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Assessment of mechanical and tribological characteristics of Silicon Nitride reinforced aluminum metal matrix composites
Composites Part B 175 (2019) 107138
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Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Assessment of mechanical and tribological characteristics of Silicon Nitride reinforced aluminum metal matrix composites G.B.Veeresh Kumar a, *, Pinaki Prasad Panigrahy b, Nithika Sureshb, Pramod R b, C.S.P. Rao a a b
Department of Mechanical Engineering, National Institute of Technology - Andhra Pradesh, Tadepalligudem, Andhra Pradesh, India Department of Mechanical Engineering, Amrita School of Engineering, Bengaluru Campus, Amrita Vishwa Vidyapeetham, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Aluminum Silicon nitride Metal matrix composites Hardness Strength Wear
The present paper focuses on the investigation of physical, mechanical and tribological characteristics of Al6063 alloy reinforced with Silicon Nitride powder. The Al6063-Silicon Nitride Metal Matrix Composites were fabri cated by following stir casting method of liquid metallurgy technique. The amount of reinforcement incorpo ration in matrix material was from 0 to 10 wt% varied in intervals of 2. The obtained composites were used in the investigative studies related to physical, mechanical & tribological experimentations. The tests were performed on the Al6063 alloy and its composites as per in harmony with the ASTM Standards. The test results it can be observed and appreciated that increasing the reinforcement percentage, the characteristics like hardness and density increased monolithically and significantly. The dry sliding wear test is performed using pin on disc configuration tribometer and the results state that the composite has higher wear resistance. Basically the Al6063 is relatively soft and as per dry sliding wear concern at the applications of stringers, upper and lower wings of aircraft, floor breams, seat tracks, fuselage of an aircraft’s, the wear resistance plays a crucial role in relative movement at contact surfaces, hence the present work focused on developing Al6063-Silicon Nitride Metal Matrix Composites with enhanced mechanical and tribological properties. Off all the compositions, the com posite material having the highest percentage of reinforcement showed better properties. Scanning Electron Microscope, Energy Dispersive Microscopy images were used to study the fabricated composites before and after the wear morphology during wear test.
1. Introduction The unparalleled performance of composites has been broadly deliberate by investigators [1–4]. The particulate composites hold resistance to indentation and applied in applications like automobile parts such as calipers, blocks of pistons, cylinders, cylinder embed rings, contractors, microwave channels, impellers, vibrator segment and space structures [5]. Amongst the Metal Matrix Composites (MMCs) Aluminum (Al) based MMCs have shown excellent mechanical charac teristics [6]. The most common reason behind the sudden failure of machine components is wear [7]. Munmun Bhaumik et al., fabricated Al6063–ZrO2-Alumina (Al2O3) MMCs, concluded that the relative den sity is found to increase than the base alloy, also indicated that the fractured surface of Al-MMC is brittle in nature [8]. M K Aravindan et al., studied the Al6063–SiC 10 wt% MMCs, concluded that the microstruc ture with good distribution of particles and the mechanical properties like, hardness, Ultimate Tensile Strength (UTS), Percentage (%)
Elongation and Yield Strength properties increased with rising of rein forced weight (wt) fraction of SiC [9]. K. Hemalatha et al., fabricated Al6063–Al2O3 by stir casting route up to 9 wt% and confirmed that the composites are clearly superior to Al6063 in comparison with hardness and UTS at the cost of reduced ductility [10]. C S Ramesh et al., developed Al6063–TiB2 in-situ composites and conducted dry sliding wear tests at different loads and sliding velocities, revealed that the composites have lower coefficient of friction (COF) and wear rates than Al6063 alloy. Nevertheless, the rates of wear noticed to increase with increased load applied and sliding velocity [11]. Conducted investiga tion on wear behavior of the Al6063-10 wt% Silicon Carbide (SiC) MMCs and indicated that the noteworthy process constraints for loss of wear were normal applied load, sliding velocity, sliding distance, abrasives size and noticed Mechanically Mixed Layer (MML) formation, tearing of surfaces, groove formation and particle pullout under different sliding situations [12,13]. Most of the breakdowns occurring in machines is due to wear of the
* Corresponding author. E-mail address: [email protected] (G.B.Veeresh Kumar). https://doi.org/10.1016/j.compositesb.2019.107138 Received 5 March 2019; Received in revised form 20 June 2019; Accepted 5 July 2019 Available online 6 July 2019 1359-8368/© 2019 Elsevier Ltd. All rights reserved.
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Table 1 Al6063 alloy chemical compositions by weight %’age. Chemical compositions
Si
Cu
Mn
Fe
Cr
Zn
Mg
Ti
Al
Al6063
0.60
0.10
0.10
0.30
0.10
0.10
0.80
0.01
Bal
composites is affected by temperature and load. Reports suggest that Al6061–SiC composites will have less wear rate on increase in load [17]. On performing the wear test on composite of Al6061 and short fiber fillings, noticed that these have increasing resistance to wear [18]. From a large number of publications, it is evident that the MMCs having 15% of SiC particulates as reinforcement and fabricated using powder met allurgy technique have shown good wear resistance [19]. The wear of a composite is immensely affected by the microstructure, sliding distance, sliding speed and the load applied. For Al2219–SiC composites it was observed that wear and the cracking of SiC particles increased with the increase in the load applied [20]. The factors like sliding wear are the
Table 2 The base alloy matrix and particle reinforcement materials properties. Material
Hardness (HV)
Density (g/cc)
Tensile Strength (MPa)
Al6063 Si3N4
46 750
2.7 3.17
101 525
components [14,15]. A very different mechanisms was observed when Al6063- wet grinder stone dust particulates composites were made to undergo dry sliding wear test [16]. Also, the wear rate of Al6061–SiC
Fig. 1. Energy dispersive spectroscopy of Al6063-alloy.
Fig. 2. Elemental mapping using SEM of model RUSK microscopy of Al6063 alloy. 2
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Fig. 3. Energy dispersive spectroscopy of Al6063–Si3N4 MMCs.
Fig. 4. Elemental mapping using SEM of model RUSK microscopy of Al6063–Si3N4 MMCs.
reasons for maximum wear of the composite when subjected to different loads and speeds [21]. When dry sliding is performed, due to the raised temperatures of alloy Al6061 there is a change in wear rate from slight to severe [22]. Investigation of properties of Al6061-Graphite (Gr) and Al6061-Albite and concluded, as the increase in the wt% of the Gr filler the properties like elongation, modulus and strength increased whereas hardness decreased. Increase in the Albite percentage in Al6061-Albite composite lead to the increase in hardness and reduction in the ductility [23]. In the present work the main objective is to fabricate composites containing Al6063 alloy and Silicon Nitride (Si3N4) powder as reinforcement. Further it also includes the investigation of physical, mechanical and tribological characteristics of the composites through various tests. 2. Fabrication and examination details of MMCs 2.1. Details of base matrix and particulate reinforcement materials
Fig. 5. Graph of weight to volume and rule of mixture ratio density of Al6063–Si3N4 MMCs.
The matrix material being Al6063 in ingots form was supplied by Fenfee Metallurgicals, Bangalore, India. The Table 1 below represents the composition of Al6063 alloy. The reinforcement material selected 3
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Fig. 6. a–f. Micrographs of Al6063 alloy and Si3N4 reinforced MMCs.
was Si3N4 powder and 50 μm size. This Si3N4 powder was purchased from Triveni chemicals, Gujarat, India and Table 2 below represents the properties of the matrix and reinforcement materials used.
