# Optimization of the Spark Plasma Sintering Process for High-Volume Fraction Tungsten Carbide/Al 2025 Composites

Authors: C. R. Mahesha; Suprabha R; Chintada Polayya; Moti Lal Rinawa; T. Sakthi; Neha Munjal; Ishwarya Komalnu Raghavan; P. Ganeshan; Chanakyan C
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

With an orthogonal experimental design, Spark plasma sintering method was used to create tungsten carbide with Al 2025 composites. Pressure, temperature, and hold time all had an influence on the mechanical characteristics of the composites. Pressure had the greatest effect on density and bending strength, followed by temperature and holding duration. After five minutes of sintering at 556°C under 40 MPa, a 50% tungsten carbide/Al 2025 composite material was produced, resulting in a density of 997.7 percent and a spectacular bending strength of 766.65 MPa. This study revealed the ability of high-volume fraction mixes to support huge loads.


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## Body

## 1. Introduction

In addition to Si3N4, SiO2, Al2O3, B4C/Al, TiC, and WC, PAMCs have been researched, for their outstanding mechanical, chemical, and electrical qualities [1, 2]. As a result of their extraordinary dimensional stability, high specific modulus mixtures have developed more significantly in the aviation and microelectronics productions [3–5]. Squeeze or stir casting, pouring, power metallurgy, hot pressing, and pressure less infiltration have all been employed to create silicon carbide particle/2xxx aluminium composites [6, 7]. With these processes, it is difficult to limit pores, control bonding and reactivity between interfaces, and produce composite materials with huge volumes [8]. Experiment failed to eradicate the holes that affect mechanical behavior to decline meaningfully due to high temperatures and lengthy vacuum hot pressing holding times. The tensile properties of hot-pressed tungsten carbide particles/2009 aluminiummixtures were examined by the authors [9] in this paper.Spark plasma sintering seems to be a pressure-assisted pulsed-current method in which powders are put into an electrically conducting die and fused under pressure gradient. The Spark plasma sintering technique may be employed to produce composite materials with low porosity and good mechanical characteristics [10, 11]. This process has a greater heating rate than standard preparation methods, a lower preparation temperature, and quick densification of the composite materials [12]. Improved interfacial bonding, cleaner surfaces, and smaller particle sizes are all advantages of SPS. To make 50 percent WC/6061Al composites, the authors in [13, 14] utilised Spark plasma sintering technology. Because of its 99.15 percent density and excellent interfacial attachment among the Al matrix and the tungsten carbide, it possessed a bending strength of 694 MPa. These composites were created by [15] using SPS to manufacture high-density 40 to 55 vol% tungsten carbide particles/pure aluminium composites with densities more than 99 percent [16, 17].In Taguchi’s multifactor orthogonal experimental design, the orthogonal array serves as the foundation [18–20]. It is easy to pick sample points that are equally dispersed across the whole factor test for optimum results in multifactor research. To further understand Spark plasma sintering preparation processing factors for TiB2-silicon carbide ceramic materials, a total of four treatment variables at three orthogonal experimental design degrees were examined [21, 22]. Vickers hardness was determined to be 28.5 GPa at the ideal processing conditions for this composite. In addition to reducing the number of experiments, this method produces data that can be understood by everyone [23]. The impact of processing parameters on HfB2, Al2O3, ZrB2-based ceramics, and phenolic fibre has been widely explored in the literature using orthogonal experimental design [24, 25]. The manufacturing of 50 vol percent tungsten carbide/2025Al composites has not yet been reported by Spark plasma sintering through orthogonal experimental design. tungsten carbide/2025Al/SiC composites with large volume proportions of SiC were the focus of this research, and mechanical study was employed to explore the mechanical characteristics of the composite material [26–28]. It was feasible to compare the effects of various factors on the best sintering conditions for 50 vol percent tungsten carbide/2025Al composites using orthogonal experimental design (such as temperature, pressure, and holding time) [29]. In addition to high-volume fraction composite materials, this method’s intelligence may be used to other high-volume proportion materials [30].


