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Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates
Materials Today: Proceedings xxx (xxxx) xxx
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Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates Sourabh Bhaskar ⇑, Mukesh Kumar, Amar Patnaik Mechanical Engineering Department, Malaviya National Institute of Technology, Jaipur 302017, Rajasthan, India
a r t i c l e
i n f o
Article history: Received 9 November 2019 Received in revised form 5 December 2019 Accepted 3 January 2020 Available online xxxx Keywords: Wear Friction AlN AA2024 Gr Taguchi design
a b s t r a c t The present experimental study investigates the Tribological characteristics of hybrid aluminium metal matrix composite comprising of AA2024 aluminium alloy as matrix material reinforced with varying amount (0, 2, 4 and 6 wt.%) of AlN particulates and fixed amount (2 wt.%) of graphite particles (i.e. four composite samples like AAN-0, AAN-2, AAN-4 and AAN-6). The composite specimens are fabricated through conventional stir casting technique. Pin-on-disk wear testing apparatus is used to perform the sliding wear and friction experiments according to ASTM-G99 standard. The various controllable factors like normal load (5, 20, 35, 50 N), sliding velocity (0.654, 1.308, 1.962, 2.616 m/s), sliding distance (784.8, 1569.6, 2354.4, 3139.2 m) and environment temperature (20, 30, 40, 50 °C) are used to analyze the specific wear rate and coefficient of friction under steady state conditions. Taguchi experimental design is applied to find out the significant level of each factor influencing the specific wear rate. From the steady state experimentations, it is found that both the Tribological properties (specific wear rate and coefficient of friction) have been significantly improved with the amount of AlN particles. From taguchi experimental analysis, it is concluded that the order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
1. Introduction MMCs provide superior mechanical strength, stiffness and wear resistance to different components used in various fields such as structural, aerospace, automotive, etc. Different ceramic particulates as reinforcing materials are silicon carbide (SiC), silicon nitride (Si3N4), boron nitride (BN), alumina (Al2O3), aluminium nitride (AlN), titanium nitride (TiN), magnesium oxide (MgO) etc. The AMCs filled with micro sized particulates (ceramics/intermetallic) reinforcements are found to reveal improved properties like hardness, specific strength/stiffness, thermal resistance, wear resistance and corrosion resistance as compared with the unreinforced alloy [1]. The operating variables that govern sliding tribolAbbreviations: MMC, Metal matrix composite; AMC, Aluminum matrix composite; RSM, Response surface methodology; ANOVA, Analysis of variance; FSP, Friction stir processed; DOE, Design of Experiment; UTS, Ultimate Tensile Strength; S/N, Signal-to-Noise; SWR, Specific Wear Rate; COF, Coefficient of Friction; MML, Mechanically Mixed Layer. ⇑ Corresponding author. E-mail address: [email protected] (S. Bhaskar).
ogy of materials are normal applied load, sliding speed, sliding distance, temperature, counter surface hardness, etc. The working range of these variables is important consideration in real time evaluation of tribological performance as well as service life of components [2]. This fact has been advocated by research of eminent scholars like Kumar et al. [3] discussed the sliding wear characteristics under unlubricated conditions of Al 2618 metal matrix composite reinforced with ZrB2, Si3N4 and AlN-particles up to 8 wt.%. Fabrication was processed through stir casting technique. The Taguchi orthogonal array was used to design the experimentation and ANOVA was applied to find out the effect of each factor on the wear rate. Load was the most significant factor because it was found that specific wear rate slightly enhanced for a load range of 10 N–50 N load but it increases sharply at 50 N load for a reinforcement of 8 wt.%. Abrasive and adhesive wear were dominant mechanisms observed for lower and higher load conditions respectively. Dinaharan et al. [4] evaluated the wear rate of AA6082 AMCs reinforced with different ceramic particulates such as SiC, alumina, TiC and B4C. The composites were fabricated through FSP technique and effect of various FSP parameters on the wear rate was
https://doi.org/10.1016/j.matpr.2020.01.015 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Nomenclature AAN-0 AlN AAN-2 AlN AAN-4
Aluminium alloy composite filled with 0 wt.% (Aluminium nitride) and 2 wt.% Gr (graphite) Aluminium alloy composite reinforced with 2 wt.% 2 wt.% Gr Aluminium alloy composite reinforced with 4 wt.%
estimated using some empirical relationships by applying RSM. Lower wear rate and higher micro-hardness were obtained for TiC-particles reinforced composites. Minimum wear rate was also obtained for low tool rotational speed, high traverse speed and maximum groove width. Alaneme and Sanusi [5] have analysed the wear properties of Al-Mg-Si alloy matrix composites filled with alumina, rice husk ash and graphite particles fabricated through stir casting method. Wear tests were performed using Taber abrasion wear testing machine. Improved wear resistance was obtained for 73.5–74.5% alumina, 25% rice husk ash and 0.5–1.5% graphite. The composites without graphite had shown more wear than those containing graphite particles. The improved wear behaviour was due to the lubricating effect of graphite particles which formed a layer between the two mating surfaces. It was also found that wear resistance have been reduced as the amount of graphite increased from 0.5 to 1.5%. Pramanik [6] reported the influence of different sliding parameters such as sliding distance, pressure and sliding speed on the wear properties of AA6061 matrix composite reinforced with 10 vol% Al2O3 particles. Wear tests were performed on pin-on-disc testing machine. It was shown that the wear loss was much lowered for composite when compared with base alloy with all the changing factors like pressure, distance and speed. The possible wear mechanism for composite was three body abrasion wear. The filled alumina particles provide resistance to the deformation of composite surface and enhanced the wear characteristics of the composite. Kumar et al. [7] investigated the tribological properties of AA6061-T6/AlNp composite fabricated through liquid metallurgy route. A regression model was developed for predicting the wear characteristics under sliding conditions of AA6061 matrix composite reinforced with AlN particulates. A central composite design was applied for designing the experiments and pin-ondisc testing machine was used for conducting the experimentations. It was found that the wear loss of the composite increased with increasing the sliding velocity, distance and normal load. The wear loss of the composite was decreased with increasing in mass fraction of AlN particles from 0 to 20%. Delamination was the main wear mechanism observed at larger sliding velocity. Ploughing and abrasive wear mechanisms were also obtained. Adhesive wear mechanism was more effective in AA6061 alloy, where as abrasive wear was effective in AA6061/AlNp composites. Ravindran et al. [8] fabricated the hybrid AA2024 matrix composites reinforced with fixed 5 wt.% of graphite and varied (5, 10, 15, 20 wt.%) of SiC particles through powder metallurgy process. Sliding wear experiments were conducted as per the ASTM G99-05 standard on pin-on-disc machine. Various controlling parameters were used such as load (5–30 N), varying sliding speed like 1000 or 3000 m and sliding speeds such as 1 and 2 m/s. The wear rate was found to be decreased with increasing the content of SiC particles due to the increased hardness of the composite with the addition of hard ceramic particulates. The wear resistance decreased with increasing normal load and sliding distance. The lower wear loss was observed for 20 wt.% SiC and 5 wt.% graphite reinforced aluminium matrix composite. Kumar and Dhiman [9] have evaluated the specific wear rate of the hybrid AA7075 MMCs filled with SiC (7 wt.%) as hard ceramic particles and graphite