2.3. Experimental details The casts obtained using stir casting were machined as per required specifications to ASTM standards. The test samples were then used for the investigation of properties like microstructure, hardness, density, tensile strength and wear resistance. The density was found out using rule of mixtures formula and the obtained readings compared with the experimental values. The metallurgical microscopy of Japan make (NIKHON model 150 ECLIPSE) was used to get microstructural images of the specimens and Field Emission Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS): JEOL JSM-7100F at Center for Nano and Material Sciences, Jain University, Bangalore was used to study the SEM images of the composites. Hardness test is done using MRB 250 Brinell hardness testing machine. The percentage elon gation and the tensile strength of the specimen was found using a tensometer. The specimens for tensile test were machined according to ASTM E8 M15a standards. Ducom, Bangalore make computerized pin on disc tribometer was used to find the wear rate of the composites on the application of different loads like 10 N–60 N. Cylindrical specimens used were dimensioned to be 10 mm in length and 10 mm diameter. These specimens were made to slide against EN31 steel counter disc of 60 HRC hardness. The wear height loss is recorded for every 30 s during each test using a 1.0 μm accuracy LVDT transducer in order to plot graphs
2.2. Fabrication of MMCs As liquid metallurgy technique is very economical and enables to fabricate composites with uniform distribution. Stir casting method of liquid metallurgy was used to fabricate the composite. The ingots of Al6063 alloy were put into the crucible furnace and were heated to about 710 � C. After obtaining the alloy in its molten form catalyst such as Magnesium chips, Hexachloroethane tablets (degassing tablets) and Coverall were added in order to increase the wettability, remove gases from the molten alloy and to form a layer between atmosphere and molten material respectively. A stirrer made of steel coated with graphite was used to stir the molten material at a constant speed of 400 rpm. Later Si3N4 reinforcement powder was wrapped into Al foils and was preheated to 350 � C using a muffle furnace, before adding it into the vortex formed due to stirring. The stirring was done for 10 min to ensure uniform distribution of the reinforcement. After this the molten material was transferred into a mold box of 150 mm length and 25 mm diameter. The composite casts were obtained by adding different per centages (0%–10%) of Si3N4 powder. 4
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Fig. 7. a–f. SEM images of Al6063 alloy and Si3N4 reinforced MMCs.
Fig. 9. UTS on Al6063–Si3N4 MMCs with increase in the percentage of reinforcement.
Fig. 8. Hardness of Al6063–Si3N4 MMCs with increasing percentage of reinforcement. 5
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Fig. 10. Surface plot on correlating the UTS and hardness with the increase in the reinforcement content.
fabricated Al6063–Si3N4 MMCs. The micrograph and corresponding elemental mapping are displayed in Fig. 4 indicated the presence of nitrogen with the Al, Mg and Si which proves the fabrication of MMCs used in the current investigations. 3.2. Density of Al6063–Si3N4 MMCs The theoretical densities for different compositions was evaluated by rule of mixtures and practical densities were evaluated using weight to volume ratio. Both theoretical and practical density values were compared in the graph shown in Fig. 5. From the graph it is evident that the theoretical density is greater than that of practical density. The density of the Al6063– Si3N4 composite material increases by an amount of 1.74% as the content of Si3N4 increases from 0 to 10 wt%. The improvement in the density can be attributed to the fact that the Si3N4 possess higher density and its presence in the matrix improves the hardness of the composite [3]. This may be due to the presence of casting defects. However, in both the cases the density was found to increase as the percentage of Si3N4 reinforcement increases. This increase in the density is due to the addition of high-density reinforcement. It was even confirmed from the figure that the density of MMCs is greater than that of the matrix material [24].
Fig. 11. Al6063–Si3N4 MMCs percentage elongation with the increase in the reinforcement.
between volumetric wear loss and sliding distance. The disc is rotated at a constant speed of 500 rpm and the sliding distance was 6 km. The SEM images of the worn surfaces and the fractured specimens were taken in order to study the type of wear occurring and the type of fracture. 3. Results and discussions
3.3. Microstructure investigations
3.1. SEM and EDS studies of Al6063 alloy and Al6063–Si3N4 MMCs
Fig. 6 a-f displays the Optical Microphotographs (OM) and similarly Fig. 7 a-f exhibits the SEM micrographs of Al6063 and Al6063–Si3N4 MMCs. From obtained photographs a uniform Si3N4 reinforcement dis tribution in the Al6063 was observed. Furthermore, figures indicated that the consistency of the fabricated composites. The micrographs also clearly display the increase in filler contents in the composite. It is correspondingly apparent from the microphotograph that minor amount of porosity observed. It is described further that the lower porosity of metal matrix composites is always related with higher hardness [25]. Additionally, from the microphotograph a decent bonding amongst the matrix and the filler particulates were noticed, hence enhanced transmission of load from Al6063 on to Si3N4 filler particles. In the Figs. 6 and 7, the microstructure 6a, demonstrates that the microphotographs contain very small portion solid solution of Al den drites, while 6b to 6f micrograph shows that the microphotographs contain Al solid solution dendrites with few unsystematically dispersed Si3N4 elements.
The Al, Magnesium (Mg) and Silicon (Si) alloy, Al6XXX series considered for the present study was Al6063 and the procured Al alloy was subjected to the SEM and EDS Studies. The Si and Mg particulates presence in Al is confirmed by EDS analysis as is shown in Fig. 1. The Fig. 2, is presented with the fabricated Al6063 base alloy ma terial has been subjected to the elemental mapping using the SEM of model RUSK microscopy. The micrograph and corresponding elemental mapping are displayed in Fig. 2, which shows the presence of Al, Mg and Si in the alloy which further confirms the composition of the Al6063 alloy with major alloying elements presence. The EDS image of the fabricated Al6063–Si3N4 MMCs are presented with in the Fig. 3, which clearly represents the presence of the Nitrogen elements along with the base material Al and the alloying elements Mg and Si. Approving the fabrication of the Al6063–Si3N4 MMCs by the liquid metallurgy technique. The Fig. 4, is presented with the elemental mapping results of the 6
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Fig. 12. (a). Volume wear loss of composites with sliding distance at 10 N load. (b). Volume wear loss of MMCs with sliding distance at 20 N load. (c). Volume wear loss of composites with sliding distance at 30 N load. (d). Volume wear loss of composites with sliding distance at 40 N load. (e). Volume wear loss of composites with sliding distance at 50 N load. (f). Volume wear loss of composites with sliding distance at 60 N load.
7
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Fig. 13. Effect of load on the volume wear loss with increased sliding distance on Al6063-8 wt% Si3N4 MMCs.
indentation test shows 86% increment in hardness values of Al6063–Si3N4 MMCs with Si3N4 from 0 to 10 wt% reinforcement in the Al6063 alloy [26]. This shows that the presence of ceramics of higher hardness than that of the base matrix can extensively improve the property of the composite. 3.5. Ultimate Tensile Strength (UTS) of Al6063–Si3N4 MMCs The dimensions of the tensile specimen were taken according to ASTM E8-M15a standards. The increase in the tensile strength of the specimen with the increase in the percentage of reinforcement is depicted in the Fig. 9. The testing was done at room temperature and was observed that the results were similar to the studies made by the investigators [27]. Results of the tensile test stated that the tensile strength of the specimen increase with the increase in the reinforcement from 0% to 10%. The mechanical property UTS enhanced by an amount of 77% with the increase in the Si3N4 filler content from 0 to 10 wt% in the matrix Al6063 and increase in the UTS may be attributed to the grain refinement and even distribution of the reinforcement material in the matrix [28]. The rise in the tensile strength is also as a result of increase in hardness and density. Fig. 10 is represented with correlation between the UTS and hardness with the increase in the reinforcement content. As it was mentioned in the several researchers in the literature the hardness is directly pro portional to the UTS and the same is evident from the Fig. 10. As the hardness is increased with increase in the reinforcement content the wear resistance offered by the Al6063–Si3N4 MMCs will increase.
Fig. 14. Variation in volume wear loss with increased %‘age of reinforcement of Al6063 alloy and Si3N4 filled MMCs.
