Engineering Commons^™

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 …

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 …

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 …

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 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 …

A Dynamic Bifurcation Criterion For Thermal Runaway During The Flash Sintering Of Ceramics, Joao Gustavo

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

In this work we mathematically model the densification of ceramics under flash sintering using a model based on a system of nonlinear differential equations. Approaches to analyze the system either by numerical solutions or via bifurcation theory are presented. The shown model explains the two main features of flash sintering: A characteristic electrical field threshold dependent on the temperature, and an incubation time to flash sintering.

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 …

Generating Mgal2o4 Whiskers Using Carbothermic Reactions And Sps/Fast, Anton Salomon

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The study is focussed on the rapid generation of whisker-like magnesia-aluminate spinel (MgAl₂O₄) crystals. Two recently developed carbon-bonded refractory ceramics, pyrolyzed MgO-C and Al₂O₃-C [1], were used as the starting materials. The heating to 1600 °C was performed in a SPS/FAST device to facilitate carbothermic reactions, which resulted in the reduction of the specific oxide and the subsequent nucleation and growth of fibre-like crystals.

The research was based on a recently published study [2] that had established the possibility of the MgAl₂O₄ whisker formation in a composite structure consisting …

Discoloration Of Spark–Plasma–Sintered Transparent Mgal2o4 Spinel, Koji Morita

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

It is reported that the spark-plasma-sintered (SPSed) transparent oxides exhibit a discoloration. The discoloration is known to be more remarkable in the SPSed oxides than the HIP/HP processed ones. In order to understand the discoloration phenomena, the discoloration was investigated by spectroscopic techniques using a spinel (MgAl₂O₄) as the reference material.

The discoloration is explained by the combination of carbon contaminations and lattice defects (color centers), which are introduced in the spinel matrix depending on the SPS conditions. For high heating rate of ³50°C/min, carbon contamination occurred by evaporating the carbon phases from the carbon papers …

Exploring Length Scale–Property Relationships In Dense Nanocrystalline Materials, Javier Garay

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The influence of nano-scale defects (grain/phase boundaries, pores, etc) can be significantly different from micro-scale features. We will discuss how interfaces in nanocrystalline materials interact with light (phonons) and heat (phonons) and how precise control of these defects can be used to tune materials properties. We will start by discussing how current activated pressure assisted densification (CAPAD) can be leveraged to produce dense nanocrystalline samples by effectively overcoming the grain growth challenge. In particular the effect of the relevant processing parameters, pressure, time and temperature on grain sizes will be presented and density will be presented. We will present experimental …

Electrical Field Effects In Spark Plasma Sintering Of Hyperstoichiometric Uo2, Marco Cologna

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Recent research in the field assisted sintering of actinide oxides and nitrides has shown the great potential of the technique, but has also evidenced the need for a better understanding of the behavior of such class of materials during processing with current/fields [1-3]. Uranium dioxide, due to its multiple oxidation states and semiconductor characteristic, represents a good model material to investigate some of the peculiar effects of the electric field in the processing of materials. The stoichiometry of UO₂ is of paramount importance, since it governs its fundamental properties, such as the thermal and electrical conductivity, the diffusion coefficients …

Development Of Electric Current Activated/Assisted Sintering (Ecas/Sps), Salvatore Grasso

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The electric current activated/assisted sintering (ECAS) is an ever growing class of versatile techniques for sintering particulate materials. ECAS was pioneered by Bloxam in 1906. As illustrated in Fig. 1, ECAS development is emblematic of its technological and scientific importance. Nowadays, most of the scientific attention is focused on the Spark Plasma Sintering (SPS) technology originated in 1966 by Dr. Inoue [1].

Essentially, SPS exploits the same punch/die system concept as the more familiar hot pressing (HP) process. The powder is placed in the die and subsequently pressed between two counter-sliding punches. Mechanical loading is normally uniaxial. SPS and HP …

Ceramics Of Potassium Sodium Niobate By Field–Assisted Sintering Techniques: Spark Plasma Sintering Versus Spark Plasma Texturing, Paula Maria Vilarinho

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Potassium sodium niobate (KNN) is one of the most promising lead-free systems. However, undoped KNN has poor sinterability and by conventional sintering results in inadequate densification and, consequently, in inferior physical and electrical properties. The highly volatile alkaline sodium and potassium do not permit the increase of the sintering temperature somehow required to densify the niobium based ceramics. This conflict can be solved if the mass transport during the sintering step is enhanced, since the temperature and time needed for consolidation must be reduced in order to avoid volatilization. Among the methods reported for activation of the mass transport during …

Benefits Of Sps Sintering On Microstructure And Piezoelectric Properties Of Knn–Based Ceramics, Florian Jean

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

PZT and its derivatives exhibit a wide range of piezoelectric properties allowing their applications in transducers, actuators and sensors. However, due to the toxicity of lead for human health and environment, many studies are carried out on lead-free piezoelectric materials. Among these materials, (K,Na)NbO₃ (KNN)-based solid solutions seem to be promising candidates owing to their high dielectric, piezoelectric and mechanical characteristics shown by Saito et al. in 2004. However, reaching high density for these materials appears difficult and alkali volatilization may occur during sintering process. In order to overcome these difficulties, in the present work, K_0.5Na_{0.5 …}

Engineering Of Lightweight Ceramic Composites By Spark Plasma Sintering, Oleg Vasylkiv

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

It is well recognised that value of porosity and grain size influences mechanical properties such as fracture toughness, elastic modulus and strength dramatically. Boron carbide (B₄C), as well as other lightweight ceramics like TiB₂, B₆O requires high consolidation temperatures owing to its poor sinterability. Therefore such decrease of ceramics properties becomes a materials processing issue since during consolidation process on the final stage of sintering (either pressure-assisted or pressureless one) grain growth starts. To overcome this problem, various metallic and non-metallic binders are used to obtain dense borides. However, the presence of a metallic …

