Microstructure, Mechanical Properties, and Corrosion Behavior of Boron Carbide Reinforced Aluminum Alloy (Al-Fe-Si-Zn-Cu) Matrix Composites Produced via Powder Metallurgy Route

In this paper, Al-Fe-Si-Zn-Cu (AA8079) matrix composites with several weight percentages of B4C (0, 5, 10, and 15) were synthesized by powder metallurgy (PM). The essential amount of powders was milled to yield different compositions such as AA8079, AA8079-5 wt.%B4C, AA8079-10 wt.%B4C, and AA8079-15 wt.%B4C. The influence of powder metallurgy parameters on properties’ density, hardness, and compressive strength was examined. The green compacts were produced at three various pressures: 300 MPa, 400 MPa, and 500 MPa. The fabricated green compacts were sintered at 375 °C, 475 °C, and 575 °C for the time period of 1, 2 and 3 h, respectively. Furthermore, the sintered samples were subjected to X-ray diffraction (XRD) analysis, Energy Dispersive Analysis (EDAX), and Scanning Electron Microscope (SEM) examinations. The SEM examination confirmed the uniform dispersal of B4C reinforcement with AA8079 matrix. Corrosion behavior of the composites samples was explored. From the studies, it is witnessed that the rise in PM process parameters enhances the density, hardness, compressive strength, and corrosion resistance.


Introduction
Metal based composites have extensive uses in numerous engineering areas owing to its extreme properties, namely superior precise stiffness, strength/weight ratio, and wear opposition [1]. Traditionally PM has been recognized as suitable method to synthesize metal parts with uniform and fine microstructures. By following this method (PM) various kinds of materials can be easily mixed to attain unique properties [2]. PM is a frequent and fast developing technology, taking up all metallic and alloy materials and a widespread variability of dimensions [3]. Compared to other conventional fabrication methods, the PM route is recognized to be capable in the fabrication of aluminum alloy based MMC [4]. Due to the collective effect of metallic and ceramic materials, aluminum metal matrix composites have tremendous uses such as automotive and aircraft, owing to its low density and specific strength [5]. Aluminum alloy has numerous merits compared to Fe alloys, powder metallurgy process parameters. Furthermore, this work has made an effort to synthesize AA8079-B 4 C composites at different powder metallurgy process parameters to analyze the microstructure, mechanical, and corrosion behavior. The effect of parameters on the hardness, density, CS, corrosion properties, and microstructure have been analyzed in detail.

Experimental Details
AA8079 was manufactured via mixing the 99.5% elemental powders aluminum (100 µm), copper (10 µm), iron (10 µm), silicon (8 µm), and zinc (10 µm). Boron carbide of size 10 µm was utilized as reinforcement. The aluminum and B 4 C was purchased from kemphasol, Mumbai, India. The other powders, such as copper, iron, silicon, and zinc were purchased from Lobachemi, Mumbai, India. SEM image of the as procured Al and B 4 C powders are displayed in Figure 1a,b.
B4C particle. From the literature review it has been found that the development of aluminum alloy is a challenging task. Hence, ball milling was used to develop aluminum alloy in the present work. However, the mixing of alloying element and reinforcement particle with the major constituent could be possible by selecting suitable ball milling and powder metallurgy process parameters. Furthermore, this work has made an effort to synthesize AA8079-B4C composites at different powder metallurgy process parameters to analyze the microstructure, mechanical, and corrosion behavior. The effect of parameters on the hardness, density, CS, corrosion properties, and microstructure have been analyzed in detail.

