Microwave Sintering Process Research Articles

An investigation into the microstructure and mechanical properties of V2AlC MAX phase prepared by microwave sintering

The present study investigated the mechanical properties and microstructure of V2AlC MAX phase prepared by the microwave sintering process. The powders mixture of the V-Al-C system with the molar ratio of 2:1.5:1 was mixed through a mixer mill for 10 min in the ethanol media without any aggressive milling condition. The microwave sintering process was performed at the sintering temperatures of 1200, 1300 and 1400 °C without any soaking times and the protective atmosphere in the graphite bed. The XRD patterns showed the formation of the V2AlC max phase at the sintering temperature of 1200 °C with VC and Al2O3 compounds. In contrast, the sample sintered at 1300 °C displayed completely matched peaks with the reference pattern of the V2AlC MAX phase. Moreover, the related XRD patterns belonging to the specimen sintered at 1400 °C demonstrated the formation of VC and Al2O3 compounds as the dominant crystalline phases. The microstructure studies also showed the formation of the nano-layered MAX phases at the sintering temperatures of 1200 and 1300 °C. However, in the case of the sintering temperature of 1400 °C, the VC phases turned into the nano-blades shape after the cooling process. The highest bending strength of 189 ± 21 MPa was obtained for the specimen sintered at 1300 °C, while the highest Vickers hardness of 892 ± 15 Hv was calculated for the sample sintered at 1400 °C as the ceramic composite with the VC-Al2O3 composition.

Investigation on in-situ formed Al3V-Al-VC nano composite through conventional, microwave and spark plasma sintering

In the present study, the effect of heating methods has been studied on the microstructure and mechanical properties of in-situ formed Al3V-Al-VC nano-composite. 5 and 15 wt % of VC were added to Al matrix and conventional and microwave sintering processes were performed at 600 °C. While spark plasma sintering process was done at 450 °C with initial and final pressure of 10 and 30 MPa, respectively. The XRD results revealed the formation of Al3V intermetallic compound in microwave sintered sample, while in both spark plasma sintered and conventionally prepared specimens, the only crystalline phases were Al and VC. Microstructure studies, demonstrated a uniform distribution of 5wt% VC reinforcement in Al matrix but the 15wt%VC addition led to form agglomerates in all prepared samples. The highest bending strength (275 ± 13 MPa) and hardness (260 ± 13 Vickers) were obtained in the spark plasma sintered sample with 15wt% of VC content.

Effects of Cu particle size on CuSnFeNi/diamond composite processed using hybrid microwave sintering

ABSTRACTThe paper investigates the effects of Cu particle size on diamond composites experimentally. The hybrid microwave sintering process is proposed to obtain the particle size microstructure throughout the rapid heating. The effects of Cu particles on the hardness, flexural strength, and thermal conductivity are experimentally investigated. The experimental results indicate that the Cu particle size has a significant impact on the physical and mechanical properties of the CuSnFeNi/diamond composites. The smaller the Cu particle size, the larger thermal conductivity, the hardness, and flexural strength are obtained. This study provides an effective means to enhance the mechanical properties of the CuSnFeNi/diamond composite by adjusting the Cu particle size.

Rapid sintering of ceramic solid electrolytes LiZr2(PO4)3 and Li1.2Ca0.1Zr1.9(PO4)3 using a microwave sintering process at low temperatures

NASICON-type LiZr2(PO4)3 (LZP) has a high bulk ionic conductivity (∼10−4 S cm−1) and a wide electrochemical stability window between 0 and 5.5 V. However, LZP suffers from a problem in which its desirable rhombohedral phase transforms to the triclinic phase (∼10−8 S cm−1) below 50 °C. In this work, we reported a rhombohedral-structured LiZr2(PO4)3 (α-LZP) at room temperature with a high total Li-ion conductivity (2.8 × 10−6 S cm−1) by a microwave sintering process. Moreover, this approach realized a drastic reduction in the sintering temperature from the typical 1200 °C–900 °C with only a 4 h holding time. Using this approach, we also demonstrated the successful synthesis of Ca-incorporated Li1.2Ca0.1Zr1.9(PO4)3 (LCZP) with an ionic conductivity of 1.7 × 10−5 S cm−1.

