. Lange and B. I.Davis, J. Am. Ceram.Soc. 66(10) (1983) J. L. Kang, Sintering: densification, grain Growth and microstructure, London, Elsevier, This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( by the Authors. Licensed by HCTL Open, India. Page 9