Hybrid Microwave Sintering Research Articles

A hybrid microwave sintered PZT composite as a flexible piezoelectric nanogenerator.

Interest in piezoelectric nanogenerators has grown extensively due to high piezoelectric coefficients. Piezoelectric ceramic-based devices have dominated research in large-scale energy harvesting. Morphotropic phase boundary PbZr0.52Ti0.48O3 (MPB-PZT) synthesized using Hybrid Microwave Sintering (HMS) at a low temperature (940 °C) for 20 min has emerged as a dense ceramic. The Rietveld refinement studies confirm its dual phase (tetragonal (P4mm) and rhombohedral (R3m)). The PZT ceramic is exploited as a piezoelectric material, which can improve the output piezoelectric potential of a piezoelectric nanogenerator (PENG). Multi-walled carbon nanotubes (MWCNTs) are evenly distributed in the PZT composite to reduce the internal resistance of the PENG. According to the percolation theory, small amounts of MWCNTs dispersed within the composite ink can significantly improve the output voltage of the PENG by acting as conductive bridges between the polymer (polyvinylpyrrolidone (PVP)) and ceramic particles. The concentration of PZT and the amount of MWCNTs are changed to enhance the device's output voltage. As a result, an optimized PENG with a PZT (1.5 g)/MWCNT (0.06 wt%)/PVP (4 g) (PVP - polyvinylpyrrolidone) composite film is obtained. The PENGs are mechanically poled. The optimised output voltage of the PENG is 16 Vpp, which could light up a series of 20 commercial light emitting diodes (LEDs). The PENG is attached to footwear and is noticed to efficiently harvest energy from daily human activities which demonstrate its practical applications.

Development of Magnesium Nanocomposites by Powder Metallurgy for Multifunctional Applications: Review

Magnesium is a lightweight metal that holds great potential in automotive, aerospace and biomedical applications. Magnesium when incorporated with nanoparticles, exhibits simultaneous improvements in mechanical, tribological and biological properties without altering its density. This article presents a short review and analysis of mechanical (tensile and compressive), ignition, damping, tribological and in vitro degradation (corrosion and biocompatibility) behaviour of magnesium- based nanocomposites. Owing to the flexibility in tailoring for multiple applications, powder metallurgy routes are being explored to target unique microstructures, novel compositions and high performance in magnesium-based nanocomposites. The mechanical and in vitro study of magnesium nanocomposite synthesized by powder metallurgy route demonstrates improved strength, controlled degradation and good biocompatibility. The article also proposes a powder metallurgy route incorporating hybrid microwave sintering as a promising environment-friendly technique to develop magnesium nanocomposites for biomedical applications.

Investigation on the combined effect of ZnO nanorods and Y2O3 nanoparticles on the microstructural and mechanical response of aluminium

In this work Al-ZnO-Y2O3 hybrid composites were fabricated utilizing powder metallurgy and hybrid microwave sintering approach from the powder blend of Al, ZnO and Y2O3. Depth sensing nano-indentation technique was adopted to assess the nano-hardness and elastic modulus of the composite material. Thermal analysis of the composite materials was done to gain an insight into surface decomposition and phase transformation behaviour. A strong interfacial bonding with clear interface between matrix and reinforcement was observed during the microstructural analysis of the composite material. The results of the current study exhibit ~89% improvement in the nano-hardness and ~11% improvement in the elastic modulus value. The improvement in the material response is attributed to the reasonably uniform distribution of ZnO and Y2O3 in the hybrid composite materials. The results of this study validate the capability of combined presence of ZnO and Y2O3 reinforcements to enhance the hardness and elastic modulus of aluminium.

Synthesized Nanorods Hydroxyapatite by Microwave-Assisted Technology for In Vitro Osteoporotic Bone Regeneration through Wnt/β-Catenin Pathway.

