Pulsed Electric Current Sintering Research Articles

Influence of electron irradiation on self‐healing and thermal oxidation of SiC dispersed yttrium silicate composites

AbstractElectron irradiation‐induced acceleration of self‐healing and high‐temperature oxidation has been discovered in SiC/Y2Si2O7–Y2SiO5 composites. Bulk samples were produced by pulsed electric current sintering. These samples were exposed to an electron beam from the pulsed intense relativistic electron beam accelerator with a beam energy of 2 MeV at irradiation doses of 10–40 kGy. The self‐healing and high‐temperature oxidation experiments were carried out at 1100–1300°C for 1–24 h in laboratory air. Electron irradiation significantly improved the self‐healing effectiveness. The closure of surface cracks was caused by the volume expansion of SiC via transformation to SiO2 and the outward diffusion of Y3+ ions. Electron irradiation also increased the thickness of the internally oxidized zone, formed by the inward diffusion of O2− ions. Enhanced self‐healing and oxidation behavior were associated with defect formation induced by electron beam exposure, which facilitated the diffusion of ions within the crystal lattice.

Electron Irradiation of Self-Healing and Internal Ooxidation of Self-Healing Ceramics

Influence of electron irradiation on self-healing and internal oxidation was studied in the present work. Usage of self-healing ceramics are very useful to improve anti-accident performance of nuclear power plants. However self-healing performance of their structural ceramics may be affected with any irradiations of several radioactive rays such as electrons, neutrons and gamma-ray. Two self-healing ceramics, alumina ceramics dispersed with nickel particles (Ni/Al2O3) and yttrium silicate ceramics dispersed with silicon carbide particles (SiC/YSiO) were selected as the samples to study the influence of electron irradiation. Their self-healing ceramics were densified with pulsed electric current sintering technique. The samples were irradiated with accelerating electrons with 2MeV at different radiation dose from 1 to 1000 kGy at room temperature. Vickers indentations were introduced into the irradiated samples to make surface cracks. Then Ni/Al2O3 samples were heated at 1100°C for 6 h in air. SiC/YSiO samples were done at 1100°C for 6 h and 1300°C for 1 h in air. Self-healing of surface cracks was evaluated with the fraction of disappearance of surface crack length against the initial crack length. Depth of the internal oxidation was measured from the cross-sectional images of scanning electron microscopy. With respect to Ni/Al2O3 ceramics, electron irradiation did not affect disappearance of surface cracks and depth of internal oxidation with the heat treatment in air. On the other hand, self-healing and internal oxidation on SiC/YSiO ceramics were enhanced with electron irradiation in the present study. Point defects in YSiO are most likely increased by electron irradiation and causes increases in inward diffusion of oxygen ions for internal oxidation and outward diffusion of yttrium ions for self-healing. On the other hand, point defects in Al2O3 are inert against the electron irradiation in the present experimental conditions.

Influence of Cutting Surface Condition and Composition on High-Temperature Oxidation Behavior of Ti2 Al C MAX Phase Ceramics

