SYNTHESIS OF BERYL REINFORCED ALUMINIUM METAL MATRIX COMPOSITES THROUGH VACUUM SINTERING

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Al- beryl metal matrix composites (MMC) containing beryl (5%, 10%, 15%, 20% and 30 wt. %) were fabricated using vacuum sintering. Al- beryl powders were selected as starting materials The beryl as a mineral phase was initially crushed, and mechanically sieved to various sizes. The final particle sizes in the range of 30±10 μm were made. Beryl content in Al was varied from 5 to 30-wt%. The green pellets were made to 25 mm diameter with a load of 1.02 MPa and sintered in a vacuum furnace maintained at 600ºC. The hardness results clearly demonstrated that increasing beryl from 5 to 15-wt% in vacuum sintering was responsible for increased hardness values. The microstructural examination clearly demonstrated that vacuum sintering at 600ºC has led not only to improved density level but also to improved sliding wear properties. Key words: Aluminium, Beryl, Metal Matrix Composites, Sintering.
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  http://www.iaeme.com/IJMET/index.asp 703 editor@iaeme.com International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 7, July 2017, pp. 703–716, Article ID: IJMET_08_07_079 Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=7 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed SYNTHESIS OF BERYL REINFORCED ALUMINIUM METAL MATRIX COMPOSITES THROUGH VACUUM SINTERING S.K. Rajendra Research Scholar, Mechanical Engineering, Jain University, Bengaluru and Associate Professor, Department of Industrial Engineering and Management, Dr. Ambedkar Institute of Technology, Bengaluru, Karnataka, India C.M. Ramesha Department of Mechanical Engineering, Ramaiah Institute of Technology, Bengaluru, Karnataka, India ABSTRACT  Al- beryl metal matrix composites (MMC) containing beryl (5%, 10%, 15%, 20% and 30 wt. %) were fabricated using vacuum sintering. Al- beryl powders were selected as starting materials The beryl as a mineral phase was initially crushed, and mechanically sieved to various sizes. The final particle sizes in the range of 30±10 µm were made. Beryl content in Al was varied from 5 to 30-wt%. The green pellets were made to 25 mm diameter with a load of 1.02 MPa and sintered in a vacuum furnace maintained at 600ºC. The hardness results clearly demonstrated that increasing beryl  from 5 to 15-wt% in vacuum sintering was responsible for increased hardness values. The microstructural examination clearly demonstrated that vacuum sintering at 600ºC has led not only to improved density level but also to improved sliding wear properties. Key words: Aluminium, Beryl, Metal Matrix Composites, Sintering. Cite this Article: S.K. Rajendra and C.M. Ramesha, Synthesis of Beryl Reinforced Aluminium Metal Matrix Composites Through Vacuum Sintering.  International  Journal of Mechanical Engineering and Technology , 8(7), 2017, pp. 703–716. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=7 1. INTRODUCTION Composite materials are well known for their tailor made properties by combining two or more properties. The tailorable properties of MMCs suit the needs of extremely good thermal stability, associated with high strength; ductility and toughness at a higher temperature are desirable for design application in aero gas turbine engines. Al based MMCs having hard ceramic materials has improved specific strength, specific modulus, and wear resistance. Many of these properties help in defence, automobile, marine, and aerospace application. Al based  Synthesis of Beryl Reinforced Aluminium Metal Matrix Composites Through Vacuum Sintering http://www.iaeme.com/IJMET/index.asp 704 editor@iaeme.com MMCs have been extensively studied. The incorporation of second phase particles [18, 19] such as Al 2 O 3 , SiC, TiN, and TiO 2 , in Al alloy improves physical, mechanical, and tribological properties. These ceramic particles have high density and high hardness. In liquid metallurgy vertex route technique settling of ceramic particles was the limitation especially for hard ceramic particle. In preparation of Al based MMCs with light ceramic particles, the ceramic particles are comes out as a slag. Among various ceramic additions to Al, SiC has given much greater attention by many researchers but the Al-SiC still has limitations such as the formulation of Al 4 C 3  during high temperatures which impairs the mechanical properties of the Al MMCs. Thus, efforts are made to overcome the problems by incorporating other reinforcing materials such as beryl and also synthesis through vacuum sintering [1, 4, 5, 6]. The present investigation is aimed with three specific points. The first one is selection of ceramic particles such as beryl with a density of ~2.65 g/cc, which is lighter than other ceramic particles such as SiC, Al 2 O 3 , TiN, and has similar density of Al. The beryl has a hardness of ~ 1800 Hv. The second aim is to fabricate Al based MMCs using beryl as reinforcing particles using vacuum sintering of powder metallurgy route. The third aim is to study the hardness, wear rate, and wear resistance. 