3.4. Hardness of Al6063–Si3N4 MMCs Hardness being the important aspect of all materials which is directly affects the toughness, strength and resistance to wear of the material would be estimated. The hardness tests for the specimens were done in the hardness testing machine. In accordance with the ASTM E10-07a standards and normal temperature conditions the test was performed on specimens of size 10 mm length and 10 mm diameter. The test was conducted on Al6063 and its composites of reinforcement Si3N4 of varying weight percent from 0 to 10 wt%. A steel ball intender with 100 kg load applied, was used to evaluate the hardness. Each value is an average of five readings. Fig. 8 shows the results of the test conducted on the specimen. It may be apparent that the hardness of the composites is much greater than that of cast alloy. As the reinforcement wt% increases the hardness is found to increase. The upgrade in hardness may be due to the reinforcement Si3N4 possess greater hardness and its apparition in the matrix enhances the hardness of the composites as a whole. The
3.6. Ductility of Al6063–Si3N4 MMCs All the properties of the composite material greatly increase with the increase in the amount of reinforcement but ductility decreased with the increase in the reinforcement. Fig. 11 shows the decrease in the per centage elongation of the MMCs as the reinforcement was raised from 0% to 10%. This reduction in the ductility is due to increase in the hardness. It was concluded from the results that the percentage elon gation of the MMCs reduced as the percentage of reinforcement is raised from 0% to 10%. An amount of 7.6% decrease in the percentage elon gation was noticed with respect to the increase in the reinforcement content. The results were similar to those gotten by many scientists [29, 8
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Fig. 15. (a) Worn-out Al6063 base alloy. (b). Worn-out Al6063-2 wt% Si3N4. (c). Worn-out Al6063-4 wt% Si3N4. (d). Worn-out Al6063-6 wt% Si3N4. (e). Worn-out Al6063-8 wt% Si3N4. (f). Worn-out Al6063-10 wt% Si3N4.
30].
rise in temperature of the MMCs. As the temperature increased the material gets softer and thus resulted in the increased volumetric wear loss. In Fig. 12a, on application of 10 N load the volume wear loss reduced gradually with the increased amount of reinforcement. This suggests that there is an increase in the hardness which results in the increased wear resistance. As in Fig. 12 noticed, at all the sliding distances measured throughout, the volume wear loss of the composite materials was lower when related to the matrix and decreased with increased Si3N4 content in the composite. This can be accredited to enhanced hardness of the composite material. Increased hardness results in improvement of seizure and wear resistance of materials [31]. The variation in volume wear loss with load is shown by Fig. 13. The applied load affects the wear rate of matrix and composite materials and is the dominating factor regulating the wear behavior [32]. The wear rate varies inline [33,34] with the applied normal load, which indicates the Archard’s law, and the same is significantly lower in composites [35]. Further with increased loads, there is always higher volume wear
3.7. Dry sliding wear studies of Al6063–Si3N4 MMCs The wear resistance of the MMCs were examined using pin-on-disc tribometer. Many experiments were conducted on Al-MMCs to find out the wear properties of these composites and many reports were submitted regarding these in the past 25 years. In this paper the dry sliding wear test is performed on the MMCs at room temperature. The standards followed for this test were ASTM-G99 standards. The sliding velocity is kept constant to 3.14 m s 1. The results from the wear test were used to plot the graphs between volumetric wear loss and sliding distance on application of different loads from 10 to 60 N. The Fig. 12a–f represents the volumetric loss occurring at different sliding distance when different loads are applied. From the figures it was concluded that the volumetric wear increases with the increase in sliding distance. This is because as the sliding dis tance increases there was a change in the frictional force which caused a 9
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loss for matrix and composites. Nevertheless, at all the considered loads, resistance offered by the composites were superior than that of the matrix. Increased loads result in the delamination further, leading to higher wear volume loss of the matrix and composites as detected by researchers [36]. The variation of volume wear loss of matrix and composites with the increased Si3N4 shown in Fig. 14. It can be noticed that the volume wear loss of composites decreases with increase in Si3N4 reinforcement con tents in matrix. Nevertheless, for a given Si3N4 reinforcement wt%, the composites possess lower volume wear loss then the base Al6063. The enhancement in resistance to the wear of composites with increase in Si3N4 reinforcement may be accredited to the enhancement in hardness of the composite. Improved hardness results in lower wear rate as described by numerous scientists [37]. Fig. 15, presented with the SEM microphotographs of worn-out surfaces of Al6063 and its Si3N4 composites at a load of 60 N and 6 km sliding distance. The 8 wt% of Si3N4 composites, at 60 N load, exhibits lower wear. The Degree of grooves formed at the worn surface of the matrix and composites containing lower volume fractions of Si3N4 reinforcement are quite larger at higher loads, and undergo higher plastic deformation causing severe wear. This is quite evident from SEM microphotographs shown in Fig. 15a–f. The groove formation in the worn-out surfaces of the composite materials reduced with increase in Si3N4 indicating lower material loss as shown in SEM photographs in Fig. 15. The morphological studies of wear surface with SEM implies the occurrence of adhesive and abrasive wear mechanism in Al6063–Si3N4 MMCs. Fig. 15a shows the monolithic alloy worn surface at min pa rameters like applied load, sliding velocity and sliding distance and disclose the patches of severely damaged areas, as well as deep abrasion grooves due to low speed and the delamination [20], as well as severe wear noticed in the monolithic alloy. Similarly, as the Si3N4 filler con tent increases in the Al6063 the amount of wear loss decreases and offers more and more resistance to wear, this may be attributed to increase in the hardness of the Al6063–Si3N4 MMCs. Initially at the beaning of the wear, the material may be subjected to abrasive wear mechanism and later as the sliding distances increases then the adhered partials may come out of the composite material and act like an abrasive particle between the pin and the disc leading to the abrasive wear mechanisms. In the worn-out surfaces SEM images in Fig. 15 a to f., the bright color patches indicate the delaminated and worn-out particles as a result of sever wear and the river lines seen in all the samples are the wear tracks as a result of study state wear. Al6063–Si3N4 MMCs were fabricated, physical, mechanical and were properties were examined and indicated an increase in the hardness, tensile strength and wear resistance of MMCs. From the Scanning Electron Microscopy (SEM) studies concluded that as the reinforcement particulates were distributed evenly in the matrix which results in the enhancement of the above mentioned properties. The main strength ening mechanisms were estimated by Hall-Petch strengthening, Orowan strengthening and the CTE mismatch and elastic modulus mismatch between the reinforcements and metal matrix [38].