AlN AAN-6 AlN
2 wt.% Gr Aluminium alloy composite reinforced with 6 wt.% 2 wt.% Gr
(3 wt.%) as soft solid lubricant. Liquid metallurgy technique was used for the production of composites. Design of experiments was done according to full factorial method. Specific wear rate was examined on pin-on-disc wear tester and influence of various sliding factors on wear behaviour was discussed. The wear rate has been reduced at low load in the range of 20–40 N and at low speed in the range of 2–4 m/s. Mazahery and Shabani [10] evaluated the sliding wear behaviour of AA2024 alloy matrix composite reinforced with various volume fractions (0, 5, 10, 15, 20, 25, 30) of coated B4C particles fabricated by squeeze casting method. The weight loss was observed for varying sliding distances (0, 200, 400, 600, 800, 1000 m). The fabricated composite had more wear resistance as compared to the matrix alloy and improved with higher particle content. It was also found that the weight loss was increased with increasing sliding distance for unreinforced alloy and for all the composites. Minimum weight loss was obtained for the composite reinforced with 30% volume fractions. Sahin and Kilicli [11] have evaluated the influence of applied load and weight fraction under the abrasive wear conditions of AA2014 MMCs reinforced with SiC-particles. The composite was fabricated through liquid metallurgy technique. The wear properties were investigated for various factors such as abrasive particle size (50 lm), weight fraction (10%) and applied load (0, 5, 10, 15, 20, 25, 30, 35 N) using pin-on-disc apparatus. The wear resistance of the aluminium matrix composite was found to be increased with increasing weight percentage of SiC-particles. With increasing applied load the value of wear rate also increased but lowered wear rate was obtained for 10 wt.% SiC-particles when compared with the base alloy. Rao and Das [12] investigated the sliding wear behaviour of high strength aluminium alloys such as AA7010, AA7009, AA2024 and influence of SiC addition on the sliding wear of AMCs. The composite was fabricated through stir casting technique. The sliding wear tests were performed on pin-on-disc wear apparatus with various applied pressure and fixed sliding speed and also for various volume fractions. Improved wear properties was obtained with increasing amount of the SiC-particles addition. Lowest wear rate was obtained for AA7010 alloy composite and highest wear rate was obtained for AA2024 alloy composite irrespective of the SiC amount. Rajeev et al. [13] investigated the influence of various operating parameters like applied load (15 and 45 N), sliding distance (500 and 1500 m), reciprocating velocity (0.2 and 0.4 m/s), counter surface temperature (60 and 120 °C) and weight content of silicon particles (6 and 18 wt.%) on dry reciprocating wear characteristics of A319, A390 metal matrix composites reinforced with SiC particles. Higher wear resistance was observed for the higher amount of silicon particles addition. All the operating parameters were the influential controlling factors affecting the wear rate of composite specimens. Herbert et al. [14] evaluated the wear characteristics under dry conditions of as cast, mushy state rolled Al-Cu alloy and its composites filled with TiB2 particulates. The wear resistance was enhanced by incorporating TiB2 particulates. SWR was reduced as the load increased due to increased plastic deformation was observed at higher loads. Umanath et al. [15] have performed the statistical analyses of dry sliding wear characteristics of hybrid Al alloy composite filled with
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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ceramic particulates were added in the AA2024 alloy. The ceramic particles were preheated at 700 °C for 3 h before mixing in the melt alloy. To increase the wettability of ceramic particulates with the matrix alloy, Mg (2 wt.%) was added in the slurry prior to the addition of preheated particles. A mechanical stirrer made of stainless steel has been used for mixing the ceramic particulates in the alloy at 500 °C. The stirring was done at 450 rpm for 2–3 min in order to achieve uniform distribution of particles. The molten metal was then poured into permanent mould of cast iron having dimensions 140 90 10 mm3 and the temperature was then lowered gradually [18]. The fabricated aluminum alloy composites were evaluated under dry sliding conditions to analyze the specific wear rate and coefficient of friction using pin-on-disc tribometer (Model TR-20, Ducom, Banglore, India) as per ASTM G 99 standard with hardened steel disc (EN-31) of hardness 60–70 HRC. For experiments, track diameter of 50 mm was kept fixed throughout the experimental work. The working range of selected parameters is given in Table 2. The weight loss of the composite specimen was obtained using LVDT transducer by measuring the reduced length in vertical direction in micro-meters. The weight loss was also calculated using electronic balance (accuracy of ±0.001 mg). Finally, the specific wear rate (mm3/N-m) was calculated as:
5 and 15 wt.% of (SiC + Al2O3) filler particulates. Lower wear loss was obtained for large amount of filler particles, smaller applied load, minimum rotational speed and higher hardness of counter surface. Dharmalingam et al. [16] investigated the sliding wear characteristics of Al hybrid metal matrix composite comprising Al-Si10Mg alloy as matrix material, 2 and 4 wt.% MoS2, 5 wt.% Al2O3 particles through pin-on-disc apparatus. Optimum wear performance of the composite material was evaluated using Grey relational analysis and Taguchi design of experiment. Minimum SWR was achieved for applied normal load of 30 N, sliding speed of 4 m/s and amount of MoS2 was 4 wt.%. Kok [17] examined the abrasive wear characteristics of AA2024 alloy composite filled with 30 wt.% Al2O3 particles. Significant improvement in wear resistance was observed as compared to the base alloy with the addition of Al2O3 ceramic particulates. Number of researchers has been observed that the incorporation of ceramic particulates like SiC, Al2O3, Si3N4, TiC etc. increases the hardness and sliding wear resistance of metal alloy composite material. But there is little attempt has been observed to explore the potential of hybrid reinforcement containing hard ceramic particles like AlN along with soft solid lubricant like graphite to fabricate metal alloy composite for tribological applications. The incorporation of solid lubricant particles as partial reinforcement enhances the wear resistance of metal composites. Hence there is an opportunity to improve the sliding wear and friction properties of metal alloy composite by using above mentioned particulate materials as reinforcement. Hence the main objective of the study is to analyze the Tribological performance of the Al-AlN-Gr hybrid composite under the influence of various controllable parameters.