## 2. Materials and Methods

### 2.1. Materials

Tungsten carbide and 2025Al powders with particle sizes of 10 micron were employed as starting materials. Its chemical makeup is composed of Al and 4.7 percent Cu with the remainder being composed of 0.9 percent Mg, 0.6% iron, 0.6% silicon, and just 0.1% magnesium (mass fraction). Utilizing a 3:1 ball-to-powder weightage ratio in a zirconia tank, planetary ball mixing machine ran at 280 rpm for 2 hours to mix the tungsten carbide and 2025 Al particles. Particle fracture or Al flaking was not evident in either powder when comparing tungsten carbide with 2025Al powders. The combined powder was sintering in a graphite mould that had been precompressed at 10 MPa for 5 minutes with a Spark plasma sintering device. To assess the relative importance of various variables during SPS, an orthogonal table is created (Table1). Although the infrared thermometer’s lowest measurement temperature was 100°C, the instrument reported 100°C when the mold’s temperature fell below the required minimum.Table 1
The orthogonal experimental design’s factors and levels.
LevelABC150032525254353550545


### 2.2. Characterization and Evaluation

With the use of a universal testing apparatus, samples measuring 3 × 4 × 36 mm were tested for an average bending rate of 0.25 mm/min. An electronic analytical balance was employed to calculate the density of the composite. For the compactness and bending tests, a minimum of five samples were employed [31].


## 2.1. Materials

Tungsten carbide and 2025Al powders with particle sizes of 10 micron were employed as starting materials. Its chemical makeup is composed of Al and 4.7 percent Cu with the remainder being composed of 0.9 percent Mg, 0.6% iron, 0.6% silicon, and just 0.1% magnesium (mass fraction). Utilizing a 3:1 ball-to-powder weightage ratio in a zirconia tank, planetary ball mixing machine ran at 280 rpm for 2 hours to mix the tungsten carbide and 2025 Al particles. Particle fracture or Al flaking was not evident in either powder when comparing tungsten carbide with 2025Al powders. The combined powder was sintering in a graphite mould that had been precompressed at 10 MPa for 5 minutes with a Spark plasma sintering device. To assess the relative importance of various variables during SPS, an orthogonal table is created (Table1). Although the infrared thermometer’s lowest measurement temperature was 100°C, the instrument reported 100°C when the mold’s temperature fell below the required minimum.Table 1
The orthogonal experimental design’s factors and levels.
LevelABC150032525254353550545


## 2.2. Characterization and Evaluation

With the use of a universal testing apparatus, samples measuring 3 × 4 × 36 mm were tested for an average bending rate of 0.25 mm/min. An electronic analytical balance was employed to calculate the density of the composite. For the compactness and bending tests, a minimum of five samples were employed [31].