This research presents an optimal and inexpensive, without any additives, method for the synthesis and sintering of hydroxyapatite (HA) by microwave-assisted technology (MAT) furnace. The target sintering temperature of the furnace (1100 ℃) was held for one and two hours for conventional sintering. With regard to the microwave hybrid sintering, it was held at 100%MW for 20 and 30 min. FTIR, XRD, TGA, SEM/EDS, and TEM were assessed to determine HA phase composition, and structural as well as thermal decomposition behavior. The in vitro effects of sintered HA discs on cultured aged mice-isolated osteoblast cells and hydrocortisone-induced osteoclast cells were assessed by measuring ALP, osteocalcin, TRAP, calcium, and Alizarin red S staining. Moreover, their effects on cell differentiation (CD90 and CD 105 and PARR- ɣ) and death markers (GSK3b, MAPK, and β-catenin) were evaluated. The results demonstrate the production of ≈35 nm crystal-sized pure hydroxyapatite nanorod-like particles with a high degree of crystallinity and no impurities as required for biomedical application. HA increased osteogenesis (ALP, osteocalcin, and calcium) markers and decreased cell resorption markers. In addition, HA nanorods reversed the effect of cortisone on cell differentiation and death markers. In conclusion, microwave hybrid sintered HA is a potential nanomaterial for osteoporotic bone regeneration as HA reversed the cortisone adverse effect on osteoblast cell death through canonical and non-canonical pathways.

Electrochemical behavior of various grade P/M stainless steels processed by rapid microwave hybrid sintering (super-solidus) method

Three categories of stainless steel P/M samples were prepared using the microwave hybrid heating method at super-solidus state temperature (1300 °C). The effect of sintering parameters on pore morphologies and electrochemical behavior of the samples were analysed with different holding time. The electrochemical/electrical characteristics were derived from the PDP/EIS measurements and it has shown an increase in passive film capability with the holding time. The 316L, 430L and 410 have exhibited 37%, 23% and 53% decrement respectively in corrosion rate upon increasing holding time from 30 to 60 min. A parameter active area factor deduces from EIS measurements is decreased by 6–18 times. The variation in corrosion morphologies for three grades of stainless steel is characterized through E-MAP analysis.

Densification behavior of microwave hybrid sintered Al2O3 bimodal powder mixtures and comparison with 3D modeling and simulation

In this study, slip casting and microwave hybrid sintering of Al2O3 bimodal powder mixtures were conducted to observe the effect on packing factor and densification behavior of different compositions. The powder mixtures contained up to 50 vol% fine particles. It was found that the green density increased remarkably with the addition of fine particles into coarse ones, and the composition having 30 vol% fine particles had the highest relative density of 72.7%. A similar behavior was also observed in sintered samples, where the sintered densities were also higher for bimodal compositions. Moreover, 3D modeling of the system was carried out, and the sintering behavior was simulated and compared with the experimental data. It was shown that with the same relative green density of 50% solid volume for all samples, the composition with 40 vol% fine particles exhibited the highest relative sintered density of 92.1%. The sintering behavior was also predicted for highly dense modeled structures, which could not be obtained experimentally, and pore analysis was performed. It was observed that the closed porosity increased with the addition of fine particles, while the pore size distribution significantly reduced, where 81.4 vol% pores had pore sizes of only up to 0.28 μm.

Development of Lightweight Magnesium/Glass Micro Balloon Syntactic Foams Using Microwave Approach with Superior Thermal and Mechanical Properties