wear loss. Additionally, the reinforcement Si3N4 significantly contrib uted in enhancing the resistance to wear of Al6063–Si3N4 MMCs. From the complete investigations it can be determined that Al6063-10 wt% Si3N4 exhibits excellent mechanical and tribological characteristics. Acknowledgements The writers apprise their appreciation to the Director, Prof. C S P Rao, National Institute of Technology, Andhra Pradesh, Tadepalligudem and Management of Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Amrita University Bengaluru Campus, Bengaluru for their motivation and backing throughout the investigation studies. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.compositesb.2019.107138. References [1] Anirudh V, Vigneshwaran M, Vijay E, Pramod R, Veeresh Kumar GB. Influence of titanium diboride and graphite reinforcement on Al6061 alloyvol 5. Elsevier’s Materials Today: Proceedings; 2018. p. 25341–9. https://doi.org/10.1016/j.matpr .2018.10.337. [2] Annigeri Ulhas K, Veeresh Kumar GB. Method of stir casting of Aluminum metal matrix Composites. A Rev Elsevier Mater Today: Proc 2017;4(2):1140–6. https:// doi.org/10.1016/j.matpr.2017.01.130. [3] Veeresh Kumar GB, Rao CSP, Selvaraj N. Studies on mechanical and dry sliding wear of Al6061–SiC composites. Composites Part B 2012;43:1185–91. https://doi. org/10.1016/j.compositesb.2011.08.046. [4] Veeresh Kumar GB, Rao CSP, Selvaraj N. Mechanical and dry sliding wear behavior of Al7075 alloy-reinforced with SiC particles. J Compos Mater year 2012;46(10): 1201–9. https://doi.org/10.1177/0021998311414948. [5] Veeresh Kumar GB, Swamy ARK, Ramesha A. Studies on properties of as-cast Al6061-WC-Gr hybrid MMCs. J Compos Mater 2012;46(17):2111–22. https://doi. org/10.1177/0021998311430156. [6] Veeresh Kumar GB, Shivakumar Gouda PS, Pramod R, Rao CSP. Synthesis and characterization of TiO2 reinforced Al6061 composites. Adv Compos Lett January February 2017;26(01):18–23. https://doi.org/10.1007/BF00456563. [7] Veeresh Kumar GB, Rao CSP, Selvaraj N. Mechanical and tribological behavior of particulate reinforced Aluminum metal matrix composites – a review. J Miner Mater Charact Eng USA 2010;10(1):59–91. https://doi.org/10.4236/ jmmce.2011.101005. [8] Bhaumik Munmun, Maity Kalipada. Fabrication and characterization of the Al6063/5%ZrO2/5%Al2O3 composite. IOP Conf Ser Mater Sci Eng 2017;178: 012011. https://doi.org/10.1088/1757-899X/178/1/012011. [9] Aravindan MK, Balamurugan K, Murali G. Effect of reinforcement of AL-6063 with SiC on mechanical behavior and microstructure of metal matrix composites. Carbon Sci Technol 2014;6/2. ISSN: 0974-0546:388–94. http://www.applied-sc ience-innovations.com/cst-web-site/CST-6-2-2014/CST%20-%2095.pdf. [10] Hemalatha K, KVenkatachalapathy VS, Alagumurthy N. Processing and synthesis of metal matrix Al6063/Al2O3 metal matrix composite by stir casting process. J Eng Res Appl Nov-Dec 2013;3(Issue 6). ISSN: 2248-9622:1390–4. [11] Ramesh CS, Ahamed Abrar. Friction and wear behaviour of cast Al 6063 based in situ metal matrix composites. Wear 2011;271:1928–39. https://doi.org/10.1016/j. wear.2010.12.048. [12] Singh Sarbjit. Wear behavior of Al-6063/SiC metal matrix composites reinforced with different particles sizes using taguchi’s methodology. Mater Today: Proc 2017;4:10148–52. https://doi.org/10.1016/j.matpr.2017.06.338. [13] A Dvivedi, V R Rajeev, P Kumar, and I Singh, "Tribological characteristics of Al 6063–SiCp metal–matrix composite under reciprocating and wet conditions", Proceedings of. IMechE Vol. vol 226, Pages 138-149 Part J: J. Engineering Tribology. [DOI: 10.1177/1350650111425738]. [14] Veeresh Kumar GB, Rao CSP, Selvaraj N, Bhagyashekar MS. Studies on Al6061-SiC and Al7075-Al2O3 metal matrix composites. J Miner Mater Charact Eng, (JMMCE), USA 2009;9(1):47–59. https://doi.org/10.4236/jmmce.2010.91004. [15] Pramod R, Veeresh Kumar GB. Artificial neural networks for predicting the tribological behavior of Al7075-SiC metal matrix composites. J Mater Sci Eng 2014;1(3). ISSN: 2374-149X:06–11. [16] Francis Xavier L, Suresh Paramasivam. Wear behavior of aluminium metal matrix composite prepared from industrial waste. Sci World J 2016:6538345. 8 pages, http://doi.org/10.1155/2016/6538345. [17] Mishra Ashok kumar, Srivastava Rajesh Kumar. Wear behaviour of Al-6061/SiC metal matrix composites. J Inst Eng (India): Ser C 2016 ISSN: 2250-0545. https:// doi.org/10.1007/s40032-016-0284-3. [18] Mahallawi Iman El, Ahmed Shash, eid amer Amer. Nanoreinforced cast Al-Si alloys with Al2O3, TiO2 and ZrO2 nanoparticles. Metall Met Open Access J 2015;(5): 802–21. https://doi.org/10.3390/met5020802. May 2015. [19] Naim Shaikh Mohd Bilal, Arif Sajjad, Arif Siddiqui Mohammad. Fabrication and characterization of aluminium hybrid composites reinforced with fly ash and
4. Conclusions The noteworthy conclusions of the studies carried-out on Al6063–Si3N4 MMCs are as follows. The liquid metallurgy techniques (stir casting route) was successfully followed in the fabrication of Al6063–Si3N4 MMCs with filler content up to 10 wt%. The densities of the MMCs were improved than the base alloy. The microstructure studies discovered the uniform distribution of particulates in the matrix alloy. Hardness of the MMCs found increased with increase in filler content. The tensile strength characteristics of the MMCs were found to increase than that of base alloy and Al6063-10 wt% Si3N4 MMCs dis played greater tensile strength values then other materials studied. The resistance to wear of the MMCs was higher than that of base alloy. Increased applied loads and sliding distances resulted in higher volume 10
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[20] [21] [22] [23]
[24] [25] [26]
[27]
[28]
Composites Part B 175 (2019) 107138 [29] Madhusudan Siddabathula, Mohiuddin Sarcar Mohammed Moulana, Rama Mohan Rao Narsipalli Bhargava. Mechanical properties of Aluminum-Copper(p) composite metallic materials. J Appl Res Technol October 2016;14(5):293–9. https://doi. org/10.1016/j.jart.2016.05.009. [30] Swamy ARK, Ramesha A, Veeresh Kumar GB, Prakash JN. Effect of particulate reinforcements on the mechanical properties of Al6061-WC and Al6061-Gr MMCs. J Miner Mater Charact Eng 2011;10(No.12):1141–52. https://doi.org/10.4236/ jmmce.2011.1012087. [31] Ramesh CS, Anwar Khan AR, Ravikumar N, Savanprabhu P. Prediction of wear coefficient of Al6061–TiO2 composites. Wear 2005;259:602–8. https://doi.org/ 10.1016/j.wear.2005.02.115. [32] Kumar Bannaravuri Praveen, Kumar Birru Anil. Strengthening of mechanical and tribological properties of Al-4.5%Cu matrix alloy with the addition of bamboo leaf ash. Results Phys September 2018;10:360–73. https://doi.org/10.1016/j.rinp.20 18.06.004. [33] Hamid Abdulhaqq A, Ghosh PK, Jain SC, Ray Subrata. The influence of porosity and particles content on dry sliding wear of cast in situ Al (Ti)–Al2O3 (TiO2) composite. Wear 25 June 2008;265(1–2):14–26. https://doi.org/10.1016/j. wear.2007.08.018. [34] Sharma SC. The sliding wear behavior of Al6061–garnet particulate composites. Wear 2001;249:1036–45. https://doi.org/10.1016/S0043-1648(01)00810-9. [35] Tyagi Rajnesh. Synthesis and tribological characterization of in situ cast Al–TiC composites. Wear 2005;259:569–76. https://doi.org/10.1016/j.wear.2005.01.0 51. [36] Ramesh CS, Seshadri SK. Tribological characteristics of nickel composite coatings. Wear 2003;255:893–902. https://doi.org/10.1016/S0043-1648(03)00080-2. [37] Yang LJ. Wear coefficient equation for aluminium based matrix composites against steel disc. Wear 2003;255:879–92. https://doi.org/10.1016/S0043-1648(03) 00191-1. [38] Shayan Mehrdad, Eghbali Beitallah, Niroumand Behzad. Synthesis of AA2024(SiO2npþTiO2np) hybrid nanocomposite via stir casting process. Mater Sci Eng A 2019;756:484–91. https://doi.org/10.1016/j.msea.2019.04.089.