Experimental Details
AA8079 was manufactured via mixing the 99.5% elemental powders aluminum (100 μm), copper (10 μm), iron (10 μm), silicon (8 μm), and zinc (10 μm). Boron carbide of size 10 μm was utilized as reinforcement. The aluminum and B4C was purchased from kemphasol, Mumbai, India. The other powders, such as copper, iron, silicon, and zinc were purchased from Lobachemi, Mumbai, India. SEM image of the as procured Al and B4C powders are displayed in Figure 1a,b. The composite powders were synthesized using high energy ball mill for 10 h (VBCRC Planetary ball mill). The drum speed was 100 rpm. A steel ball with 10 mm diameter was used. The ball to powder ratio was 5:1. To avoid the temperature rising, a cooling process was carried out every 10 min as per [27]. The green compacts were made into billets of dimensions 24 mm diameter and 12 mm height using a computer servocontrolled ball screw driven UTM (Model: M Series). To avoid the friction between the punch and die, zinc stearate was used as lubricant. Figure 2 shows the details of powders and ball milling setup. The composite powders were synthesized using high energy ball mill for 10 h (VBCRC Planetary ball mill). The drum speed was 100 rpm. A steel ball with 10 mm diameter was used. The ball to powder ratio was 5:1. To avoid the temperature rising, a cooling process was carried out every 10 min as per [27]. The green compacts were made into billets of dimensions 24 mm diameter and 12 mm height using a computer servo-controlled ball screw driven UTM (Model: M Series). To avoid the friction between the punch and die, zinc stearate was used as lubricant. Figure 2 shows the details of powders and ball milling setup.
Then, the green compacts were sintered at various temperatures of 375 • C, 475 • C, and 575 • C for a period of 1, 2, and 3 h, respectively, using electric muffle furnace (HITECH India) below controlled atmosphere to evade oxidation; the sintered samples were retained in the furnace until it reaches the room temperature [28]. By following the rule of mixture, the sintered density was measured for all the samples by Archimedes principle. Three readings were measured, and their average value was taken [29]. XRD analysis was accompanied on the Al and B 4 C sintered preforms to study the phase identification using X-ray diffractometer (Broker Eco D 8). The chemical compositional examination was examined via energy dispersive analysis (via EDAX-AMETEK-TSL). Figure 3 shows the details of testing conducted for the composite samples. Then, the green compacts were sintered at various temperatures of 375 °C, 475 °C, and 575 ο C for a period of 1, 2, and 3 h, respectively, using electric muffle furnace (HITECH India) below controlled atmosphere to evade oxidation; the sintered samples were retained in the furnace until it reaches the room temperature [28]. By following the rule of mixture, the sintered density was measured for all the samples by Archimedes principle. Three readings were measured, and their average value was taken [29]. XRD analysis was accompanied on the Al and B4C sintered preforms to study the phase identification using X-ray diffractometer (Broker Eco D 8). The chemical compositional examination was examined via energy dispersive analysis (via EDAX-AMETEK-TSL). Figure 3 shows the details of testing conducted for the composite samples.   Then, the green compacts were sintered at various temperatures of 375 °C, 475 °C, and 575 ο C for a period of 1, 2, and 3 h, respectively, using electric muffle furnace (HITECH India) below controlled atmosphere to evade oxidation; the sintered samples were retained in the furnace until it reaches the room temperature [28]. By following the rule of mixture, the sintered density was measured for all the samples by Archimedes principle. Three readings were measured, and their average value was taken [29]. XRD analysis was accompanied on the Al and B4C sintered preforms to study the phase identification using X-ray diffractometer (Broker Eco D 8). The chemical compositional examination was examined via energy dispersive analysis (via EDAX-AMETEK-TSL). Figure 3 shows the details of testing conducted for the composite samples.  The microstructure analysis of sintered composite samples was performed by SEM (ZESIS model). The micro Vickers hardness test was carried out using micro Vickers hardness tester (Model: MV-1 PC), test was carried out at a load of 0.3 kg and a stay time of 10 s, as per ASTM standard E384-08. The compressive test was carried using computer controlled universal testing machine (Tinius Olsen) having a capacity of 50 kN in accordance with ASTM standard E9-89a. Electrochemical measurement was achieved by utilizing Versa STAT MC. Later, for polarization examinations, electrodes were utilized for the electrochemical impedance spectroscopy (EIS) examination deprived of any surface treatment. The AA8079/B 4 C composite samples with 1.0 cm 2 surface area are wide-open to corrosion medium of 3.5% NaCl solutions. The potentio-dynamic current-potential curves were obtained by polarizing the specimen from −0.1 V to +0.1 V on open circuit potential at a scan rate of 0.05 mV/s. EIS measurements was conducted utilizing a small amplitude AC signal of 10 Mv over a frequency of 100 kHz-0.01 Hz [30,31]. The microstructures of samples after compression test were examined utilizing the SEM.

Results and Discussions
This section explains the microstructure and characterization studies of sintered composite preforms, and the effect of PM parameters on the density, hardness, CS, corrosion behavior, and the microstructure of the composites after compression test.