Magnesium matrix syntactic foams (MgMSFs) are emerging lightweight materials with unique capabilities to exhibit remarkable thermal, acoustic, and mechanical properties. In the current study, lightweight glass micro balloon (GMB)-reinforced Mg syntactic foams were synthesized via the powder metallurgy technique using hybrid microwave sintering. The processing employed in the study yielded MgMSFs with refined grain sizes, no secondary phases, and reasonably uniform distributions of hollow reinforcement particles. The developed MgMSFs exhibited densities 8%, 16%, and 26% lower than that of the pure Mg. The coefficient of thermal expansion reduced (up to 20%) while the ignition resistance improved (up to 20 °C) with the amount of GMB in the magnesium matrix. The MgMSFs also exhibited a progressive increase in hardness with the amount of GMB. Although the MgMSFs showed a decrease in the yield strength with the addition of GMB hollow particles, the ultimate compression strength, fracture strain, and energy absorption capabilities increased noticeably. The best ultimate compression strength at 321 MPa, which was ~26% higher than that of the pure Mg, was displayed by the Mg-5GMB composite, while the Mg-20GMB composite showed the best fracture strain and energy absorption capability, which were higher by ~39 and 65%, respectively, when compared to pure Mg. The specific strength of all composites remained superior to that of monolithic magnesium. Particular efforts were made in the present study to interrelate the processing, microstructural features, and properties of MgMSFs.

Metallurgical and wear study of MWCNT-reinforced h-AMMC fabricated through microwave hybrid sintering

Abstract The present work deals with the outcomes of a novel approach for developing a multi-walled carbon nanotube-reinforced hybrid aluminium metal matrix composite. Microwave hybrid sintering in combination with cold compaction of the powder metallurgy route was followed for the fabrication of composites. Microwave hybrid sintering was carried out using a microwave oven operating at 2.45 GHz frequency and 900 W power. For this purpose, Al5083 was used as the matrix material, and silicon carbide (15 wt.%) and multi-walled carbon nanotubes (0.5 wt.%) the reinforcements. The fabricated composites were then characterized by hardness, microstructure, and porosity. An investigation on the wear resistance of the base alloy and the conventional and microwave sintered composites followed this. The findings of the present study reveal the fact that the addition of carbon nano-tubes in the composite and the use of microwave energy over conventional sintering have a significant effect on the property enhancement of the developed hybrid composite.

Performance of Sn-3.0Ag-0.5Cu Composite Solder with Kaolin Geopolymer Ceramic Reinforcement on Microstructure and Mechanical Properties under Isothermal Ageing.

This paper elucidates the effect of isothermal ageing at temperature of 85 °C, 125 °C and 150 °C for 100, 500 and 1000 h on Sn-3.0Ag-0.5Cu (SAC305) lead-free solder with the addition of 1 wt% kaolin geopolymer ceramic (KGC) reinforcement particles. SAC305-KGC composite solders were fabricated through powder metallurgy using a hybrid microwave sintering method and reflowed on copper substrate printed circuit board with an organic solderability preservative surface finish. The results revealed that, the addition of KGC was beneficial in improving the total thickness of interfacial intermetallic compound (IMC) layer. At higher isothermal ageing of 150 °C and 1000 h, the IMC layer in SAC305-KGC composite solder was towards a planar-type morphology. Moreover, the growth of total interfacial IMC layer and Cu3Sn layer during isothermal ageing was found to be controlled by bulk diffusion and grain-boundary process, respectively. The activation energy possessed by SAC305-KGC composite solder for total interfacial IMC layer and Cu3Sn IMC was 74 kJ/mol and 104 kJ/mol, respectively. Based on a lap shear test, the shear strength of SAC305-KGC composite solder exhibited higher shear strength than non-reinforced SAC305 solder. Meanwhile, the solder joints failure mode after shear testing was a combination of brittle and ductile modes at higher ageing temperature and time for SAC305-KGC composite solder.

