Engineering Commons^™

Spark Plasma Sintering: From The Thermal Gradient To Advanced Ceramic Composites, Dmytro Demirskyi

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

It is well recognized that spark plasma sintering (SPS) is one of the most popular consolidation methods used to produce metal, ceramics and their composites. The better properties of the materials consolidated using SPS is usually attributed to: (i) shorter processing cycle and (ii) lower processing temperature. Hence, it is sometimes debated that there is a specific role of pulsed electric current or local thermal gradient which affect the consolidation process during SPS by changing mass-transport mechanism or local phase composition.

This work summarizes some model experiments on the initial and final stages of SPS consolidation process to verify possible …

Self-Organized Structure In Current-Activated Pressure-Assisted Densification (Capad), Sebastian Angst

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Using nanostructured thermoelectrics led to a significant improvement of the figure of merit. An easily upscalable and cheap way of producing nanostructured bulk material is current-activated pressure-assisted densification (CAPAD). This process is quite complex and it has been shown that the powder morphology gives a feedback to the process itself [1,2]. We investigated the influence of particle properties of binary mixtures on the evolving structure. For this purpose we use a network model [3] based on the Onsager-de Groot-Callen theory. In the simulations we find that depending on the difference between the Seebeck coefficients of both materials either a well …

Fabrication Of A Vitreous Porcelain By Conventional Sintering And Spark Plasma Sintering, Wirat Lerdprom

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

A vitreous porcelain body was fabricated by a conventional sintering and spark plasma sintering (SPS). The effects of sintering parameters such as heating rate, dwell time, temperature, and pressure were investigated. The porcelain sintered using the SPS techniques attained higher apparent bulk density of 2.52 g/cm³ compared with a conventionally sintered porcelain, which is 2.39 g/cm³, however, both of them exhibited similar water absorption of 0.01%. The SPS sintered porcelain presented a dense microstructure, which cannot be seen in conventionally sintered porcelain products. Mineralogically, the SPS sintered porcelain contained residual albite, quartz, mullite and glass while the …

Abnormal Grain Growth In Pressure Assisted Sintering Of Bala4ti4o15, Ana Senos

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The application of compressive stresses during sintering is known to be an efficient way to eliminate porosity at lower temperatures by the direct positive effect on the sintering driving force. Therefore, it is the basis of some special sintering techniques, such as: Hot pressing (HP), Hot isostatic pressing (HIP), Hot forging (HF) and, together with the electric field, in the Electric field assisted sintering (EFAS). Despite the fact that the role of applied stress on the densification is well established, its effect on the movement of grain boundaries (GBs) for grain growth in 2D/3D ceramics has not been sufficiently addressed …

Growth Behavior Of Faceted Na1/2bi1/2tio3-Batio3 Grains In Single And Two-Step Sintering In Support For The Microstructural Evolution Principle, Seok Ko

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

We investigated the grain growth behavior in 89Na_1/2Bi_1/2TiO₃-11BaTiO₃ (mol %, NBT-11BT) at 1100 and 1200 °C, and also under two-step sintering at 1200 (first) and 1100 °C (second). When the powder compacts were sintered at 1100 and 1200 °C, the initial growth behavior was quite normal; however, the subsequent growth behavior was distinctively abnormal and moderately abnormal, respectively. This difference in growth behavior is attributed to a change in the critical driving force for appreciable migration of the boundary with temperature and can be explained by the coupling effect of the maximum driving …

Microstructure And Mechanical Properties Of Spark Plasma Sintered Tungsten-Copper– Zinc Composites, Thabiso Langa, S. Diouf

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Tungsten/Copper (W/Cu) composites, generally used for applications whereby the combination of high heat resistance, high electrical and thermal conductivity and low thermal expansion is required, are suitable for hard working conditions such as intensive electrical sparks, gouging spark erosion, surface melting, welding, material transfer etc. However, the large disparity between the melting point of tungsten (3410 °C) and that of copper (1083 °C) make their production through traditional processes very difficult. Furthermore the difficulty of approaching near theoretical densities even by using liquid phase sintering, due to the negligible mutual solubility of the constituents and high wetting angle of liquid …

