Tribological Behavior of Powder Metallurgy Processed Carbon Nanotube Reinforced Alsi Functionally Graded Materials

Tribological behavior of powder metallurgically processes AlSi-MWCNT functionally graded materials was apparatus with pins on discs was examined. Using a Taguchi design of experiments, the signal-to-noise ratio, the analysis of variance, and an orthogonal array were all used to determine the best testing parameters. Analysis revealed wear loss occurs due to increase in load and sliding distance and reduced with MWCNT increased content in FGM. The composites with 1wt% of FGM exhibited both excellent wear resistance and friction coefficients. Wear mechanisms help in understanding the morphology of worn surfaces. The wear mechanism is dictated by delamination layer and other oxide layers. Overall, the findings showed that AlSi-MWCNT functionally graded materials are regarded as remarkable materials in industries where wear-resistant components are crucial, such as aerospace and automotive engineering.


Introduction
Aluminum (Al) is the most abundantly used nonferrous alloy in engineering and structural applications due to its high strength to weight ratio.Especially in automobile and aircraft industries, Aluminum and its alloys widely used because of its reduction in weight and good mechanical properties. 1 less utilization of steel family materials due to the invent of metallurgy in Al and its alloys along with the manufacturing processes. 2T reinforced FGCM imparts higher enhancement in properties such as electrical conductivity, better thermal stability, heat resistance, barrier resistance, thermo mechanical properties, low density compared to conventional composites. 3,4 GCM exhibits high strength to weight ratio, high stiffness to weight ratio, better fatigue resistance, wear resistance, elevated temperature properties compared to metals.
Overall properties of the materials such as physical/ chemical properties (ex: melting point, hardness, wear resistance.Stability, conductivity, reactivity and optical sensitivity) can be manipulated. 5NT reinforced FGCM function better than larger structures and machines.
If the material size is less than 100nm, we call that material as nano material.One of the nano materials is carbon nanotube (CNT).Physical and chemical properties of the CNT are comparatively outstanding to steel, carbon fiber, due to which it finds application in lot of industries.Small size of carbon nanotube makes its surface area more.Increase in surface area helps in catalytic and chemical reaction.The mechanical, thermal, optical and physical properties quite outstanding compared to bulk micron materials.Enhancement in the physical, chemical and mechanical properties of composite will be done with CNT. 6, 7 8 FGM composite for piston rings can be produced using aluminum silicon alloy powder and 2 weight percent MWCNT as reinforcement.These were first ball milled for six days at a speed of 40 rpm.Green compacts using cold compaction, then sinters using hot compaction at 550 o C and 35MPa of pressure in a vacuum. 9Functionally graded material with layers of variable CNT from 0-0.5wt% and Al as the base layer.The rectangular block, which was 75mm broad and 6mm thick, created a sheet with just aluminum on the bottom and a successful steady increase in CNT content from 0.1wt% to 0.5wt%.FGM is created in a rectangular block that is 6mm thick and 75mm broad.CNT patches that are black as seen by optical microscopy.
The two types of wear mechanisms in the dry sliding of Al-Si alloys are oxidative wear and metallic wear. 10

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Lower applied loads resulted in oxidative wear.This results in the formation of an aluminum oxide layer on both the wearing Al-Si surface and the counter face.Wear was caused by the oxidation of the asperities, followed by the fracture and compaction of the oxidized wear debris into this film.

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At higher applied stresses, metallic wear mechanisms were more prevalent.Plastic deformation and fracture, considerable material transfer between the sliding surfaces, and the generation of wear debris were characteristics of the Al-Si wear surface.