Ws ¼
Dm
ð1Þ
q:Vs:t:Fn
where, Ws is the specific wear rate in mm3/N-m,Dm is the mass loss of composite during test (g), q is the density of the composite (g/cm3), Vs is the sliding velocity (m/s), t is the test duration (s), Fn is the normal load (N) [19]. In the present study, Taguchi design of experiment has been used to perform the optimization for specific wear rate and coefficient of friction. Taguchi method is widely accepted technique by which number of experiments is reduced and optimal results can be estimated by combining the experimental and analytical concepts to evaluate the effect of each factor on the measured response, so that overall performance can be significantly enhanced. In this work, the minimum specific wear rate is analysed by using lower-the-better (LB) performance characteristics in terms of S/N ratio. In the present work, five input factors are used (Table 2) and L16 orthogonal array design has been applied to find out the specific wear rate and coefficient of friction of the prepared composite. The S/N ratio with LB characteristic can be expressed as [20]
2. Experimental details In the present study, AA2024 alloy has been used as the base matrix material while AlN and Gr particles have been used as the reinforcement material. Aluminium alloy 2024, containing 4.5% copper and 1.5% Mg, develops the highest strength of any naturally aged Al-Cu type of alloy. The size of the ceramic particles varies from 60 to 80 lm. The chemical composition of AA2024 alloy has been given in Table 1. The purpose of utilization of reinforcement material is to further enhance the mechanical, thermal, thermo-mechanical and wear properties of choose matrix material. The ceramic particulate filled alloy composite was fabricated through simple stir casting technique. The melting of alloy AA2024 was carried separately using muffle furnace and molten metal was held at 750 °C for 15 min, the temperature was lowered up to 600 °C in mushy zone i.e. between solidus and liquidus temperatures. The preheated
S 1 X 2 ¼ 10log Y N N
ð2Þ
where, N = number of observations and Y = observed data.
Table 1 Chemical composition of AA2024 alloy. Component
Al
Cr
Cu
Fe
Mg
Mn
Si
Ti
Weight %
90.7–94.7
Max 0.1
3.8–4.9
Max 0.5
1.2–1.8
0.3–0.9
Max 0.5
Max 0.15
Table 2 Working range of selected parameters. Control factors
Sliding Velocity (A) Filler Content (B) Normal Load (C) Sliding Distance (D) Environment Temperature (E)
Level I
II
III
IV
Units
0.654 0 5 784.8 20
1.308 2 20 1569.6 30
1.962 4 35 2354.4 40
2.616 6 50 3139.2 50
m/s wt.% N m °C
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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3. Results and discussions 3.1. Steady-state-specific wear rate and coefficient of friction The specific wear rate of the prepared alloy composites under steady state (sliding velocity of 0.654–2.616 m/s; sliding distance of 1569.6 m, normal load of 20 N, and environment temperature of 30 °C) condition is shown in Fig. 1. From figure, the following observations are obtained: (i) SWR of the fabricated composite has shown increasing trend with sliding velocity irrespective of the filler content. (ii) The order of specific wear rate is AAN0 > AAN-2 > AAN-4 > AAN-6. The decreasing trend of SWR with the increasing amount of AlN particles is attributed to the presence of both hard AlN particles and soft solid lubricant (graphite) as a partial reinforcement, which generates a tribo-layer on the contacting surfaces [7]. The variation of coefficient of friction with sliding velocity of SiC-filled metal alloy composite has shown in Fig. 2. The coefficient of friction of alloy composite is increased as the sliding velocity increased. From the plot it is observed that (i) the coefficient of friction have an increasing trend with the sliding velocity (0.654– 2.616 m/s) irrespective of the filler content. (ii) the magnitude of coefficient of friction is reduced as the amount of AlN increased
from 0 to 6 wt.%, hence therefore order of coefficient of friction is AAN-0 > AAN-2 > AAN-4 > AAN-6. Hence lower coefficient of friction has been achieved for 6 wt.% AlN particles. The increased coefficient of friction can be attributed to the severe plastic deformation takes place due to the presence of hard ceramic particulates as the sliding velocity has been increased. As the sliding speed increases, asperities fluctuations were also takes place that causes stick-slip phenomenon [21]. The influence of normal load (5, 20, 35, 50 N) on SWR of the fabricated composites is shown in Fig. 3. From figure it is observed that the SWR is increased as the value of load increases from 5 to 50 N. But the SWR is found to be reduced with the amount of AlN particles. This enhancement in the wear resistance can be attributed to the dispersion of hard AlN particulates that improved the hardness of the prepared composite and successfully support the normal load and provide a resistance to cut and scratch given from hard counter surface [22]. The different observations of coefficient of friction with normal applied load (5–50 N) of the fabricated composites filled with various wt.% of AlN particles are shown in Fig. 4. From Figure it can be seen that the coefficient of friction have an increasing trend with the normal applied load irrespective of the AlN particle content. The magnitude of the coefficient of friction has been reduced with increasing amount of AlN particle content and the optimal order is AAN-0 > AAN-2 > AAN-4 > AAN-6. Hence lower value of coefficient
Fig. 1. Effect of sliding velocity on specific wear rate of AA2024 alloy composites. Fig. 3. Effect of normal load on specific wear rate of AA2024 alloy composites.
Fig. 2. Effect of sliding velocity on coefficient of friction of AA2024 alloy composites.
Fig. 4. Effect of normal load on coefficient of friction of AA2024 alloy composites.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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of friction has been achieved for 6 wt.% AlN filled composite. The enhancement in coefficient of friction with the normal load may be due to the presence of three body abrasion wear phenomenon
Fig. 5. Effect of sliding distance on specific wear rate of AA2024 alloy composites.
that could take place as a result of the deformation of mechanically mixed layer formed between two mating surfaces during the period of sliding [21]. The variations of specific wear rate with sliding distance (784.8–3139.2 m) are shown in Fig. 5 for AlN filled AA2024 alloy composites. The specific wear rate was found to be decreased up to 1500 m and after that it gradually decreased and almost took a constant trend with increasing sliding distance from 1500 m to 3000 m irrespective of the particle content of filler. At specific load conditions, the order of SWR is AAN-0 > AAN-2 > AAN-4 > AAN-6. The decreasing trend of SWR with increasing sliding distance may be attributed to the plastic deformation of sharp asperities contacts during initial-run-in-period that will fill the valley of material in both the mating surfaces and consequently increased the work hardening of Al-alloy, hence reducing the wear rate with increasing sliding distance for low load and speed [6]. The variations of coefficient of friction with sliding distance (784.8–3139.2 m) of the fabricated aluminium alloy composite filled with AlN particles are shown in Fig. 6. The coefficient of friction was found to be increased with the sliding distance irrespective of the filler content. Hence the optimal order was AAN-0 > AAN-2 > AAN-4 > AAN-6. The enhancement of the coefficient of friction with the sliding distance can be attributed to the more exposure of hard SiC particles that increased the severe plastic deformation and transfer of Al matrix alloy to the counter surface as the contact time between two mating surfaces increased within the specified range of sliding distance (784.8–3139.2 m) [23].
3.2. Taguchi design experimental analyses
Fig. 6. Effect of sliding distance on coefficient of friction of AA2024 alloy composites.
In order to find out the correlation between the SWR and its controlling parameters, Taguchi experimental design approach is used. Taguchi design of experiments generates a ranking order of controlling parameters according to their influences on measured response within least experimental test runs, hence provide satisfactory conclusions [24]. In the present work, five controlling variables each with four levels have been used and shown in Table 2. The experimental test results for SWR of AA2024 alloy composite filled with AlN particles in terms of signal-to-noise ratio as computed by the MINITAB 16 software are shown in Table 3. The corresponding response plots are shown in Fig. 7 and also the signal-to-noise ratio for the 16 tests is calculated as 69.24 dB using MINITAB 16 software. The order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature (Table 4).
Table 3 Experimental layout of L16 orthogonal array. Expt. No.
