Indian Journal of Science and Technology, Vol 9(20), DOI: 10.17485/ijst/2016/v9i20/84294, May 2016 ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645 Evaluation of Microstructure, Mechanical and Wear Properties of Aluminium Reinforced with Boron Carbide Nano Composite A. Devaraju 1 * and K. Pazhanivel 2 1 Department of Mechanical Engineering, Adhi College of Engineering and Technology, Affiliated to Anna University, Chennai, Kanchipuram - 631 605, Tamil Nadu, India; adevaa2011@gmail.com 2 Department of Mechanical Engineering, Thiruvalluvar College of Engineering and Technology, Affiliated to Anna University, Chennai, Vandavasi - 604 505, Tamil Nadu, India Abstract Background/Objectives: In recent days, the demand of light-weight materials is being increased in industrial applications. Especially, nanocomposites are used in aerospace, automobile sector and bio-medical applications. Methods/Statistical Analysis: In this context, in the current study, aluminium alloy - boron carbide composites were fabricated and its microstructure analysis was evaluated with the help of Optical Microscope (OP). Further, a detailed study was done to evaluate the mechanical and wear resistance of the fabricated composites. Findings: The OP pictures reveal that boron carbide particles were uniformly distributed in aluminium matrix. When the amount of boron carbide is increased, the density of the composites is decreased which resulted 1. The micro hardness is increased. 2. The ultimate compressive strength is also increased and 3. Wear resistance is also increased. Application/Improvements: This study proves that the aluminium reinforced with Boron Carbide composite exhibits better performance than aluminium AL1100 in all aspects. Hence, aluminium reinforced with Boron Carbide composite can be used in aerospace applications. Keywords: Mechanical Properties, Microstructure, Micro Hardness, Nanocomposite, Wear Resistance 1. Introduction Synthetic fiber reinforced composites are widely used in aerospace industries as they are having greater toughness and rigidity 1. A detailed review on Polymer nano-composites suggests that replacing composites by nano-composites in sandwich structures could produce improved properties than the simple sandwich structures 2. 3 An innovative attempt was done on Polypropylene/Montmorillonite (PP/MMT) nano-composites and proves that PP/MMT nano-composites maintain its mechanical properties at cryogenic temperature. These studies were useful to select the current study on nanocomposite material. Studied about the wear behavior of Nanostructured Aluminium (Al) and boron carbide (B 4 C) composites and conclude that Nano crystallization of Al matrix and incorporation of B 4 C Nano particles into the A1 matrix improve the wear performance and also increase their hardness 4. Studied on self-mating of A1-B 4 C Nano composites and found that tribo film was formed which reduce friction and wear 5. Analyzed the influence of particle properties on erosive wear of sintered boron carbide 6. Studied the effect of small amounts of boron (less than 195 ppm) added to 16% Cr white iron 7. It was found that boron addition increases wear resistance of white irons by 40% on average. Conducted aware study of boron carbide *Author for correspondence
Evaluation of Microstructure, Mechanical and Wear Properties of Aluminium Reinforced with Boron Carbide Nano Composite ceramics like B 4 C TiB 2 used in abrasive wear jets 8. B 4 C TiB 2 nozzles was compared with B 4 C nozzles. It was concluded that B 4 C nozzle is performed better wear resistance than B 4 C TiB 2 nozzle. Conducted experiments on aluminium matrix composite with addition of B 4 C as reinforcement to evaluate the mean grain size of ceramic, metal composites, made from boron carbide (B4C), aluminium (Al), nickel (Ni) powders 9. Conducted experiments in the wettability of B 4 C with Al and Al-Ti (1%) alloy using the sessile-drop method at different temperatures 10. It was found that addition of titanium to aluminum enhances the wettability of B 4 C which reduces surface and mechanical properties. Conducted experiments in three aluminium metal matrix composites containing reinforcing particles of B 4 C, SiC and Al 2 O 3 (0.20 vol.