## 3. Results and Discussion

### 3.1. Analyzing Orthogonal Experiment

The L9 table was designated because of its orthogonal design and its three sintering temperatures, holding time, and pressure levels. Table2 reveals the analysed results of the L9 orthogonal array. With Kij (i = 1, 2, 3) and R as key factors, the orthogonal experiment is evaluated using the evaluation indices listed in Table 3. In order to compute R, which is the difference between highest and lowest values in relevant aspect column, Kmax and Kmin values are utilised. Kij is the average of the test scores at the jth grade level (j = 1, 2, 3). The best factor level will be determined by associating K values. The R value can indicate how much the K value varies.Table 2
Analyzing the results of theL9 orthogonal array.
S. No.ABCDensityRelative densityBending strengthCminMPa(g/cm3)(%)(MPa)11112.8596.8692.42 ± 25.5221222.9098.4738.12 ± 46.2731332.9098.4712.87 ± 82.5242132.8998.8759.25 ± 12.1252212.7996.7632.17 ± 20.0462322.9199.1767.75 ± 24.8273122.9297.2692.24 ± 56.7283232.9999.4710.26 ± 71.6593312.9194.6586.42 ± 9.72Table 3
Calculation indices of theL9 orthogonal array.
Orthogonal arrayABCDensityK112.942.902.85K122.912.902.92K132.882.912.93R0.030.020.06Level of optimumA2B3C3Bending strengthK11709.1709.26632.42K12716.12692.42732.87K13658.18691.27726.34R51.8322.9493.62Level of optimumA2B1C2WC/Al will function better if it has a larger density and flexural strength; consequently, the greatestK value should be used. It was determined that A2 (525°C), B1 (3 minutes), and C2 (35 MPa) were the best parameters for producing a dense composite (35 MPa). These are the best parameters for enhancing the bending strength. Various influences on the WC/2025Al composite are represented by the R value. Bending strength and density were most affected by the sintering pressure, surveyed by the holding duration and sintering pressure, in this study, B < A < C.Orthogonal test analysis cannot predict inaccuracy in testing since it does not know how much each element has changed or whether there has been a random fluctuation in findings, in spite of its simplicity. This is a concern that is often overlooked in orthogonal studies. The test findings were subjected to an analysis of variance in order to address this issue. SPSS Statistics was used to conduct the experimental variance analyses.The significance of each component was evaluated at theP=0.05 level of consequence for each individual. To be deemed significant, the test index must have an effect on the P value of less than 0.05. A, B, and C can explain 85.4% of the density variation in table, which demonstrates that R2 = 0.854. Temperature, time, and pressure may account for 88% of the density change during sintering according to R2 = 0.984%. F = 1.891; P = 0.346; P=0.159; and F = 5.307; P=0.159; bending strength was not changed by the sintering temperature. Sintering time F = 0.388; P=0.721. An error of this magnitude (df = 2) and a low degree of freedom (df = 2) meant that the test was ineffective in distinguishing between variables of interest. ANOVA a higher sum of squares (SS) shows a bigger effect. C > A > B: density and bending strength were most strongly influenced by sintering pressure, whereas the holding time had the least impact.Before a single index analysis approach is utilised to discover and optimise the complete scheme, the average weighting methodology is often employed to address multi-index orthogonal test concerns. The findings of the study are wrong since this method fails to take into account the differences and relative weights of the various indicators. As a result, the matrix approach was developed to quantify the degree to which each test aspect influences each directory and to swiftly establish the major and minor order of the components based on the weights. With this method, the issue of determining the best design for multi-index orthogonal tests is eliminated. The data are first organized into a three-tiered structural model. Experimentation index layer, component layer, and the flat layer make up the three layers (S). The formulas are given in equations (1)–(3), correspondingly, where Ti=1/∑j=13Kij and Si=Rj/∑i=13Rij.