Ti2AlC, one of the MAX phase ceramics, has metal-like properties (electrical conductivity, high fracture toughness and good machinability) and ceramic-like properties (low density, high-temperature oxidation resistance and high bending strength). Ti2AlC ceramics can be cut with cemented carbide tools and the mechanical strength does not decrease significantly after cutting. Ti2AlC ceramics have potential as high-strength machinable ceramics for use in high temperature components. However, the oxidation resistance of Ti2AlC ceramics decreases after cutting because the cutting damages inhibit the formation of protective Al2O3 scale. There are few discussions on the effect of cutting surface conditions on oxidation resistance of Ti2AlC ceramics. The continued growth of the protective Al2O3 scale requires a sufficient Al supply during high-temperature oxidation. The oxidation resistance of Ti2AlC ceramics is reduced when a non-protective TiO2 scale forms on the surface. As one of the common methods to prevent the growth of the TiO2 scale is Nb addition in Ti-based alloys and compounds. The oxidation resistance of as-machined Ti2AlC ceramics may be improved by increasing the amount of Al and Nb additions. This study reports the influences of cutting surface conditions and composition on oxidation behavior of Ti2AlC ceramics. Commercial Ti, Al, C and Nb powders were mixed in Ti:Al:C:Nb molar ratios of 2:1.2:0.9:0 and 1.9:1.2:0.9:0.1 with the corresponding samples receiving the designations Al1 and Al1.2Nb. The powder mixture was annealed for 12 h in a vacuum at 1300°C. The synthesized powder was consolidated over 15 min using a pulsed electric current sintering technique at 1300°C, in a vacuum, and under a uniaxial pressure of 30 MPa. The phases present in the sintered samples were also identified by XRD. Milling tests were performed on a 4 x 4 mm sample surface using a 2 mm diameter end-mill mounted on a plane milling machine. Dry cutting was performed with a spindle speed, feed rate, and cut depth of 4000 rpm, 46 mm/min, and 100 μm. Threading tests were cut into an JIS-M6 bolt shape with a thickness of 3 mm with a lathe and diamond saw. The surface roughness of each sample was measured using a surface texture measuring instrument. The samples were heated in an electric furnace at 1200°C for 4 h in laboratory air. The surface and cross-sections of the oxidized samples were observed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX).The main peaks of all sintered samples in these XRD patterns were identified as originating from Ti2AlC and minor peaks originating from TiAl3 (Al-rich phase). The average arithmetic mean roughness (R a) values of the end-milled and threaded surfaces were 0.8 and 4.5 μm. The SEM and EDX results show that a continuous Al2O3 scale formed on the end-milled surface of Al1.2 and Al1.2Nb after the oxidation test. The results of SEM and EDX investigations indicate that a non-protective TiO2 scale had formed on the threaded surface of Al1 and a continuous Al2O3 scale with a thickness of less than 4 μm was formed on the threaded surface of Al1.2Nb after the oxidation test. The Al-rich phase provided the Al necessary for the formation of a continuous Al2O3 scale on the end-milled surface. The oxidation resistance of Ti2AlC ceramics was greatly reduced in the case of screw-like shapes with high R a values and many corners on the cutting surface. The addition of Nb improves the oxidation resistance of Ti2AlC ceramics under such cutting surface conditions. The cause of non-protective oxidation was the destruction of the Al2O3 scale because of the growth of TiO2 scale. The TiO2 scale tends to form at corners where continuous Al2O3 scale formation is difficult. One of the factors that improves the oxidation resistance of Ti2AlC ceramics with screw shapes is the suppression of TiO2 growth by Nb addition. The higher Al concentration and the addition of Nb remarkably increase the oxidation resistance of the Ti2AlC ceramics after cutting.

Effect of addition on microstructures and mechanical properties of cBN/Cu-Zn-Ti composites via the pulse electric current sintering

In order to improve the performance of metal-bonded grinding wheels, the cBN/Cu-Zn-Ti composites were fabricated by pulse current sintering with several different Co contents (i.e., 5, 10, and 15 wt%) were added. The specimen microstructure, interfacial analysis and fracture morphology of pulse current sintering cBN grain were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The mechanical properties of hardness, wear resistance, and three-point bending strength of the fabricated specimens were tested. The electrochemical properties was also tested. The specimen shape fabricated by pulse current sintering using the composite Cu-Zn-Ti alloy doped by Co was better than pure Cu-Zn-Ti alloy. The microscopic analysis revealed that TiB2 and TiN were maintained between the Cu-Zn-Ti composites and cBN. With the addition of Co, the hardness, flexural strength and wear resistance of the specimens are improved. The new phase CoTi3 enhancing strength of the metal composite via the Orowan mechanism. The S5 specimen containing 15 wt% Co particles has the highest flexural strength, which is 485.83 MPa and satisfies the requirements of high speed grinding. Meanwhile, when the Co content reaches 10 %, the lowest friction coefficient (0.217) and lowest wear rate (0.81 mg) are achieved for the sample. With the addition of Co, the corrosion resistance of the material is significantly improved.