Sliding Velocity (m/s)
Filler Content (wt.%)
Normal Load (N)
Sliding Distance (m)
Environment Temperature (°C)
Specific Wear Rate (mm3/N-m)
S/N Ratio (db)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0.654 0.654 0.654 0.654 1.308 1.308 1.308 1.308 1.962 1.962 1.962 1.962 2.616 2.616 2.616 2.616
0 2 4 6 0 2 4 6 0 2 4 6 0 2 4 6
5 20 35 50 20 5 50 35 35 50 5 20 50 35 20 5
784.8 1569.6 2354.4 3139.2 2354.4 3139.2 784.8 1569.6 3139.2 2354.4 1569.6 784.8 1569.6 784.8 3139.2 2354.4
20 30 40 50 50 40 30 20 30 20 50 40 40 50 20 30
9.05E03 1.84E03 1.48E04 1.07E04 2.54E04 7.79E04 1.92E04 1.75E04 1.42E04 4.89E05 1.14E03 5.89E04 1.34E04 4.19E04 1.54E04 5.74E04
40.87 54.68 76.60 79.45 71.91 62.17 74.34 75.14 76.97 86.22 58.85 64.59 77.47 67.55 76.24 64.82
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Main Effects Plot for SN ratios Data M eans Sliding velocity (m/s)
80
Filler content (wt.%)
Normal load (N)
75
Mean of SN ratios
70 65 60 0.654
1.308
1.962
2.616
Sliding distance (m)
80
0
2
4
6
5
20
35
50
Environment temperature (C)
75 70 65 60 784.8
1569.6
2354.4
3139.2
20
30
40
50
Signal-to-noise: Smaller is better Fig. 7. Effect of input control factors on specific wear rate of AA2024 alloy composites.
Table 4 Significance order of input control factors. Level
Sliding velocity (m/s)
Filler content (wt.%)
Normal load (N)
Sliding distance (m)
Environment Temperature (°C)
1. 2. 3. 4. Delta Rank
62.90 70.89 71.66 71.52 8.76 3
66.80 67.65 71.51 71.0 4.71 4
56.67 66.85 74.07 79.37 22.69 1
61.84 66.53 74.88 73.71 13.05 2
69.62 67.70 70.21 69.44 2.50 5
4. Conclusions In the present study AA2024 alloy composite filled with (0, 2, 4, 6 wt.%) AlN particles and fixed 2 wt.% graphite particles are successfully fabricated through stir casting technique. Various tribological characteristics have been investigated and following conclusions were made. 1. The steady state specific wear rate increased under different sliding velocities irrespective of the filler content. The order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding velocities. The coefficient of friction is found to increase with sliding velocity for all the filler content. The order of coefficient of friction with filler content was AAN0 > AAN-2 > AAN-4 > AAN-6 across all sliding velocities. 2. For various values of normal loads (5–50 N), the steady state SWR increases with increasing values of normal load irrespective of the filler content. The order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all normal loads. The coefficient of friction is found to increase with normal loads for all the filler content. The order of coefficient of friction with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all normal loads. 3. The SWR under steady state conditions for different values of sliding distance shows decreasing trend with the sliding dis-
tance irrespective of the filler content. The decreasing order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding distances. The coefficient of friction shows increasing trend with the sliding distance for all the filler content. The reducing order of coefficient of friction with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding distance. 4. From taguchi experimental analysis, it is concluded that order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature.
CRediT authorship contribution statement Sourabh Bhaskar: Conceptualization, Methodology. Mukesh Kumar: Supervision, Writing - review & editing. Amar Patnaik: Supervision.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Acknowledgement The authors express their sincere gratitude to Department of Mechanical Engineering of Malaviya National Institute of Technology, Jaipur-302017, Rajasthan, India for their all kind of financial as well as other miscellaneous infrastructural support. References [1] J. Singh, A. Chauhan, Overview of wear performance of aluminium matrix composites reinforced with ceramic materials under the influence of controllable variables, Ceram. Int. 42 (2016) 56–81, https://doi.org/10.1016/j. ceramint.2015.08.150. [2] M.A. Maleque, S. Dyuti, M.M. Rahman, Material selection method in design of automotive brake disc, Proc. World Congr. Eng. III (2010) 1–5. [3] N. Mathan Kumar, S. Senthil Kumaran, L.A. Kumaraswamidhas, Aerospace application on Al 2618 with reinforced – Si3N4, AlN and ZrB2 in-situ composites, J. Alloys Compd. 672 (2016) 238–250, https://doi.org/10.1016/ j.jallcom.2016.02.155. [4] I. Dinaharan, N. Murugan, A. Thangarasu, Development of empirical relationships for prediction of mechanical and wear properties of AA6082 aluminum matrix composites produced using friction stir processing, Eng. Sci. Technol. an Int. J. 19 (2016) 1132–1144, https://doi.org/10.1016/ j.jestch.2016.02.004. [5] K.K. Alaneme, K.O. Sanusi, Microstructural characteristics, mechanical and wear behaviour of aluminium matrix hybrid composites reinforced with alumina, rice husk ash and graphite, Eng. Sci. Technol. an Int. J. 18 (2015) 416– 422, https://doi.org/10.1016/j.jestch.2015.02.003. [6] A. Pramanik, Effects of reinforcement on wear resistance of aluminum matrix composites, Trans. Nonferrous Met. Soc. China (English Ed.) 26 (2016) 348– 358, https://doi.org/10.1016/S1003-6326(16)64125-0. [7] B.A. Kumar, N. Murugan, I. Dinaharan, Dry, sliding wear behavior of stir cast AA6061-T6/AlNp composite, Trans. Nonferrous Met. Soc. China (English Ed.) 24 (2014) 2785–2795, https://doi.org/10.1016/S1003-6326(14)63410-5. [8] P. Ravindran, K. Manisekar, P. Rathika, P. Narayanasamy, Tribological properties of powder metallurgy - processed aluminium self lubricating hybrid composites with SiC additions, Mater. Des. 45 (2013) 561–570, https:// doi.org/10.1016/j.matdes.2012.09.015. [9] R. Kumar, S. Dhiman, A study of sliding wear behaviors of Al-7075 alloy and Al7075 hybrid composite by response surface methodology analysis, Mater. Des. 50 (2013) 351–359, https://doi.org/10.1016/j.matdes.2013.02.038. [10] A. Mazahery, M.O. Shabani, Influence of the hard coated B4C particulates on wear resistance of Al-Cu alloys, Compos. Part B Eng. 43 (2012) 1302–1308, https://doi.org/10.1016/j.compositesb.2012.01.011.