(1)M=K1100K1200K13000K2100K2200K23000K3100K3200K33,(2)T=T1000T2000T3,(3)ST=S1S2S3.According to equation, the weight matrix (k) which influences the assessment index is listed in the following equation:(4)k=MxTxS,kT=k1k2k3.Density was the first sign of success in this endeavor. Equations (5)–(8) demonstrate that to compute the weight matrix (8),(5)M=2.93002.94002.900002,92002.92002.930002.87002.94002.95,(6)T=18.7200018.8000018.78,(7)ST=0.040.130.010.130.080.13,(8)kD=MxTxS=0.10340.10370.10230.02550.02550.02560.10060.20610.2068,(9)kBS=0.10690.10750.09900.04540.04390.04370.09490.19560.1940.The weightage matrix of the five pointers that passed the OED test is the sum ofK−D and K−BS, assuming that the outcomes of these five indicators are of equal importance. The results of the computations may be seen in equation (1).(10)k=kd+kbs2=0.10520.10560.10070.03540.03470.03470.09770.20080.2004=A1A2A3B1B2B3C1C2C3.FactorA1 is 0.1052, Factor A2 is 0.1056, and Factor A3 is 0.1007; A2 is the most significant factor in the test results. Using the same kind of analysis, B1 and C2 have the greatest weights. As a result, the ideal orthogonal test scheme is A2B1C2, which means that the optimal WC/2025Al sintering process parameters are 550 C, 3 min of holding time, and 45 MPa of pressure. According to [32], TiN materials were synthesized at different temperatures in the radial direction of the specimen. Due to the high temperature at the material’s centre, SPS can make Al matrix composites with electrically isolating reinforcing elements. Al will be expelled from the mould with a colossal number of holes after it is taken from the mould. Low speed (500 rpm) and zirconia as the grinding medium and container guaranteed that the particles remained in their original form and did not introduce any impurities into the environment.High mechanical characteristics may be achieved by combining reinforcement with Al matrix in PAMCs at the right interfacial interface. High temperatures and pressures are commonly used in traditional techniques (such as extrusion and stirring casting) to make WC/Al composites; however, this is because the two materials have limited wettability. Brittle reactants like Al4C3 and MgAl2O4 are common because of this. Remarkably, the material properties, thermal conductivity, and resistance to abrasive corrosion are all affected by the hydrolysis of the flake-shaped Al4C3. No other current methods for preventing the production of Al4C3 have a negative impact on densities (such as reducing processing temperatures and holding times) or performance (such as adding Mg or Si or doing a pre-oxidation treatment with WC). Low temperature, short-term preparation methods such as SPS have been described in the literature as being capable of producing more easily interfacial products-free composites, according to the literature.(11)4AL1+3SiCs⟶Al4C3s+3Si1,4SiO2s+4Al1+2Mg1,Al4C3s+12H2Og⟶4AlOH3s+3CH4g⟶MgAl2O4s+5Si1,Al4C3s+18H2O1⟶4AlOH3s+3CO2g+12H2g.Figure1 depicts WC/2025Al composites with variant SPS preparation circumstances. A summary of its entire behavior is seen in Table 2.Figure 1
Bending curves of the 50 percent WC/Al 2025 composites made by Spark plasma sintering through variant conditions.When heated to 525°C for five minutes under 35 MPa, the material had a bending strength of 766.65 Mega Pascal (A2B3C2). Sintering at 550°C for 5 minutes under 30 MPa (A3B3C1) reduced the mixture’s bending strength (584.83 mpa) and elasticity (A3B3C1) due to the material’s large holes. WC/Al 2025 amalgamated density and contact configurations are affected by the sintering temperature, according to Yu and colleagues. Because of the alloy leakage, the density of the material reduced to around 96%, and the strength decreased from 367 to 211 MPa at 530°C. Figures 2(a) and 2(b) display density and bending strength values in the form of graph. After 2 minutes of holding time, the density of WC/Al 2025 went from 2.93 g/cm3 to 2.94 g/cm3, which may be ascribed to the molten Al filling the space between the WC and filling the larger holes, but not filling smaller ones. An increase in density of 2.90  g/cm3 occurred as the sintering temperature reached 570°C. Bending strength declined from 713.93 MPa to 690.78 MPa, a 3.2 percent drop, and the composites’ density was 2.92 g/cm3 after two and three minutes of holding. However, holding for 5 minutes, bending strength dropped to 692.45 Mega Pascal, while density raised to 2.95 g/cm3. The test’s sensitivity might have been low due to the experiment’s low degree of freedom and large error. A 40 MPa boost to the sintering pressure improves density by 0.34 percent but reduces bending strength by 0.80 percent. Figure 3 shows the comparison between WC/Al composite bending strength and temperature preparation.Figure 2
Impact factors of (a) density and (b) ending strength.
(a)(b)Figure 3
A comparison between WC/Al composite bending strength and temperature preparation.


