Pulse Electric Current Sintering Process Research Articles

Effect of two-step heating on transparency of MgAl2O4 ceramics fabricated by pulsed electric current sintering process

In this work, MgAl2O4 transparent ceramics was fabricated from combustion-synthesized nanopowders by pulsed electric current sintering (PECS) combined with two-step sintering. Ceramic powder was densitified using two-step heating, namely the first-step temperature was 1100 oC with holding time of 60 min and the second-step temperatures in range from 1300 oC to 1450 oC with 20 min duration. The results showed that the transparent ceramic samples sintered at 1100 oC/60 min – 1400 oC/20 min had grain size of 177 ± 8 nm, relative density about 99 %, transmittance up to 80 %, and Vickers hardness of 18 GPa. These values were higher than that of samples obtained by one-step sintering at 1400 oC.

One-step rapid synthesis of n-type Y-doped Mg3Sb2 by pulsed electric current sintering and investigation of its thermoelectric properties

The one-step rapid synthesis of n-type Y-doped Mg3Sb2 semiconductors (Mg3Sb2Yx; x = 0.000–0.05) has been performed via a pulsed electric current sintering process using Mg, Sb, and Y2O3 starting powders. The synthesized samples are composed of an α-Mg3Sb2 phase and a trace MgO phase. Because of the Y doping into Mg3Sb2, the room-temperature electron concentration increases up to ~7.6 × 1019 cm−3, which is considerably higher than the maximum values obtained for previously reported Te-doped Mg3Sb2 (~2 × 1019 cm−3). In the samples with the composition of x = 0.01–0.03, a dimensionless thermoelectric figure of merit of ~1.0 at 773 K is achieved by increasing the value of the thermoelectric power factor.

DENSIFICATION AND MECHANICAL PROPERTIES OF FEMN13-TiC COMPOSITES FABRICATED BY PULSED ELECTRIC CURRENT SINTERING PROCESS

In the present work, FeMn13-40 wt.% TiC composites was fabricated by pulsed electric current sintering (PECS) process at different temperatures between 990 and 1020°C under a pressure of 60 MPa with a holding time of 5 min in the vacuum. Phase identification was done using the X-ray diffraction. The relative density, the microstructure and the hardness of the samples were characterized. The results showed that the relative density of FeMn13-TiC composites increased with the increase of sintering temperature. The lowest porosity (3.84%) and the highest hardness (70.54 HRC) of the sample were achieved by PECS process, namely sintering at the temperature of 1020°C under the applied pressure of 60 MPa for 5 min.

Synthesis and Properties of Pulsed Electric Current Sintered AlN/Cu Composites

ABSTRACTThis research shows the development of alternative Cu-based materials for applications where enhanced thermal properties are desired. Cu/AlN composites were fabricated from mixtures of pure Cu and copper plated AlN-Cu composite powders. The ceramic phase was added in amounts of 10, 20 and 30 vol.% and the mixtures sintered by pulsed electric current sintering process (PECS). The results showed that the AlN particles are homogeneously distributed in the copper matrix and that the true contacts between hard particles are reduced because of the deposited copper on their surfaces, improving the connectivity of the matrix phase and bonding at the metal-ceramic interface. The relative density of the Cu/AlN composites was major than 97% in all cases. Thermal conductivity of the composites was high and decreased with the ceramic content from 359 to 194 W/mK, for 10 and 30% AlN, respectively. The coefficient of thermal expansion followed a lineal behavior with temperature and is also reduced with the ceramic content.