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[11] Y. Sahin, V. Kilicli, Abrasive wear behaviour of SiCp/Al alloy composite in comparison with ausferritic ductile iron, Wear 271 (2011) 2766–2774, https:// doi.org/10.1016/j.wear.2011.05.022. [12] R.N. Rao, S. Das, Effect of matrix alloy and influence of SiC particle on the sliding wear characteristics of aluminium alloy composites, Mater. Des. 31 (2010) 1200–1207, https://doi.org/10.1016/j.matdes.2009.09.032. [13] V.R. Rajeev, D.K. Dwivedi, S.C. Jain, Dry reciprocating wear of Al-Si-SiCp composites: a statistical analysis, Tribol. Int. 43 (2010) 1532–1541, https://doi. org/10.1016/j.triboint.2010.02.014. [14] M.A. Herbert, R. Maiti, R. Mitra, M. Chakraborty, Wear behaviour of cast and mushy state rolled Al-4.5Cu alloy and in-situ Al4.5Cu-5TiB2 composite, Wear 265 (2008) 1606–1618, https://doi.org/10.1016/j.wear.2008.03.010. [15] K. Umanath, K. Palanikumar, S.T. Selvamani, Analysis of dry sliding wear behaviour of Al6061/SiC/Al2O3 hybrid metal matrix composites, Compos. Part B Eng. 53 (2013) 159–168, https://doi.org/10.1016/j.compositesb.2013.04.051. [16] S. Dharmalingam, R. Subramanian, K. Somasundara Vinoth, B. Anandavel, Optimization of tribological properties in aluminum hybrid metal matrix composites using gray-taguchi method, J. Mater. Eng. Perform. 20 (2011) 1457–1466, https://doi.org/10.1007/s11665-010-9800-4. [17] M. Kök, Abrasive wear of Al2O3 particle reinforced 2024 aluminium alloy composites fabricated by vortex method, Compos. Part A Appl. Sci. Manuf. 37 (2006) 457–464, https://doi.org/10.1016/j.compositesa.2005.05.038. [18] T.G. Mamatha, A. Patnaik, S. Biswas, B.K. Satapathy, A.K. Redhewall, Thermomechanical and crack position on stress intensity factor in particle-reinforced Zinc-aluminium alloy composites, Comput. Mater. Sci. 55 (2012) 100–112, https://doi.org/10.1016/j.commatsci.2011.11.028. [19] A. Kumar, A. Patnaik, I.K. Bhat, Investigation of nickel metal powder on tribological and mechanical properties of Al-7075 alloy composites for gear materials, Powder Metall. 60 (2017) 371–383, https://doi.org/10.1080/ 00325899.2017.1318481. [20] A. Patnaik, A. Satapathy, S.S. Mahapatra, R.R. Dash, Tribo-performance of polyester hybrid composites: damage assessment and parameter optimization using Taguchi design, Mater. Des. 30 (2009) 57–67, https://doi.org/10.1016/ j.matdes.2008.04.057. [21] S. Gangwar, A. Patnaik, I.K. Bhat, Tribological and thermomechanical analysis of CaO (quicklime) particulates filled ZA-27 alloy composites for bearing application, Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 232 (2018) 20–34, https://doi.org/10.1177/1464420715609196. [22] M. Uthayakumar, S. Aravindan, K. Rajkumar, Wear performance of Al-SiC-B4C hybrid composites under dry sliding conditions, Mater. Des. 47 (2013) 456– 464, https://doi.org/10.1016/j.matdes.2012.11.059. [23] A.P. Sannino, H.A. Rack, Tribological investigation of 2009 Al-20 vol.% SiCp/174 PH Part I: composite performance, Wear 197 (2009) 151–159. [24] A. Kumar, A. Patnaik, I.K. Bhat, tribology analysis of cobalt particulate filled Al 7075 alloy for gear materials: a comparative study, Silicon (2018) 1–17, https://doi.org/10.1007/s12633-018-9920-2.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates Sourabh Bhaskar ⇑, Mukesh Kumar, Amar Patnaik Mechanical Engineering Department, Malaviya National Institute of Technology, Jaipur 302017, Rajasthan, India
a r t i c l e
i n f o
Article history: Received 9 November 2019 Received in revised form 5 December 2019 Accepted 3 January 2020 Available online xxxx Keywords: Wear Friction AlN AA2024 Gr Taguchi design
a b s t r a c t The present experimental study investigates the Tribological characteristics of hybrid aluminium metal matrix composite comprising of AA2024 aluminium alloy as matrix material reinforced with varying amount (0, 2, 4 and 6 wt.%) of AlN particulates and fixed amount (2 wt.%) of graphite particles (i.e. four composite samples like AAN-0, AAN-2, AAN-4 and AAN-6). The composite specimens are fabricated through conventional stir casting technique. Pin-on-disk wear testing apparatus is used to perform the sliding wear and friction experiments according to ASTM-G99 standard. The various controllable factors like normal load (5, 20, 35, 50 N), sliding velocity (0.654, 1.308, 1.962, 2.616 m/s), sliding distance (784.8, 1569.6, 2354.4, 3139.2 m) and environment temperature (20, 30, 40, 50 °C) are used to analyze the specific wear rate and coefficient of friction under steady state conditions. Taguchi experimental design is applied to find out the significant level of each factor influencing the specific wear rate. From the steady state experimentations, it is found that both the Tribological properties (specific wear rate and coefficient of friction) have been significantly improved with the amount of AlN particles. From taguchi experimental analysis, it is concluded that the order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
1. Introduction MMCs provide superior mechanical strength, stiffness and wear resistance to different components used in various fields such as structural, aerospace, automotive, etc. Different ceramic particulates as reinforcing materials are silicon carbide (SiC), silicon nitride (Si3N4), boron nitride (BN), alumina (Al2O3), aluminium nitride (AlN), titanium nitride (TiN), magnesium oxide (MgO) etc. The AMCs filled with micro sized particulates (ceramics/intermetallic) reinforcements are found to reveal improved properties like hardness, specific strength/stiffness, thermal resistance, wear resistance and corrosion resistance as compared with the unreinforced alloy [1]. The operating variables that govern sliding tribolAbbreviations: MMC, Metal matrix composite; AMC, Aluminum matrix composite; RSM, Response surface methodology; ANOVA, Analysis of variance; FSP, Friction stir processed; DOE, Design of Experiment; UTS, Ultimate Tensile Strength; S/N, Signal-to-Noise; SWR, Specific Wear Rate; COF, Coefficient of Friction; MML, Mechanically Mixed Layer. ⇑ Corresponding author. E-mail address: [email protected] (S. Bhaskar).