Structural and Mechanical Properties of Amorphous Si3N4 Nanoparticles Reinforced Al Matrix Composites Prepared by Microwave Sintering

The present study focuses on the synthesis and characterization of amorphous silicon nitride (Si3N4) reinforced aluminum matrix nanocomposites through the microwave sintering process. The effect of Si3N4 (0, 1, 2 and 3 wt.%) nanoparticles addition to the microstructure and mechanical properties of the Al-Si3N4 nanocomposites were investigated. The density of Al-Si3N4 nanocomposites increased with increased Si3N4 content, while porosity decreased. X-ray diffraction (XRD) analysis reveals the presence of Si3N4 nanoparticles in Al matrix. Microstructural investigation of the nanocomposites shows the uniform distribution of Si3N4 nanoparticles in the aluminum matrix. Mechanical properties of the composites were found to increase with an increasing volume fraction of amorphous Si3N4 reinforcement particles. Al-Si3N4 nanocomposites exhibits higher hardness, yield strength and enhanced compressive performance than the pure Al matrix. A maximum increase of approximately 72% and 37% in ultimate compressive strength and 0.2% yield strength are achieved. Among the synthesized nanocomposites, Al-3wt.% Si3N4 nanocomposites displayed the maximum hardness (77 ± 2 Hv) and compressive strength (364 ± 2 MPa) with minimum porosity level of 1.1%.

Experimental investigation on mechanical properties and microstructure of hybrid copper matrix composites through microwave sintering process

Experimental investigation on mechanical properties and microstructure of hybrid copper matrix composites through microwave sintering process

Structural, mechanical and thermal characteristics of Al-Cu-Li particle reinforced Al-matrix composites synthesized by microwave sintering and hot extrusion

In this study, Al-Cu-Li (5, 10 and 15 vol%) alloy particles reinforced Aluminum matrix composites were synthesized by powder metallurgy route incorporating microwave sintering and hot extrusion processes. The effects of novel Al based alloy reinforcement on the microstructure, mechanical and thermal characteristics of the Al/Al-Cu-Li composites were investigated. Uniformly distributed Al-Cu-Li alloy particles were observed in the microstructure of the composites. The synthesized materials were characterized for microhardness, co-efficient of thermal expansion, tensile and compressive properties. The results reveal that, hardness, Young's modulus, ultimate compression strength, ultimate tensile strength, yield strength and elongation of Al/15Al-Cu-Li composite improved by ∼186%, 53%, 42%, 47%, 41%, and 48%, respectively in comparison to pure Al. This increase in strength and hardness values is attributed to the distribution of hard and brittle aluminum-based alloy phases in the ductile Al matrix. Furthermore, coefficient of thermal expansion of composites revealed the better thermal stability behavior for Al/15Al-Cu-Li composite compared to pure Al. The results of the present study suggest that the Al/15Al-Cu-Li composite is a very promising candidate for aerospace applications, which are extremely demanding in terms of both comprehensive mechanical properties and lightweight.

Microwave assisted sintering of nanocristalline PMN-PT/CoFe2O4 prepared by rapid one pot pechini synthesis: Dielectric and magnetoelectric characteristics

This paper analyzes the ultrarrapid microwave sintering process versus the conventional sintering process of the nanocrystalline composite (1-x)PMN-PT/(x)CoFe2O4, synthetized by the polymeric precursor method based on the novel one pot methodology aiming to achieve particulate composites ensuring an exceptionally homogeneous two-phase distribution. Main attention was paid to the sintering method effect on the microstructural attribute and physical properties. The activation energy for the initial stage of conventional sintering was calculated as a reference for microwave sintering. The microstructure characterizations revealed that microwave sintering without PbO loss control obtained a particulate composite with high homogeneous fine microstructures and great distribution of the Fe2CoO4 phase in the PMN-PT matrix with high electrical resistivity. Furthermore, the results showed that the sintering method has a substantial effect on their grain size and consequently on magnetoelectric properties.