Features Of Grain Growth And Grain Boundary Formation Under Microwave And Spark Plasma Sintering Conditions, Ostap Zgalat, Andrey Ragulya

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The feedback properties of particulate nanomaterials versus their structure parameters (grain size, pore size), were found much more sensitive than that in conventional materials [1-3]. Among them field assisted sintering techniques including SPS and microwave sintering (MWS) were intensively developed [4-9]. The effect of inhibited grains growth for nanomaterials was established for Field Assisted Sintering Technology [4,5,8,9].

The FAST or Spark Plasma Sintering (SPS) is a rapid rate consolidation technology where effect of electromagnetic field enhanced by external pressure. The studies of FAST densification for nano-TiN shows the possibility to substantially inhibit the grain growth and fabricate materials with grains …

Observations On Flash Sintering Of Uranium Dioxide, Kenneth Mcclellan

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The recent prioritization on development of nuclear fuels with enhanced accident tolerance has led the community to consider fuel systems that offer improvements in certain performance characteristics such as fission gas retention, oxidation resistance and thermal conduction. Advanced fuels being studied for enhanced accident tolerance often have unique characteristics that make conventional sintering routes undesirable for or incapable of yielding the required fuel pellet characteristics. For illustration, UO₂-composite fuels with second phases for increased thermal conductivity, such as SiC, can have deleterious reactions with the UO₂ fuel above operating temperatures but below temperatures required to sinter a …

Modelling And Fem Simulation Of Electric Field Assisted Sintering Of Tungsten Carbide (Wc), Sree Koundinya

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Numerical modeling of sintering and its process variants (such as Hot Pressing, Hot Isostatic Pressing (HIP), Field Assisted Sintering Technique (FAST) or Spark Plasma Sintering (SPS), etc.) has been a field of interest among researchers and industrialists due to its efficiency in predicting various sintering characteristics such as densification, volumetric and shape changes. Thus, various mathematical models have been developed over the years, where, earlier models for sintering included rheological investigations which were able to capture the macroscopic shape and volume changes of a porous body over the process of sintering and were known as phenomenological models [1]. Due to …

Densification Of Dense Nano Crystalline Zinc Oxide Under Electric Field, Olivier Guillon

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The retention of nanocrystallinity in dense ceramics is still a challenge, even with the application of stress-assisted methods like Spark Plasma Sintering. The effect of bound water combined with high heating rates seems to significantly promote the densification of zinc oxide nanoparticles. Hence, dense nano-grained ZnO could be synthesized at a temperature of only 400 °C with minimal grain growth. Microstructural analysis as well as chemical and spectroscopic methods can help identify the mechanisms involved in this peculiar behavior. The direct effect of electric field seems to be in these conditions negligible. Nevertheless, the sintering behavior can be also modified …

Application Of Microwave Energy To Consolidate Titanium Powder, R. Sadangi

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Titanium (Ti) has many attractive attributes for military, industrial, and aerospace applications including high specific strength, no magnetic signature, and excellent corrosion resistance. However, its use has been limited by high processing costs. Powder metallurgy is a cost effective way to fabricate high-quality, near-net-shape products. Consolidation of titanium powder compacts is performed in vacuum furnace and the overall processing cycle times can vary from hours to days. Microwave sintering of titanium is a recent development in powder metallurgy of titanium. Microwave sintering is energy efficient compared to conventional sintering methods due to direct microwave heating of the titanium powder compacts …

Fast One-Step Synthesis And Sintering Of Materials Promoted By Electric Fields, Lilian Menezes

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

CaCu₃Ti₄O₁₂ (CCTO) has attracted great attention because of its potential application in microelectronic devices, as showing very high ɛ′ values (~ 12,000) with good stability from room temperature to 300 °C [1]. This material is usually prepared through conventional synthesis (solid-state reaction) at 1000 °C followed by sintering at 1100 °C, for dwell times of several hours. These high annealing temperatures and times lead to ceramics with micro-sized grains, exceeding significantly 1.0 µm in most cases. Field-assisted flash sintering [2] was here considered for producing high-quality CCTO electroceramics, from a powder originally synthesized via …