Heterogeneity of grain refinement and texture formation during pulsed electric current sintering of conductive powder: A case study in copper powder

The heterogeneity of grain refinement and texture formation in conductive copper powder during pulsed electric current sintering have been investigated by means of microstructural analysis of the particle-contacting zone of the samples sintered with micron-sized powders. The particle-contacting region was indicated to experience a higher level of grain refinement than the particle center due to the inhomogeneous temperature distribution among the particle when pulsed electric current passed through. Meanwhile, two main textures of Cube (1 0 0)[0 0 1] texture and Goss (1 1 0)[0 0 1] texture were directly detected in the sintered Cu samples by a combination of electron backscatter diffraction and X-ray diffraction. Based on the experimental results, a feasible mechanism for the formation of texture during the pulsed electric current sintering has been proposed by considering the applied uniaxial pressure and pulsed electric current as well as the rearrangement of grains. In addition, the effects of heterogeneous grain refinement and texture formation on the tensile properties of the sintered Cu samples were also discussed based on the tensile properties and fractographic. These results would contribute to the basic understanding of the sintering mechanisms in pulsed electric current sintering process.

Development of a novel TiNbTa material potentially suitable for bone replacement implants

A novel (β+γ)-TiNbTa alloy has been developed by a combined low energy mechanical alloying (LEMA) and pulsed electric current sintering process (PECS). Microstructurally, this material presents interesting characteristics, such as a submicrometric range of particle size, a body-centered phase (β-TiNbTa) and, mainly, a novel face-centered cubic Ti-based alloy (γ-TiNbTa) not previously reported. Related to mechanical performance, the novel (β+γ)-TiNbTa shows a lower E (49±3GPa) and an outstanding yield strength (σy>1860MPa). This combination of original microstructure and properties makes to the (β+γ)-TiNbTa a novel material potentially suitable as biomaterial to fabricate bone replacement implants, avoiding the undesirable and detrimental stress-shielding problem and even the usual damage on the mechanical strength of Ti-based foams biomaterials.

Densification and mechanical properties of pulsed electric current sintered B4C with in situ synthesized Al3BC obtained by the molten-salt method

The in situ generated ternary compound Al3BC shows good dispersion on the surfaces of B4C particles (10±0.6μm), obtained using the molten-salt method rather than the ball-milling method, which can form a conductive network in the pulse electric current sintering process to improve the sinterability of B4C. The sintering behaviour, microstructure and mechanical properties of compacts were investigated at different sintering temperatures and Al3BC contents. The study found that the relative density, elastic modulus, Vickers hardness, and fracture toughness of samples reached as high as 100%, 495GPa, 37.0GPa, and 6.32MPam1/2 at 1700°C, respectively, when the content of Al3BC was 18wt.%. The crack propagation mode can provide an explanation for the higher toughness than that of pure B4C (3.19 MPam0.5). Additionally, the good dispersion of Al3BC in B4C was found to change the fracture mode from the single transgranular mode to a mixture of intergranular and transgranular modes. The compositions of the compacts were almost pure B4C.

Electromagnetic radio frequency heating in the pulsed electric current sintering (PECS) process

Abstract

Formation of M<sub>5</sub>Si<sub>3</sub> Type Si-Ti-Zr System Intermetallic Compounds by Pulse Electric Current Sintering with Self-Propagating High Temperature Synthesis

Pulse electric current sintering (PECS) is applied to synthesis M5Si3 type Si-Ti-Zr system intermetallic compounds, Si3TixZr(5-x) x=0-5, directly from raw powders of silicon, titanium and zirconium. Almost full conversion to Si3TixZr(5-x) are achieved by PECS method with self-propagating high temperature synthesis (SHS) reaction. The adiabatic temperatures are susceptible to sintering behaviors such as vacuum pressure in chamber and displacement of pressure axis on the PECS process. The large quantities of gases are released in Zr-rich samples. The bulk shapes with almost dense samples are obtained at Ti-rich samples.

Energy-Saving Sintering of Electrically Conductive Powders by Modified Pulsed Electric Current Heating Using an Electrically Nonconductive Die

Sintering of Cu and thermoelectric Ca3Co4O9 was tried using a modified pulsed electric current sintering (PECS) process, where an electrically nonconductive die was used instead of a conventional graphite die. The pulsed electric current flowed through graphite punches and sample powder, which caused the Joule heating of the powder compact itself, resulting in sintering under smaller power consumption. Especially for the Ca3Co4O9 powder, densification during sintering was also accelerated by this modified PECS process.