Corrosion behavior and in-vitro bioactivity of porous Mg/Al2O3 and Mg/Si3N4 metal matrix composites fabricated using microwave sintering process

Abstract In the present work the corrosion behavior and in-vitro bioactivity of two kinds of porous Mg-metal matrix nano-composites separately reinforced with Al2O3 whiskers and Si3N4 particles were reported. 10 wt% of reinforcement was mixed with magnesium using high-energy ball milling and ethanol media for 10 min. After that, 10 ml ethylene glycol was added to milled mixture at the final stage of drying on a heater/stirrer at 70 °C. After stirring for 12 h, the powder mixtures were uniaxially pressed at 300 MPa to produce bar-shaped green specimens. The microwave sintering was performed at 650 °C without soaking time in a graphite bed. Porosity of about 50% was measured for both sintered composites using Archimedes principle. The XRD investigations revealed Mg2Al3 and MgO phases as the result of reaction between Mg and Al2O3. Moreover, the reaction products in Mg- Si3N4 composite were Mg2Si, Mg3N2 and Si. The corrosion tests showed that the polarization resistance of both prepared composites is higher than that of pure Mg. Mg-Al2O3 composite also showed lower corrosion current density compared to Mg- Si3N4 composite (1.42E−4 and 1.36E−3 A cm−2, respectively). In-vitro bioactivity analysis of composites showed high level of needle-shaped CA-P inside porosities of Mg-Si3N4 composite; while in the case of Mg-Al2O3 composite a lower amount and smaller needle-shaped particles were found.

Study on the growth kinetics of Al2O3 columnar crystal in Al2O3 matrix composite ceramics prepared by microwave sintering

In this paper, the grain growth kinetics of 10Nb2O5-7.5La2O3-82.5Al2O3 (volume fraction) composite ceramics prepared by microwave sintering were researched. The effect of microwave sintering processes on the grain growth kinetics of Al2O3 columnar crystal were investigated, and the effect of sintering methods on the grain growth kinetics of Al2O3 columnar crystal were analyzed by comparison with conventional sintering. The growth mechanisms of Al2O3 columnar crystal in the composite ceramic were proposed. The results show that there are three phases of Al2O3, LaNbO4 and Nb2O5 in the composite ceramic, the grain growth kinetics exponents of Al2O3 columnar crystal in the composite ceramics decrease with the increase of sintering temperature, and the growth activation energies increase with the increase of holding time; the grain growth kinetics exponents in the minor axis direction are larger than those in the major axis direction. The decisive factor for the growth rate of Al2O3 columnar crystal is the wettability of liquid phase LaNbO4 on grain boundaries under high temperature conditions. The grain growth kinetics exponents of the major axis and minor axis of Al2O3 columnar crystal during microwave sintering are lower than those of conventional sintering. Therefore, the microwave sintering technology is superior to conventional sintering technology in promoting the growth of Al2O3 columnar crystal in the composite ceramics.

Microwave-assisted synthesis of Cu–ZrB2 MM Nano-composite using double pressing double sintering method

In this research work, copper (Cu)–ZrB2 nano-composites were synthesized with different weight percentages of ZrB2 by double pressing double sintering method. The nano size of ZrB2 were distributed in the powder Cu by ball milling with ZrO2 balls in which the size of ZrB2 is < 20 nanometers and the amount of ZrB2 particles varies between 0 and 12% of the mixture. Particles were fully distributed and pressed, and the pressed pellets were sintered both, in an Ar atmosphere of tube furnace at 650 °C and microwave oven. Microwave sintering process allows us to reduce the sintering time by 16 min. Study on the nano-composite microstructures showed that the reinforcing particles were uniformly distributed in the matrix. The Cu–ZrB2 nano-composite samples were characterized using micro-hardness, X-ray diffraction analysis, scanning electron microcopy, abrasion, compressive strength and flexural strength tests. An increase in the percentage of ZrB2 nanoparticle led to an improvement in the mechanical properties of the product. The optimum amount of the reinforcing ZrB2 was determined to be 10% of the mixture.