Characterization Studies on Sintered Preforms
The microstructure analysis of the as-sintered AA8079, AA8079-5 wt.%B 4 C, AA8079-10 wt.%B 4 C, and AA8079-15 wt.%B 4 C composites preforms has been studied using SEM. Figure 4a displays the microstructure of AA8079; it ensures the absence of B 4 C content, and it can be seen that pores are witnessed for unreinforced AA8079. Furthermore, no pore has been found in the composite preforms, due to occupation of B 4 C particle in the matrix. Figure  s, as per ASTM standard E384-08. The compressive test was carried using computer controlled universal testing machine (Tinius Olsen) having a capacity of 50 kN in accordance with ASTM standard E9-89a. Electrochemical measurement was achieved by utilizing Versa STAT MC. Later, for polarization examinations, electrodes were utilized for the electrochemical impedance spectroscopy (EIS) examination deprived of any surface treatment. The AA8079/B4C composite samples with 1.0 cm 2 surface area are wide-open to corrosion medium of 3.5%NaCl solutions. The potentio-dynamic current-potential curves were obtained by polarizing the specimen from −0.1 V to +0.1 V on open circuit potential at a scan rate of 0.05 mV/s. EIS measurements was conducted utilizing a small amplitude AC signal of 10 Mv over a frequency of 100 kHz-0.01 Hz [30,31]. The microstructures of samples after compression test were examined utilizing the SEM.

Results and Discussions:
This section explains the microstructure and characterization studies of sintered composite preforms, and the effect of PM parameters on the density, hardness, CS, corrosion behavior, and the microstructure of the composites after compression test.

Characterization Studies on Sintered Preforms
The microstructure analysis of the as-sintered AA8079, AA8079-5wt.%B4C, AA8079-10wt.%B4C, and AA8079-15wt.%B4C composites preforms has been studied using SEM. Figure 4a displays the microstructure of AA8079; it ensures the absence of B4C content, and it can be seen that pores are witnessed for unreinforced AA8079. Furthermore, no pore has been found in the composite preforms, due to occupation of B4C particle in the matrix. Figure   From Figure 4c, the uniform distribution of B4C particle can be seen, and no pores or crack has been found. Enhanced interfacial connection was attained amid the matrix and B4C particles. Figure 4d displays the SEM image of composite containing 15wt.% of B4C, From Figure 4c, the uniform distribution of B 4 C particle can be seen, and no pores or crack has been found. Enhanced interfacial connection was attained amid the matrix and B 4 C particles. Figure 4d displays the SEM image of composite containing 15 wt.% of B 4 C, and from the image no agglomeration of particles was observed.
Some researchers reported agglomeration issues for the inclusion of 10 wt.% of B 4 C in Al matrix. However, in this work, we overcome that problem by selecting the suitable ball milling parameters [32][33][34]. Due to higher pressure amid the compaction, a dense microstructure was acquired which was supportive in material strength enhancement, with fine distribution of reinforcement with matrix. Particles were combined and filled closely with matrix which enhanced the mechanical properties. The separation of B 4 C with matrix is also of note. The SEM revealed the occurrence of the distributed phase, which is the B 4 C is dispersed evenly in the matrix.
The EDAX analysis of the sintered composites preforms are displayed in Figure 5. Figure 5a displays the occurrence of Al peaks with high intensity, and Cu, Fe, Si, and Zn peaks with very low intensities. Figure 5b-d displays the existence of Al peaks with great intensity, and B, C, Cu, Fe, Si, and Zn peaks were also observed for composite samples. The results show that elemental and reinforcement particles were homogenously dispersed with the aluminum matrix due to the proper milling, compaction, and sintering process. From this analysis it is obvious that the occurrence of respective elements of alloy and composite samples is evident. It is clear that 5 to 15 wt.% of B 4 C was predicted with fine dispersal with matrix.  Figure 6 noticeably shows the XRD patterns of preforms sintered at 575 °C . Amid the various compounds identified, aluminum influenced the strongest peak, and it ensures the Al is the major content in this material. The occurrence of B4C peaks reveals the occurrence of B4C in (110), (104), (021), (211), and (205) planes. The intensity of B4C peaks enhances with the raise in weight percentage of B4C in the composites. XRD results confirm the occurrence of aluminum in the major peak, and the occurrence of B4C, exposed by small peak, and it ensures the respective weight percentage of the composites. Furthermore, it has been confirmed that no intermetallic compounds were formed during the sintering process as reported by the previous researchers [35,36]. Peaks for Fe, Si, Zn, and Cu interrelated to the AA8079 were not witnessed due to the development of a solid solution.   (205) planes. The intensity of B 4 C peaks enhances with the raise in weight percentage of B 4 C in the composites. XRD results confirm the occurrence of aluminum in the major peak, and the occurrence of B 4 C, exposed by small peak, and it ensures the respective weight percentage of the composites. Furthermore, it has been confirmed that no intermetallic compounds were formed during the sintering process as reported by the previous researchers [35,36]. Peaks for Fe, Si, Zn, and Cu interrelated to the AA8079 were not witnessed due to the development of a solid solution.
the occurrence of aluminum in the major peak, and the occurrence of B4C, exposed by small peak, and it ensures the respective weight percentage of the composites. Furthermore, it has been confirmed that no intermetallic compounds were formed during the sintering process as reported by the previous researchers [35,36]. Peaks for Fe, Si, Zn, and Cu interrelated to the AA8079 were not witnessed due to the development of a solid solution.