Effects of sintering temperature and pressure on fabrication of porous Al2O3 by pulsed electric current sintering process

Effects of sintering temperature and pressure on fabrication of porous Al2O3 by pulsed electric current sintering process

Influence of HEA reinforcement on pulse electric current sintered Aluminium Composites: Microstructure, Density, and nanomechanical properties

This study investigates how different compositions of high-entropy alloys (HEAs), known for their strength and thermal stability, affect the microstructure, density, and nanomechanical properties of aluminium matrix composites produced by pulse electric current sintering (PECS). Commercial aluminium was reinforced with 5%, 7%, and 10% HEA and sintered using PECS. Microstructural analysis showed improved particle bonding and dispersion, resulting in enhanced mechanical properties. Although relative density slightly decreased with higher HEA content, there was a significant enhancement in nanohardness and elastic modulus. The composites exhibited improved resistance to plastic deformation and increased stiffness, thus, highlighting the effectiveness of HEA reinforcement in optimizing aluminium composites for high-strength, lightweight, and advanced engineering applications. These findings offer valuable insights for developing next-generation materials suited to demanding engineering environments.

Microstructure, phase evolution and mechanical properties of nickel-silicon carbide reinforced Ti6Al4V alloy processed by pulsed electric current sintering

In this work, fully densified Ni–SiC reinforced Ti6Al4V matrix composites were consolidated by pulsed electric current sintering (PECS) technique. The microstructural evolution and mechanical properties of the developed composites with varying SiC contents were investigated. The microstructural study revealed in-situ precipitation of TiC, Ti5Si3 and Ti3SiC2 strengthening phases within the composites. The α colony size in the composites was notably reduced compared to the fabricated SiC-deficient samples due to the addition of SiC additive into the Ti6Al4V alloy matrix. The in-situ precipitated phases enhanced the mechanical properties of the composites. Composite reinforced with 10 wt% SiC (TNi10SiC) displayed the highest hardness value of 609.8 ± 50.9 HV0.5 among the sintered samples, translating to an increment of about 88 % compared to the unreinforced sample T. Among the sintered samples, the highest flexural strength of 2094.32 ± 97.67 MPa was obtained for the TNi5SiC composite, after which the flexural strength deteriorates with increasing SiC content as witnessed in TNi10SiC composite with the least flexural strength of 863.67 ± 71.57 MPa due to agglomeration of the reinforcement phases within the composite. Samples reinforced with 0 wt% SiC experienced a ductile fracture, and the composites containing 2.5 wt% - 5 wt% SiC content witnessed intergranular and interlamellar fractures. However, at higher SiC content, reinforcement pull-out and debonding of the agglomerated reinforcement phases predominates, and composites fail by brittle fracture.

Formation of macroscopic black dots in transparent alumina ceramics prepared by pulsed electric current sintering

Transparent alumina ceramics produced by pulsed electric current sintering (PECS) include black dots, which can be observed with the naked eye. These black dots have porous structures caused by the aggregates in the raw powder. In order to investigate the detailed mechanism of black dot formation, transparent alumina ceramics were prepared by sintering α-alumina granules to produce large pseudo-aggregates and introducing them into α-alumina powder for PECS. Macroscopic black dots were formed in the sample. Characteristic Raman peaks of graphite were detected in porous parts of these macroscopic black dots. Analysis of gas phases generated from graphite sheets for PECS suspected to be involved in carbon contamination showed CO and CO2 generation. In thermodynamic calculations on carbon activity during PECS, gas phase including CO and CO2 generated from the hot graphite mold/sheet permeates the porous part of the cold sample, and the carbon activity of gases including CO and CO2 on the porous surface theoretically exceeds unity. Then, CO is adsorbed and decomposed on the porous surface, resulting in carbon contamination. The formation of macroscopic black dots is caused by carbon deposition in agglomerates of the raw powder from CO generated by graphite sheets during PECS.