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Wear experiments on samples of Al-Si alloy and CNT-reinforced Al composites were performed utilizing a pin-on-disc machine and steel discs.As a result of the given load, three unique wear regimes were discovered. 11 case of mild wear conditions, the 1 wt.%CNTs reinforced Al6061 composite displayed lower wear rate and friction coefficient compared to the monolithic Al6061.It is a simple, efficient and systematic approach in determining optimal parameters.In traditional approach of conducting experiments, one to one experiment with another factor remains constant.It is a tedious process.It does not include interaction between various parameters and its effect.Effect of all parameters at a time cannot be analyzed in traditional method.Taguchi method overcomes all the shortcomings of the traditional approach.
Taguchi method helps in identifying optimizing process parameters and factors on response output. 13Observation of experiments transformed into signal-to-noise (S/N) ratio.Base on type characteristics of the problem, there are different types of signal-to-noise (S/N) ratio.
There are three categories of signal-to-noise (S/N) ratio.
• Smaller-the-better • Higher-the-better • Nominal-the-best The smaller-the-better characteristic applies to the S/N ratio for the wear loss and friction coefficient that are at their lowest.
The loss function can be transformed logarithmically to determine the S/N ratio, as shown below.
S/N = -10 log1/n (∑y 2 ) Where 'n' is the number of observations and 'y' is the observed data.
The four control parameters studied at three levels as shown in Table 1.The experiments were conducted as per Table 2 Using Minitab-17 software mean response graphs were plotted.ANOVA analysis helps in determining percentage contribution each parameter. 12

Results and Discussion
Table 2 Experimental technique using L27 (2 13 ) orthogonal array S/N ratio's for both wear loss and coefficient of friction computed using Minitab-17 shown in Table .3and Table 4.

Influence of Testing Parameters on Wear Loss
The primary consequences of the influence of the various testing conditions on both wear loss and coefficient of friction are depicted in Fig. 2 as a graph.If a parameter's line in the main effect plot is nearly horizontal, the parameter has no discernible effect.The most substantial impact, however, is on the line parameter with the maximum inclination.The parameter-B (load) was evidently the most important component in the main effect plot.Composition-A, sliding speed-C and sliding distance-D are influential in wear loss.Increase in the load of the functionally graded composite material leads to more loss of the material and hence more wear occurs in the material.
Initially wear was less, as the load increases the wear loss gain the momentum.Because it has the largest inclination among the other parameters, sliding speed has the greatest impact on coefficient of friction.The parameters such as composition, load and sliding distance having less influential on coefficient of friction.Increase in the sliding speed leads to asperity-asperity contact time and more surface area contact occur leads to more friction.Larger the friction between the functionally graded material and disc leads to more coefficient of friction.

For Wear Loss
For Coefficient of friction

Confirmation Experiment
Taguchi strongly advises the use of the confirmation experiment to validate the results of experiments.
The confirmation experiment was carried out using a mixture of the optimal levels after the optimum conditions were established to compare the outcomes with the anticipated performance [14].Table 7. demonstrates the use of the ideal parameters to compare the estimated wear loss to the actual wear loss.It should be emphasised that the estimated and observed findings showed good agreement.
From the initial testing conditions to the ideal testing parameters, the S/N ratio increased by 5.7218dB and 2.01248dB, respectively.This meant that the wear loss was reduced by roughly 87.17% and the coefficient of friction loss by 81.23%.This result suggests that the model developed in this study can be utilised to accurately forecast the composites' wear behaviour and friction coefficient.The creation of grooves, which are caused by the ploughing action of hard asperities on the counter disc, characterises the wear mechanisms. 15,16,17,18 Fi6 (a-b): SEM morphology of functionally graded composite material with 2wt% MWCNT substrate layer for a load of 20N

Conclusion
Tribological properties are determined for axial layer functionally graded composite material.L27 orthogonal Taguchi technique is followed to determine the minimum wear and less coefficient of friction with the combination of optimum factors.ANOVA technique is implemented to determine influence of each factor.The conclusions drawn are as follows: • The composites with 1wt% of FGM exhibited both excellent wear resistance and friction coefficients.