Effect of PM Parameters on Density
The influence of compaction pressure (CP), sintering temperature (S.Temp) and sintering time (ST) on the density are provided in Figure 7a-c. Table 1 provides the effect of PM parameters on density. Figure 7a shows the density of AA8079-5 wt.%B 4

Effect of PM Parameters on Density
The influence of compaction pressure (CP), sintering temperature (S.Temp) and sintering time (ST) on the density are provided in Figure 7a-c. Table 1 provides the effect of PM parameters on density. Figure 7a shows the density of AA8079-5wt.%B4C composites with respect to CP, S.Temp, and ST. The increase in CP, S.Temp, and ST increases the density of the AA8079-5wt.%B4C composites. For AA8079-5wt.%B4C composites, maximum density of 2.96 g/cm 3 Figure 7b shows the density for the AA8079-10 wt.%B 4 C composites. The increase in CP, S.Temp, and ST increases the density of the AA8079-10 wt.%B 4 C composites. For AA8079-10 wt.%B 4 C composites, maximum density of 3.25 g/cm 3 was obtained at CP of 500 MPa, S.Temp of 575 • C, ST of (1, 2, and 3 h). Enhancement in ST offers much time for pore closure in the matrix; henceforth, densification is perceived to rise with the rise in ST. At 575 • C, the density enhances due to a decrease in pores. Amid the sintering process, reduction in the samples occurs, despite the volume of diffusion of atoms from the grain boundary sources to the voids, which results in density enhancement. Figure 7c shows the density for the AA8079-15 wt.%B 4 C composites. The increase in CP, S.Temp, and ST increases the density of the AA8079-15 wt.%B 4 C composites. For AA8079-15 wt.%B 4 C composites, maximum density of 3.45 g/cm 3 was obtained at CP of 500 MPa, S.Temp of 575 • C, and ST of 3 h. It could be understood that an increase in CP, S.Temp, and ST enhances the density of the AA8079-B 4 C composites. This is due to the fact that diffusion of particles and decrease in porosity occurred; it results in improved density as reported by Patel et al. [27]. Generally, the current investigation stated that to fabricate AA8079-B 4 C composites at a maximum density, the specimen would be compacted to 500 MPa and sintered at 575 • C temperature for 3 h.  Table 2 provides the effect of PM parameters on micro hardness. The maximum hardness is witnessed for the specimens compacted at 500 MPa, and sintered at 575 • C for 3 h. From Figure 8a-c, the hardness of specimens improves whereas enhancing the CP from 300 MPa to 500 MPa, S.Temp from 375 • C to 575 • C, and ST from 1 h to 3 h. At CP greater than 500 MPa, the applied loads force the particles to transfer, blending with one another and blocking the voids, henceforth attaining maximum hardness for AA8079-B 4 C composites. Increasing the CP, S.Temp, and ST results in hardness enhancement due to maximum densification. When the PM process parameters increased, pores and voids present in the samples were completely occupied by the B 4 C particles. This could be one of the reasons for hardness increment.  The applied load results in particle deformation; however, alterations in particle size and shape improve the hardness. The hardness upsurges while enhancing the CP, S.Temp, and ST. It is obvious that when the CP, S.Temp, and ST increase, the hardness of the composites enhances due to particle-to-particle appropriate bonding. Furthermore, B 4 C is the third hardest material, due to the fact that the hardness of the composites increased gradually. These outcomes are all around concurred with the earlier findings of different researchers [7,8,37,38]. When the samples prepared at maximum PM process parameters at that time grain refinement and proper dispersal of B 4 C with AA8079 occurred, it resulted in maximum hardness enhancement. At maximum sintering temperature, particle-to-particle binding takes place, forming a better bond by the diffusion of atoms in a solid-state bonding method. Improved ductility, dispersion strengthening mechanism, and refinement of grain size result in enhanced hardness [39][40][41].  Table 3 provides the effect of PM parameters on compressive strength. The maximum compressive strength is perceived for the specimens compacted at 500 MPa, sintered at 575 • C for 3 h. From Figure 9a-c, the compressive strength of specimens improves, enhancing the CP from 300 MPa to 500 MPa, the S.Temp from 375 • C to 575 • C, and the ST from 1 h to 3 h. From this, it is observed that the rise in S.Temp and ST increases the compressive strength. It is understood that the upsurge in CP, S.Temp, and ST enhances the compressive strength. This could be elucidated through the way that a rise in CP, S.Temp, and ST improves the heat treatment method by which appropriate holding and dissemination of particles is accomplished [42][43][44][45][46].   Additionally, the compressive strength of the composites totally relies upon the PM parameters, which create the enhancement in properties conceivable. As indicated by this examination, the most elevated compressive strength was noticed for the specimen compacted at 500 MPa, and sintered at 575 • C for 3 h. The enhancement in the compressive strength may be accredited to the shifting of load from matrix to the hard reinforcement [47,48]. The increasing strength of these composites as the B 4 C wt.% rises could be ascribed to the dispersal strengthening effect [49]. The maximum plastic deformation and strain hardening acquaint with powder amid compaction at maximum pressure to produce good results, leading to maximum compressive strength. The enhancement in loading resistance enhances the compressive strength [50]. Higher plastic deformation and strain hardening introduced in the powder during compaction at higher pressures yield better results and contributed to higher compression strength [51].