Finite element simulation of hybrid microwave sintering based on power approach

Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption, and reduced sintering temperature. However, the technique is not fully understood, difficult to control, and often relies on experience and trial-and-error approach. Consequently, hot spots, uneven heating, thermal runaway, and shape distortion develop in sintered compacts. Therefore, developing a model that can simulate the sintering process, enhance predictability, and determine the critical sintering conditions is essential. Multiphysics finite element (FE) modelling of hybrid MW sintering of a magnesium alloy AZ61 compact was undertaken in this study. The FE model coupled the electromagnetic, heat conduction, and densification equations. The model utilised parameters related to the furnace, compact, and susceptor to predict the spatial distribution of electric field, thermal response, and densification in the compact. A power-based sintering criterion was developed to predict the sintering of the compact and estimate its critical sintering energy. Modelling results showed that heating time, compact size, and thickness of the susceptor are critical to the sintering process. It was also shown that the susceptor not only mediated the sintering of the compact but also homogenised its temperature and densification. Thus, MW sintering of the compact was predicted to occur at 500 °C for 8 to 10 min with a predicted relative density of about 0.98. Experimental MW sintering data showed good concurrence with the developed model. These results are useful for controlling the MW sintering process, eliminating trial-and-error, and determining the critical sintering conditions.

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Abstract Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process. The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured. It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders. The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%. Mechanical properties were controlled by Al2O3 content, dispersion of nano reinforcements and grain size. The optimum hardness and strength properties were achieved through incorporation of 10 wt.% Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles (NPs) at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement. Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time. The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix. The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.

Magnetoelectric and magnetodielectric coupling in partially Ni-doped CoFe2O4 and 0.15(Ba0·7Ca0·3TiO3)–0.85(BaZr0·2Ti0·8O3) composites prepared via clean microwave sintering

Multiferroic composites with high magnetoelectric coupling at room temperature are considered as the most significant materials due to their potential application in many electronic devices. Furthermore, ultrafast, eco-friendly energy-efficient innovative techniques to develop multifunctional materials have attracted abundant importance. In this study, we report on ferrite–ferroelectric particulate composites prepared via clean, eco-friendly, ultrafast, hybrid-microwave sintering. Partially Ni-doped CoFe2O4 was selected as a magnetostrictive phase due to its considerable value of the magnetostriction coefficient, λ11 ≈ −118 ppm, saturation magnetization Ms ≈ 80 emu/gm, and μB ≈ 3.37 and mixed with a 0.15(Ba0·7Ca0·3TiO3)–0.85(BaZr0·2Ti0·8O3) ferroelectric phase in different content ratios of 10%, 20%, 30%, and 40%. The multiferroic properties of the sintered composite samples were investigated considering magnetoelectric and magnetodielectric couplings. The highest value of the magnetoelectric coupling coefficient, αME = 22..09 mV/Oe·cm was observed for the composite with 40% ferrite content, while similar composite exhibits the higher value of the magnetodielectric coupling coefficient which is 3.52% at 1 kHz (frequency) and 1 T (magnetic field). X-ray diffraction and Raman spectroscopy confirmed the phases of the ferrite and ferroelectric constituents without revealing any additional phases. The impedance and AC conductivity of the multiferroic compositions were analyzed under various temperatures and by applying a magnetic field at room temperature. The temperature-dependent dielectric nature confirms that the addition of Ni-doped CoFe2O4 into a ferroelectric constituent substantially influences the dielectric constant in the paraelectric region. These results may offer an alternative technique for the preparation of multiferroic composites with improved coupling properties.

Investigation into Physical, Microstructural and Mechanical Behaviour of Titanium dioxide Nanoparticulate Reinforced Magnesium Composite

ABSTRACT In the present work, monolithic pure magnesium (Mg) and magnesium with 1.5, 2.5 & 5.0 wt. % of titanium dioxide (TiO2) nanoparticulate composites were synthesised using powder metallurgy technique followed by two-stage hybrid microwave sintering and hot extrusion at 350°C with an extrusion ratio of 16:1. Mass density, porosity, microstructure, microhardness and compressive strength of the composite were critically investigated as per ASTM standards. Microstructural characterisation reveals the quantitative elements such as Mg, Ti and O, its composition, refined grain size of matrix, grain boundary and uniform distribution of TiO2 nanoparticles in the magnesium matrix. Mass density and microhardness were observed to increase steadily with increase in addition of TiO2 nanoparticles. Further, maximum compressive strength was obtained for Mg5TiO2 composite. Harder and fine grain TiO2 nanoparticulate was responsible for appreciable mechanical behaviour of composite. Refined magnesium grains also contributed appreciably for significant mechanical behaviour through the nucleation effect.