%) were processed 11. From the fracture surface analysis, B 4 C reinforced Al composite seemed to exhibit a better interfacial bonding compared to the other two composites. Even though reasonable research works were done on aluminium alloy - boron carbide composites, microstructure, mechanical and wear properties have not been studied in detail. Hence, in this work, aluminium alloy - boron carbide composites were fabricated and it s mechanical and wear properties were evaluated. 2. Methodology 2.1 Materials In the present study, boron carbide particles of 30 microns size were reinforced with LM6 aluminium alloy (LM6 Al) in 2.5, 5, 7.5 and 10 wt. % and hereafter, it is termed as A2.5, A5, A7.5 and A10, respectively. The main composition of LM6 Al is about 86 to 88% of aluminium and 11 to 13% of silicon. The fabrication of LM6 Al-B4C composites were carried out by stir casting process. Boron carbide particles were preheated around 800ºC for 2 hours to oxidize their surfaces. 2.2 Compression Test The dimensions of cylindrical compressive specimens were diameter of 10 mm and length of 15 mm. 2.3 Microstructure Optical microscope was used to record the surface microstructure of Al and Al-B 4 C composite. Before placing the sample under Optical microscope, all the samples were mirror polished as per standard procedure and then these were etched carefully by Kellar Solution. 2.4 Vickers Hardness Test Vickers hardness test was carried out for the Al and Al-B 4 Ccomposite material. The time for the application of the force was 10 s, and the test force was maintained for 0.3 kg. After the force was removed, the diagonal lengths of the indentation were measured and Vickers hardness number, HV, was calculated as HV = Constant Test force/surface area of indentation Three tests were conducted for each sample and the average result is reported. 2.5 Wear Test The standard high carbon steel (EN31) was selected as disc material. The fabricated Al-B 4 C composite was used as pin in the geometry of 10 mm diameter and 30 = \mm length. Dry sliding wear experiments were conducted in air at room temperature using a pin-on-disc tribo-meter. The specimen was cut from the cast samples as per ASTM standard (ASTM G99). The wear tests were conducted under three different loads of 8N, 16N, and 25N and two different sliding speeds of 1.0 m/s, and 2 m/s. Pin weight loss was measured at each loading conditions. 3. Results and Discussion 3.1 Micro Structural Analysis The distribution of silicon carbide and boron carbide inside the aluminum matrix is investigated by Optical Metallurgical microscope. The microstructure of base metal (Al) is presented in Figure 1(a) as polished and Figure 1(b) after etched. The etched sample shows the fine grained microstructure with grain size less than 2-3 microns. The microstructure of Al- B 4 C nanocomposite is presented in Figure 2(a) as polished and Figure 2(b) after etched. The surface of the sample was taken in polished condition so as to observe the metal matrix to see any particles other than the base metal was present. The optical microscope picture (Figure 2(a) and 2(b)) reveals that the distribution of ceramic particles inside the matrix of aluminum and it is uniform over the matrix. This uniformity was obtained by stirring it for a period of 10 minutes. The ceramic particles appear black against a bright background. 2 Indian Journal of Science and Technology
A. Devaraju and K. Pazhanivel (a) Figure 1. (b) Microstructure of Al sample (a) as polished and (b) After etched. (a) (b) Figure 2. Microstructure of Aluminum Boron Carbide (Al-B4C) composite sample (a) as polished and (b) After etched. Indian Journal of Science and Technology 3