Microstructure Analysis of Specimens after Compression Test
The microstructure of the preforms after the compression test are shown in Figure 10a-d. The observable large pore sizes in sintered samples are reduced in the AA8079 matrix after compression testing. During the compression test the compressive load improved the microstructure of the produced powder metallurgy materials. Furthermore, no pores were found in the composite samples. After the compression test, grain boundaries are elongated due to deformation of the samples, and the hard ceramic particles are finely covered by the matrix materials due to deformation. Figure 10b,c displays the homogenous distribution of B 4 C particle into the matrix alloy. It is clear from the SEM images in Figure 10b-d that virtuous interfacial bond occurs amid the AA8079 and boron carbide. Due to the appropriate compressive force applied over the samples, the particles are distributed evenly within the matrix. Furthermore, it is witnessed that B 4 C particles are reoriented in the way of metal flow during compression process. Additionally, the compressive strength of the composites totally relies upon the PM parameters, which create the enhancement in properties conceivable. As indicated by this examination, the most elevated compressive strength was noticed for the specimen compacted at 500 MPa, and sintered at 575 °C for 3 h. The enhancement in the compressive strength may be accredited to the shifting of load from matrix to the hard reinforcement [47,48]. The increasing strength of these composites as the B4C wt.% rises could be ascribed to the dispersal strengthening effect [49]. The maximum plastic deformation and strain hardening acquaint with powder amid compaction at maximum pressure to produce good results, leading to maximum compressive strength. The enhancement in loading resistance enhances the compressive strength [50]. Higher plastic deformation and strain hardening introduced in the powder during compaction at higher pressures yield better results and contributed to higher compression strength [51].