silicon carbide through powder metallurgy. Mater Res Express March 2018;5(4). https://doi.org/10.1088/2053-1591/aab829. Basavarajappa S, Chandramohan G, Mukund K, Ashwin M, Prabu M. Dry sliding wear behavior of Al 2219/SiCp-Gr hybrid metal matrix composites. J Mater Eng Perform 2006;15:668. https://doi.org/10.1361/105994906X150803. Basavarajappa S, Chandramohan G. Wear studies on metal matrix composites taguchi approach. J Mater Sci Technol 2005;21(6):845–50. http://www.jmst. org/EN/volumn/volumn_895.shtml#J. Mahesh Naidu K, Reddy Chandra Mohan. An investigation on dry sliding wear behaviour of AA6061-AlNp composite. IOP Conf Ser Mater Sci Eng 2018;330: 012053. https://doi.org/10.1088/1757-899X/330/1/012053. Ramesh A, Prakash JN, Shiva Shankare Gowda AS, Appaiah Sonnappa. Comparison of the mechanical properties of AL6061/albite and AL6061/graphite metal matrix composites. J Miner Mater Charact Eng 2009;8(2):93–106. https://doi.org/ 10.4236/jmmce.2009.82009. Yang LJ. A test methodology for the determination of wear coefficient. Wear 2005; 259:1453–61. https://doi.org/10.1016/j.wear.2005.01.026. Veeresh Kumar, G. B., Pramod, R., Shivakumar Gouda, P. S., C.S.P. Rao, “Effect of tungsten carbide reinforcement on the aluminium 6061 alloy”, J Test Eval, ISSN 0090-3973, https://doi.org/10.1520/JTE20170545. Abu-Warda A, Utrilla MV, Escalera MD, Otero E, L� opez MD. The effect of TiB2 content on the properties of AA6005/TiB2 nanocomposites fabricated by mechanical alloying method. Powder Technol 2018;328:235–44. https://doi.org /10.1016/j.powtec.2018.01.028. KumarThandalam Satish, Ramanathan Subramanian, Sundarrajan Shalini. Synthesis, microstructural and mechanical properties of ex situ zircon particles (ZrSiO4) reinforced Metal Matrix Composites (MMCs): a review. J Mater Res Technol July–September 2015;4(3):333–47. https://doi.org/10.1016/j.jmrt.20 15.03.003. Shulin Lü, Pan Xiao, Du Yuan, Hu Kun, Wu Shusen. Preparation of Al matrix nanocomposites by diluting the compositegranules containing nano-SiCp under ultrasonic vibaration. J Mater Sci Technol 2018;34:1609–17. https://doi.org/10 .1016/j.jmst.2018.01.003.
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Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Assessment of mechanical and tribological characteristics of Silicon Nitride reinforced aluminum metal matrix composites G.B.Veeresh Kumar a, *, Pinaki Prasad Panigrahy b, Nithika Sureshb, Pramod R b, C.S.P. Rao a a b
Department of Mechanical Engineering, National Institute of Technology - Andhra Pradesh, Tadepalligudem, Andhra Pradesh, India Department of Mechanical Engineering, Amrita School of Engineering, Bengaluru Campus, Amrita Vishwa Vidyapeetham, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Aluminum Silicon nitride Metal matrix composites Hardness Strength Wear
The present paper focuses on the investigation of physical, mechanical and tribological characteristics of Al6063 alloy reinforced with Silicon Nitride powder. The Al6063-Silicon Nitride Metal Matrix Composites were fabri cated by following stir casting method of liquid metallurgy technique. The amount of reinforcement incorpo ration in matrix material was from 0 to 10 wt% varied in intervals of 2. The obtained composites were used in the investigative studies related to physical, mechanical & tribological experimentations. The tests were performed on the Al6063 alloy and its composites as per in harmony with the ASTM Standards. The test results it can be observed and appreciated that increasing the reinforcement percentage, the characteristics like hardness and density increased monolithically and significantly. The dry sliding wear test is performed using pin on disc configuration tribometer and the results state that the composite has higher wear resistance. Basically the Al6063 is relatively soft and as per dry sliding wear concern at the applications of stringers, upper and lower wings of aircraft, floor breams, seat tracks, fuselage of an aircraft’s, the wear resistance plays a crucial role in relative movement at contact surfaces, hence the present work focused on developing Al6063-Silicon Nitride Metal Matrix Composites with enhanced mechanical and tribological properties. Off all the compositions, the com posite material having the highest percentage of reinforcement showed better properties. Scanning Electron Microscope, Energy Dispersive Microscopy images were used to study the fabricated composites before and after the wear morphology during wear test.
1. Introduction The unparalleled performance of composites has been broadly deliberate by investigators [1–4]. The particulate composites hold resistance to indentation and applied in applications like automobile parts such as calipers, blocks of pistons, cylinders, cylinder embed rings, contractors, microwave channels, impellers, vibrator segment and space structures [5]. Amongst the Metal Matrix Composites (MMCs) Aluminum (Al) based MMCs have shown excellent mechanical charac teristics [6]. The most common reason behind the sudden failure of machine components is wear [7]. Munmun Bhaumik et al., fabricated Al6063–ZrO2-Alumina (Al2O3) MMCs, concluded that the relative den sity is found to increase than the base alloy, also indicated that the fractured surface of Al-MMC is brittle in nature [8]. M K Aravindan et al., studied the Al6063–SiC 10 wt% MMCs, concluded that the microstruc ture with good distribution of particles and the mechanical properties like, hardness, Ultimate Tensile Strength (UTS), Percentage (%)
Elongation and Yield Strength properties increased with rising of rein forced weight (wt) fraction of SiC [9]. K. Hemalatha et al., fabricated Al6063–Al2O3 by stir casting route up to 9 wt% and confirmed that the composites are clearly superior to Al6063 in comparison with hardness and UTS at the cost of reduced ductility [10]. C S Ramesh et al., developed Al6063–TiB2 in-situ composites and conducted dry sliding wear tests at different loads and sliding velocities, revealed that the composites have lower coefficient of friction (COF) and wear rates than Al6063 alloy. Nevertheless, the rates of wear noticed to increase with increased load applied and sliding velocity [11]. Conducted investiga tion on wear behavior of the Al6063-10 wt% Silicon Carbide (SiC) MMCs and indicated that the noteworthy process constraints for loss of wear were normal applied load, sliding velocity, sliding distance, abrasives size and noticed Mechanically Mixed Layer (MML) formation, tearing of surfaces, groove formation and particle pullout under different sliding situations [12,13]. Most of the breakdowns occurring in machines is due to wear of the
* Corresponding author. E-mail address: [email protected] (G.B.Veeresh Kumar). https://doi.org/10.1016/j.compositesb.2019.107138 Received 5 March 2019; Received in revised form 20 June 2019; Accepted 5 July 2019 Available online 6 July 2019 1359-8368/© 2019 Elsevier Ltd. All rights reserved.
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Table 1 Al6063 alloy chemical compositions by weight %’age. Chemical compositions
Si
Cu
Mn
Fe
Cr
Zn
Mg
Ti
Al
Al6063
0.60
0.10
0.10
0.30
0.10
0.10
0.80
0.01
Bal
composites is affected by temperature and load. Reports suggest that Al6061–SiC composites will have less wear rate on increase in load [17]. On performing the wear test on composite of Al6061 and short fiber fillings, noticed that these have increasing resistance to wear [18]. From a large number of publications, it is evident that the MMCs having 15% of SiC particulates as reinforcement and fabricated using powder met allurgy technique have shown good wear resistance [19]. The wear of a composite is immensely affected by the microstructure, sliding distance, sliding speed and the load applied. For Al2219–SiC composites it was observed that wear and the cracking of SiC particles increased with the increase in the load applied [20]. The factors like sliding wear are the
Table 2 The base alloy matrix and particle reinforcement materials properties. Material
Hardness (HV)
Density (g/cc)
Tensile Strength (MPa)
Al6063 Si3N4
46 750
2.7 3.17
101 525
components [14,15]. A very different mechanisms was observed when Al6063- wet grinder stone dust particulates composites were made to undergo dry sliding wear test [16]. Also, the wear rate of Al6061–SiC
Fig. 1. Energy dispersive spectroscopy of Al6063-alloy.
