Prediction of wear volume and friction coefficients of SS304 alloy using grey taguchi-based response surface methodology

The present investigation is centered on examining the tribological characteristics within a pin-on-disk configuration resembling a cylinder on a flat contact surface. The pin, constructed from Stainless Steel 304 alloy, underwent sliding experiments under varying speeds (1, 2, and 3 m s−1) and normal loads (10, 15, and 20 N) across track diameters of 60 and 120 mm. The experiments aimed to mitigate wear and friction in movable components, thus conducted for up to 2000 s in the experimental setup without any lubrication. Observations of the coefficients of friction stabilization and wear rate were made by manipulating the input parameters to anticipate the failure range. Higher coefficients of friction and increased wear rates were noted at lower sliding speeds, with wear rates stabilizing at higher speeds. Interestingly, despite a higher coefficient of friction stabilization and wear rate at a 120 mm track diameter, wear decreased. Optical Microscopy studies were carried out to examine surface damage for all normal loads and sliding speeds using both 60 mm and 120 mm track diameters. Additionally, this study employs Grey Taguchi-based Response Surface Methodology (GT-RSM) to forecast and regulate wear and friction. The findings of this study have practical implications for industries such as automotive, aerospace, and others employing SS 304 alloys in their operational components.


Introduction
Wear and friction are key factors contributing to economic losses in diverse mobile applications, such as gears, aerospace components, and naval industries.Consequently, there is a substantial demand for materials capable of prolonging the service life of engineering machinery and parts by minimizing wear.In a pin-on-disk configuration, friction tends to exhibit more variability, influenced by sliding speed, and this variability arises from the unevenness of the wear track [1].The incorporation of copper (Cu) into Al-Mg-Cu alloys, constituting up to 5% of its weight, has led to a reduction in wear loss and an increased coefficient of friction when compared to aluminum-based alloys.This improvement is attributed to the formation of a tribofilm at the contact interface.The investigation into wear and friction properties involved AA 6061 composites reinforced with garnet particulates, utilizing a pin-on-disk tribometer [2].Normal loads (10 N-50 N) and sliding speeds (1.25 m s −1 -3.05 m s −1 ) were altered during the experiments.Elevated wear rates resulted in heightened contact temperatures and the material transitioning to a plastic state.At higher temperatures, an oxide layer forms on the contact surface, impeding temperature conduction.Accumulation of heat at the contact surface leads to material deformation and the generation of debris.The wear rate displayed minimal variation up to a specific normal load, beyond which it increased, aligning with an elevation in sliding speed.The friction coefficient initially decreased and then rose with increasing sliding velocity, accompanied by an augmentation in normal load.A notable increase in wear rate occurred when the sliding speed surpassed 4.5 m s −1 .Sliding speed plays a pivotal role in generating frictional heat during metal sliding, where the flash temperature at asperity contacts exceeds the mean contact temperature [3].Softening of contact asperities occurs when the flash temperature reaches the base metal's melting point.At high sliding speeds, a lower coefficient of friction is observed due to material softening and oxidation processes.Greater oxidation of metal surfaces is observed at sliding speeds exceeding 1 m s −1 [4].Recent studies have pointed out increased wear rates at higher normal loads [5] and sliding velocities in Al-SiC-B4C hybrid composites, attributed to high-stress concentration [6].In steel contacts, the friction coefficient at sliding velocities less than 1 m s −1 depends on surface roughness [7], while velocities exceeding 1 m s −1 correlate with surface pressure and sliding speed [8].The literature review identified limited studies on the combined impact of wear and the coefficient of friction on SS 304 alloys.Consequently, this study aims to establish an empirical relationship between the coefficient of friction and wear during full sliding.Regression models were explored to understand the combined effect of wear and friction on input process parameters, offering a solution to prevent failure.