Electric Current As A Driving Force For Interphase Growth In Spark Plasma Sintered Dielectric Composites, Catherine Elissalde

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

All-oxide composites are increasingly investigated in the field of microelectronics and telecommunications because of their multi-functionalities. Dielectric properties can be tuned in ferroelectric-based composites performed by Spark plasma sintering (SPS) through a control of composition, grain size, architecture and charged defects at interfaces. Using SPS on ceramic bilayers made of ferroelectric Ba_0.65Sr_0.35TiO₃ (BST65/35) and TiO₂ dielectric phases, we show that the reactivity at their interfaces is dependent on the direction of the current and/or on the sintering temperature. The electric current promotes an interphase growth whose thickness depends on the bilayer stacking and on …

Low–Temperature Spark Plasma Sintering Of Transparent Ceramics By Using Sic Molding Set, Byung-Nam Kim

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Hydroxyapatite (HAP) and alumina ceramics were sintered at low temperatures by using the SiC molding set during spark plasma sintering (SPS). Transparent ceramics were obtained at 800 ˚C and 1000 ˚C for HAP and alumina, respectively. The SiC is electrically conductive (3x10⁴ S/m), so that the molding set (mold, punch and spacer) was directly heated during SPS without external heating. Compared to the conventional graphite molding set, the voltage level during heating was higher due to lower conductivity. When the graphite molding set was used, the temperature required for transparent HAP and alumina was about 950 ˚C and 1150 …

Microscopic Densification Mechanisms Of Metallic Systems By Spark Plasma Sintering, Jean Philippe Monchoux

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

This study reports on the microscopic mechanisms accounting for the fast densification kinetics of metallic materials processed by spark plasma sintering (SPS). Metallic systems have been chosen in reason of their elevated electric conductivity. Hence, an important fraction of the electric current of the SPS passes through the powder, and electrically induced new mechanisms, or acceleration of conventional ones (e.g. plasticity, diffusion), can be expected. TiAl powder and Ag-Zn diffusion couple have thus been chosen to study the influence of the electric current on plasticity and on diffusion, respectively.

An originality of this work was to observe by transmission electron …

Sps For Chemical Preparations, Ihor Veremchuk

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The Spark Plasma Sintering (SPS) has been developed for shaping materials by combining simultaneously uniaxial pressure (using direct contact with the sample) and the application of an direct electric field. Even though the key mechanisms controlling SPS are still debated, this technique shows a number of advantages – (i) reduction of sintering time, (ii) rapid densification and (iii) grain growth suspension – which are helpful for tailoring the microstructure of functional materials and thus optimize their electronic transport, mechanical and/or thermal properties.

The diffusion rate of SPS conditions was reported to become extremely large at relative low temperatures due to …

The Influence Of Doping On Flash Sintering Condition In Srti1–Xfexo3–Δ, Neta Shomrat

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The innovative flash sintering process raised a great interest in the past few years due to its applicability in various engineering fields and the interesting scientific questions it evokes. This technique could be beneficial in many applications since it reduces the time and cost of the sintering process. Joule heating can explain the sudden temperature rise of the sample, which enhances the rate of grain boundary diffusion. However, for a given material the temperature of the sample remains lower than the temperature at conventional sintering. Although Joule heating is a significant phenomenon, it is proposed that lattice defects and their …

Flash Sintering Of Glass Containing Alumina Bodies, Mattia Biesuz

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Flash sintering of glass containing alumina bodies

The Mechanisms Of Field Assisted Sintering In Metallic Systems, Johannes Trapp

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Using the advantages of Spark Plasma Sintering to produce superior materials, e.g. with potentially new phases, first requires a profound understanding of the densification mechanisms that are active during the process. The research presented contributes to this understanding by connecting temperature and pressure distribution in the particles with rate and activation energy of densification in pure copper.

Activation energy (Q) has been determined using a method originally developed by J. E. Dorn. Therewith, the activation energy for diffusion controlled processes can be extracted from densification rate measurements without the results being influenced by errors in measuring the density of the …

Electric Field Effects On Grain Boundary Formation And Grain Growth, Klaus Van Benthem, Hasti Majidi, Jorgen Rufner, Wei Qin

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The application of electric fields can enable the accelerated consolidation of materials during field assisted sintering, such as spark plasma sintering or flash sintering. Although such techniques are already employed for the synthesis of a wide variety of microstructures with unique macroscopic properties, a fundamental understanding of the atomic-scale mechanisms for grain boundary formation and subsequent migration in the presence of electrostatic potentials is mostly absent from the literature. We have designed experiments to specifically de-couple the effects of heating and applied electrostatic fields during consolidation. In situ transmission electron microscopy studies were carried out with new sample holder designs …

Electric Field–Assisted Flash Sintering Of Fine–Grained And High–Permittivity Cacu3ti4o12 Electroceramics, 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 …

Direct Microwave Sintering Of Gamma–Alumina Powder: Effect Of Alpha Seeding And Magnesia Doping, Carry Claude

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Microwave sintering as a rapid processing technic has been extensively investigated in the past decades. During microwave heating, the material couples with the electric field, absorbs the electric energy in its bulk and transforms it into heat. The microwave coupling behaviour depends on the dielectric loss factor. In most of pure oxide ceramics such as alumina the loss factor is very low at room temperature and increases with increasing temperature. Routinely a high dielectric loss material is used as a susceptor for heating the green specimen up to a temperature at which it significantly couples with the microwaves ; this …