Hybrid Microwave Sintering Research Articles

Investigating influence of hybrid (yttria + copper) nanoparticulate reinforcements on microstructural development and tensile response of magnesium

In the present study, an attempt has been made to tailor the properties of monolithic magnesium by initially reinforcing it with a predetermined amount of nanosize yttria particulates followed by hybridising it with nanocopper particulates in two different volume percentages of 0·3 and 0·6 vol.-% respectively. Both the monolithic magnesium and magnesium nanocomposites were synthesised using the blend press sinter powder metallurgy technique followed by hot extrusion. For sintering of the materials, an innovative hybrid microwave sintering method was chosen with the objective of realising savings in both time and energy. Test results revealed that both strength and ductility of pure magnesium increased with the addition of yttria and a hybrid reinforcement mixture of yttria and copper nanoparticulates. The best combination of properties in uniaxial tension was obtained for the Mg/(0·7Y2O3+0·3Cu) hybrid nanocomposite. The observed improvement in properties is attributed to synergistic influences of a noticeable reduction in grain size of the hybrid nanocomposite, coexistence of both Y2O3 and copper to a reasonable extent, and a fairly uniform distribution of the reinforcement particulates and intermetallics. A scientific attempt is made in this study to highlight the significance of using hybrid reinforcements, at nanolength scale, in a pure magnesium matrix to obtain a noticeable increase in tensile properties.

Effect of addition of nano-copper and extrusion temperature on the microstructure and mechanical response of tin

Abstract In the present study, 0.35 and 1.1 vol.% of nano-size copper were incorporated into pure tin using hybrid microwave sintering assisted powder metallurgy route. Microwave sintered samples were extruded both at room temperature and at 230 °C. Microstructural characterization studies were conducted on the extruded samples to investigate the distribution characteristics of secondary phase, grains and pores morphology. Resistivity of solder samples was also investigated and found to be not affected by the high temperature extrusion. Room temperature tensile test results revealed that hot extruded Sn–Cu samples exhibited higher strengths and ductility when compared to room temperature extruded samples. On the contrary, the tensile properties of pure tin remained independent of extrusion temperature. An attempt is made in this study to correlate the presence of copper and effect of extrusion temperature on the microstructural evolution and mechanical response of tin.

Using microwaves to synthesize pure aluminum and metastable Al/Cu nanocomposites with superior properties

The processing of aluminum using powder metallurgy techniques is a challenging task due to the presence of thin oxide films on the surface of the metal particles which prevent strong bonding between particles during sintering. In this study, an innovative hybrid microwave sintering technique is utilized to process pure aluminum and Al/Cu nanocomposites without the need of any protective atmosphere. Hybrid microwave sintering involves the heating of aluminum compacts using both microwave energy and radiant heating. Significant savings in time and energy can be achieved using the fabrication methodology. Results revealed that processing methodology used in this study provides a simple and inexpensive option to existing processing methodologies to synthesize pure Al and Al/Cu nanocomposites with superior combination of properties.

Utilizing energy efficient microwave sintering to significantly enhance the tensile response of a lead-free solder

This study investigates the effects of conventional sintering and hybrid microwave sintering techniques on the microstructure evolution and tensile properties of a Sn–Ag–Cu solder. A significant energy saving of up to 99% was achieved using the hybrid microwave assisted sintering approach. Hybrid microwave sintered samples exhibited better densification (in terms of lower porosity level) and this indicates the ability of microwaves to sinter solder materials more effectively. Furthermore, tensile results revealed that samples hybrid microwave sintered at 210 °C exhibited the best enhancement in yield strength and ultimate tensile strength, with no compromise in the failure strain, as compared with other widely used commercial solders. The morphology of pores and interparticle spacing were observed to be the two key factors influencing the mechanical properties of the solders.

Improving sinterability of ceramics using hybrid microwave heating

Microwave processing, as a new method for sintering ceramics, has key advantages such as increased heating rate, uniform heating and reduced cost compared to conventional methods. It is generally accepted that microwave sintering can improve the macroscopic mechanical performances of ceramics, however, the performances of microwave-sintered ceramics on the microscopic scale are rarely investigated. In the present study, the ceramics are sintered by hybrid microwave sintering (HMS), which combines the characteristics of microwave heating and conventional heating. To evaluate the homogeneous performance of the sintered ceramics, the behaviors of thermal residual stress distribution in the microwave-sintered and conventionally sintered ceramics were investigated by X-ray diffraction technique. The thermal residual stress investigation shows microwaves can sinter ceramics in entire volume while offering improved mechanical properties. Subsequently, the distribution behaviors of pore ratio and hardness in the ceramics were investigated, respectively. The experiment results confirm that the sinterability of ceramics is homogenously improved by hybrid microwave sintering.

Effect of heating rate during hybrid microwave sintering on the tensile properties of magnesium and Mg/Y2O3 nanocomposite

Abstract In the present study, pure magnesium and a Mg/Y2O3 nanocomposite were microwave sintered using heating rates of 49 and 20 °C/min. Results obtained from extruded rods revealed that average hardness and strengths of both Mg and Mg/Y2O3 samples were higher when they were sintered at higher heating rate. Ductility of pure Mg, however, reduced at higher heating rate while it remained similar for Mg/Y2O3 nanocomposite. An attempt is made to correlate tensile properties with the end microstructural features of the samples sintered at two different heating rates.