Materials and methods
Dry sliding experiments were conducted by Pin on a disk tribometer using SS304 Alloy Material to understand the coefficient of friction stabilization [9] value and wear volume [10], which are important properties for this experiment.
The chemical composition and mechanical properties of the SS304 alloy material are listed in table 1.The pins and disks were fashioned from commercially available SS304 Alloy rods, each having dimensions of 180 mm in diameter and 200 mm in length.Using a hack-saw cutting machine, 14 mm thick disks were precisely cut from the SS304 alloy rods.Subsequently, a Computer Numerical Controlled (CNC) milling machine was utilized to reduce the thickness of these disks and shape them into smaller disks measuring 8 mm ± 0.1 mm in thickness and 165 mm ± 0.1 mm in diameter.The fabrication process also included the creation of pins with a cross-sectional area of (6 mm × 6 mm) and a length of 30 mm ± 0.1 mm.One end of the pin was designed with a semi-cylindrical shape featuring a radius of 3 mm.

Experimental set-up
Experiments were carried out using SS304 alloys as both pins and disk specimens.The full sliding tests were conducted under dry sliding conditions, employing a pin-on-disk tribometer setup with a cylindrical pin in a flat contact configuration.Figure 1 illustrates the schematic representation of the experimental setup, where the stationary rigid pin-holder arm arrangement secured the cylindrical pin specimens.
The experiments were conducted at different loads (1, 1.5, and 2 kg) and sliding speeds (1, 2, and 3 m s −1 ).At 32 °C with 84% relative humidity.Preliminary studies on surface roughness (Ra) of the disk track.The surfaces of both the pin and disk were meticulously cleaned with an acetone solution to eliminate any lingering oily residues on the contact surfaces.A white cotton cloth was employed to wipe away dust and moisture particles.Prior to conducting the tribological tests, the surface roughness (Ra) of the disks was assessed using a surface roughness tester.Table 2. Provides a compilation of the surface roughness values for SS 304 alloys.
A wear test was conducted using a pin-on-disk tribometer [11], wherein the surfaces of both the pin and the disk were cleansed with an acetone solution.Prior to the experiment, the weights of the pin and disk were precisely measured using a digital weighing balance machine with an accuracy of 0.001 g.The surface roughness values of the disk were measured at different locations on the track, at 60 and 120 mm.The range of surface roughness (Ra) values of 60 mm track diameter were 0.31-0.35μm, and the roughness values were between 0.33-0.38μm for disk specimens with 120 mm track diameter.

Results and discussion
The friction coefficient is influenced by various factors including sliding speed, load, surface roughness, and frictional heat [12].Among these parameters, sliding speed holds particular significance in dynamic conditions.Hence, a tribological test was executed through a pin-on-disk experiment.This experiment took place under ambient conditions, with a maximum duration of 200 s.Varied normal loads, namely 1, 1.5, and 2 kg, were applied at sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 while maintaining a constant track diameter of 60 mm.The primary emphasis of this study lies in understanding the initial stabilization of the friction coefficient for SS 304 alloys.

Wear behaviour study
In the wear behaviour study under a normal load of 1 kg and a sliding speed of 1 m s −1 , the coefficient of friction initially increased gradually.Figure 2(a) illustrates the wear volume over time durations at various sliding speeds with a track diameter of 60 mm.Beyond the initial 5 s, the sliding track contact area underwent the removal of weak surface asperities, with subsequent observations of small undulations occurring between 5 and 28 s.Following this, the friction coefficient stabilized at μ = 0.0068 after 28 s. Figure 2(b) shows various worn-out surfaces under different loads and sliding velocities for 120 mm track diameter.At a sliding speed of 2 m s −1 , a similar trend was observed, with the friction coefficient stabilizing at μ = 0.0038.When the sliding speed was increased to 3 m s −1 , the coefficient of friction initially rose.Between 5 and 121 s, significant undulation occurred due to surface asperities acting as rollers between the contacts.Eventually, the friction coefficient stabilized at μ = 0.0022.The coefficient of friction is typically obtained by measuring the friction force acting between the two sliding surfaces and dividing it by the normal force pressing the surfaces together.This measurement is often done using a load cell and a sensor that can detect the frictional force.