## 3.1. Analyzing Orthogonal Experiment

The L9 table was designated because of its orthogonal design and its three sintering temperatures, holding time, and pressure levels. Table2 reveals the analysed results of the L9 orthogonal array. With Kij (i = 1, 2, 3) and R as key factors, the orthogonal experiment is evaluated using the evaluation indices listed in Table 3. In order to compute R, which is the difference between highest and lowest values in relevant aspect column, Kmax and Kmin values are utilised. Kij is the average of the test scores at the jth grade level (j = 1, 2, 3). The best factor level will be determined by associating K values. The R value can indicate how much the K value varies.Table 2
Analyzing the results of theL9 orthogonal array.
S. No.ABCDensityRelative densityBending strengthCminMPa(g/cm3)(%)(MPa)11112.8596.8692.42 ± 25.5221222.9098.4738.12 ± 46.2731332.9098.4712.87 ± 82.5242132.8998.8759.25 ± 12.1252212.7996.7632.17 ± 20.0462322.9199.1767.75 ± 24.8273122.9297.2692.24 ± 56.7283232.9999.4710.26 ± 71.6593312.9194.6586.42 ± 9.72Table 3
Calculation indices of theL9 orthogonal array.
Orthogonal arrayABCDensityK112.942.902.85K122.912.902.92K132.882.912.93R0.030.020.06Level of optimumA2B3C3Bending strengthK11709.1709.26632.42K12716.12692.42732.87K13658.18691.27726.34R51.8322.9493.62Level of optimumA2B1C2WC/Al will function better if it has a larger density and flexural strength; consequently, the greatestK value should be used. It was determined that A2 (525°C), B1 (3 minutes), and C2 (35 MPa) were the best parameters for producing a dense composite (35 MPa). These are the best parameters for enhancing the bending strength. Various influences on the WC/2025Al composite are represented by the R value. Bending strength and density were most affected by the sintering pressure, surveyed by the holding duration and sintering pressure, in this study, B < A < C.Orthogonal test analysis cannot predict inaccuracy in testing since it does not know how much each element has changed or whether there has been a random fluctuation in findings, in spite of its simplicity. This is a concern that is often overlooked in orthogonal studies. The test findings were subjected to an analysis of variance in order to address this issue. SPSS Statistics was used to conduct the experimental variance analyses.The significance of each component was evaluated at theP=0.05 level of consequence for each individual. To be deemed significant, the test index must have an effect on the P value of less than 0.05. A, B, and C can explain 85.4% of the density variation in table, which demonstrates that R2 = 0.854. Temperature, time, and pressure may account for 88% of the density change during sintering according to R2 = 0.984%. F = 1.891; P = 0.346; P=0.159; and F = 5.307; P=0.159; bending strength was not changed by the sintering temperature. Sintering time F = 0.388; P=0.721. An error of this magnitude (df = 2) and a low degree of freedom (df = 2) meant that the test was ineffective in distinguishing between variables of interest. ANOVA a higher sum of squares (SS) shows a bigger effect. C > A > B: density and bending strength were most strongly influenced by sintering pressure, whereas the holding time had the least impact.Before a single index analysis approach is utilised to discover and optimise the complete scheme, the average weighting methodology is often employed to address multi-index orthogonal test concerns. The findings of the study are wrong since this method fails to take into account the differences and relative weights of the various indicators. As a result, the matrix approach was developed to quantify the degree to which each test aspect influences each directory and to swiftly establish the major and minor order of the components based on the weights. With this method, the issue of determining the best design for multi-index orthogonal tests is eliminated. The data are first organized into a three-tiered structural model. Experimentation index layer, component layer, and the flat layer make up the three layers (S). The formulas are given in equations (1)–(3), correspondingly, where Ti=1/∑j=13Kij and Si=Rj/∑i=13Rij.(1)M=K1100K1200K13000K2100K2200K23000K3100K3200K33,(2)T=T1000T2000T3,(3)ST=S1S2S3.According to equation, the weight matrix (k) which influences the assessment index is listed in the following equation:(4)k=MxTxS,kT=k1k2k3.Density was the first sign of success in this endeavor. Equations (5)–(8) demonstrate that to compute the weight matrix (8),(5)M=2.93002.94002.900002,92002.92002.930002.87002.94002.95,(6)T=18.7200018.8000018.78,(7)ST=0.040.130.010.130.080.13,(8)kD=MxTxS=0.10340.10370.10230.02550.02550.02560.10060.20610.2068,(9)kBS=0.10690.10750.09900.04540.04390.04370.09490.19560.1940.The weightage matrix of the five pointers that passed the OED test is the sum ofK−D and K−BS, assuming that the outcomes of these five indicators are of equal importance. The results of the computations may be seen in equation (1).