Sinterização de cerâmicas em microondas. Parte III: Sinterização de zircônia, mulita e alumina

O aquecimento utilizando microondas possui muitas vantagens com relação aos métodos convencionais de aquecimento, como redução no tempo de processamento, economia de energia e melhora na uniformidade microestrutural dos corpos cerâmicos. Assim esse trabalho tem por objetivo a utilização da sinterização híbrida com microondas na queima rápida de materiais cerâmicos. Foram utilizados materiais que requerem altas temperaturas para densificação. Foram sinterizados materiais que apresentam bruscas e acentuadas mudanças nas suas propriedades dielétricas com a elevação da temperatura, zircônia, e materiais com baixas perdas dielétricas na temperatura ambiente, que apresentam dificuldades de aquecimento com microondas em baixas temperaturas, alumina e mulita. Foi utilizando material susceptor como agente auxiliar de aquecimento. Com base nos resultados obtidos pode-se concluir que o sistema de sinterização híbrida desenvolvido pode ser utilizado com sucesso na sinterização rápida e uniforme dos materiais estudados, sendo possível a sinterização de zircônia em ciclos de 20 min, mulita em ciclos de 16 min e alumina em ciclos de 40 min.

Electrophoretic deposition of zirconia layers for thermal barrier coatings

This paper presents an exploratory investigation of a production route for thermal barrier coatings (TBCs) from a stable zirconia nanopowder suspension by means of electrophoretic deposition (EPD) on a low carbon steel substrate, followed by a consolidation by hybrid microwave sintering.

TLM simulation of microwave hybrid sintering of multiple samples in a multimode cavity

AbstractMicrowave heating technology is a powerful mean to ensure successful sintering of ceramic materials. In sintering experiments, low loss insulators, conductors and high‐loss ceramics are microwaved so as to get optimal mechanical and structural properties. It is known that low‐loss ceramic materials such alumina and zirconia exhibit long waiting time before reaching a critical coupling temperature at which microwaves can be readily absorbed. On the other hand, some ceramics such as silicon carbid have a high loss factor and therefore can be used as a process stimulus for microwave sintering of microwave transparent ceramics. Furthermore, successful sintering experiments often require the use of carefully designed insulating structure in order to minimize thermal gradients caused by heat loss from surfaces. All these problems have led to the introduction of microwave hybrid heating (MHH) schemes using higher dielectric loss susceptors, insulation or coating. Since MHH depend mainly on human expertise, the optimization of sintering experiments will certainly benefit from numerical simulations. The transmission line matrix (TLM) is used to study two MHH schemes where both a susceptor and an insulating matrix were, respectively, used as process stimulus for microwave heating of multiple alumina samples within a three‐dimensional multimode cavity. The effects of such MHH schemes and target settings on electric field distribution and power absorption rates are reported in this paper. Copyright © 2003 John Wiley & Sons, Ltd.

Hybrid microwave sintering of hardmetals and graded oxide composites

Hybrid microwave sintering of hardmetals and graded oxide composites

Properties of Lead Zirconate Titanate Ceramics Determined Using Microwave and Hot-Press Hybrid Sintering Process

Piezoelectric materials play an important role in smart material and structural systems, and high-performance piezoelectric actuators with larger force and displacement output are in demand. It was shown in our previous work that the hybrid sintering process using a 28 GHz microwave technique and hot pressing offers advantages over conventional technologies reference. It was also confirmed that the maximum achieved value of piezoelectric constant d31 of the specimens of the hybrid-sintering process is approximately 360×10-12 m/V, which is about 38% larger than 260×10-12 m/V, the d31 of the conventionally sintered specimens. In this study, the material properties, including electromechanical coupling factor, Young's modulus, frequency constant, Curie temperature and dielectric constant, of the specimens fabricated with the microwave sintering process were further investigated for different sintering temperatures. The Curie point Tc decreases, but the dielectric constant εr at Tc increases with the grain size of specimens for all sintering methods. The influence of grain size on Tc and εr can be attributed to the residual stress induced by the lattice mismatch between the cubic phase and the tetragonal-rhombohedral mixed phase.

Fabrication of High-Performance Lead Zirconate Titanate Actuators Using the Microwave and Hot-Press Hybrid Sintering Processes

It has been shown in our previous work that the 28 GHz microwave sintering process can improve the performances of piezoelectric actuators. The improved performances include larger output force, higher strength and a larger electromechanical coupling factor. The improvement in performances is attributed to the repression of grain growth due to rapid heating and improvement of the microstructure because of internal heating. The sintering time was reduced to 1/10 the time needed for the conventional technology due to the larger power and uniform heating in the microwave sintering process. In this study, the microwave sintering process was combined with the hot-press sintering process for further improvement of the performances of lead zirconate titanate (PZT) actuators and the sintering conditions of the hybrid process were investigated. It was confirmed that the combination of microwave and hot-press sintering processes can improve the performances of sintered PZT. In particular, it was found that the piezoelectric constant d31 could be improved by as much as 30%.