Wear behaviour for different track diameters
Figure 3 illustrates the changes in wear volume over time at different sliding speeds, considering track diameters of 60 mm and 120 mm, and applying normal loads of 1, 1.5, and 2 kg with sliding speeds of 1, 2, and 3 m s −1 .
Wear volume was assessed across different normal loads: 1 kg (a), 1.5 kg (b), and 2 kg (c), coupled with varying sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 .Under a normal load of 1 kg (a) and a sliding speed of 1 m s −1 , the wear volume increased gradually as the Fe oxide layer was removed, leading to the formation of wear grooves.At a sliding speed of 1 m s −1 , the wear volume peaked at 380 mm 3 .Elevating the sliding speed to 2 m s −1 resulted in a rapid surge in wear volume after 74 s, attributed to abrasive wear involving active contact surface asperities, reaching a peak of 980 mm 3 .The wear volume stabilized after 165 s.For a sliding speed of 3 m s −1 , the wear volume increased after 51 s due to the higher sliding speed creating a robust abrasive bond with the pin and disk contact track surface roughness [13].The maximum wear volume of 1600 mm 3 was observed at 78 s, stabilizing at 81 s.A similar pattern was noted for a normal load of 1.5 kg at sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 .At a sliding speed of 1 m s −1 , the maximum wear volume reached 500 mm 3 .For a sliding speed of   This could be due to the smaller contact area and higher contact pressures associated with the smaller track diameter, leading to more localized wear and potentially higher wear rates.The wear volume stabilization values for the 120 mm track diameter are generally higher, indicating a larger contact area and lower contact pressures compared to the 60 mm track diameter.This could result in more distributed wear and potentially lower wear rates overall, although other factors such as material properties and sliding speeds also play a significant role.

Comparison of wear behaviour
At a normal load of 1 kg and a sliding speed of 1 m s −1 , the wear volume demonstrates slight undulation for 18 s, attributed to the hardness of the disk surface.Subsequently, after 20 s, the wear volume gradually rises due to the removal of the iron oxide layer, resulting in a well-contacted surface [15].Under these conditions, a wear volume of 580 mm 3 was observed.The outcomes regarding wear volume stabilization for track diameters of 60 mm and 120 mm are outlined in table 3.At a sliding speed of 2 m s −1 , the wear volume increases steadily, indicating good conformity with the track surface contact [16].With a normal load of 1 kg and a sliding speed of 2 m s −1 , a wear volume of 620 mm 3 was recorded.While in the sliding speed of 3 m s −1 , there is a rapid escalation in wear volume attributed to the increased sliding speed.A wear volume of 1400 mm 3 was recorded within 95 s, followed by stabilization after a brief period.Under a normal load of 1.5 kg and sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 , distinct wear volumes were observed.At a sliding speed of 1 m s −1 , the maximum wear volume reached 670 mm 3 .For a sliding speed of 2 m s −1 , the wear volume showed slight undulation until 35 s, attributed to the roughness and hardness of the contact surfaces.Subsequently, the wear volume increased due to the formation of chipping [17], stabilizing  after 41 s, with a maximum wear volume of 600 mm 3 .At a sliding speed of 3 m s −1 , the wear volume increased rapidly, reaching 950 mm 3 within 22 s.Under a normal load of 2 kg and sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 , wear volumes were recorded.At a sliding speed of 1 m s −1 , the wear volume increased gradually, reaching a maximum of 690 mm 3 .For a sliding speed of 2 m s −1 , the wear volume increased due to the heightened sliding speed, following a similar trend observed at sliding speeds of 1 m s −1 and 2 m s −1 .At a sliding speed of 2 m s −1 , the maximum wear volume was 880 mm 3 .However, at a sliding speed of 3 m s −1 , the wear volume increased significantly due to the higher sliding speed.Between 18 s and 180 s, more undulation in wear volume was observed, attributed to wear debris formation resulting from abrasion and adhesion-induced plowing on the contact surface.In this specific combination of process parameters, a maximum wear volume of 771 mm 3 was observed in the stainless-steel material.The contact area between the surfaces might change at different loads and speeds, affecting the wear behavior.At higher loads, the contact area might be more stable, leading to lower wear rates.The wear debris generated at higher loads and speeds might act as a protective layer, reducing further wear.