(10)k=kd+kbs2=0.10520.10560.10070.03540.03470.03470.09770.20080.2004=A1A2A3B1B2B3C1C2C3.FactorA1 is 0.1052, Factor A2 is 0.1056, and Factor A3 is 0.1007; A2 is the most significant factor in the test results. Using the same kind of analysis, B1 and C2 have the greatest weights. As a result, the ideal orthogonal test scheme is A2B1C2, which means that the optimal WC/2025Al sintering process parameters are 550 C, 3 min of holding time, and 45 MPa of pressure. According to [32], TiN materials were synthesized at different temperatures in the radial direction of the specimen. Due to the high temperature at the material’s centre, SPS can make Al matrix composites with electrically isolating reinforcing elements. Al will be expelled from the mould with a colossal number of holes after it is taken from the mould. Low speed (500 rpm) and zirconia as the grinding medium and container guaranteed that the particles remained in their original form and did not introduce any impurities into the environment.High mechanical characteristics may be achieved by combining reinforcement with Al matrix in PAMCs at the right interfacial interface. High temperatures and pressures are commonly used in traditional techniques (such as extrusion and stirring casting) to make WC/Al composites; however, this is because the two materials have limited wettability. Brittle reactants like Al4C3 and MgAl2O4 are common because of this. Remarkably, the material properties, thermal conductivity, and resistance to abrasive corrosion are all affected by the hydrolysis of the flake-shaped Al4C3. No other current methods for preventing the production of Al4C3 have a negative impact on densities (such as reducing processing temperatures and holding times) or performance (such as adding Mg or Si or doing a pre-oxidation treatment with WC). Low temperature, short-term preparation methods such as SPS have been described in the literature as being capable of producing more easily interfacial products-free composites, according to the literature.(11)4AL1+3SiCs⟶Al4C3s+3Si1,4SiO2s+4Al1+2Mg1,Al4C3s+12H2Og⟶4AlOH3s+3CH4g⟶MgAl2O4s+5Si1,Al4C3s+18H2O1⟶4AlOH3s+3CO2g+12H2g.Figure1 depicts WC/2025Al composites with variant SPS preparation circumstances. A summary of its entire behavior is seen in Table 2.Figure 1
Bending curves of the 50 percent WC/Al 2025 composites made by Spark plasma sintering through variant conditions.When heated to 525°C for five minutes under 35 MPa, the material had a bending strength of 766.65 Mega Pascal (A2B3C2). Sintering at 550°C for 5 minutes under 30 MPa (A3B3C1) reduced the mixture’s bending strength (584.83 mpa) and elasticity (A3B3C1) due to the material’s large holes. WC/Al 2025 amalgamated density and contact configurations are affected by the sintering temperature, according to Yu and colleagues. Because of the alloy leakage, the density of the material reduced to around 96%, and the strength decreased from 367 to 211 MPa at 530°C. Figures 2(a) and 2(b) display density and bending strength values in the form of graph. After 2 minutes of holding time, the density of WC/Al 2025 went from 2.93 g/cm3 to 2.94 g/cm3, which may be ascribed to the molten Al filling the space between the WC and filling the larger holes, but not filling smaller ones. An increase in density of 2.90  g/cm3 occurred as the sintering temperature reached 570°C. Bending strength declined from 713.93 MPa to 690.78 MPa, a 3.2 percent drop, and the composites’ density was 2.92 g/cm3 after two and three minutes of holding. However, holding for 5 minutes, bending strength dropped to 692.45 Mega Pascal, while density raised to 2.95 g/cm3. The test’s sensitivity might have been low due to the experiment’s low degree of freedom and large error. A 40 MPa boost to the sintering pressure improves density by 0.34 percent but reduces bending strength by 0.80 percent. Figure 3 shows the comparison between WC/Al composite bending strength and temperature preparation.Figure 2
Impact factors of (a) density and (b) ending strength.
(a)(b)Figure 3
A comparison between WC/Al composite bending strength and temperature preparation.


## 4. Conclusions

A 50 vol% tungsten carbide/Al 2025 composite was made using Spark plasma sintering in this investigation. When performing visual, ANOVA, and matrix analyses, orthogonal experimental design was employed to find the best possible combination of each index. The following findings can be drawn from this investigation:(1)
The sintering pressure, temperature, and holding time have most impact on SPS density and bending strength. Density and strength increase first when pressure and temperature rise.(2)
On five minutes run at 525°C and 35 MPa produced a tungsten carbide/Al 2025 combination with a 99.7% density and 766.65 MPa bend strength. The developed composite material had no brittle interfacial products, the Al matrix was equally dispersed, and the interface was strongly bound. The tungsten carbide particles in the material shattered, allowing the particles to be drawn out, causing the material to fracture.



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*Source: 6433716-2022-06-29.xml*