Microstructure Analysis of Specimens after Compression Test
The microstructure of the preforms after the compression test are shown in Figure  10a-d. The observable large pore sizes in sintered samples are reduced in the AA8079 matrix after compression testing. During the compression test the compressive load improved the microstructure of the produced powder metallurgy materials. Furthermore, no pores were found in the composite samples. After the compression test, grain boundaries are elongated due to deformation of the samples, and the hard ceramic particles are finely covered by the matrix materials due to deformation. Figure 10b,c displays the homogenous distribution of B4C particle into the matrix alloy. It is clear from the SEM images in Figure 10b-d that virtuous interfacial bond occurs amid the AA8079 and boron carbide. Due to the appropriate compressive force applied over the samples, the particles are distributed evenly within the matrix. Furthermore, it is witnessed that B4C particles are reoriented in the way of metal flow during compression process

Corrosion Behavior
The corrosion behavior of composite samples has been studied by using electroanalytical techniques such as polarization and impedance measurements (EIS). The polarization curve of samples are displayed in Figure 11a-d. Tafel plots indicate that the corrosion rate of the composites reduced with raising the B4C weight percentage. Hence, galvanic influence amid them is detached. The witnessed increase in corrosion resistance for composites is dispensed to probable electrochemical decoupling between B4C particles and AA8079 matrix [15]. Soorya Prakash et al. reported that corrosion resistance rises considerably with a rise in hard particulate reinforcement such as B4C [52]. In inorganic acid forms, corrosion rate enhances as polarization curves are moved to a higher current density area associated to neutral chloride forms. B4C particles perform as physical protectors to stop the actuation and rate of development for pitting corrosion. The anodic polarization curves for AA8079 and AA8079-B4C display the endurance in corrosion current density, representing the exposure of pitting corrosion. The B4C particles which are utilized as reinforcing elements impede the creation of oxide layer and thus reduce the composites corrosion rate expressively.

Corrosion Behavior
The corrosion behavior of composite samples has been studied by using electroanalytical techniques such as polarization and impedance measurements (EIS). The polarization curve of samples are displayed in Figure 11a-d. Tafel plots indicate that the corrosion rate of the composites reduced with raising the B 4 C weight percentage. Hence, galvanic influence amid them is detached. The witnessed increase in corrosion resistance for composites is dispensed to probable electrochemical decoupling between B 4 C particles and AA8079 matrix [15]. Soorya Prakash et al. reported that corrosion resistance rises considerably with a rise in hard particulate reinforcement such as B 4 C [52]. In inorganic acid forms, corrosion rate enhances as polarization curves are moved to a higher current density area associated to neutral chloride forms. B 4 C particles perform as physical protectors to stop the actuation and rate of development for pitting corrosion. The anodic polarization curves for AA8079 and AA8079-B 4 C display the endurance in corrosion current density, representing the exposure of pitting corrosion. The B 4 C particles which are utilized as reinforcing elements impede the creation of oxide layer and thus reduce the composites corrosion rate expressively.
The Nyquist plots observed in 3.5% Nacl solution for the AA8079, AA8079-5 wt.%B 4 C, AA8079-10 wt.%B 4 C, and AA8079-15 wt.%B 4 C composites are shown in Figure 12a-d. EIS for all the samples were detected after OCP recorded for 1 h. The occurrence of a defensive oxide film on the layers of composites is despite the attribution of a high frequency capacitive loop. The preforms are occupied through the oxide film capacitance; furthermore, the capacitance arcs diameters increased with an increase in the B 4 C particle; perhaps the opposition of the surface oxide film on the samples upsurges with the enhancement in B 4 C reinforcement. The uneven semicircle displays a non-ideal electrochemical performance on the electrode surface, which is despite the frequency distribution, roughness of the metal surface, and inhomogeneity. The Nyquist plot displays capacitive loop which is linked to the behavior of double layer capacitance, along with the charge transfer process amid electrolyte and metal surface. The diameter of the semicircle decreases with an increase in acid concentration, indicating an increase in the corrosion rate. A rise in the diameters of the Nyquist plots indicates the improved protective nature of the inhibitor against damage of material in the corrosive solution [53]. It could be understood that corrosion resistance increases when increasing the B 4 C weight percentage. The Nyquist plots observed in 3.5% Nacl solution for the AA8079, AA8079-5wt.%B4C, AA8079-10wt.%B4C, and AA8079-15wt.%B4C composites are shown in Figure 12a-d. EIS for all the samples were detected after OCP recorded for 1 h. The occurrence of a defensive oxide film on the layers of composites is despite the attribution of a high frequency capacitive loop. The preforms are occupied through the oxide film capacitance; furthermore, the capacitance arcs diameters increased with an increase in the B4C particle; perhaps the opposition of the surface oxide film on the samples upsurges with the enhancement in