Friction behaviour analysis
Under a normal load of 1 kg (a), the coefficient of friction exhibited a significant increase from 5 s to 40 s at a sliding speed of 1 m s −1 , attributed to robust adherence with surface asperities.After 40 s, the friction coefficient stabilized, reaching a value of 0.0044.At a sliding speed of 2 m s −1 , the friction coefficient initially increased.Consequently, higher undulation was observed from 5 s to 115 s.Subsequently, the surface asperities became flattened, leading to the stabilization (μ) = 0.0025 after 115 s.A similar trend was initially noticed at a sliding speed of 3 m s −1 .Experimental observations from 5 s to 72 s revealed increased undulation due to third-body interaction.The friction coefficient stabilized at (μ) = 0.0021 for a sliding speed of 3 m s −1 .For normal loads at 1.5 kg and 2 kg, at sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 , the friction coefficient initially increased, and undulation was observed from 5 s to 47 s due to third-body interaction.Throughout the experiment, most surface asperities migrated to the outer track area of the disk surface.Figure 4 illustrates the variation in coefficient of friction results for normal loads of 1, 1.5, and 2 kg for track diameters of 60 mm and 120 mm.According to experimental observations, the friction coefficient stabilized at (μ) = 0.0067, 0.0038, and 0.0042 for sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 , respectively.As the sliding speed increases, the surface asperities undergo melting upon making contact with the element.This initiates a thermal process, leading to a gradual transition from a striking to a slipping condition at the contacts [18].Under various normal loads and sliding speed conditions, the friction coefficient value stabilizes at an optimized level.A smaller track diameter can lead to higher COF values due to higher contact pressures and potentially more localized contact between the surfaces.For the 60 mm track diameter, the COF values are generally higher compared to the 120 mm track diameter at the same weight and sliding speed.This is consistent with the expected effect of track diameter on COF.The contact area between the surfaces is inversely proportional to the track diameter.Smaller track diameters result in smaller contact areas, leading to higher contact pressures and higher COF values.Smaller track diameters can also result in higher effective surface roughness, which can increase the COF.Different materials can exhibit different COF behaviours under varying loads and track diameters due to differences in their surface properties and wear mechanisms.In summary, both weight and track diameter can significantly affect the COF of samples at 1 m/s sliding speed.Higher weights and smaller track diameters generally lead to higher COF values due to higher contact pressures and potentially more localized contact between the surfaces.