Nanomaterials Processed by Spark Plasma Sintering

The spark plasma sintering (SPS), a variant of field-assisted sintering (FAST) or pulsed electric current sintering (PECS), is a novel pressure assisted pulsed electric current sintering process, which utilizes ON-OFF DC pulse energizing. Due to the repeated application of an ON-OFF DC pulse voltage and current flow between powder particles, the spark discharges and the Joule heating (local high temperature state) are therefore dispersed to the overall specimen.The SPS process is based on the electrical spark discharge phenomenon and is a high efficient, energy saving technique with a high heating rate and a short holding time. The problem of rapid grain growth of nanomaterials during conventional sintering can be inhibited to a larger extent by using the SPS technique. The SPS can be used for diverse novel bulk material applications, but it is particularly suitable for the processing of nanomaterials. Despite such anticipated advantages, the optimization of the process window (heating rate-temperature-time) in SPS process is a challenging task. More importantly, the underlying mechanisms for superfast densification still remains to be explored.

Bloating in (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055%PbI2 Thermoelectric Specimens as a Result of Processing Conditions

Lead chalcogenides such as (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055%PbI2 have received attention due to their encouraging thermoelectric properties. For the hot pressing (HP) and pulsed electric current sintering (PECS) techniques used in this study, decomposition reactions can generate porosity (bloating). Porosity in turn can degrade electrical, thermal, and mechanical properties. In this study, microstructural observations (scanning electron microscopy) and room-temperature elasticity measurements (resonant ultrasound spectroscopy) were used to characterize bloating generated during post-densification anneals. Although every HP specimen bloated during post-densification annealing, no bloating was observed for the PECS specimens processed from dry milled only powders. The lack of bloating for the annealed PECS specimens may be related to the electrical discharge intrinsic in the PECS process, which reportedly cleans the powder particle surfaces during densification.

Effects of pressure and temperature on sintering of Cr-doped Al2O3 by pulsed electric current sintering process

The aluminium oxide crystal, Al2O3, which contains a small amount of chromium, Cr, is called ruby. Pulsed electric current sintering (PECS) was applied to sinter ruby polycrystals. Cr2O3-Al2O3 powder mixture prepared by drying an aqueous slurry containing amounts of Al2O3 and Cr(NO3)3 was consolidated by PECS process. The PECS process was performed in vacuum at sintering temperature raging from 1100 to 1300°C with heating rate of 2 K/min under applied uniaxial pressure varied from 40 to 100 MPa. This study found that highly densified and transparent Cr-doped Al2O3 can be obtained by the PECS process with the high applied pressure at sintering temperature of 1200°C.

パルス通電焼結法を応用したオーステナイト系ステンレス鋼へのCr-Si系金属間化合物皮膜の調製

Cr-Si intermetallic compound coatings were coated on an austenitic stainless steel SUS310S substrate by pulsed electric current sintering process to improve its wear and oxidation resistances. The coating was carried out for 0.6-10.8 ks at 1073-1323 K at a coating pressure of 60 MPa. As a result of pin-on-disk wear test, the wear property of the coatings was more excellent than that of the substrate. The tensile strength of the coatings was 10-20 MPa. These coatings fractured at the interface between the coatings and the substrate during tensile test. As a result of hot hardness test, the coatings showed higher hardness than the substrate, even at high temperature. Hardness of the coatings fell gradually up to the transition temperature of 870 K and decreased rapidly on further heating. As a result of oxidation-testing for 700 ks at 1123 K, the mass increase of the coatings after oxidizing was less than that of the substrate. These results indicate that wear resistance and strength at elevated temperature could be given to the substrate without deteriorating oxidation resistance.

Preparation of Homogeneous Nb-Al Intermetallic Compound Sheet by Multi-Layered Rolling and Subsequent Heat Treatment

The intermetallic compound Nb3Al is widely investigated because of its high temperature strength, superior superconductivity and relatively small density. As Nb3Al has an extremely high melting point and lack of deformability, it is impossible to prepare it by using the conventional metallurgy. In this study, a Nb-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Nb and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Nb/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Nb/Al sheet. Accumulated foils were roll-bonded at 573 K. The rolling reduction at 1 pass was ~50%, and the final rolling reduction at 4 passes was ~94%. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). A homogeneous intermetallic compound of Nb3Al could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 0.9 ks at 1673 K.

