3.2 Optical Microscope analysis
Fig. 4 a-d shows the optical micrograph of the Al6063-12%Si3N4-(2 and 4%) of CuN2O6 MMCs fabricated by the PM technique. The white area depicts the Si3N4 particles, while the black area depicts the CuN2O6 particles. It is elucidated from OM pictures that the reinforcing particles in the Al 6063 alloy were dispersed equally. The micrograph depicts the increase in CuN2O6 content distribution in MMCs. The propensity reaction and the alloying materials utilized in the processing are responsible for the good bonding observed between the reinforcement and the matrix. Strong interfacial bonding was developed in the fabricated composites during the sintering process due to the chemical reaction between the matrix and reinforcement. There are no cracks, and micropores were found in the MMCs, always increasing the density and hardness of the composites by the existence of reinforcement particles. The absence of agglomerations in the composites can be attributed to the uniform distribution of reinforcement particles. The formation of unnecessary intermetallic compounds was indeed minimal due to low sintering temperature and short time.
3.3 XRD analysis
Fig. 5 shows the XRD patterns of the AA6063/Si3N4/CuN2O6 composites reinforced with Si3N4 and 2, 4, and 6% CuN2O6 particles as developed by PM revealed that the presence of metallic compounds Al, Cu, Si3N4, and CuN2O6 particles. The composite of AA6063/Si3N4/2%CuN2O6 has high Al and Si3N4 peaks and weak CuN2O6 peaks, as seen in the XRD patterns. It's because there are fewer CuN2O6 particles in the mix. When the amount of CuN2O6 was added at 4 and 6 wt.%, significant peaks of CuN2O6 were observed.
The hardness test was carried out on the specimens measuring 10mm in length and 10mm in diameter, per the ASTM E10-07a standards under room temperature circumstances. The test was conducted on AA6063 composites with a different weight percentage of ceramic and inorganic compound reinforcement. Each value is based on a five-reading average. Fig. 6 shows the outcomes of the test on the given specimen. It is confirmed from the hardness plot that the composites' hardness is substantially more than the base alloy's. The hardness of the material increases as the reinforcing weight percent increases. The overall hardness of the composite increases because of the higher hardness of Si3N4.
Further, increase the hardness of composite by adding inorganic reinforcement of CuN2O6. Because of the reinforcement particles absorbed into the aluminium matrix, there was an increase in the surface area and a simultaneous reduction in the size of the aluminium matrix grains. Consequently, the hardness of the AA6063 composite also improved. The hard reinforcement of Si3N4 having higher surface area particles reduces the possibility of plastic deformation which ultimately increases the hardness of powder metallurgy manufactured AMCs. Furthermore, because of the low ductile percentage of matrix metal in the composite, hard and brittle Si3N4 particles in the soft and ductile AA6063 matrix diminishes the plasticity component of processed AMCs, which enhances the hardness of produced AMCs greatly. The alloy formation increases as the copper nitrate level rises, resulting in a continuous layer between the aluminum and the copper nitrate particles. Deformation turns out to be considerably more difficult, which results in higher hardness levels, as previously stated . Increased reinforcement in the matrix generates an increase in dislocation density during the sintering process. The composite hardness has been increased due to a thermal mismatch between the aluminium matrix and the reinforcement. Furthermore, the temperature differential and the difference in thermal expansion between the two elements, such as aluminium matrix and reinforcement, are responsible for high hardness. Hence, the aluminium matrix deforms to encapsulate the smaller volume expansion in the plastic of Si3N4 and CuN2O6 particles, creating tremendous internal stress. Hardness and restriction of plastic deformation increase due to better dislocation density at the particle-matrix interface. Sureshkumar et al.  reported an increase in the amount of reinforcement in the matrix the hardness of AMCs also increased.
3.5 ANOVA and the effects of factors
An analysis of variance (ANOVA) table 5 was developed to establish the order of essential components and their interactions. As well as the impact of several process parameters such as load, reinforcement (Si3N4+CuN2O6), sliding speed, and sliding distance. This study was conducted with a 5% level of confidence in the soundness of the outcomes. The wear characteristic of prepared composite of ANOVA is shown in Table. 5. Interaction between reinforcement and load (p=31.66%), reinforcement and sliding distance, CuN2O6 reinforcement (p=28.47%) had a significant impact on wear loss is reported in Table. 5. The influences of sliding distance, load, and sliding velocity alone were less influential on wear loss, while the interactions between sliding speed and reinforcement did not affect the wear loss.