Synthesis and characterization of zinc oxide reinforced aluminum metal matrix composite produced by microwave sintering

The study focuses on the microstructural, phase transformation, and physical and mechanical aspects of aluminum/zinc oxide composite produced by a hybrid microwave sintering technique. In the present case, zinc oxide nanorods were synthesized through a cost-effective thermal decomposition method. The obtained zinc oxide nanorods’ length was in the range of 76–168 nm observed through high-resolution transmission electron microscopy images and crystallinity nature was confirmed by the bright spot in the selected area electron diffraction pattern. Two different wt% (i.e. 0.5 and 2) of zinc oxide nanorods were utilized for the fabrication of the composite material. The diffraction pattern of the milled powder and energy dispersive spectroscopy results shows effective diffusion of zinc oxide nanorods in the aluminum. The elemental mapping of milled powder illustrates the uniform distribution of the reinforcement over matrix material. The micro-hardness results exhibit a higher hardness of 27.78% with a small fraction of 2 wt%. The nano-indentation results confirm the improvement in the nano-hardness by 32.21% with 2 wt% of zinc oxide with a marginal decrease in elastic modulus by 4.92%.

Microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites, and effects of ZrO2 crystal structure on mechanical properties, thermal properties, and sintering kinetics

Structural ceramics such as Al2O3 and Al2O3–ZrO2 composites are widely used in harsh environment applications. The conventional sintering process for fabrication of these ceramics is time-consuming method that requires large amount of energy. Microwave sintering is a novel way to resolve this problem. However, to date, very limited research has been carried out to study the effects of different ZrO2 crystal structures on Al2O3–ZrO2 composites, especially on the sintering kinetics, when fabricated by microwave sintering.The microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites was performed in this study. Tetragonal zirconia and cubic zirconia were used as two different reinforcements for an α–alumina matrix, and the mechanical and thermal properties were studied. It was found that Al2O3 experienced a remarkable increase in fracture toughness of up to 42% when t-ZrO2 was added. Al2O3–c-ZrO2 also showed increased fracture toughness. The sintering kinetics were also thoroughly investigated, and the average activation energy values for the intermediate stage of sintering were estimated to be 246 ± 11 kJ/mol for pure Al2O3, 319 ± 71 kJ/mol for Al2O3–c-ZrO2, and 342 ± 77 kJ/mol for Al2O3–t-ZrO2. These values indicated that the activation energy was increased by the addition of either type of ZrO2, with the highest value shown by Al2O3–t-ZrO2.

Effect of ball milling and metal filler alloy on microstructural bonding of Al2O3-SiC nano ceramic composite

The ceramic composite (Al2O3 + 5 vol% nano SiC + 5 vol% Ni) was prepared with powder processing followed by microwave hybrid sintering in a conventional microwave oven (2.45 GHz, 900 W) at 1600 °C. Post sintering the relative densification, hardness and microstructure of the ball milled and the unmilled sample were examined and compared. Also the effect of ball milling and metal filler (Nickel) on microstructural bonding of alumina/SiC nano ceramic composite has been studied. Ball milled sintered composite achieved 93% relative densification and has higher indentation resistance as compared to unmilled sintered composite.