Effects of Pulsed Current Waveforms on Sample Temperature and Sintering Behavior in PECS of Alumina

Pure Al2O3 powder was sintered by a pulsed electric current sintering (PECS) process with different pulse current waveforms from two types of power generators: an inverter (frequency 16 kHz) type and a pulsed direct current (DC) (frequency 300 Hz) type. The sample temperature during the PECS process as well as the sintering behavior was investigated. The effects of pulse current waveform on the sintering process were discussed. For the same die temperature ranging from 1100 to 1400°C at holding period, the sample temperature under experiments using the inverter was higher than that under experiments using the pulsed DC. Densification and grain growth were predominated by sample temperature and did not depend on the pulse current waveform directly.

Sintering of aluminium alloy powders using pulse electric current sintering process

Sintering of aluminium alloy powders using pulse electric current sintering process

Preparation of Homogeneous Fe-Al Intermetallic Compound Sheet by Multi-Layered Rolling and Subsequent Heat Treatment

Iron aluminides exhibit good resistance to high-temperature oxidizing and sulphidizing environments and have potential for structural applications at high temperatures under corrosive environments. In this study, an Fe-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Fe and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Fe/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Fe/Al sheet. Accumulated foils were rolled and bonded at room temperature or 573 K. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). Vickers microhardness testing was used for hardness determination. A homogeneous intermetallic compound of Fe3Al or FeAl could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 3.6 ks at 1173 K.

Transparent Nanometric Cubic and Tetragonal Zirconia Obtained by High‐Pressure Pulsed Electric Current Sintering

AbstractTransparent samples of cubic (8 mol % yttria) and tetragonal (3 mol % yttria) zirconia were prepared from nanometric powders by the pulsed electric current sintering process. The crystallite size of the resulting dense samples was about 50 nm in both cases. The consolidation pressure had a positive effect on the occurrence of transparency for both modifications. Transmittance in the near infrared for 1 mm thick samples is above the 60 % for the cubic (8 %YSZ) and above 50 % for the tetragonal (3 % YSZ) zirconia, representing between 70 and 80 % of the theoretical values of the two modifications. Samples had a yellowish‐brown coloration which was attributed to the presence of color centers. Annealing in oxygen improved transmittance initially, but prolonged annealing resulted in translucent samples. The role of porosity in transmittance is analyzed.

The influence of percolation during pulsed electric current sintering of ZrO 2–TiN powder compacts with varying TiN content

A series of ZrO 2–TiN composite powder compacts with varying TiN content was densified using the field assisted sintering technique, also known as spark plasma sintering or pulsed electric current sintering (PECS). The TiN content was varied between 35 and 90 vol.% in order to obtain an electrical conductive composite material that can be shaped by electrical discharge machining. The influence of the TiN content on the densification behaviour was investigated experimentally, whereas its influence on the temperature and current distribution in the PECS tool set-up was simulated using a previously developed finite element model. The predicted temperature distribution was confirmed experimentally using a double pyrometer set-up, one focusing on the outer die wall surface and one on the bottom of a borehole in the upper punch. The changing thermal and electrical properties of the sintering ZrO 2–TiN powder compacts were calculated using mixture rules. Using a double pyrometer set-up, a clear relationship could be verified experimentally between the changing electrical properties of the sintering compact and the temperature redistribution in the punch/die/sample set-up during the PECS process. The homogeneity of sintering inside the PECS equipment is discussed in detail and suggestions are made in order to promote a more homogeneous sintering process. Carbon felt, acting as a thermal insulator, was placed around the die in order to minimize the radiation heat losses and to minimize the thermal gradients during heating and the dwell period at maximum temperature. The mechanical and electrical properties of the different composite materials are discussed as functions of the TiN content.