The Effect of Rapid Microwave Sintering Process on the Electrical Conductivity, Thermal Conductivity and Mechanical Properties of Al-TiC Composites

In this research, electrical conductivity, thermal conductivity and mechanical properties of the Al-TiC composites which were sintered via microwave-assisted process were investigated. The specimens were sintered for 3, 5 and 8 minutes. The results have shown that the sample which contains 4 vol. % TiC and was sintered for 8 minutes, has the highest electrical and thermal conductivities among the other obtained ones. Besides that, the sample which contains 8 vol. % TiC and was sintered for 3 minutes, has dedicated the highest hardness and density to itself. Scanning electron microscopy (SEM) micrographs have illustrated that by increasing the amount of TiC up to 12 vol. %, the agglomeration of particles occurs. The X-ray diffraction (XRD) investigations have shown that due to the short duration of the sintering process in the microwave method, there is no trace of TiO2 and Al4C3 as pernicious phases. According to the obtained results, it becomes clear that increasing the amount of TiC powder leads to the reduction of electrical and thermal properties of the samples and increasing the sintering duration, leads to the increase of the mentioned properties.

Fast Fabrication of SOFCs with Screen-Printed YSZ Electrolyte Films By Flash Light Sintering

Solid oxide fuel cells (SOFCs) are attractive energy conversion system because of their high energy conversion efficiency, fuel flexibility and no emission of pollutant. SOFCs are composed of a dense electrolyte and two porous electrodes of anode and cathode. In the fabrication of SOFCs, many fabrication techniques such as screen-printing, tape casting, sol-gel, sputtering, chemical vapor deposition (CVD) and atomic layer deposition (ALD) are used to fabricate the solid electrolyte and the electrodes. Among various fabrication techniques, screen-printing is most widely used method in the industry because it is easy, scalable and economical process. Meanwhile, for the fabrication of solid electrolyte in this technique, high temperature sintering process is essential because the electrolyte should be fully densified to prevent any penetration of electrons and fuels. However, this high process temperature takes a considerable amount of time and thus causes significant manufacturing costs. Therefore, reducing the sintering temperature and long process time is one of the major challenges to reduce the fabrication cost and facilitate the commercialization of SOFCs. In recent years, to address these issues, many researchers demonstrated alternative sintering processes to reduce the sintering temperature and process time. For example, several researchers proposed rapid thermal annealing (RTA) process as an alternative sintering process because it can raise temperature to the target temperature within short time [1,2]. However, this process still requires relatively long maintaining and cooling processes. In addition, the excimer laser ablation annealing and the microwave sintering process have been also suggested but there are still limitations such as extremely narrow spot size and complexity of microwave interactions with materials respectively [3,4]. On the other hand, the flash light sintering process presented here uses white light flash irradiation with a broad visible wavelength range as a heat treatment source and this process has many advantages such as simplicity, scalability, and cost-effectiveness. Above all, because this process conducted within a few seconds at room temperature under ambient conditions, it can effectively reduce the manufacturing time and cost. Our previous works successfully demonstrated that the YSZ thin films deposited by solution-based process was annealed by flash light sintering and it showed comparable material properties to the conventional thermal sintering process [5]. In this work, the YSZ electrolyte films were fabricated by conventional screen-printing method and flash light sintering process was employed as an alternative sintering process of conventional thermal sintering method. In the sintering process, the effect of various pulse conditions and additional substrate heating were investigated. Microstructure, crystallinity and sintering behaviors of sintered films were analyzed to demonstrate the effectiveness of flash light sintering process. Reference [1] Wang, S. J. & Ong, C. K. Rapid thermal annealing efect on crystalline yttria-stabilized zirconia gate dielectrics. Semiconductor Science and Technology 18, 154 (2003). [2] Beltrán, N. H., Balocchi, C., Errazu, X., Avila, R. E. & Piderit, G. Rapid thermal annealing of zirconia flms deposited by spray pyrolysis. Journal of Electronic Materials 27, L9–L11 (1998). [3] Hao, H., Xu, L., Huang, Y., Zhang, X. & Xie, Z. Kinetics mechanism of microwave sintering in ceramic materials. Science in China Series E: Technological Sciences 52, 2727–2731 (2009). [4] Bayati, R. et al. Modifcation of properties of yttria stabilized zirconia epitaxial thin flms by excimer laser annealing. ACS applied materials & interfaces 6, 22316–22325 (2014). [5] Park, J.S. et al. Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films. Scientific reports 7, 12458 (2017)