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ANOVA results revealed that the most important factors influencing the sliding wear of the functionally graded composite material were the composites themselves (in terms of their individual percentage contributions) that load (p=29.89%)having maximum influence on the wear loss Composition (p=7.73%),sliding speed (p=0.5%),sliding distance (p=1.54%)having contribution towards wear loss.The interactions had less effect on the wear loss.

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The ideal testing parameters for the best wear resistance were a composition of 1wt%, a load of 10N, a sliding speed of 1.5m/sec, and a sliding distance of 2000m.For the best friction results, use a composition of 1wt%, a weight of 30N, a sliding speed of 1m/sec, and a sliding distance of 2000m.

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In a Taguchi experimental analysis, the ideal control factors for wear loss and friction coefficient were discovered to be A1B1C2D3 and A1B3C1D3 respectively.• SEM studies of the worn surfaces revealed that the wear mechanism involved with the AlSi-1wt% MWCNT composites was oxidative wear with severe plastic deformation.

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The AlSi-1.5wt%MWCNT functionally graded composites had oxidative wear and delamination wear as their wear mechanisms.The main wear mechanism in the functionally graded AlSi-2wt% MWCNT composites was delamination wear.

Fig. 4 :
Fig.4: Interaction plot for a) wear loss and b) coefficient of friction

Fig. 4 (
Fig.4 (a-b): SEM morphology of functionally graded composite material with 1wt% MWCNT substrate layer for a load of 20N Wear Mechanism of Functionally Graded Composite Material Figure 4 (a-b): indicates SEM morphology of worn surfaces of functionally graded composite material with 1wt% MWCNT substrate layer for a load of 20N.Clearly exhibited the permanent grooves and fracture of oxide layer.These leads to increase more wear loss in the FGCM of 0.5wt%.

Fig. 5 (Figure 5
Fig.5 (a-b): SEM morphology of functionally graded composite material with 1.5wt% MWCNT substrate layer for a load of 20N Figure 5 (a-b): indicates SEM morphology of functionally graded composite material with 1.5wt% MWCNT substrate layer for a load of 20N.SEM images indicating finer grooves with plastic deformation at the edges of the grooves.The surfaces appear to smooth due to reinforcement of multi wall carbon nanotube.Due to proper dispersion of multi wall carbon nanotube in the Aluminum silicon matrix, there is a reduction in wear loss of the material and fine groove formation.

Figure 6 (
Figure 6 (a-b): indicates SEM morphology of functionally graded composite material with 2wt% MWCNT substrate layer for a load of 20N.SEM images indicating finer grooves the surfaces appear to intact due to reinforcement of multi wall carbon nanotube.Due to proper dispersion of multi wall carbon nanotube in the Aluminum silicon matrix, there is a reduction in wear loss of the material and fine groove formation.Thus, it indicates the increase 12

Materials and Methods Synthesis Technique For 2-Layer Functionally Graded Composite Material for Wear Test
11layer functionally graded material composite with Aluminum silicon alloy is base part and Aluminum silicon alloy with MWCNT is substrate.Fig.1:FGMwith2-layers of base & substrateWhere in base part composition remains same i.e., only Aluminum silicon alloy for all samples but substrate will vary with AlSi & MWCNT content.11

Table 5
Mat. Sci.Res.India, Vol.20(2), pg.88-99 (2023) a composition of 1wt%, load of 10N, sliding speed of 1.5m/sec and sliding distance of 2000m for the best wear resistance.A composition of 1wt%, load of 30N, sliding speed of 1m/sec and sliding distance of 2000m for the best friction values.
13 & Table5.6.The response shows the average of the selected characteristics for each level of the factors.The response table ranks based on Delta statistics, which compare the relative magnitude of effects.The Delta statistics is the highest average for each factor minus the lowest average of the same.Ranks are assigned based on Delta values: Rank1 is assigned to highest Delta value, rank2 on second highest delta value and so on.13Theoptimum testing conditions were PASHA & RAJAPRAKASH,