ogy of materials are normal applied load, sliding speed, sliding distance, temperature, counter surface hardness, etc. The working range of these variables is important consideration in real time evaluation of tribological performance as well as service life of components [2]. This fact has been advocated by research of eminent scholars like Kumar et al. [3] discussed the sliding wear characteristics under unlubricated conditions of Al 2618 metal matrix composite reinforced with ZrB2, Si3N4 and AlN-particles up to 8 wt.%. Fabrication was processed through stir casting technique. The Taguchi orthogonal array was used to design the experimentation and ANOVA was applied to find out the effect of each factor on the wear rate. Load was the most significant factor because it was found that specific wear rate slightly enhanced for a load range of 10 N–50 N load but it increases sharply at 50 N load for a reinforcement of 8 wt.%. Abrasive and adhesive wear were dominant mechanisms observed for lower and higher load conditions respectively. Dinaharan et al. [4] evaluated the wear rate of AA6082 AMCs reinforced with different ceramic particulates such as SiC, alumina, TiC and B4C. The composites were fabricated through FSP technique and effect of various FSP parameters on the wear rate was
https://doi.org/10.1016/j.matpr.2020.01.015 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Nomenclature AAN-0 AlN AAN-2 AlN AAN-4
Aluminium alloy composite filled with 0 wt.% (Aluminium nitride) and 2 wt.% Gr (graphite) Aluminium alloy composite reinforced with 2 wt.% 2 wt.% Gr Aluminium alloy composite reinforced with 4 wt.%
estimated using some empirical relationships by applying RSM. Lower wear rate and higher micro-hardness were obtained for TiC-particles reinforced composites. Minimum wear rate was also obtained for low tool rotational speed, high traverse speed and maximum groove width. Alaneme and Sanusi [5] have analysed the wear properties of Al-Mg-Si alloy matrix composites filled with alumina, rice husk ash and graphite particles fabricated through stir casting method. Wear tests were performed using Taber abrasion wear testing machine. Improved wear resistance was obtained for 73.5–74.5% alumina, 25% rice husk ash and 0.5–1.5% graphite. The composites without graphite had shown more wear than those containing graphite particles. The improved wear behaviour was due to the lubricating effect of graphite particles which formed a layer between the two mating surfaces. It was also found that wear resistance have been reduced as the amount of graphite increased from 0.5 to 1.5%. Pramanik [6] reported the influence of different sliding parameters such as sliding distance, pressure and sliding speed on the wear properties of AA6061 matrix composite reinforced with 10 vol% Al2O3 particles. Wear tests were performed on pin-on-disc testing machine. It was shown that the wear loss was much lowered for composite when compared with base alloy with all the changing factors like pressure, distance and speed. The possible wear mechanism for composite was three body abrasion wear. The filled alumina particles provide resistance to the deformation of composite surface and enhanced the wear characteristics of the composite. Kumar et al. [7] investigated the tribological properties of AA6061-T6/AlNp composite fabricated through liquid metallurgy route. A regression model was developed for predicting the wear characteristics under sliding conditions of AA6061 matrix composite reinforced with AlN particulates. A central composite design was applied for designing the experiments and pin-ondisc testing machine was used for conducting the experimentations. It was found that the wear loss of the composite increased with increasing the sliding velocity, distance and normal load. The wear loss of the composite was decreased with increasing in mass fraction of AlN particles from 0 to 20%. Delamination was the main wear mechanism observed at larger sliding velocity. Ploughing and abrasive wear mechanisms were also obtained. Adhesive wear mechanism was more effective in AA6061 alloy, where as abrasive wear was effective in AA6061/AlNp composites. Ravindran et al. [8] fabricated the hybrid AA2024 matrix composites reinforced with fixed 5 wt.% of graphite and varied (5, 10, 15, 20 wt.%) of SiC particles through powder metallurgy process. Sliding wear experiments were conducted as per the ASTM G99-05 standard on pin-on-disc machine. Various controlling parameters were used such as load (5–30 N), varying sliding speed like 1000 or 3000 m and sliding speeds such as 1 and 2 m/s. The wear rate was found to be decreased with increasing the content of SiC particles due to the increased hardness of the composite with the addition of hard ceramic particulates. The wear resistance decreased with increasing normal load and sliding distance. The lower wear loss was observed for 20 wt.% SiC and 5 wt.% graphite reinforced aluminium matrix composite. Kumar and Dhiman [9] have evaluated the specific wear rate of the hybrid AA7075 MMCs filled with SiC (7 wt.%) as hard ceramic particles and graphite
AlN AAN-6 AlN
2 wt.% Gr Aluminium alloy composite reinforced with 6 wt.% 2 wt.% Gr
(3 wt.%) as soft solid lubricant. Liquid metallurgy technique was used for the production of composites. Design of experiments was done according to full factorial method. Specific wear rate was examined on pin-on-disc wear tester and influence of various sliding factors on wear behaviour was discussed. The wear rate has been reduced at low load in the range of 20–40 N and at low speed in the range of 2–4 m/s. Mazahery and Shabani [10] evaluated the sliding wear behaviour of AA2024 alloy matrix composite reinforced with various volume fractions (0, 5, 10, 15, 20, 25, 30) of coated B4C particles fabricated by squeeze casting method. The weight loss was observed for varying sliding distances (0, 200, 400, 600, 800, 1000 m). The fabricated composite had more wear resistance as compared to the matrix alloy and improved with higher particle content. It was also found that the weight loss was increased with increasing sliding distance for unreinforced alloy and for all the composites. Minimum weight loss was obtained for the composite reinforced with 30% volume fractions. Sahin and Kilicli [11] have evaluated the influence of applied load and weight fraction under the abrasive wear conditions of AA2014 MMCs reinforced with SiC-particles. The composite was fabricated through liquid metallurgy technique. The wear properties were investigated for various factors such as abrasive particle size (50 lm), weight fraction (10%) and applied load (0, 5, 10, 15, 20, 25, 30, 35 N) using pin-on-disc apparatus. The wear resistance of the aluminium matrix composite was found to be increased with increasing weight percentage of SiC-particles. With increasing applied load the value of wear rate also increased but lowered wear rate was obtained for 10 wt.% SiC-particles when compared with the base alloy. Rao and Das [12] investigated the sliding wear behaviour of high strength aluminium alloys such as AA7010, AA7009, AA2024 and influence of SiC addition on the sliding wear of AMCs. The composite was fabricated through stir casting technique. The sliding wear tests were performed on pin-on-disc wear apparatus with various applied pressure and fixed sliding speed and also for various volume fractions. Improved wear properties was obtained with increasing amount of the SiC-particles addition. Lowest wear rate was obtained for AA7010 alloy composite and highest wear rate was obtained for AA2024 alloy composite irrespective of the SiC amount. Rajeev et al. [13] investigated the influence of various operating parameters like applied load (15 and 45 N), sliding distance (500 and 1500 m), reciprocating velocity (0.2 and 0.4 m/s), counter surface temperature (60 and 120 °C) and weight content of silicon particles (6 and 18 wt.%) on dry reciprocating wear characteristics of A319, A390 metal matrix composites reinforced with SiC particles. Higher wear resistance was observed for the higher amount of silicon particles addition. All the operating parameters were the influential controlling factors affecting the wear rate of composite specimens. Herbert et al. [14] evaluated the wear characteristics under dry conditions of as cast, mushy state rolled Al-Cu alloy and its composites filled with TiB2 particulates. The wear resistance was enhanced by incorporating TiB2 particulates. SWR was reduced as the load increased due to increased plastic deformation was observed at higher loads. Umanath et al. [15] have performed the statistical analyses of dry sliding wear characteristics of hybrid Al alloy composite filled with