Densification, microstructure, and nanomechanical evaluation of pulsed electric sintered zirconia-silicon nitride reinforced Ti-6Al-4 V alloy

In this study, the influence of silicon nitride (Si3N4) and zirconia (ZrO2) ceramics was examined on the titanium alloy using the pulsed electric current sintering technique to investigate the microstructural behavior, densification, and nanomechanical properties of these composites. Si3N4 and ZrO2 were dispersed in Ti-6Al-4 V at a functional pressure of 50 MPa, a sintering temperature of 1200 °C, a heating rate of 100 °C/min, and a holding time of 10 min. The ternary composite samples were prepared viz, Cs1 (Ti6Al4V-3 vol.% Si3N4-15 vol.% ZrO2), Cs2 (Ti6Al4V-3 vol.% Si3N4-10 vol.% ZrO2), and Cs3 (Ti6Al4V-3 vol.% Si3N4-5 vol.% ZrO2). The bulk morphology of the composites was studied using scanning electron microscopy (SEM) equipped with EDS, and the phase contents were identified with an X-ray diffractometer (XRD). The relative density results for the tri-composites showed that the Cs1 sample recorded the highest at 99.94%, producing a fully dense sintered composite. However, there was a drop in the relative density of composites Cs2 and Cs3, recording 97.73% and 97.11%, respectively, comparable to the unreinforced Ti-6Al-4 V alloy with 98.65%. The nanoindentation examination conducted for the trio-composites showed linear mechanical responses/improvement, with Vickers hardness, from 589.31 to 865.70 MPa; nano hardness, from 6.466 to 9.441 GPa, and elastic modulus, from 113.52 to 185.95 GPa.

Characterization of pulse electric current sintered Ti-6Al-4V ternary composites: Role of YSZ-Si3N4 ceramics addition on structural modification and hydrogen desorption

In this study, we fabricated Ti-6Al-4V composites using pulse electric current (spark plasma) sintering technique and examined the influence of yttria-stabilized zirconia (YSZ) and silicon nitride (Si3N4) particles on microstructural, mechanical properties. Moreover, we investigated the effects of YSZ and Si3N4 on hydrogen uptake rate of the fabricated composites. The formation of new phases in addition to the parent α and β phases corroborates the increased hardness property exhibited by the Ti-6Al-4V composites. Further, the improvement in the hardness property was ascribed to Orowan strengthening effect due to resistance offered by cross dislocation pinning effect of closely packed particles. From the nanomechanical test, the penetration depth of the unreinforced Ti-6Al-4V alloy was maximum at a value of 272.57 nm, while all the reinforced alloys exhibited reduced penetration depth, thereby increasing the stiffness and strength of the Ti-6Al-4V composites. Other nanomechanical analyses such as nanohardness, elastic modulus, and creep were also improved in the reinforced composites in comparison with the Ti-6Al-4V alloy. The amount of hydrogen absorbed by the specimens was measured, and the Ti-6Al-4V composite with the highest proportion of Si3N4 reinforcement exhibited the highest hydrogen concentration.

High-Temperature Oxidation Behavior of Ni/Al2O3 Composites with Various Ni Content

Al2O3 composites dispersed with 1, 5, 10, and 15 vol% nickel particles were prepared using a pulsed electric current sintering technique. High-temperature oxidation was conducted at temperatures ranging from 1200°C to 1350°C for 6–24 h in air. After oxidation, the sample surface mainly consisted of NiAl2O4 oxide. The growth of the oxidized zone in all sample groups followed a parabolic pattern. The influence of the Ni content on the high-temperature oxidation behavior of Ni/Al2O3 is discussed. A kinetic model was proposed to explain the growth of the oxidized zone. The diffusion coefficient of oxygen ions through the grain boundaries of the Al2O3 matrix can be obtained using the proposed model, which is in agreement with those in the literature.

Recent Developments of High-Pressure Spark Plasma Sintering: An Overview of Current Applications, Challenges and Future Directions.