Fig. 2. Elemental mapping using SEM of model RUSK microscopy of Al6063 alloy. 2
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Fig. 3. Energy dispersive spectroscopy of Al6063–Si3N4 MMCs.
Fig. 4. Elemental mapping using SEM of model RUSK microscopy of Al6063–Si3N4 MMCs.
reasons for maximum wear of the composite when subjected to different loads and speeds [21]. When dry sliding is performed, due to the raised temperatures of alloy Al6061 there is a change in wear rate from slight to severe [22]. Investigation of properties of Al6061-Graphite (Gr) and Al6061-Albite and concluded, as the increase in the wt% of the Gr filler the properties like elongation, modulus and strength increased whereas hardness decreased. Increase in the Albite percentage in Al6061-Albite composite lead to the increase in hardness and reduction in the ductility [23]. In the present work the main objective is to fabricate composites containing Al6063 alloy and Silicon Nitride (Si3N4) powder as reinforcement. Further it also includes the investigation of physical, mechanical and tribological characteristics of the composites through various tests. 2. Fabrication and examination details of MMCs 2.1. Details of base matrix and particulate reinforcement materials
Fig. 5. Graph of weight to volume and rule of mixture ratio density of Al6063–Si3N4 MMCs.
The matrix material being Al6063 in ingots form was supplied by Fenfee Metallurgicals, Bangalore, India. The Table 1 below represents the composition of Al6063 alloy. The reinforcement material selected 3
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Fig. 6. a–f. Micrographs of Al6063 alloy and Si3N4 reinforced MMCs.
was Si3N4 powder and 50 μm size. This Si3N4 powder was purchased from Triveni chemicals, Gujarat, India and Table 2 below represents the properties of the matrix and reinforcement materials used.
2.3. Experimental details The casts obtained using stir casting were machined as per required specifications to ASTM standards. The test samples were then used for the investigation of properties like microstructure, hardness, density, tensile strength and wear resistance. The density was found out using rule of mixtures formula and the obtained readings compared with the experimental values. The metallurgical microscopy of Japan make (NIKHON model 150 ECLIPSE) was used to get microstructural images of the specimens and Field Emission Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS): JEOL JSM-7100F at Center for Nano and Material Sciences, Jain University, Bangalore was used to study the SEM images of the composites. Hardness test is done using MRB 250 Brinell hardness testing machine. The percentage elon gation and the tensile strength of the specimen was found using a tensometer. The specimens for tensile test were machined according to ASTM E8 M15a standards. Ducom, Bangalore make computerized pin on disc tribometer was used to find the wear rate of the composites on the application of different loads like 10 N–60 N. Cylindrical specimens used were dimensioned to be 10 mm in length and 10 mm diameter. These specimens were made to slide against EN31 steel counter disc of 60 HRC hardness. The wear height loss is recorded for every 30 s during each test using a 1.0 μm accuracy LVDT transducer in order to plot graphs
2.2. Fabrication of MMCs As liquid metallurgy technique is very economical and enables to fabricate composites with uniform distribution. Stir casting method of liquid metallurgy was used to fabricate the composite. The ingots of Al6063 alloy were put into the crucible furnace and were heated to about 710 � C. After obtaining the alloy in its molten form catalyst such as Magnesium chips, Hexachloroethane tablets (degassing tablets) and Coverall were added in order to increase the wettability, remove gases from the molten alloy and to form a layer between atmosphere and molten material respectively. A stirrer made of steel coated with graphite was used to stir the molten material at a constant speed of 400 rpm. Later Si3N4 reinforcement powder was wrapped into Al foils and was preheated to 350 � C using a muffle furnace, before adding it into the vortex formed due to stirring. The stirring was done for 10 min to ensure uniform distribution of the reinforcement. After this the molten material was transferred into a mold box of 150 mm length and 25 mm diameter. The composite casts were obtained by adding different per centages (0%–10%) of Si3N4 powder. 4
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Fig. 7. a–f. SEM images of Al6063 alloy and Si3N4 reinforced MMCs.
Fig. 9. UTS on Al6063–Si3N4 MMCs with increase in the percentage of reinforcement.
Fig. 8. Hardness of Al6063–Si3N4 MMCs with increasing percentage of reinforcement. 5
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Fig. 10. Surface plot on correlating the UTS and hardness with the increase in the reinforcement content.
fabricated Al6063–Si3N4 MMCs. The micrograph and corresponding elemental mapping are displayed in Fig. 4 indicated the presence of nitrogen with the Al, Mg and Si which proves the fabrication of MMCs used in the current investigations. 3.2. Density of Al6063–Si3N4 MMCs The theoretical densities for different compositions was evaluated by rule of mixtures and practical densities were evaluated using weight to volume ratio. Both theoretical and practical density values were compared in the graph shown in Fig. 5. From the graph it is evident that the theoretical density is greater than that of practical density. The density of the Al6063– Si3N4 composite material increases by an amount of 1.74% as the content of Si3N4 increases from 0 to 10 wt%. The improvement in the density can be attributed to the fact that the Si3N4 possess higher density and its presence in the matrix improves the hardness of the composite [3]. This may be due to the presence of casting defects. However, in both the cases the density was found to increase as the percentage of Si3N4 reinforcement increases. This increase in the density is due to the addition of high-density reinforcement. It was even confirmed from the figure that the density of MMCs is greater than that of the matrix material [24].
Fig. 11. Al6063–Si3N4 MMCs percentage elongation with the increase in the reinforcement.
between volumetric wear loss and sliding distance. The disc is rotated at a constant speed of 500 rpm and the sliding distance was 6 km. The SEM images of the worn surfaces and the fractured specimens were taken in order to study the type of wear occurring and the type of fracture. 3. Results and discussions
3.3. Microstructure investigations
3.1. SEM and EDS studies of Al6063 alloy and Al6063–Si3N4 MMCs
Fig. 6 a-f displays the Optical Microphotographs (OM) and similarly Fig. 7 a-f exhibits the SEM micrographs of Al6063 and Al6063–Si3N4 MMCs. From obtained photographs a uniform Si3N4 reinforcement dis tribution in the Al6063 was observed. Furthermore, figures indicated that the consistency of the fabricated composites. The micrographs also clearly display the increase in filler contents in the composite. It is correspondingly apparent from the microphotograph that minor amount of porosity observed. It is described further that the lower porosity of metal matrix composites is always related with higher hardness [25]. Additionally, from the microphotograph a decent bonding amongst the matrix and the filler particulates were noticed, hence enhanced transmission of load from Al6063 on to Si3N4 filler particles. In the Figs. 6 and 7, the microstructure 6a, demonstrates that the microphotographs contain very small portion solid solution of Al den drites, while 6b to 6f micrograph shows that the microphotographs contain Al solid solution dendrites with few unsystematically dispersed Si3N4 elements.