Comparison of friction behaviour
Under a normal load of 1.5 kg and a sliding speed of 1 m s −1 , there is an increasing trend in the coefficient of friction.Over an extended duration from 7 s to 178 s, significant undulation is observed, attributed to the utilization of abrasives that play a significant role with hard particles between the contact surfaces.The friction coefficient stabilizes at (μ) = 0.0067.Similarly, at a sliding speed of 2 m s −1 , the friction coefficient follows a comparable pattern, stabilizing at μ = 0.0058 by 19 s.For a sliding speed of 3 m s −1 , the coefficient of friction initially increases.From 5 s to 51 s, there is a significant influence of adhesion due to the presence of the Fe-oxide layer with contaminants and surface asperities in mating contact.The friction coefficient stabilizes at (μ) = 0.0038.
Under normal loads of 1.5 kg and 2 kg with sliding speeds of 1 m s −1 and 2 m s −1 , the coefficient of friction increases in a similar trend.For normal loads of 2 kg with sliding speeds of 1 m s −1 and 2 m s −1 , the friction coefficient stabilizes at values of (μ) = 0.0071 and 0.0053, respectively.After 7 s, the friction coefficient stabilizes at (μ) = 0.0022, as indicated in table 4, which presents the results of the coefficient of friction stabilization values for track diameters of 60 mm and 120 mm.
At a normal load of 1 kg and a sliding speed of 1 m s −1 , the COF is 0.0044 (60 mm) and 0.0068 (120 mm), while the wear volume stabilization values are 380 mm 3 (60 mm) and 580 mm 3 (120 mm).This suggests a lower COF but a higher wear volume at the 120 mm track diameter.At a normal load of 2 kg and a sliding speed of 3 m s −1 , the COF is 0.0041 (60 mm) and 0.0019 (120 mm), while the wear volume stabilization values are 769 mm 3 (60 mm) and 778 mm 3 (120 mm).This shows a lower COF but a similar wear volume at the 120 mm track diameter.

Microscopic analysis of wear surfaces
The examination of pin and disk surfaces using optical microscope images was conducted both before and after the experimental contact, a crucial step for failure analysis [19].Optical microscopy images illustrating the damaged disks and their track surfaces are presented in figure 8.The pin-on-disk experiment encompassed track diameters of 60 mm and 120 mm, incorporating various normal loads (1 kg, 1.5 kg, and 2 kg) and sliding speeds (1 m s −1 , 2 m s −1 , and 3 m s −1 ).All experiments were limited to a maximum duration of 200 s, conducted under ambient conditions with a temperature of 32 °C and a relative humidity of 84%, specifically in dry sliding conditions.Figure 5 displays an optical microscopy image capturing the damaged disks at a 60 mm track surface, depicting normal loads of 1 kg, 1.5 kg, and 2 kg with a sliding speed of 1 m s −1 .In the initial 5 s, the removal of the Fe oxide layer occurred, leading to the formation of wear grooves dominated by metallic adhesion after this duration.The application of a normal load of 1 kg at sliding speeds of 2 m s −1 and 3 m s −1 intensified the effect with an increase in sliding speed.The maximum load strain accumulated at the contact surface, causing surface asperities to detach onto the track surface, resulting in more wear debris formation at the wear track [20].At a sliding speed of 3 m s −1 , small pit formation occurred due to the detachment of surface asperities [21].Under a normal load of 1.5 kg and a sliding speed of 2 m s −1 , crater formation took place on the worn track surface with small pit formation observed at a sliding speed of 3 m s −1 .
Under a normal load of 2 kg and a sliding speed of 2 m s −1 , the combination of increased load and sliding speed resulted in more pronounced cratering and abrasion on the wear track surface.When the sliding speed was increased to 3 m s −1 with the elevated load, the generation and addition of heat became more significant.This occurred as the surface asperities melted and impacted the deposited track surface due to heat dissipation.Figure 6 illustrates optical microscopy images depicting the wear damage on disks at the 120 mm track surface under different normal loads (1 kg, 1.5 kg, and 2 kg) and various sliding speeds (1 m s −1 , 2 m s −1 , and 3 m s −1 ).Under normal loads of 2 kg with a sliding speed of 3 m s −1 , the coefficient of friction increases due to strong adhesion bonds with active surface asperities.Under normal loads of 1, 1.5, and 2 kg with a sliding speed of 1 m s −1 , the removal of the Fe-oxide layer took approximately 7 s.
Following this, metallic adhesion dominated, and a few areas on the contact surface exhibited void formation [22] as a consequence of wear groove formation.When the normal load was 1 kg with a sliding speed of 2 m s −1 , pit formation increased notably due to the heightened sliding speed, coupled with an increase in the track diameter to 120 mm.At a sliding speed of 3 m s −1 , a crater with deposited metal on the track surface was observed for a normal load of 1.5 kg and a speed of 2 m s −1 .Surface asperities melted, and pit formation intensified due to the elevated sliding speed for an increased load value at a track diameter of 120 mm.At a sliding speed of 3 m s −1 , wear debris melted due to frictional heat generation.For a normal load of 2 kg with a sliding speed of 2 m s −1 , track surface aspiration and pit formation increased owing to the escalated sliding speed and an increase in the load for a track diameter of 120 mm.As the sliding speed was increased to 3 m s −1 , more metal abrasion was observed on the track surface.