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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ceramic particulates were added in the AA2024 alloy. The ceramic particles were preheated at 700 °C for 3 h before mixing in the melt alloy. To increase the wettability of ceramic particulates with the matrix alloy, Mg (2 wt.%) was added in the slurry prior to the addition of preheated particles. A mechanical stirrer made of stainless steel has been used for mixing the ceramic particulates in the alloy at 500 °C. The stirring was done at 450 rpm for 2–3 min in order to achieve uniform distribution of particles. The molten metal was then poured into permanent mould of cast iron having dimensions 140 90 10 mm3 and the temperature was then lowered gradually [18]. The fabricated aluminum alloy composites were evaluated under dry sliding conditions to analyze the specific wear rate and coefficient of friction using pin-on-disc tribometer (Model TR-20, Ducom, Banglore, India) as per ASTM G 99 standard with hardened steel disc (EN-31) of hardness 60–70 HRC. For experiments, track diameter of 50 mm was kept fixed throughout the experimental work. The working range of selected parameters is given in Table 2. The weight loss of the composite specimen was obtained using LVDT transducer by measuring the reduced length in vertical direction in micro-meters. The weight loss was also calculated using electronic balance (accuracy of ±0.001 mg). Finally, the specific wear rate (mm3/N-m) was calculated as:
5 and 15 wt.% of (SiC + Al2O3) filler particulates. Lower wear loss was obtained for large amount of filler particles, smaller applied load, minimum rotational speed and higher hardness of counter surface. Dharmalingam et al. [16] investigated the sliding wear characteristics of Al hybrid metal matrix composite comprising Al-Si10Mg alloy as matrix material, 2 and 4 wt.% MoS2, 5 wt.% Al2O3 particles through pin-on-disc apparatus. Optimum wear performance of the composite material was evaluated using Grey relational analysis and Taguchi design of experiment. Minimum SWR was achieved for applied normal load of 30 N, sliding speed of 4 m/s and amount of MoS2 was 4 wt.%. Kok [17] examined the abrasive wear characteristics of AA2024 alloy composite filled with 30 wt.% Al2O3 particles. Significant improvement in wear resistance was observed as compared to the base alloy with the addition of Al2O3 ceramic particulates. Number of researchers has been observed that the incorporation of ceramic particulates like SiC, Al2O3, Si3N4, TiC etc. increases the hardness and sliding wear resistance of metal alloy composite material. But there is little attempt has been observed to explore the potential of hybrid reinforcement containing hard ceramic particles like AlN along with soft solid lubricant like graphite to fabricate metal alloy composite for tribological applications. The incorporation of solid lubricant particles as partial reinforcement enhances the wear resistance of metal composites. Hence there is an opportunity to improve the sliding wear and friction properties of metal alloy composite by using above mentioned particulate materials as reinforcement. Hence the main objective of the study is to analyze the Tribological performance of the Al-AlN-Gr hybrid composite under the influence of various controllable parameters.
Ws ¼
Dm
ð1Þ
q:Vs:t:Fn
where, Ws is the specific wear rate in mm3/N-m,Dm is the mass loss of composite during test (g), q is the density of the composite (g/cm3), Vs is the sliding velocity (m/s), t is the test duration (s), Fn is the normal load (N) [19]. In the present study, Taguchi design of experiment has been used to perform the optimization for specific wear rate and coefficient of friction. Taguchi method is widely accepted technique by which number of experiments is reduced and optimal results can be estimated by combining the experimental and analytical concepts to evaluate the effect of each factor on the measured response, so that overall performance can be significantly enhanced. In this work, the minimum specific wear rate is analysed by using lower-the-better (LB) performance characteristics in terms of S/N ratio. In the present work, five input factors are used (Table 2) and L16 orthogonal array design has been applied to find out the specific wear rate and coefficient of friction of the prepared composite. The S/N ratio with LB characteristic can be expressed as [20]
2. Experimental details In the present study, AA2024 alloy has been used as the base matrix material while AlN and Gr particles have been used as the reinforcement material. Aluminium alloy 2024, containing 4.5% copper and 1.5% Mg, develops the highest strength of any naturally aged Al-Cu type of alloy. The size of the ceramic particles varies from 60 to 80 lm. The chemical composition of AA2024 alloy has been given in Table 1. The purpose of utilization of reinforcement material is to further enhance the mechanical, thermal, thermo-mechanical and wear properties of choose matrix material. The ceramic particulate filled alloy composite was fabricated through simple stir casting technique. The melting of alloy AA2024 was carried separately using muffle furnace and molten metal was held at 750 °C for 15 min, the temperature was lowered up to 600 °C in mushy zone i.e. between solidus and liquidus temperatures. The preheated
S 1 X 2 ¼ 10log Y N N
ð2Þ
where, N = number of observations and Y = observed data.
Table 1 Chemical composition of AA2024 alloy. Component
Al
Cr
Cu
Fe
Mg
Mn
Si
Ti
Weight %
90.7–94.7
Max 0.1
3.8–4.9
Max 0.5
1.2–1.8
0.3–0.9
Max 0.5
Max 0.15
Table 2 Working range of selected parameters. Control factors
Sliding Velocity (A) Filler Content (B) Normal Load (C) Sliding Distance (D) Environment Temperature (E)
Level I
II
III
IV
Units
0.654 0 5 784.8 20
1.308 2 20 1569.6 30
1.962 4 35 2354.4 40
2.616 6 50 3139.2 50
m/s wt.% N m °C
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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3. Results and discussions 3.1. Steady-state-specific wear rate and coefficient of friction The specific wear rate of the prepared alloy composites under steady state (sliding velocity of 0.654–2.616 m/s; sliding distance of 1569.6 m, normal load of 20 N, and environment temperature of 30 °C) condition is shown in Fig. 1. From figure, the following observations are obtained: (i) SWR of the fabricated composite has shown increasing trend with sliding velocity irrespective of the filler content. (ii) The order of specific wear rate is AAN0 > AAN-2 > AAN-4 > AAN-6. The decreasing trend of SWR with the increasing amount of AlN particles is attributed to the presence of both hard AlN particles and soft solid lubricant (graphite) as a partial reinforcement, which generates a tribo-layer on the contacting surfaces [7]. The variation of coefficient of friction with sliding velocity of SiC-filled metal alloy composite has shown in Fig. 2. The coefficient of friction of alloy composite is increased as the sliding velocity increased. From the plot it is observed that (i) the coefficient of friction have an increasing trend with the sliding velocity (0.654– 2.616 m/s) irrespective of the filler content. (ii) the magnitude of coefficient of friction is reduced as the amount of AlN increased
from 0 to 6 wt.%, hence therefore order of coefficient of friction is AAN-0 > AAN-2 > AAN-4 > AAN-6. Hence lower coefficient of friction has been achieved for 6 wt.% AlN particles. The increased coefficient of friction can be attributed to the severe plastic deformation takes place due to the presence of hard ceramic particulates as the sliding velocity has been increased. As the sliding speed increases, asperities fluctuations were also takes place that causes stick-slip phenomenon [21]. The influence of normal load (5, 20, 35, 50 N) on SWR of the fabricated composites is shown in Fig. 3. From figure it is observed that the SWR is increased as the value of load increases from 5 to 50 N. But the SWR is found to be reduced with the amount of AlN particles. This enhancement in the wear resistance can be attributed to the dispersion of hard AlN particulates that improved the hardness of the prepared composite and successfully support the normal load and provide a resistance to cut and scratch given from hard counter surface [22]. The different observations of coefficient of friction with normal applied load (5–50 N) of the fabricated composites filled with various wt.% of AlN particles are shown in Fig. 4. From Figure it can be seen that the coefficient of friction have an increasing trend with the normal applied load irrespective of the AlN particle content. The magnitude of the coefficient of friction has been reduced with increasing amount of AlN particle content and the optimal order is AAN-0 > AAN-2 > AAN-4 > AAN-6. Hence lower value of coefficient
Fig. 1. Effect of sliding velocity on specific wear rate of AA2024 alloy composites. Fig. 3. Effect of normal load on specific wear rate of AA2024 alloy composites.
