Charles Maniere | San Diego State University (original) (raw)

Papers by Charles Maniere

Journal of Materials Science, 2015

Intermetallics, 2017

Spark Plasma Sintering (SPS) is a process which allows powder densification, applying simultaneou... more Spark Plasma Sintering (SPS) is a process which allows powder densification, applying simultaneously a uniaxial external load and pulsed direct current of very high intensity through tools. This process is attracting significant attention, with a tremendous increase of studies in the metal powder densification field. Its growing popularity lies in the very fast heating rate and short cycle time driven by the Joule effect, which limits grain growth. However, this process implements different coupled electrical, thermal and mechanical phenomena. All this makes the process difficult to develop and to apply for routine industrial production, which has motivated the development of numerical simulation tools in order to understand and optimize the process. Up to now, very few models integrating the coupling between heat generation, electric transfer and mechanics have been proposed. In particular, a numerical predictive model for powder densification requires a good understanding of the mechanical behavior, in our case a viscoplastic compressive law (Abouaf mechanical model). In this article, we will discuss the characterization of the material during densification, focusing on the creep behaviors of dense and porous state materials used to simulate sintering in the Abouaf framework. Validations of the creep law parameters and also of the densification parameters will be presented and subsequently discussed.

Graphical Abstract Abstract: One of the main contemporary challenges of sintering simulations is ... more Graphical Abstract Abstract: One of the main contemporary challenges of sintering simulations is taking into account all the coupled physics present in the sintering process. The model should predict the convection, surface to surface radiation, conduction, specimen sintering phenomena, and also the proportional integral derivative regulation. A fluid dynamics thermo-mechanical model (FDTM) is implemented to predict the degree of uniformity of heating and compaction of a large size gear shape specimens under various process conditions. The FDTM model is validated by a dilatometer test indicating a very good agreement with the experimental data. The complex shape sintering simulation shows that the temperature and densification gradients depend strongly on the sample thickness. A large volume of material can be easily heated if the specimen's shape allows the hot gas to make its way inside the sample volume. If this condition is not satisfied, it is shown that a large and closed volume of material can generate significant temperature and density gradients.

The stability of the proportional-integral-derivative (PID) control of temperature in the spark p... more The stability of the proportional-integral-derivative (PID) control of temperature in the spark plasma sintering (SPS) process is investigated. The PID regulations of this process are tested for different SPS tooling dimensions, physical parameters conditions, and areas of temperature control. It is shown that the PID regulation quality strongly depends on the heating time lag between the area of heat generation and the area of the temperature control. Tooling temperature rate maps are studied to reveal potential areas for highly efficient PID control. The convergence of the model and experiment indicates that even with non-optimal initial PID coefficients, it is possible to reduce the temperature regulation inaccuracy to less than 4 K by positioning the temperature control location in highly responsive areas revealed by the finite-element calculations of the temperature spatial distribution.

An optimized process for the densification of a complex shape part is studied. Production of samp... more An optimized process for the densification of a complex shape part is studied. Production of samples with a complex shape is very difficult in uniaxial die compaction processes because of the thickness differences responsible for densification inhomogeneities. To solve this problem in the case of a particular shape, we propose a solution consisting of homogenization of the shrinkage distances by means of the use of a sacrificial material. This solution was first studied by a finite element approach and then tested experimentally. We obtained a part of complex shape with an overall relative density of 99% and a homogeneous microstructure.

In order to model the current density distribution and the temperature changes of the tools used ... more In order to model the current density distribution and the temperature changes of the tools used during a spark-plasma-sintering (SPS) cycle, the variation of the power delivered by an SPS machine and the graphite-Papyex ® -graphite electrical contacts were studied experimentally. The electric device was also characterized; in particular current pulse characteristics and their behavior with time were studied in various conditions of temperature, pulses sequences, materials and total electric power dissipated. It is well known that the performance of an electric contact is dependent on the applied pressure and the temperature. First, by varying the pressure during the SPS cycle the effect of the electric contacts is clearly seen. Secondly, in order to determine the behavior of such contacts experimentally over a pressure range of 10-50 MPa and temperatures of 50-800 • C, a Doehlert experimental design was used.