Grey taguchi-based response surface methodology
Grey Taguchi-based Response Surface Methodology (GT-RSM) is employed to analyze responses [23], including wear volume stabilization and the coefficient of friction.This analysis involves varying input process parameters such as track diameter, normal load, and sliding speed.The response values for various input process parameter settings are presented in the table 5.
Signal-to-noise (SN) ratios are computed under the 'smaller the better' condition for both output responses, namely wear volume stabilization and coefficient of friction.The formula to calculate the SN ratio is provided in the following equation (5.1).
where n is the number of replicates, y i is the observed response, i is the number of experiment.Table 6 presents the calculated SN ratio information for wear volume stabilization and coefficient of friction.Grey Relational Grade (GRG) values, as presented in table 7, are derived from the average values of grey relational coefficients.These coefficients are calculated for output responses, including wear volume stabilization and coefficient of friction values.GRG values are determined by averaging Grey relational coefficient values.These values offer insights into both output responses, specifically wear volume stabilization and coefficient of friction, with consideration for the 'smaller the better' condition.Figure 7 depicts the residual plots of the GRG values, accompanied by results such as normal probability plot, versus fits, histogram, and observation order.
The findings in figure 7 reveal that there are only a limited number of outliers in the experimental observation order.The majority of the results closely align with the mean line, indicating a strong correlation with statistical outcomes.

Response table for GRG
The GRG characteristics are calculated for 'smaller the better' condition and the results are shown in the table 8.
Thus, the size of the track diameter significantly influences the output responses.Track diameter of 120 mm (level 2), normal load of 10 N (level 1) and sliding speed of 3 m s −1 (level 3) is found to be the optimum input process parameter combination for controlling the wear volume and friction.The response surface graphs for GRG show that the increase in track diameter has a considerable increase in the GRG values.The normal load of 15 N has a lower GRG value compared with the loads of 10 N and 20 N. The response surface and contour surface plots in figures 8(a)-(f), which shows that the wear and friction   combination is more at the track diameter of 120 mm and a normal load of 2 kg.In case of cumulative effect of slicing speed and normal load, GRG values are more for lower load value of 10 N at sliding speed of 3 m s −1 in the track diameter of 120 mm.The response surface graph in the figures 8(a)-(f), is to understand the influence of sliding speed, track diameter and normal load over the output responses such as GRG, which represents the cumulative response of the output responses such as coefficient of friction and wear volume stabilization.There is a steep increase in the output response such as GRG with the increase in track diameter from 60 mm to 120 mm.The same effect is found at the maximum sliding speed of 3 m s −1 at lower track diameters.The coefficient of friction and wear is not just a material property or contact property, it depends on many parameters such as materials of contact pair [24], loading conditions [25], environment application [26], etc.The normal load and sliding velocity are the deciding parameters, which play an important role in controlling the wear and friction [27] in the functional application parts.This study can be extended to SS 304 metal AM parts printed using Direct Energy Deposition [28] or Powder Bed Fusion [29] processes.