Evaluation of Microstructure, Mechanical and Wear Properties of Aluminium Reinforced with Boron Carbide Nano Composite It is observed that, the distribution of aluminum particles is more even. The average size of the aluminum particles visualized as 100 μm. Microstructure shows fine particles distribution in aluminium solid solution. The matrix primary is aluminium. The matrix shows the etched matrix of the aluminium sample with the particles dispersion. The particles are uniformly distributed. The primary matrix shows the fine grained microstructure with grain size less than 2-3 microns. The dark particles are the composite particles (B 4 C). 3.2 Hardness Test Result Analysis The hardness value of base metal (LM6 Al)) was 29HV and Aluminium-boron carbide of all fabricated composites was between 38HV and 46HV. Hence, these results confirm that hardness value was increased due to uniform dispersion of boron carbide in the aluminium matrix. 3.3 Wear Properties In order to identify the optimal percentage of B 4 C addition for the reinforcement with Aluminium alloy, the series of wear tests such as EN31 disc vs. LM6 Al pin, EN31 disc vs. A2.5 pin, EN31 disc vs. A5 pin, EN31 disc vs. A7.5 and EN31 disc vs. A10 pin at 8N, 16N and 25N for the sliding distance of 1000 m and sliding speed of 1 m/s, were conducted and the mass loss of pin is presented in Figure 3. It was observed that the wear loss is high for untreated Aluminium alloy. Alternatively, when percentage of the reinforcement with B 4 C is increased, wear loss gets reduced. It is due to the reinforced boron comes between sliding body and acted as dry lubricant. From the Figure 3, it was found that 7.5% reinforcement of boron carbide (A7.5) is the optimum percentage of reinforcement which shows the lowest wear. It proves that the addition of B 4 C reduces the wear rate in all percentage of B 4 C. It is because of B 4 C segregation between the sliding bodies and act as a solid lubricant. Since it was found that 7.5% reinforcement of boron carbide (A7.5) is the optimum percentage of reinforcement, it should be verified at higher sliding distance and higher sliding speed. The higher sliding distance and higher sliding speed was selected as 2200 m and 2 m/s respectively. The pin wear loss during wear tests of EN31 disc vs. LM6 Al pin and EN31 disc vs. A7.5 at 8N, 16N and 25N for the Sliding distance of 2000 m and sliding speed of 2 m/s is presented in Figure 4. When the load is increased, mass loss is also increased at all samples for the Figure 3. The pin wear loss during wear tests of EN31 disc vs. LM6 Al pin, EN31 disc vs. A2.5 pin, EN31 disc vs. A5 pin, EN31 disc vs. A7.5 and EN31 disc vs. A10 pin at 8N, 16N and 25N for the sliding distance of 1000m and sliding speed of 1m/s. Figure 4. The pin wear loss during wear tests of EN31 disc vs. LM6 Al pin and EN31 disc vs. A7.5 at 8N, 16N and 25N for the Sliding distance of 2200 m and sliding speed of 2 m/s. selected higher sliding distance and higher sliding speed. It is due to heating effect to thermal softening and seizure. Also it brings more sliding contact and thereby causes enhanced wear. However, untreated LM6 Al pin shows more wear than 7.5% reinforced samples. Moreover, till 16N the mass loss was low. Hence we can conclude 16N and 7.5% of B 4 C reinforcement is the optimum for the selected wear test conditions. 4 Indian Journal of Science and Technology
A. Devaraju and K. Pazhanivel Figure 5. Ultimate load for 2.5, 5, 7.5 and 10 wt. % of B4C reinforced samples. 3.4 Compressive Test Result Analysis A Compressive test is a mechanical test which is conducted to measure the maximum amount of compressive load required to make fracture on the material. The samples were prepared in the form of a cylinder. The samples were compressed between the platens of a compression-testing machine by a gradually applied load. During the test, deformation at various loads was recorded and the corresponding displacement was also noted. The ultimate load of LM6 Al was 2800 KN. It is increased for all B 4 C reinforced samples as 3500 KN for A2.5, 3700 KN for A5, 4500 KN for A7.5 and 3950 KN for A10. It was found that at maximum load of 4500 KN and it is for A9 samples. Ultimate load of all B 4 C reinforced samples is presented in Figure 5 and it reveals that when percentage of B 4 C is increased beyond 7.5%, its strength is started to getting down. Figure 6(a) and Figure 6(b) shows compression test report of A7.5 and A10 samples. The compression test helps to conclude that B 4 C reinforcement should be within 7.5%. 