The Al, Magnesium (Mg) and Silicon (Si) alloy, Al6XXX series considered for the present study was Al6063 and the procured Al alloy was subjected to the SEM and EDS Studies. The Si and Mg particulates presence in Al is confirmed by EDS analysis as is shown in Fig. 1. The Fig. 2, is presented with the fabricated Al6063 base alloy ma terial has been subjected to the elemental mapping using the SEM of model RUSK microscopy. The micrograph and corresponding elemental mapping are displayed in Fig. 2, which shows the presence of Al, Mg and Si in the alloy which further confirms the composition of the Al6063 alloy with major alloying elements presence. The EDS image of the fabricated Al6063–Si3N4 MMCs are presented with in the Fig. 3, which clearly represents the presence of the Nitrogen elements along with the base material Al and the alloying elements Mg and Si. Approving the fabrication of the Al6063–Si3N4 MMCs by the liquid metallurgy technique. The Fig. 4, is presented with the elemental mapping results of the 6
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Fig. 12. (a). Volume wear loss of composites with sliding distance at 10 N load. (b). Volume wear loss of MMCs with sliding distance at 20 N load. (c). Volume wear loss of composites with sliding distance at 30 N load. (d). Volume wear loss of composites with sliding distance at 40 N load. (e). Volume wear loss of composites with sliding distance at 50 N load. (f). Volume wear loss of composites with sliding distance at 60 N load.
7
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Fig. 13. Effect of load on the volume wear loss with increased sliding distance on Al6063-8 wt% Si3N4 MMCs.
indentation test shows 86% increment in hardness values of Al6063–Si3N4 MMCs with Si3N4 from 0 to 10 wt% reinforcement in the Al6063 alloy [26]. This shows that the presence of ceramics of higher hardness than that of the base matrix can extensively improve the property of the composite. 3.5. Ultimate Tensile Strength (UTS) of Al6063–Si3N4 MMCs The dimensions of the tensile specimen were taken according to ASTM E8-M15a standards. The increase in the tensile strength of the specimen with the increase in the percentage of reinforcement is depicted in the Fig. 9. The testing was done at room temperature and was observed that the results were similar to the studies made by the investigators [27]. Results of the tensile test stated that the tensile strength of the specimen increase with the increase in the reinforcement from 0% to 10%. The mechanical property UTS enhanced by an amount of 77% with the increase in the Si3N4 filler content from 0 to 10 wt% in the matrix Al6063 and increase in the UTS may be attributed to the grain refinement and even distribution of the reinforcement material in the matrix [28]. The rise in the tensile strength is also as a result of increase in hardness and density. Fig. 10 is represented with correlation between the UTS and hardness with the increase in the reinforcement content. As it was mentioned in the several researchers in the literature the hardness is directly pro portional to the UTS and the same is evident from the Fig. 10. As the hardness is increased with increase in the reinforcement content the wear resistance offered by the Al6063–Si3N4 MMCs will increase.
Fig. 14. Variation in volume wear loss with increased %‘age of reinforcement of Al6063 alloy and Si3N4 filled MMCs.
3.4. Hardness of Al6063–Si3N4 MMCs Hardness being the important aspect of all materials which is directly affects the toughness, strength and resistance to wear of the material would be estimated. The hardness tests for the specimens were done in the hardness testing machine. In accordance with the ASTM E10-07a standards and normal temperature conditions the test was performed on specimens of size 10 mm length and 10 mm diameter. The test was conducted on Al6063 and its composites of reinforcement Si3N4 of varying weight percent from 0 to 10 wt%. A steel ball intender with 100 kg load applied, was used to evaluate the hardness. Each value is an average of five readings. Fig. 8 shows the results of the test conducted on the specimen. It may be apparent that the hardness of the composites is much greater than that of cast alloy. As the reinforcement wt% increases the hardness is found to increase. The upgrade in hardness may be due to the reinforcement Si3N4 possess greater hardness and its apparition in the matrix enhances the hardness of the composites as a whole. The
3.6. Ductility of Al6063–Si3N4 MMCs All the properties of the composite material greatly increase with the increase in the amount of reinforcement but ductility decreased with the increase in the reinforcement. Fig. 11 shows the decrease in the per centage elongation of the MMCs as the reinforcement was raised from 0% to 10%. This reduction in the ductility is due to increase in the hardness. It was concluded from the results that the percentage elon gation of the MMCs reduced as the percentage of reinforcement is raised from 0% to 10%. An amount of 7.6% decrease in the percentage elon gation was noticed with respect to the increase in the reinforcement content. The results were similar to those gotten by many scientists [29, 8
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Fig. 15. (a) Worn-out Al6063 base alloy. (b). Worn-out Al6063-2 wt% Si3N4. (c). Worn-out Al6063-4 wt% Si3N4. (d). Worn-out Al6063-6 wt% Si3N4. (e). Worn-out Al6063-8 wt% Si3N4. (f). Worn-out Al6063-10 wt% Si3N4.
30].
rise in temperature of the MMCs. As the temperature increased the material gets softer and thus resulted in the increased volumetric wear loss. In Fig. 12a, on application of 10 N load the volume wear loss reduced gradually with the increased amount of reinforcement. This suggests that there is an increase in the hardness which results in the increased wear resistance. As in Fig. 12 noticed, at all the sliding distances measured throughout, the volume wear loss of the composite materials was lower when related to the matrix and decreased with increased Si3N4 content in the composite. This can be accredited to enhanced hardness of the composite material. Increased hardness results in improvement of seizure and wear resistance of materials [31]. The variation in volume wear loss with load is shown by Fig. 13. The applied load affects the wear rate of matrix and composite materials and is the dominating factor regulating the wear behavior [32]. The wear rate varies inline [33,34] with the applied normal load, which indicates the Archard’s law, and the same is significantly lower in composites [35]. Further with increased loads, there is always higher volume wear
3.7. Dry sliding wear studies of Al6063–Si3N4 MMCs The wear resistance of the MMCs were examined using pin-on-disc tribometer. Many experiments were conducted on Al-MMCs to find out the wear properties of these composites and many reports were submitted regarding these in the past 25 years. In this paper the dry sliding wear test is performed on the MMCs at room temperature. The standards followed for this test were ASTM-G99 standards. The sliding velocity is kept constant to 3.14 m s 1. The results from the wear test were used to plot the graphs between volumetric wear loss and sliding distance on application of different loads from 10 to 60 N. The Fig. 12a–f represents the volumetric loss occurring at different sliding distance when different loads are applied. From the figures it was concluded that the volumetric wear increases with the increase in sliding distance. This is because as the sliding dis tance increases there was a change in the frictional force which caused a 9
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loss for matrix and composites. Nevertheless, at all the considered loads, resistance offered by the composites were superior than that of the matrix. Increased loads result in the delamination further, leading to higher wear volume loss of the matrix and composites as detected by researchers [36]. The variation of volume wear loss of matrix and composites with the increased Si3N4 shown in Fig. 14. It can be noticed that the volume wear loss of composites decreases with increase in Si3N4 reinforcement con tents in matrix. Nevertheless, for a given Si3N4 reinforcement wt%, the composites possess lower volume wear loss then the base Al6063. The enhancement in resistance to the wear of composites with increase in Si3N4 reinforcement may be accredited to the enhancement in hardness of the composite. Improved hardness results in lower wear rate as described by numerous scientists [37]. Fig. 15, presented with the SEM microphotographs of worn-out surfaces of Al6063 and its Si3N4 composites at a load of 60 N and 6 km sliding distance. The 8 wt% of Si3N4 composites, at 60 N load, exhibits lower wear. The Degree of grooves formed at the worn surface of the matrix and composites containing lower volume fractions of Si3N4 reinforcement are quite larger at higher loads, and undergo higher plastic deformation causing severe wear. This is quite evident from SEM microphotographs shown in Fig. 15a–f. The groove formation in the worn-out surfaces of the composite materials reduced with increase in Si3N4 indicating lower material loss as shown in SEM photographs in Fig. 15. The morphological studies of wear surface with SEM implies the occurrence of adhesive and abrasive wear mechanism in Al6063–Si3N4 MMCs. Fig. 15a shows the monolithic alloy worn surface at min pa rameters like applied load, sliding velocity and sliding distance and disclose the patches of severely damaged areas, as well as deep abrasion grooves due to low speed and the delamination [20], as well as severe wear noticed in the monolithic alloy. Similarly, as the Si3N4 filler con tent increases in the Al6063 the amount of wear loss decreases and offers more and more resistance to wear, this may be attributed to increase in the hardness of the Al6063–Si3N4 MMCs. Initially at the beaning of the wear, the material may be subjected to abrasive wear mechanism and later as the sliding distances increases then the adhered partials may come out of the composite material and act like an abrasive particle between the pin and the disc leading to the abrasive wear mechanisms. In the worn-out surfaces SEM images in Fig. 15 a to f., the bright color patches indicate the delaminated and worn-out particles as a result of sever wear and the river lines seen in all the samples are the wear tracks as a result of study state wear. Al6063–Si3N4 MMCs were fabricated, physical, mechanical and were properties were examined and indicated an increase in the hardness, tensile strength and wear resistance of MMCs. From the Scanning Electron Microscopy (SEM) studies concluded that as the reinforcement particulates were distributed evenly in the matrix which results in the enhancement of the above mentioned properties. The main strength ening mechanisms were estimated by Hall-Petch strengthening, Orowan strengthening and the CTE mismatch and elastic modulus mismatch between the reinforcements and metal matrix [38].