Magnetoelectric, magnetodielectric effect and dielectric, magnetic properties of microwave-sintered lead-free x(Co0.9Ni0.1Fe2O4)-(1-x)[0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3)] particulate multiferroic composite

Materials with two distinct (magnetostrictive-ferroelectric) phases, i.e., x (Co0·9Ni0·1Fe2O4) -(1-x) [0.5 (Ba0·7Ca0·3TiO3) −0.5 (BaZr0·2Ti0·8O3)], combined at ratios of 10:90, 20:80, 30:70, and 40:60 were prepared using a hydroxide coprecipitation method. These multiferroic composites were subjected to sintering via the hybrid microwave sintering technique at 1200 °C for 20 min. Ni-substituted CFO exhibited excellent magnetic properties at room temperature, with Ms ≈ 80 emu/g, μB ≈ 3.37, Mr ≈ 19.05 emu/g, and Hc ≈ 599 Oe, as well as a high value of the magnetostriction coefficient (λ12 ≈ −118 ppm). The magnetostrictive-ferroelectric crystal phases in each composite were confirmed via X-ray diffraction analysis. The highest value of the linear magneto-electric coefficient was α = 21.6 mV/cm-Oe at a frequency of 1 kHz for the 40CNFO-60(BCT-BZT) composite, and a similar sample had the highest value of the magnetodielectric coefficient, which was approximately 3.3% at f = 1 kHz with an applied magnetic field of 1 T. The typical ferromagnetic and ferroelectric nature of each composite was confirmed by M − H and P–E hysteresis loops, respectively at room temperature. Two anomalies were observed in the temperature-dependent dielectric permittivity one at ~140 °C and another above 500 °C confirming the coexistence of two materials with distinct transition points, i.e., BCT-BZT and CNFO, respectively.

Study effects on diamond concentration of CuSnFeNi/diamond composite on grinding WC

There are still some challenges to use metal matrix composites reinforced with diamond particles in grinding field because it is difficult to find a suitable metal matrix to balance the mechanical properties and grinding performance. In order to solve this problem, CuSnFeSn/diamond composites were fabricated by introducing hybrid microwave sintering with diamond concentration ranging from 40 to 70%. The microstructure, physical and mechanical properties, and critical grinding performance were investigated. Best balance of mechanical properties and grinding surface roughness occurred when the diamond concentration is 60%. It holds a hardness of 98.5 ± 0.5HRB, a flexural strength of 266.98 ± 15.6 MPa, an elastic modulus 46.62 ± 8.48GPa, and WC sample surface roughness Ra14.92 ± 2.92 nm. The grinding experiment results reveal that there are three wear modes in the processing, which are adhesive wear, plastic deformation, and sliding friction.

Compressive Characteristics of Aluminum-Fly Ash Syntactic Foams Processed by Microwave Sintering

Aluminum-fly ash (FA) syntactic foams were synthesized via powder metallurgy and hybrid microwave sintering for 30 minutes. This minimized the formation of unwanted brittle interfacial products. Sphericity of FA microspheres was preserved, and significant density reduction of about 36 pct was achieved. Compressive strength and energy-absorption characteristics of the samples reduced as the volume fraction (vol pct) of FA microspheres increased from 20 to 40 pct. These materials have potential applications as lightweight energy-absorption materials.

Structural and mechanical properties of microwave hybrid sintered aluminium silicon carbide composite

ABSTRACTMicrowave material processing is recognized for many advantages, namely, substantial reduction in cycle time resulting in large energy savings, selective and volumetric heating, providing fine microstructure, improved mechanical properties and eco-friendliness. In our experiment, we have converted a conventional microwave into a microwave hybrid sintering furnace to microwave hybrid sintering, results improved densification of metal-matrix composite. In the present study, the composite of aluminium matrix composites (AMCs) reinforced with SiC particles was sintered by varying the composition of SiC. The microstructure and mechanical properties of AMCs were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and hardness. The results show as the amount of SiC was increasing in the compacts; the hardness was increasing and was varying between 50 and 60 HRF. SEM analysis shows uniform distribution of silicon carbide in the aluminium matrix. XRD analysis shows the presence of SiC, aluminium and aluminium oxide as foreign impurity due to some oxidation. These compositions were also confirmed by the EDX analysis. The composite sintered density was changed from 2.323 to 2.583 gm/cm3. It is concluded, using microwave hybrid sintering, improved mechanical and physical properties can be obtained of metal-matrix composite.