4. Conclusion Boron carbide particles of 30 microns size were reinforced with LM6 Aluminium alloy (LM6 Al) in 2.5, 5, 7.5 and 10 wt.%. Figure 6. Compression test result of (a) A9 sample and (b) A12 sample. The surface microstructure shows the fine grained microstructure with grain size less than 2-3 microns. The composite particles (B 4 C) are appeared as dark particles. The hardness value was increased for all B 4 C reinforced samples and is due to uniform dispersion of boron carbide in the Aluminium matrix. Wear tests of Aluminium-Boron Carbide (nano) composite pin vs. steel disc were carried at room temperature under dry sliding conditions. Tests were conducted as a function of speed and percentage of B 4 C reinforcement. The following conclusion can be made from the wear study, 1. 7.5% reinforcement of boron carbide (A7.5) is the optimum percentage of reinforcement which shows the lowest wear and 2. Indian Journal of Science and Technology 5
Evaluation of Microstructure, Mechanical and Wear Properties of Aluminium Reinforced with Boron Carbide Nano Composite 16N is the optimum load for the selected wear test conditions. It was also observed that increase of compression strength with increase in percentage of B 4 C reinforcement in nanocomposite. The maximum Strength will be obtained in 7.5% of B 4 C reinforced nano-composite. Flexural strength will be slightly decreases with increase beyond 7.5% addition of B 4 C compared substrate material. But there is an increase of flexural modulus while increasing the % of nano-clay at all samples. Properties which have been shown to undergo substantial improvements including Mechanical properties such as strength, modulus and dimensional stability. 5. References 1. Punyamurthy R, Sampathkumar D, Bennehalli B, Patel R, Gouda R, Srinivasa CV. Influence of fiber content and effect of chemical pre-treatments on mechanical characterization of natural abaca epoxy composites. Indian Journal of Science and Technology. 2015; 8(11):1-11. 2. Puggal S, Dhall S, Singh, Litt MS. A review on polymer nanocomposites: Synthesis, characterization and mechanical properties. Indian Journal of Science and Technology. 2016; 9(4):1-6. 3. Manoharan N, Selvakumar V. Cryogenic mechanical properties of PP/MMT polymer nanocomposites. Indian Journal of Science and Technology. 2014; 7(S7):16-23. 4. Abdollahi A, Alizadeh A, Baharvandi HR. Dry sliding tribological behavior and mechanical propertiesof Al 2 024 5 wt.% B 4 C nanocomposit produced by mechanical milling and hot extrusion. Materials and Design. 2014; 55:471 81. 5. Li X, Gao Y, Pan W, Wang X, Song L, Zhong Z, Wu S. Fabrication and characterization of B 4 C-based ceramic composites with different mass fractions of hexagonal boron nitride. Ceramic International. 2015; 41(1):322-30. 6. Shipway PH, Hutchings IM. Influence of particle properties on the erosive wear of sintered boron carbide. Wear of Materials: International Conference on Wear of Materials. 1991; p. 63-70. 7. Kerti I, Toptan F. Micro structural variations in cast B4C-reinforced aluminium matrix composites (AMCs). Materials Letters. 2008; 62:1215 8. 8. Shorowordi KM, Haseeb ASMA, Celis JP. Tribo-surface characteristics of Al B 4 C and Al SiC composites worn under different contact pressures. Wear. 2006; 261:634 41. 9. Sarpun IH, Ozkan V, Tuncel S, Unal R. Determination of mean grain size by ultrasonic methods of Tungsten carbide and boron carbide composites sintered at various temperatures. 4 th International Conference on NDT; 2011. p. 11-4. 10. Sarkar A, Kocaefe D, Chen XG. Effect of Titanium on the wetting of Boron carbide by aluminium. Fuel. 2014; 30:598 607. 11. Shorowordi KM, Laoui T, Haseeb ASMA. Experiments on three aluminium metal matrix composites containing reinforcingparticles of B4C, SiC and Al2O3. Journal of Material Processing Technology. 2003; 142(3):738 43. 6 Indian Journal of Science and Technology