Please cite this article as: C. Manière, et al., A predictive model to reflect the final stage of... more Please cite this article as: C. Manière, et al., A predictive model to reflect the final stage of spark plasma sintering of submicronic αalumina, Ceramics International (2016), http://dx.

The powder/die friction phenomenon is known to generate densification inhomogeneities in the spar... more The powder/die friction phenomenon is known to generate densification inhomogeneities in the spark plasma sintered sample. The measurement of a powder/solid friction coefficient at high temperature is very difficult if not impossible by classical means. Then, an experimental/simulation method of identification of the friction coefficient based on the sample displacement field is introduced. This reveals that the friction of contact type powder/wall is low and about 0.1 and the friction type powder/graphite-foil/wall is close to zero. The relative density inhomogeneities are limited to a maximum difference of 3%.

Direct microwave heating of 3Y-ZrO 2 is studied at frequency of 2.45 GHz. Different conditions of... more Direct microwave heating of 3Y-ZrO 2 is studied at frequency of 2.45 GHz. Different conditions of input power, sample position and size are tested. For the first time, the experimentally known instability of microwave sintering is explained coupling the effective medium approximation and finite-element method. We show how the material dielectric permittivity imaginary part which increases with temperature and relative density encourages high hot spot phenomena. It is shown that the sample location has a great impact on the temperature distribution and decreasing the sample size promotes temperature homogenization thereby assisting the overall sintering stabilization.

Direct and hybrid microwave sintering of 3Y-ZrO 2 are comparatively studied at frequency of 2.45 ... more Direct and hybrid microwave sintering of 3Y-ZrO 2 are comparatively studied at frequency of 2.45 GHz. Using the continuum theory of sintering, a fully coupled electromagnetic-thermal-mechanical (EMTM) finite element simulation is carried out to predict powder samples deformation during their microwave processing.

One of the main challenges for the industrialization of the spark plasma sintering (SPS) is to re... more One of the main challenges for the industrialization of the spark plasma sintering (SPS) is to resolve issues linked to the compaction of real parts with complex shapes. The modeling of powder compaction is an interesting tool to predict how the densification field varies during sintering. However, expressing the behavior law which reflect the powder compaction is often a difficult and long step in the model establishment. In this paper, a simple methodology for the identification of the densification parameters is proposed. Dense and porous creep tests combined with SPS die compaction tests are employed to determine a complete densification law on a Ti-6Al-4V alloy directly in a SPS machine. The compaction model obtained is successfully validated through prediction of the densification of new SPSed samples.

In the present paper, we studied the sintering of a submicronic a-alumina powder and modeled its ... more In the present paper, we studied the sintering of a submicronic a-alumina powder and modeled its behavior using Olevsky's model. We further introduced a method for the identification of the creep parameters based on SPS experiments that greatly simplify parameter determination. Subsequently, we used the set of parameters obtained to study the densification of a part with a complex shape. We clearly showed that the thickness shrinkage with different heights engender densification inhomogeneities.

Heating in spark plasma sintering is a key point of this manufacturing process that requires adva... more Heating in spark plasma sintering is a key point of this manufacturing process that requires advanced simulation to predict the thermal gradients present during the process and adjust them. Electric and thermal contact resistances have a prominent role in these gradients. Their determination is difficult as they vary with pressure and temperature. A calibration method is used to determine all of the contact resistances present within tools of different sizes. Ex situ measurements were also performed to validate the results of the in-situ calibrations. An extended predictive and scalable contacts model was developed and reveals the great importance and diversity of the contact resistances responsible for the general heating of the column and high thermal gradients between the parts. The ex/in situ comparison highlights a high lateral thermal contact resistance and the presence of a possible phenomenon of electric current facilitation across the lateral interface for the high temperatures.

Electrical and thermal contact Papyex Finite element method a b s t r a c t Spark plasma sinterin... more Electrical and thermal contact Papyex Finite element method a b s t r a c t Spark plasma sintering (SPS) is a breakthrough process for powder consolidation assisted by pulsed current and uniaxial pressure. In order to model the temperature variations of the tools during a SPS cycle, the Graphite-Papyex-Graphite contact phenomena are studied experimentally and modeled by finite element calculations. Compared to conducting materials, the thermo graphic image of an insulating sample (alumina) shows strongly localized heating along the Papyex implying contact effects are predominant. The aim of this modeling study is to determine the main contact phenomena due to Papyex. It is based on numerous experimental data and studies the case of alumina sintering. Finally the contact model is confronted to experimental thermal images.