Conclusion
The following conclusions were obtained from this wear and coefficient of friction study.Some of them are described as follows, • Coefficient of friction and wear values follow the minimization function, where the properties are better at higher sliding speed.
• But the wear values keep on increasing with the increase in sliding speed.Hence there should be trade-off values to minimize the impact of wear and friction, which causes the failure of the components.
• The coefficient of friction stabilization value is more at lower siding speeds for the track diameters of 60 mm and 120 mm.At higher siding speeds, the Coefficient of friction stabilization value was minimum for both the track diameters of 60 mm and 120 mm.
• The coefficient of friction value was higher at 120 mm track diameter on compared with 60 mm track diameter for similar loads with higher sliding speeds.This is due to the impact of more radial load on the contact surface.
• Wear rate gets decreased at a lower sliding speed for the track surface.At normal load with higher sliding speed, wear rate increases for both the track diameter.
• Surface characterisation studies were carried out to understand the impact of wear damage using an Optical microscope.
• At a lower sliding speed with a lower normal load, the wear rate was lower for both the track diameters of 60 mm and 120 mm.However, with normal load for the increase in sliding speed values, wear track surface damage is higher at both the wear track.
• Wear damage was more at 60 mm track surface than at 120 mm track diameter, surface wear damage was lower for the condition of similar loads with the same sliding speeds.
• Further, optimisation studies are carried out using GTRSM to understand the influence of wear and friction over the input process parameters.
• GRG results show a higher value of 0.66667 at experimental order 8 (Track diameter 60 mm, normal load 2 kg, sliding speed 2 mm s −1 ), which is the optimum condition to control the wear and friction.
• Further, this research can be extended to predict the coated stainless steel rods or composite rods by considering a trade-off between wear and friction values.

Figure 1 .
Figure 1.Schematic representation of pin specimen and the wear test disc test rig.

2 m s − 1 ,
the wear volume increased until stabilizing at 110 s, peaking at 903 mm3 .Under a normal load of 2 kg and sliding speeds of 1 m s −1 , 2 m s −1 , and 3 m s −1 , the wear volume gradually increased due to the removal of the Fe-oxide layer and weak surface asperities.At a sliding speed of 1 m s −1 , the maximum wear volume was 390 mm 3 .For a sliding speed of 2 m s −1 , the wear volume increased until stabilizing at 140 s, reaching a maximum of 290 mm 3 .At a sliding speed of 3 m s −1 , the wear volume increased significantly[14], with the higher load and speed inducing fatigue in surface asperities.The wear volume stabilized at 185 s, with a maximum of 780 mm 3 .The sudden increase in wear volume at this point could be due to a change in the wear mechanism or the occurrence of a localized wear event.It could indicate a failure or a change in the material's behaviour at that specific moment, possibly caused by a sudden increase in applied load, a change in surface conditions, or a defect in the material.The sudden decrease in wear volume at this point is also unusual and could be attributed to a variety of factors.It might indicate a change in the wear mechanism, such as a shift from abrasive to adhesive wear, or a change in the contact conditions between the surfaces.It could also be caused by a temporary reduction in the applied load or a change in the behaviour of the material.Generally, the wear volume stabilization values for the 60 mm track diameter are lower compared to the 120 mm track diameter.

Figure 3 .
Figure 3. Variation of wear volume rate under different sliding speeds by analyzing the tracks of 60 mm and 120 mm diameter.

Figure 4 .
Figure 4. Variation of coefficient of friction under varying sliding speeds and track diameters.

Figure 5 .
Figure 5. Optical microscopy image for damaged disks at 60 mm track surface.

Figure 6 .
Figure 6.Optical microscopy image for damaged disks at 120 mm track surface.

Table 1 .
Chemical composition and mechanical properties of SS304 alloys.

Table 2 .
Surface roughness test values of SS304 alloys.

Table 3 .
Comparison of wear volume stabilization value under different loads and sliding speeds.

Table 4 .
Comparison of coefficient of friction stabilization values under various loads and speeds.

Table 5 .
Output response values for the various input process parameter setting.

Table 6 .
Calculated Signal to Noise (SN) ratios of wear and friction coefficient.

Table 7 .
Calculated GRG values for the input process parameter setting.

Table 8 .
Mean response table for GRG.