Modification Of The Interdiffusion Process In The Fe–Al System By Sps And Field Assisted Sintering, Hanka Becker

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Utilizing the Spark Plasma Sintering (SPS) / Field Assisted Sintering Technology in electrically conductive samples, the pulsed direct current (DC) induces primarily Joule heating. Nevertheless, the applied DC is frequently reported to accelerate diffusion processes as compared with the conventional heating in a furnace [1]. Thereby, after SPS treatment, the microstructural evolution is changed against the conventional heat treatment even if the diffusion processes run at the same temperature [2]. These differences are attributed to various phenomena, whose characteristic significance depends on the material system. The present study of the reactive diffusion in the binary system Al-Fe aims at contributing …

Flash Sintering Of Srtio3, Fabian Lemke

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Since the first reports of flash sintering in 2010 the community is continuously growing. Several parameters have been identified to be important gaining access to flash sintering, e.g. the temperature change due to joule heating, changes in the microstructure, polarization of defects or other effects on the defect chemistry. Analyzing the process is raised to another level of complexity compared to conventional sintering.

Sintering and grain growth experiments under an electrical field are conducted with SrTiO3. The results are compared to our existing database, implying simulations of the defect-chemistry, to discriminate the most important parameters in the flash sintering process. …

Fast Sintering Of Alumina, Spinel And Yttria-Stabilized Zirconia Three-Phase Composites, David Kok

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Field assisted sintering experiments in air were carried out on multiphase ceramics composed of Al₂O₃, MgAl₂O₄ and cubic 8 mol% Y₂O₃ stabilized ZrO₂ (8YSZ) to investigate the grain boundary interactions as well as the sintering outcomes of an applied electric field. The ultimate goal is to develop a method to produce a dense nanocrystalline multiphase oxide ceramic for energy applications in extreme environments, without exposing the material to carbon contamination or a reducing atmosphere as is common in “spark plasma sintering” (SPS). Experiments were carried out in a modified …

Flash Sintering Of Tcp Bioceramics: Effect Of Particle Size And Influence On Β→Α Transition, Matteo Frasnelli

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

In this work, sintering behavior of tricalcium phosphate ceramics under the effect of an external electrical field (in Flash sintering configuration) was analyzed to obtain dense bio-resorbable components. The aim was to understand whether the application of the external E-field, which allows to reduce drastically sintering time and temperature, limits also the undesired β→α-TCP phase transition.

TCP powders were synthesized by solid state reaction and by wet synthesis though precipitation from aqueous solutions, this allowing to obtain amorphous calcium phosphate nano-particles, which were crystallized into nano β-TCP by thermal treatment. Then, cold-pressed green pellets were prepared and their sintering behavior …

Application Of Steel As An Alternative Tool Material For Field Assisted Sintering In Spa, Alexander Laptev

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) is a new method for fast processing of variety metallic and ceramic materials with unique microstructure frequently far from equilibrium. Despite an essential progress in fundamental understanding and in upscaling of this technique from laboratory to industrial scale, some challenges are still remaining. One of them is application of a tool made from material other then traditionally used graphite. The advantages of graphite are high electrical conductivity, low temperature dependence of strength and good machinability. At the same time, the strength of graphite is relatively low. This property restricts the pressure used …

Processing High Strength Low Oxide And Metal Impurity Zrb2 Ceramics Using Boron Carbide And Spark Plasma Sintering, Erica Corral

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Zirconium diboride is an ultra-high temperature ceramic (UHTC) with attractive material properties for use in extreme hypersonic flight environments and energy applications. The diboride phase is the basis for high temperature oxidation resistant UHTC composites using secondary phase reinforcements that also enhance high temperature properties of ZrB₂-based composites. However, the mechanical properties are limited by the impurity content found in the diboride source powder. Thus our work focuses on developing a methodology to process the high purity ZrB₂ using spark plasma sintering (SPS) and computational thermodynamics analysis coupled with high-resolution atomic scale electron microscopy. A clear path …