Preparation of mullite/B4C composites: A comparative study on the effect of heating methods

The present study investigated preparation of the mullite/B4C composites through microwave and spark plasma sintering processes. A high-energy ball mill was used to mix the nono-sized mullite and B4C powders in ethanol media for 10 min. The mixed nano-sized powders were pelletized and sintered by microwave (MW) and spark plasma sintering (SPS) processes at 1500 and 1300 °C, respectively. The XRD results revealed the reactions between mullite and B4C, and also the formation of SiC, Al2O3, Si phases in SPS sintered sample. The identified crystalline phases in the microwave sintered sample were mullite and B4C. Samples sintered in SPS reached almost full density and showed improved mechanical properties (the hardness of 16.29 ± 0.2 GPa, bending strength of 348 ± 21 MPa and fracture toughness of 3.01 ± 0.18 MPa m−1/2) than those sintered in microwave. The microstructural investigations showed the formation of needle-like mullite at some areas of sample sintered in SPS with a uniform distribution of B4C in mullite matrix alongside pore-free microstructure. The microstructure of microwave sintered sample contained a large number of pores.

Enhancing compressive, tensile, thermal and damping response of pure Al using BN nanoparticles

In the present study, aluminum based metal matrix composites containing various amounts of boron nitride (BN) nanoparticulates (0, 0.5, 1.0 and 1.5 vol.%) were fabricated by using the powder metallurgy (PM) technique involving microwave sintering and hot extrusion process. The microstructure, physical, thermal, mechanical and damping characteristics of the extruded nanocomposites were investigated. Field emission scanning electron microscopy (FE-SEM) study shows the evenly distributed BN particles in Al matrix. Mechanical analysis indicates that the compression, hardness and tensile strength of Al-BN nanocomposites increases with increasing amount of BN content. Particularly, a significant improvement in the tensile strength (∼36%) is achieved in Al-1.5 vol.% BN nanocomposite when compared to the pure aluminum (Al). This improvement strength can be attributed to the dispersion hardening of the Al matrix due to the presence of hard BN nanoparticles. Thermal analysis shows that the coefficient of thermal expansion (CTE) decreases with increasing amount of BN which may be ascribed to inherent low CTE of BN nanoparticles used as reinforcement. The addition of BN nanoparticulates enhanced the damping characteristics of pure Al with Al-1.5 vol.% BN nanocomposite exhibiting the maximum damping capacity and damping loss rate with a minimum change in elastic modulus. The improved combination of properties exhibited by Al-BN nanocomposites make them potential candidates for a wide spectrum of industries especially for weight critical applications.

Porous and non-porous alumina reinforced magnesium matrix composite through microwave and spark plasma sintering processes

In this study, Alumina reinforced Magnesium Matrix Composites have been prepared by two different sintering method: microwave and spark plasma sintering (SPS) processes. 5 wt% alumina whisker was blended with magnesium powders in ethanol media for 10 min. The sintering temperatures in the spark plasma and microwave furnace were at 420° and 700 °C, respectively. Thermodynamic investigation and XRD results revealed the formation of MgO, Mg2Al3 compounds in both sintered composites. However, microwave sintering led to form a porous composite (53.1% of theoretical density) while SPS resulted to formation of a fully dense composite. The mechanical examinations showed higher bending strength (163 ± 10 MPa) and micro-hardness (101 ± 11 Vickers) of SPS samples rather than microwave samples as it expected. By using two different sintering methods (pressure-less and pressure-assisted) and controlling processing parameters, the porosity of the final products can be changed from porous to fully dense composites.