wear loss. Additionally, the reinforcement Si3N4 significantly contrib uted in enhancing the resistance to wear of Al6063–Si3N4 MMCs. From the complete investigations it can be determined that Al6063-10 wt% Si3N4 exhibits excellent mechanical and tribological characteristics. Acknowledgements The writers apprise their appreciation to the Director, Prof. C S P Rao, National Institute of Technology, Andhra Pradesh, Tadepalligudem and Management of Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Amrita University Bengaluru Campus, Bengaluru for their motivation and backing throughout the investigation studies. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.compositesb.2019.107138. References [1] Anirudh V, Vigneshwaran M, Vijay E, Pramod R, Veeresh Kumar GB. Influence of titanium diboride and graphite reinforcement on Al6061 alloyvol 5. Elsevier’s Materials Today: Proceedings; 2018. p. 25341–9. https://doi.org/10.1016/j.matpr .2018.10.337. [2] Annigeri Ulhas K, Veeresh Kumar GB. Method of stir casting of Aluminum metal matrix Composites. A Rev Elsevier Mater Today: Proc 2017;4(2):1140–6. https:// doi.org/10.1016/j.matpr.2017.01.130. [3] Veeresh Kumar GB, Rao CSP, Selvaraj N. Studies on mechanical and dry sliding wear of Al6061–SiC composites. Composites Part B 2012;43:1185–91. https://doi. org/10.1016/j.compositesb.2011.08.046. [4] Veeresh Kumar GB, Rao CSP, Selvaraj N. Mechanical and dry sliding wear behavior of Al7075 alloy-reinforced with SiC particles. J Compos Mater year 2012;46(10): 1201–9. https://doi.org/10.1177/0021998311414948. [5] Veeresh Kumar GB, Swamy ARK, Ramesha A. Studies on properties of as-cast Al6061-WC-Gr hybrid MMCs. J Compos Mater 2012;46(17):2111–22. https://doi. org/10.1177/0021998311430156. [6] Veeresh Kumar GB, Shivakumar Gouda PS, Pramod R, Rao CSP. Synthesis and characterization of TiO2 reinforced Al6061 composites. Adv Compos Lett January February 2017;26(01):18–23. https://doi.org/10.1007/BF00456563. [7] Veeresh Kumar GB, Rao CSP, Selvaraj N. Mechanical and tribological behavior of particulate reinforced Aluminum metal matrix composites – a review. J Miner Mater Charact Eng USA 2010;10(1):59–91. https://doi.org/10.4236/ jmmce.2011.101005. [8] Bhaumik Munmun, Maity Kalipada. Fabrication and characterization of the Al6063/5%ZrO2/5%Al2O3 composite. IOP Conf Ser Mater Sci Eng 2017;178: 012011. https://doi.org/10.1088/1757-899X/178/1/012011. [9] Aravindan MK, Balamurugan K, Murali G. Effect of reinforcement of AL-6063 with SiC on mechanical behavior and microstructure of metal matrix composites. Carbon Sci Technol 2014;6/2. ISSN: 0974-0546:388–94. http://www.applied-sc ience-innovations.com/cst-web-site/CST-6-2-2014/CST%20-%2095.pdf. [10] Hemalatha K, KVenkatachalapathy VS, Alagumurthy N. Processing and synthesis of metal matrix Al6063/Al2O3 metal matrix composite by stir casting process. J Eng Res Appl Nov-Dec 2013;3(Issue 6). ISSN: 2248-9622:1390–4. [11] Ramesh CS, Ahamed Abrar. Friction and wear behaviour of cast Al 6063 based in situ metal matrix composites. Wear 2011;271:1928–39. https://doi.org/10.1016/j. wear.2010.12.048. [12] Singh Sarbjit. Wear behavior of Al-6063/SiC metal matrix composites reinforced with different particles sizes using taguchi’s methodology. Mater Today: Proc 2017;4:10148–52. https://doi.org/10.1016/j.matpr.2017.06.338. [13] A Dvivedi, V R Rajeev, P Kumar, and I Singh, "Tribological characteristics of Al 6063–SiCp metal–matrix composite under reciprocating and wet conditions", Proceedings of. IMechE Vol. vol 226, Pages 138-149 Part J: J. Engineering Tribology. [DOI: 10.1177/1350650111425738]. [14] Veeresh Kumar GB, Rao CSP, Selvaraj N, Bhagyashekar MS. Studies on Al6061-SiC and Al7075-Al2O3 metal matrix composites. J Miner Mater Charact Eng, (JMMCE), USA 2009;9(1):47–59. https://doi.org/10.4236/jmmce.2010.91004. [15] Pramod R, Veeresh Kumar GB. Artificial neural networks for predicting the tribological behavior of Al7075-SiC metal matrix composites. J Mater Sci Eng 2014;1(3). ISSN: 2374-149X:06–11. [16] Francis Xavier L, Suresh Paramasivam. Wear behavior of aluminium metal matrix composite prepared from industrial waste. Sci World J 2016:6538345. 8 pages, http://doi.org/10.1155/2016/6538345. [17] Mishra Ashok kumar, Srivastava Rajesh Kumar. Wear behaviour of Al-6061/SiC metal matrix composites. J Inst Eng (India): Ser C 2016 ISSN: 2250-0545. https:// doi.org/10.1007/s40032-016-0284-3. [18] Mahallawi Iman El, Ahmed Shash, eid amer Amer. Nanoreinforced cast Al-Si alloys with Al2O3, TiO2 and ZrO2 nanoparticles. Metall Met Open Access J 2015;(5): 802–21. https://doi.org/10.3390/met5020802. May 2015. [19] Naim Shaikh Mohd Bilal, Arif Sajjad, Arif Siddiqui Mohammad. Fabrication and characterization of aluminium hybrid composites reinforced with fly ash and
4. Conclusions The noteworthy conclusions of the studies carried-out on Al6063–Si3N4 MMCs are as follows. The liquid metallurgy techniques (stir casting route) was successfully followed in the fabrication of Al6063–Si3N4 MMCs with filler content up to 10 wt%. The densities of the MMCs were improved than the base alloy. The microstructure studies discovered the uniform distribution of particulates in the matrix alloy. Hardness of the MMCs found increased with increase in filler content. The tensile strength characteristics of the MMCs were found to increase than that of base alloy and Al6063-10 wt% Si3N4 MMCs dis played greater tensile strength values then other materials studied. The resistance to wear of the MMCs was higher than that of base alloy. Increased applied loads and sliding distances resulted in higher volume 10
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