Fig. 2. Effect of sliding velocity on coefficient of friction of AA2024 alloy composites.
Fig. 4. Effect of normal load on coefficient of friction of AA2024 alloy composites.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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of friction has been achieved for 6 wt.% AlN filled composite. The enhancement in coefficient of friction with the normal load may be due to the presence of three body abrasion wear phenomenon
Fig. 5. Effect of sliding distance on specific wear rate of AA2024 alloy composites.
that could take place as a result of the deformation of mechanically mixed layer formed between two mating surfaces during the period of sliding [21]. The variations of specific wear rate with sliding distance (784.8–3139.2 m) are shown in Fig. 5 for AlN filled AA2024 alloy composites. The specific wear rate was found to be decreased up to 1500 m and after that it gradually decreased and almost took a constant trend with increasing sliding distance from 1500 m to 3000 m irrespective of the particle content of filler. At specific load conditions, the order of SWR is AAN-0 > AAN-2 > AAN-4 > AAN-6. The decreasing trend of SWR with increasing sliding distance may be attributed to the plastic deformation of sharp asperities contacts during initial-run-in-period that will fill the valley of material in both the mating surfaces and consequently increased the work hardening of Al-alloy, hence reducing the wear rate with increasing sliding distance for low load and speed [6]. The variations of coefficient of friction with sliding distance (784.8–3139.2 m) of the fabricated aluminium alloy composite filled with AlN particles are shown in Fig. 6. The coefficient of friction was found to be increased with the sliding distance irrespective of the filler content. Hence the optimal order was AAN-0 > AAN-2 > AAN-4 > AAN-6. The enhancement of the coefficient of friction with the sliding distance can be attributed to the more exposure of hard SiC particles that increased the severe plastic deformation and transfer of Al matrix alloy to the counter surface as the contact time between two mating surfaces increased within the specified range of sliding distance (784.8–3139.2 m) [23].
3.2. Taguchi design experimental analyses
Fig. 6. Effect of sliding distance on coefficient of friction of AA2024 alloy composites.
In order to find out the correlation between the SWR and its controlling parameters, Taguchi experimental design approach is used. Taguchi design of experiments generates a ranking order of controlling parameters according to their influences on measured response within least experimental test runs, hence provide satisfactory conclusions [24]. In the present work, five controlling variables each with four levels have been used and shown in Table 2. The experimental test results for SWR of AA2024 alloy composite filled with AlN particles in terms of signal-to-noise ratio as computed by the MINITAB 16 software are shown in Table 3. The corresponding response plots are shown in Fig. 7 and also the signal-to-noise ratio for the 16 tests is calculated as 69.24 dB using MINITAB 16 software. The order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature (Table 4).
Table 3 Experimental layout of L16 orthogonal array. Expt. No.
Sliding Velocity (m/s)
Filler Content (wt.%)
Normal Load (N)
Sliding Distance (m)
Environment Temperature (°C)
Specific Wear Rate (mm3/N-m)
S/N Ratio (db)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0.654 0.654 0.654 0.654 1.308 1.308 1.308 1.308 1.962 1.962 1.962 1.962 2.616 2.616 2.616 2.616
0 2 4 6 0 2 4 6 0 2 4 6 0 2 4 6
5 20 35 50 20 5 50 35 35 50 5 20 50 35 20 5
784.8 1569.6 2354.4 3139.2 2354.4 3139.2 784.8 1569.6 3139.2 2354.4 1569.6 784.8 1569.6 784.8 3139.2 2354.4
20 30 40 50 50 40 30 20 30 20 50 40 40 50 20 30
9.05E03 1.84E03 1.48E04 1.07E04 2.54E04 7.79E04 1.92E04 1.75E04 1.42E04 4.89E05 1.14E03 5.89E04 1.34E04 4.19E04 1.54E04 5.74E04
40.87 54.68 76.60 79.45 71.91 62.17 74.34 75.14 76.97 86.22 58.85 64.59 77.47 67.55 76.24 64.82
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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S. Bhaskar et al. / Materials Today: Proceedings xxx (xxxx) xxx
Main Effects Plot for SN ratios Data M eans Sliding velocity (m/s)
80
Filler content (wt.%)
Normal load (N)
75
Mean of SN ratios
70 65 60 0.654
1.308
1.962
2.616
Sliding distance (m)
80
0
2
4
6
5
20
35
50
Environment temperature (C)
75 70 65 60 784.8
1569.6
2354.4
3139.2
20
30
40
50
Signal-to-noise: Smaller is better Fig. 7. Effect of input control factors on specific wear rate of AA2024 alloy composites.
Table 4 Significance order of input control factors. Level
Sliding velocity (m/s)
Filler content (wt.%)
Normal load (N)
Sliding distance (m)
Environment Temperature (°C)
1. 2. 3. 4. Delta Rank
62.90 70.89 71.66 71.52 8.76 3
66.80 67.65 71.51 71.0 4.71 4
56.67 66.85 74.07 79.37 22.69 1
61.84 66.53 74.88 73.71 13.05 2
69.62 67.70 70.21 69.44 2.50 5
4. Conclusions In the present study AA2024 alloy composite filled with (0, 2, 4, 6 wt.%) AlN particles and fixed 2 wt.% graphite particles are successfully fabricated through stir casting technique. Various tribological characteristics have been investigated and following conclusions were made. 1. The steady state specific wear rate increased under different sliding velocities irrespective of the filler content. The order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding velocities. The coefficient of friction is found to increase with sliding velocity for all the filler content. The order of coefficient of friction with filler content was AAN0 > AAN-2 > AAN-4 > AAN-6 across all sliding velocities. 2. For various values of normal loads (5–50 N), the steady state SWR increases with increasing values of normal load irrespective of the filler content. The order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all normal loads. The coefficient of friction is found to increase with normal loads for all the filler content. The order of coefficient of friction with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all normal loads. 3. The SWR under steady state conditions for different values of sliding distance shows decreasing trend with the sliding dis-
tance irrespective of the filler content. The decreasing order of SWR with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding distances. The coefficient of friction shows increasing trend with the sliding distance for all the filler content. The reducing order of coefficient of friction with filler content was AAN-0 > AAN-2 > AAN-4 > AAN-6 across all sliding distance. 4. From taguchi experimental analysis, it is concluded that order of significance of input control variables is as follows: normal load, sliding distance, sliding velocity, filler content and environment temperature.
CRediT authorship contribution statement Sourabh Bhaskar: Conceptualization, Methodology. Mukesh Kumar: Supervision, Writing - review & editing. Amar Patnaik: Supervision.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015
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Please cite this article as: S. Bhaskar, M. Kumar and A. Patnaik, Tribological characteristics of hybrid AA2024 alloy composite reinforced with AlN and Gr particulates, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.015