Copper dog-bone specimens are prepared by one-step spark plasma sintering (SPS). For the same SPS... more Copper dog-bone specimens are prepared by one-step spark plasma sintering (SPS). For the same SPS cycle, the influence of the nature of the die (graphite or WC-Co) on the microstructure, microhardness, and tensile strength is investigated. All samples exhibit a high Vickers microhardness and high ultimate tensile strength. A numerical electro-thermal model is developed, based on experimental data inputs such as simultaneous temperature and electrical measurements at several key locations in the SPS stack, to evaluate the temperature and current distributions for both dies. Microstructural characterizations show that samples prepared using the WC-Co die exhibit a larger grain size, pointing out that it reached a higher temperature during the SPS cycle. This is confirmed by

nanopowders and unusual phases can be retained at the nanoscale. The effect of strain and surface... more nanopowders and unusual phases can be retained at the nanoscale. The effect of strain and surface energies on the stabilization of metastable polymorphs has been evidenced. Besides, because of the large coupling between spontaneous lattice strain and polarization, ferroelectric properties are dependent on grain size in ferroelectric ceramics. Below a critical grain size, which depends strongly on the processing conditions, a decrease of the tetragonal distortion and thus a stabilization of the cubic phase are observed. Zhao et al. have provided new insights in size effect through a systematic investigation of crystal structure, phase transitions, and permittivity, performed on highly densifi ed nanocrystalline BaTiO 3 ceramics (50-1200 nm) obtained using spark plasma sintering (SPS). An additional contribution when referring to nanocrystals lies in the presence of hydroxyl defects, which can drastically affect the surface energy. As a consequence, controlling composition, defects, particle size, and crystallinity is mandatory to master the dielectric properties. This represents a major issue to face the drastic expectations in the fi eld of ferroelectric ceramics for electronic applications. However, producing well-crystallized sub-50 nm grains of narrow size distribution over a whole solid solution and keeping such fi ne grain size within the fi nal ceramic is still challenging. Although the grain size effect in BaTiO 3 has been largely reported in literature, only few studies are devoted to nanostructured barium strontium titanate ceramics (Ba 1− x Sr x TiO 3 0 ≤ x ≤ 1). Both the synthesis route used to produce the initial particles and the shaping process are major steps to reach a reliable buildup of the nanostructured materials. We emphasize here the advantages of combining supercritical fl uid synthesis and spark plasma sintering to produce functional nanostructured ceramics. These fast processes allow an accurate control of size, chemistry, and crystallinity leading to an appropriate control of the properties at the nanoscale. The supercritical fl uid method offers continuous, scalable, fast, and facile routes toward well-crystallized tailormade oxide nanoparticles. The accurate control of size through the process operating parameters can give access to the critical size of nanostructures as exemplifi ed by crystalline ZrO 2 . A critical particle size of 5-6 nm for monoclinic ZrO 2 is obtained and either monoclinic or tetragonal zirconia phases can be obtained in the continuous supercritical reactor. Beyond size Ferroelectric materials are highly sensitive to grain size reduction because strain and ferroelectric polarization have a direct connection. Using 15 nm (Ba,Sr)TiO 3 particles obtained by advanced supercritical synthesis and their densifi cation by high-pressure spark plasma sintering under air, reproducible and dense nanostructured ceramics are achieved. Taking advantage of the high pressure (up to 600 MPa) applied during the sintering step, the internal stress generated at the grain scale can be monitored to compensate for the particle surface stress due to size effect. Both the local dynamics observed by Raman scattering and the overall dielectric behavior consistently indicate a recovery of the ferroelectric properties as the sintering pressure is increased. This unique behavior shows that low-temperature and high-pressure processing enables designing nanostructured functional ceramics exhibiting original properties.

Journal of Materials Science, 2015

Intermetallics, 2017