Consolidation Behavior Of Bulk Amorphous Glasses And Foils: The Effect Of Current On Devitrification Kinetics, Olivia Graeve, James Kelly, Boyao Zhang

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

We present the application of dynamic loading and rapid heating as controlling parameters for the spark plasma sintering of an ultra-high hardness and highly corrosion resistant Fe-based amorphous alloy (Fe_49.7Cr_17.7Mn_1.9W_1.6B_15.2C_3.8Si_2.4), such that sintering temperature and time can be used as independent variables for devitrification. We develop two types of in situ composites using the dynamic loading strategy and characterize the density, phase development, and microstructure. We also develop and characterize ex situ composites by adding various crystalline powders to the amorphous metal powders and explore possible …

Field Assisted Sintering: Challenges In Scale–Up From Buttons To Body Armor, Christopher Haines

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

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Field assisted sintering technology (FAST) aka spark plasma sintering (SPS) has begun transitioning out of academic research institutions and into industry and government laboratories. With this transition, there has been considerable challenges in scaling up the sample sizes from ‘buttons’ to larger prototype parts. The primary challenges lie in areas such as temperature/density uniformity, tooling/die design, and near-net-shaping. This paper will report on the results of a 5-year manufacturing technology development program which scaled up parts from 30 mm diameter buttons to 250 mm x 200 mm tiles. We will discuss the influence of tooling material and geometry on …

Spark Plasma Sintering: Comparison Between A Fully Coupled Process Numerical Simulation And Experimental Data, David Martins

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Spark Plasma Sintering (SPS) is a process for powder compaction for which the number of studies is constantly increasing due to promising results. It consists in concurrently applying a load, and a pulsed direct current of very high intensity through graphite tooling in order to sinter powders. Regarding its application to metals, its growing popularity lies in the very fast temperature increase and short cycle time driven by the Joule’s effect, which limits grain growth. However, the different and strong interactions between the different physical phenomena make the process difficult to develop and apply for routine industrial production. That motivates …

Hybrid Heated Fast/Sps With Additional Voltage Support, Jan Raethel

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Hybrid heated FAST/SPS is a technique combining two separate, independently operated heating sources (direct electrical heating and induction heating) enabling more flexible and homogeneous heating of large sized parts. New tool concepts can be applied for example consisting of a die with inner hexagonal boron nitride (hBN) isolation. This hBN liner enables a complete pass through of the current across the densified material. Additionally, these results will be accompanied by the influence of a higher voltage source attached leading to “Flash Effect” under FAST/SPS conditions. This will be demonstrated for ZrO₂- and SiC-materials. The densification behavior as a …

Microstructure Evolution In Spark Plasma Sintered Hafnium–Tantalum Carbides, Benjamin Boesl

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Hafnium carbide and Tantalum carbide are ultrahigh temperature ceramics and possess superior oxidation resistance in oxygen rich and oxygen deficient environments respectively. This study focuses on synthesizing fully dense ceramic composites with 5 different compositions (Pure HfC, HfC-20 vol.% TaC, HfC- 50 vol.% TaC, TaC-20 vol.% HfC, and pure TaC) by spark plasma sintering without any sintering aids. A detailed analysis of the microstructural evolution with varying compositions is performed. In situ indentation at high load is carried out inside a SEM chamber to understand the deformation and cracking propagation mechanism in spark plasma sintered microstructure as a function …

Microwave And Flash Processing Of Functional Materials: Are There (M)Any Similarities?, Bala Vaidhyanathan

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Electroceramic devices such as varistors and capacitors are used in most of the modern day electronic appliances and constitute a multi-billion$ market. Conventional fabrication methods of these devices involve high sintering temperatures and long processing time. Since sintering controls the electrical properties, it is necessary to develop simpler and less demanding processing methods. Microwave sintering (MS) was demonstrated to be a viable alternative for rapid processing electroceramics as they respond to the E-field component of the electromagnetic radiation. In a recent report on ‘flash sintering’ (FS) it was demonstrated that full sintering of dog-bone shaped zirconia ceramics can be achieved …