Spark plasma sintering (SPS), also called pulsed electric current sintering (PECS) or field-assisted sintering technique (FAST) is a technique for sintering powder under moderate uniaxial pressure (max. 0.15 GPa) and high temperature (up to 2500 °C). It has been widely used over the last few years as it can achieve full densification of ceramic or metal powders with lower sintering temperature and shorter processing time compared to conventional processes, opening up new possibilities for nanomaterials densification. More recently, new frontiers of opportunities are emerging by coupling SPS with high pressure (up to ~10 GPa). A vast exciting field of academic research is now using high-pressure SPS (HP-SPS) in order to play with various parameters of sintering, like grain growth, structural stability and chemical reactivity, allowing the full densification of metastable or hard-to-sinter materials. This review summarizes the various benefits of HP-SPS for the sintering of many classes of advanced functional materials. It presents the latest research findings on various HP-SPS technologies with particular emphasis on their associated metrologies and their main outstanding results obtained. Finally, in the last section, this review lists some perspectives regarding the current challenges and future directions in which the HP-SPS field may have great breakthroughs in the coming years.

Nanostructure and nanoindentation study of pulse electric-current sintered TiB2–SiC–Cf composite

A carbon-fiber (Cf) doped TiB2–SiC composite was prepared and investigated to determine its densification behavior, micro/nanostructural properties, and mechanical characteristics. TiB2–25 vol% SiC–2 wt% Cf was prepared at 40 MPa and 1800 °C for 7 min using the pulsed electric-current sintering technique, and a relative density of 98.5% was realized. The as-sintered composite was characterized using advanced techniques, e.g., X-ray diffractometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, field-emission electron probe micro-analysis, and nanoindentation. The Cf additive could remove the surface oxide layers from the TiB2 and SiC domains, thus transforming them into TiB2 and SiC. According to micro/nanostructural studies, Cf could not retain its initial structure and was eventually converted into graphite nanosheets. In addition, the prepared composite was examined using the nanoindentation technique, and the following results were obtained for the calculated hardness, elastic modulus, and stiffness values: TiB2 > SiC > TiB2/SiC interface.

Consolidation of alumina toughened zirconia by two-step sintering

Sol-gel-synthesized ZrO2-based nanoparticles, containing 1.5mol% Y2O3 used as dopant and 25mol% Al2O3 (abbreviated as ZrO2(1.5Y)-25Al2O3), were densified by pulsed electric current sintering (PECS) accompanied with a two-step heating profile. Particularly, sintering was carried out in the temperature range from 1050 to 1200?C for 10min, followed by dwell at 1325?C for 10min. The ZrO2-based ceramics achieved by the two-step sintering was fully dense, containing 98 vol.% of tetragonal ZrO2 phase. Morphology of the sintered samples showed the submicron grains with uniform size distribution. Although the second-step sintering temperature was fixed at 1325?C, the mean grain size was increased along with the increase in the first-step sintering temperature. In addition, the material characterization of the samples after the first-step heating was tested to investigate the influence of the first-step sintering on the consolidation of ceramics achieved via the two-step sintering.

Binder derived semi-conductive graphite/alumina composites via novel one-step pulsed electric current sintering

Semi-conductive graphite/Al2O3 ceramic composites were successfully fabricated via a novel and facile approach by pulsed electric current sintering of binder embedded Al2O3 powders, which were prepared by a simple ball-milling assisted mixing of Al2O3 powder with polyvinyl alcohol solution. By altering the sintering conditions with respects to temperature and pressure controlling and concentration of binder, relative density, and microstructure of fabricated graphite/Al2O3 ceramic composites, and the electrical properties were schematically investigated in this study. The fabricated graphite/Al2O3 ceramic composites exhibit superior semi-conductive properties. Moreover, the carrier type in fabricated semi-conductive graphite/Al2O3 composites was successfully modified by adding polycarboxylic acid as a dispersant in binder embedded Al2O3 powders. The contents in this work present a new strategy for the design and development of functional ceramic composites.