3.6 The function of process parameters on wear loss
Fig.7 shows the wear loss of the prepared composite affected by the process parameter. If a parameter's line in the main effect plot is close to horizontal, that parameter has no considerable influence. The parameter line has extreme inclination has the greatest impact. The process parameter of reinforcement had the most significant effect, according to the studies. Other testing variables, including load, sliding distance, and sliding speed, had a smaller impact. The relationship between the reinforcement and the load, on the other hand, has a great effect on wear loss. The sliding distance and load increase the wear loss due to higher material removed for the composite surface. Additionally, when the sliding speed rises, wear loss decreased owing to the development of a copper-rich passive deposit on the worn surfaces, which reduced wear by covering more contact area. Compared to other situations (i.e., 0% and 2%), the composite with 4% reinforcement improved wear resistance at greater loads.
3.7 Using the Taguchi method, analyze and evaluate the findings of the tests.
The S/N ratio is the most vital criterion in the Taguchi method for assessing experimental data portrayed in Fig. 8. The maximum S/N ratio provided the optimal conditions of wear loss for this investigation. The wear loss of S/N response for hybrid composites was reported in Table. 6. Delta statistics were used for the rank of influence of parameter impact on wear. The Delta statistic is the sum of each element's highest and lowest averages. The highest Delta value is assigned to rank 1, the second-highest Delta value is assigned to rank 2, and so on. On an excellent wear resistance value, the optimal conditions were 4 wt. Percent CuN2O6, 15 N load, 200 rpm sliding speed, and 2000 m sliding distance.
3.8 Multilinear regression analysis and Confirmation test of experiment
By fitting a linear equation to the observed data, this produced model provides the link between an indicator variable and a response variable. The wear rate regression equation is as follows:
Wear loss = 0.0066 + 0.00394*A +0.001617*B+ 0.000003*C – 0.000046*D – 0.000508* A x B -0.000002* A x C + 0.000013* A x D
Where, A = reinforcement, B = Load, C = Sliding distance, D = Sliding speed
Table 8 indicates the experimental values for conducting the dry sliding wear test & adopting the best condition to compare the estimated wear result with the actual wear rate. According to the analysis, the actual wear rate differs from those calculated using regression equations, with error percentages ranging from 6.42 % to 9.25 % for wear rate according to the analysis .
3.9 EDS analysis
EDS analysis was performed on the worn surfaces of the PM-produced composite under dry sliding conditions. The presence of an oxygen peak in all EDS studies of the hybrid composites suggested that oxide formation of the worn surface occurred due to CuN2O6 inorganic reinforcement. While the composite is sliding on a steel counter surface, the combined action of temperature increase and environmental response can result in oxide layer deposition at the contact surfaces (EN31). Fig. 8 shows the EDS spectrum of the worn composite. The EDS of the worn surface discloses the existence of two-element peak intensities such as Al and Si. However, under dry sliding conditions, the Al intensity peak showed plastic deformation of the composite. Figure. 8 compared to the EDS profile of AA6063/12%Si3N4, worn surface, the acetone peak was observed. The intensity of acetone was increased as the CuN2O6 reinforcement increased. This acetone generated a protective oxide layer on the composite's surface. As inorganic reinforcement increases, the peak of Ac rises, reducing the wear rate. All fabricated composites had a carbon peak, which increased the work hardening rate of the composite, which increased abrasion resistance. Oxygen was noticed in all EDS spectrum due to the development of mated parts' worn surfaces.
3.10 Wear surface studies
The manufactured composites have fewer concentrations of carbon, silicon, and iron. Chemical reactions, such as oxidation, are stimulated by the limited heating created during the pin-on-disc test. A considerable difference was discovered after a wear study on AA6063/12%Si3N4/2%CuN2O6, with the main factor influencing wear was the formation of a generalized mechanically mixed layer (MML) seen in Fig. 9. This MML, which could contain iron and aluminium oxide, appears to be more resistant to temperature gradient without sticking. Furthermore, the hybrid composites have less plastic deformation, indicating a stronger resilience to wear, as seen by the hybrid composites' lower wear rate.
It is well known that increasing the amount of ceramic reinforcement Si3N4 and inorganic copper nitrate particles in AA6063 treated by PM methods improves the tribological characteristics of the material, since Si3N4 and copper nitrate particles protect the matrix from wear . Furthermore, compared to ceramic reinforcement alone composites, the hybrid's greater wear resistance can be explained by thermal expansion matrix work hardening and dislocation strengthening .
Fig. 9 shows the worn microstructure of the AA6063 alloy reveals a large amount of Al alloy plastic deformation. The quantity of heat generated between the rolling pin's surface and the counter disk's surface, causing plastic deformation. It is discovered that the mode of wear is adhesive. The worn micrograph of the composite shows shallower grooves with fewer pits. The depth of the grooves is lowered due to the presence of Si3N4 and inorganic reinforcement of CuN2O6 particles. Furthermore, the lesser degree of plastic deformation at the groove's borders is visible. The abrasive wear mechanism has been discovered.