2. EXPERIMENTAL PROCEDURE Commercially available aluminium powder with of 99.7% purity with average particle size of 40 ± 5 µm size of Leo Chemicals, Bangalore was selected as starting material. In addition, beryl that is abundantly available in Karnataka region in the form of rocks was selected. Finally, the powder was sieve to fine (38 – 53 µm) and coarse (106 – 150 µm). Aluminium is a metallic element of atomic number 13. Its atomic weight is 26.98 atomic mass unit; its specific gravity is 2.7 (the ratio between the density of the aluminium and water); the crystal structure of aluminium is face-centered cubic (FCC); and the atomic radius is 0.1431 nm. Aluminium is one of the easiest metal to form and has a good combination of high strength and light weight. Beryl is naturally occurring and chemically having beryllium-alumina-silicate [Be 3 Al 2 (SiO 3 ) 6 ] was used as the reinforcement material, and found following main advantages in using it as reinforcement: It has high melting point of around 1400°C, has low refractive index of 1.57-1.59, has density almost same as aluminium of around 2.65g/cc, high strength and high hardness of 1800 Hv. The composition of beryl does not contain any carbon content which helps in avoiding the formation of Al 4 C 3  during high temperature synthesis of composites; It is not radio active in nature. The particle size of the obtained beryl was in the range of 150-200 µm, in order to reduce these particles to the size of 38-53 µm, a separate set up was made using a lathe machine, where a bowl with lid was made and rotated using a lathe machine. The beryl particles which were in the range of 150-200 µm was poured along with the high carbon high chrome steel balls (50Nos) of diameter 10mm in the portable ball mill with both the sides of the coated steel cylinder with steel enclosures. A threaded long rod of length 200mm was passed through the center of both enclosures and tightened it with the help of washers and nuts. This entire setup was fixed in between the lathe canters and rotated at a speed ranging between 150-400rpm for duration of 2-5 hours. The powders that were obtained after the successful completion of process was removed and sieved. Figure 1 shows the photographs of beryl in mineral phase, and fine powder. In figure 2, SEM images of Commercial Pure Aluminium (CPAl) and beryl are shown.    S.K. Rajendra and C.M. Ramesha   http://www.iaeme.com/IJMET/index.asp 705 editor@iaeme.com Figure 1 Photographs of beryl in (a) mineral phase (b) fine powder form Figure 2: SEM images of CPAl and beryl Starting material CPAl and beryl in required quantities were taken and blended together properly using a pestle and mortar for 30 minutes and again in a ball mill for 30mins using PVA as binder to ensure uniform distribution of the beryl particles throughout the Aluminium matrix. The blended samples were then compacted in Universal testing machine at load of 5 ton applied pressure. The compacted pellets were taken and heated in a tubular furnace in an inert atmosphere (99.99% pure argon gas) at temperatures of 600°C for a holding time of 2 h to ensure the densification of the compacted powder samples. The heating rate used was 5°C/min and the holding time for each sample was 1 hour after the heating period. The samples are pushed into the cooling zone where the drop in part temperature is controlled precisely and cooled to room temperature. Vickers Micro hardness tester (Model: MVH-I, METATECH Industries, Pune, India). The tests were carried out on the polished specimens by applying a 50g (0.49N) load for 10s using a diamond indenter. The measurements were carried on the matrix of the alloys. Each micro hardness value reported in the present work is an average value of five readings to get an average values. The samples were etched with slandered Keller’s reagent and examined under both optical microscope and SEM (JEOL 840A). A pin-on-disc apparatus, Model: TR 20 LE, DUCOM, Bangalore, India, was used to perform the wear experiment. The sintered pellet has a height of 4 mm, has been raised to 40 mm by adhering the samples to steel pin of 6mm diameter, and 36 mm height. The specimens were allowed to slide against a rotating EN 32 steel disc of hardness 65 Rc, wear rate, and wear resistance were monitored as a function of sliding distance up to 1200 m at 0.5 and 0.75 kg loads. Table 1 gives the chemical composition of commercial pure Al. A wet chemical analysis method is used to analyze the presence of minor alloying elements such as Fe, And Si are 0.17, and 0.11 respectively.  Synthesis of Beryl Reinforced Aluminium Metal Matrix Composites Through Vacuum Sintering http://www.iaeme.com/IJMET/index.asp 706 editor@iaeme.com Table 1 Chemical composition (wt. %) of CPAl Fe Si Al 0.17 0.11 Balance Table 2 shows the chemical analysis of beryl powder. Chemical analysis of beryl powder was carried by a inductively coupled plasma emission spectrometer (ICP-OES: Make - Thermo fisher scientific, Model – 6300 Duo). Table 2 Chemical composition of beryl powder Test Parameter Unit Test Result Test Method Silica as SiO 2 % 57.44 ICP-OES Alumina as Al 2 O 3 % 21.01 Beryl oxide as BeO % 16.82 Iron oxide as Fe 2 O 3 % 1.31 Calcium Oxide as CaO % 1.09 Magnesium Oxide as MgO % 0.56 Sodium Oxide as Na 2 O % 0.017 Potassium Oxide as K 2 O % 1.56 Manganese Oxide as MnO % 0.017 In table 3, the composition of aluminium and wt. % of beryl for three samples A, B and C for our experimental investigation is shown. the composition gives the various composition of beryl powder in Al. Table 3 Compositions of aluminium and wt. % of beryl Sample Composition of Al Wt. % of Beryl A 90 10 B 80 20 C 70 30 Figure 3 shows the photograph of a five ton vacuum sintering furnace for pressureless and pressure sintering. Figure 3 Photograph of a five ton sintering furnace
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