Influences of Al concentration and Nb addition on oxidation behavior of Ti2AlC ceramics at high temperatures

ABSTRACT A titanium aluminum carbide, Ti2AlC, which is classified among MAX phase ceramics, was studied as a potential candidate for various mechanical components used in high-temperature applications. The impact of its chemical composition on its high-temperature oxidation process was determined. Ti2AlC powders with various Al contents and with or without Nb addition were synthesized via a conventional reaction technique followed by 16 h of annealing in vacuum at 1300°C. The synthesized Ti2AlC powders were consolidated by means of 15 min of pulsed electric current sintering at a die temperature of 1300°C in vacuum under a uniaxial pressure of 30 MPa. In the presence of an aluminum reservoir in the form of TiAl3, Ti2AlC has excellent resistance against high-temperature oxidation. The promising results concerning the addition of Nb to TiAl provided the rationale for a similar modification of Ti2AlC. The results of oxidation tests on Nb-doped Ti2AlC likewise showed excellent oxidation resistance. Alloying with Nb can improve the oxidation resistance of Ti2AlC with low Al content, allowing the formation of a protective Al2O3 scale and inhibiting the growth of TiO2.

Uncovering electromigration effect on densification during electrical field assisted sintering

Pulsed electric current sintering (PECS) was a rapid consolidation method to realize the accelerated densification process by the synergistic effects of thermal and non-thermal (electromigration) of pulsed electric current (PEC). However, due to the complexity of deconvolution of PEC and temperature and thus lack of quantitative depict of electromigration effect, the non-thermal effects of PEC were still not well understood, despite its proven significance. Here, we proposed an electromigration-related atomic diffusion D e to explicitly clarify the non-thermal effects of PEC on mass transfer. Then, through introducing an in-situ electrically insulative Al 2 O 3 thin-layer into the regular current-assisted sintering tooling, we can cutoff the PEC bypassing powder particles to investigate systematically the thermal and non-thermal effects of PEC on densification behaviors. Further, the modified model was validated by experimental data at with-current and without-current sintering modes. We demonstrated that an electromigration-related atomic diffusion D e derived herein can be used to unravel quantitatively the contribution of electromigration to densification kinetics. Our work would be helpful to understand deeply the densification mechanism of PECS and elucidate the advantage of non-thermal effect of PEC on densification, which would be used to guide design and preparation of high-performance functional materials. • The thermal and non-thermal effects of PEC on densification behaviors during sintering was systematically investigated. • The coefficients D th and D e related to thermal and electromigration effect of PEC were proposed. • As-derived coefficients were closely linked with densification kinetics of powder particles. • The contribution of electromigration to mass transfer was quantitatively depicted.

Insight into tribological and corrosion behaviour of binderless TiCxNy ceramic composites processed via pulsed electric current sintering technique

The study presents the corrosion behaviour and wear response of pulsed electric current sintered binderless TiC 50 N 50 , TiC 70 N 30 , and TiC 90 N 10 based ceramic composites, consolidated by spark plasma sintering (SPS), and the relative densities were evaluated using the Archimedes principle. The microstructural evolutions of the sintered samples were examined through various microscopy techniques, and their susceptibility to corrosion in aggressive chloride environment was assessed using open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The microstructural examination of the specimens showed the presence of different phases within the titanium carbonitride (TiCN) cermets. The wear resistance evaluated using the frictional coefficient (COF) and calculated wear rate showed that the specimens exhibited an improved resistance. The specimens further showed enhanced resistance to corrosion in the test electrolyte, as the TiC 50 N 50 cermet displayed enhanced resistance to the aggressive chloride ions in comparison to the other specimens.

Influences of Raw Powder on Transparent Al2O3 Prepared by Two-Step Pulsed Electric Current Sintering

In order to fabricate Al2O3 ceramics with high transparency, six types of commercial α-Al2O3 powders were consolidated with a two-step pulsed electric current sintering (PECS) in this study. High density in Al2O3 usually has a positive effect on its transmittance, while as some α-Al2O3 powders show low transparency with almost full-densification. It suggested that abnormal grain growth may affect transparency of Al2O3 ceramics. Since pressure sintering in Al2O3 is influenced with dynamic grain phenomena, the differences in abnormal grain growth must be influenced with difference in properties of Al2O3 powder such as crystallinity.

Characterization of anisotropic gas permeability and thermomechanical properties of highly textured porous alumina

AbstractPorous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure‐controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.