Energy Coupled To Matter For Field–Assisted Processing, Raymond Brennan, Robert Dowding, Jeffrey Zabinski

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Energy Coupled to Matter (ECM) is an emerging technology area that goes beyond the traditional limits of materials research by exploring the use of applied physics-based fields and their influence over material structures, phase development, processing, properties, and responses over multiple length scales (i.e. from atomic to macroscale). The U.S. Army Research Laboratory (ARL) defines ECM as fundamental research to discover, explore, and exploit interactions between materials and intense energy fields in order to enable significant property enhancements and unique property combinations that overcome traditional engineering tradeoffs, and allow for responsive on-demand structure-property modifications. These field-material interactions can produce outcomes …

Hybrid Heated Fast/Sps With Additional Voltage Support, Jan Raethel

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Hybrid heated FAST/SPS is a technique combining two separate, independently operated heating sources (direct electrical heating and induction heating) enabling more flexible and homogeneous heating of large sized parts. New tool concepts can be applied for example consisting of a die with inner hexagonal boron nitride (hBN) isolation. This hBN liner enables a complete pass through of the current across the densified material. Additionally, these results will be accompanied by the influence of a higher voltage source attached leading to “Flash Effect” under FAST/SPS conditions. This will be demonstrated for ZrO₂- and SiC-materials. The densification behavior as a …

Ceramics Sintering And Shaping Using The Electrical Field Assisted Sintering Method, Amiya Mukherjee, Troy Holland

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Ceramic powders are often produced by sol-gel method or by pyrolysis of some form of precursors. This presentation will emphasize the consolidation of such powders using the Electrical Field Assisted Sintering (EFAS) method. The role played by the external electrical field and/or the heating rate will be specifically investigated. This observation will be supported by in-situ sintering studies inside a TEM in the presence of a biased electrical voltage.

One can take advantage of the EFAS process to produce functionally graded material by using asymmetric die design. Similarly, one can consolidate, as well as form to shape, ceramic components in-situ …

Flash Sintering: New Opportunities, Salvatore Grasso

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

It is well know that due to both localized heating and the reduced sintering time in Spark Plasma Sintering (SPS), processing can produce a significant energy saving and metastable microstructures if compared to Hot Pressing [1]. In order to further improve the energy saving we have developed a very rapid sintering technique called Flash SPS (FSPS) with heating rates in the order of 10⁴-10⁵ ᵒC/minute. Unlike the Flash Sintering based on high voltage, FSPS is based on low voltage and it can be up-scaled to samples volumes of several tens of cubic centimeters. Flash SPS …

Growing Larger: Scaling Up During Spark Plasma Sintering Of High– Temperature Ceramics, Oleg Vasylkiv

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Recently, extensive efforts were made towards investigation and development of spark plasma sintering (SPS) as a promising technique for rapid densification of ceramics at relatively low temperatures. In this respect, SPS was used for various processes and materials including fabrication of bulk metals and ceramics and their composites. Furthermore, this ‘low temperature’ processing allowed consolidation of ceramics with strong covalent bonding to the full density. However, significant gap exists between the technological and fabrication achievements to the fundamental understanding of the SPS mechanisms. This gap is due to the complexity of the thermal, electrical and mechanical processes that may be …

Field Effects During Consolidation Of Metallic Powders, Brandon Mcwilliams

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

High electric current has been shown to enhance sintering kinetics during consolidation of many ceramic and metallic based powder materials using the process known as Electric Field Assisted Sintering (EFAS) or Spark Plasma Sintering (SPS). More recently, processes employing higher voltages and electric field strengths than these “current assisted” techniques have been shown to dramatically increase the sintering kinetics in ceramic materials in what has become known as “flash sintering”. While much work has been conducted in the area of ceramics little attention has been paid to higher field processing of metallic powders, and in general, the fundamental mechanisms governing …