Synthesis and Mechanical Response of NiTi SMA Nanoparticle Reinforced Mg Composites Synthesized through Microwave Sintering Process

The concept of developing intelligent Self-Healing Metallic Materials that can repair its damage is always fascinating and is of great interest in order to improve the quality service life of engineering components. Due to their low density, magnesium (Mg) and its alloys offer a combination of better specific strength (σ/ρ), damping characteristics and impact resistance and can suit best for the quest of intelligent self-healing materials development. In the current study, Mg is reinforced with 2 wt.% NiTi shape memory alloy (SMA) nanoparticles and the SMA particle effect on the mechanical properties and microstructural evolution of monolithic magnesium are studied. A near dense Mg-2 wt. % NiTi nanocomposite was obtained during the study. The addition of NiTi nanoparticle resulted in a ∼29 % and ∼73% enhancement in the microhardness and grain size of pure Mg. Damping capacity and loss rate of pure Mg also had a superior enhancement of ∼119% and ∼2.6 times, respectively due to the presence of NiTi nanoparticle. The compressive strength properties also exhibited a visible enhancement due to the presence of NiTi nanoparticle without compromising on the fracture strain of the material.

Scanning Electron Microscopic Studies of Microwave Sintered Al-SiC Nanocomposites and Their Properties.

Al-metal matrix composites (AMMCs) reinforced with diverse volume fraction of SiC nanoparticles were synthesized using microwave sintering process. The effects of the reinforcing SiC particles on physical, microstructure, mechanical, and electrical properties were studied. The phase, microstructural, and surface analyses of the composites were systematically conducted using X-ray diffraction (XRD), scanning electron microscope (SEM), and surface profilometer techniques, respectively. The microstructural examination revealed the homogeneous distribution of SiC particles in the Al matrix. Microhardness and compressive strength of nanocomposites were found to be increasing with the increasing volume fraction of SiC particles. Electrical conductivity of the nanocomposites decreases with increasing the SiC content.

Effect of Copper Alloying and Reinforcement Percentage on the Microstructure-Tribological Aspects of the Aluminium Alloy Composites

In this study, microstructural and tribological analysis of Aluminium Alloy composites 2024 and 2900 is done. The composite with reinforcements SiC and Al2O3 from 0-20 wt% is prepared by powder metallurgy process. As microwave sintering is the process used the core is much denser than at the surface. Strength of aluminium is increased by percentage of copper alloyed in aluminium matrix. Microstructure of the sample is examined thoroughly using scanning electron microscope. X-ray diffraction patterns are investigated for the elements present in the composites and a detailed check for the intermetallic precipitates and the impurities. A uniform microstructure is obtained by microwave sintering process. Aluminium alloy 2024 and 2900 which is microwave sintered is having round-edged porosities with high ductility and toughness. Tribological studies are carried out using pin on disc wear testing machine. The results indicated that 2900 exhibited excellent frictional coefficient behavior compared to AA 2024.

TiO2 ceramic particles-reinforced aluminum matrix composite prepared by conventional, microwave, and spark plasma sintering

Aluminum-10 wt% TiO2 metal matrix composites were fabricated with conventional, microwave, and spark plasma sintering processes. Aluminum and nano-sized TiO2 powders were mixed using a high-energy mixer, and the sintering process was done at 450℃ by spark plasma sintering and 600℃ under both microwave and conventional heating. The results showed microwave sintering led to form Al3Ti intermetallic compounds with flaky shape, while in the conventional heating at the same sintering temperature, Al3Ti was formed and confirmed by X-ray diffraction and scanning electron microscope investigations. Moreover, the nano-sized TiO2 particles as reinforcement with no additional phase were obtained by spark plasma sintering at the lowest sintering temperature. The maximum bending strength of 254 ± 12 MPa and Vickers hardness of 235 ± 13 were measured for samples sintered in microwave as a consequence of Al3Ti formation. The SEM and energy-dispersive X-ray spectroscopy analyses showed uniform distribution of Al3Ti particles in the microstructure of microwave sintered samples and nonuniform distribution of agglomerated Al3Ti particles and porosities in samples sintered by spark plasma sintering and conventional heating.