Spark Plasma Sintering Consolidation Research Articles

Mechanical Alloying Synthesis and Spark Plasma Sintering Consolidation of Al-Ti-Si-W Alloys

Al-Ti-Si-W quaternary powders were mechanically synthesized by planetary ball milling; and further consolidated by spark plasma sintering. The nominal compositions of the quaternary alloys were designed to be Al60Ti30Si5W5 and Al45Ti40Si10W5 (wt.%). The microstructural evolution of intermetallic compounds in Al-Ti-Si-W alloys included titanium aluminide, titanium silicide, and ternary alloys (AlxTiy, TixSiy, and TixAly,Siz), whereas W was embedded in the Al-Ti matrix as a single phase. The phase composition and grain size distribution were investigated using electron backscatter diffraction analysis, in which refined and uniform microstructures (less than 0.3 μm) were attributed to severe plastic deformation and rapid densification of the pre-alloyed powders. The mechanical properties were correlated with the Al content in the quaternary alloys; a high hardness of 1014.6 ±73.5 kg/mm2 was observed.

Comparative analysis of microstructure, mechanical, and corrosion properties of biodegradable Mg-3Y alloy prepared by selective laser melting and spark plasma sintering

This work explored possibilities of biodegradable magnesium alloy Mg-3Y preparation by two modern powder metallurgy techniques – spark plasma sintering (SPS) and selective laser melting (SLM). The powder material was consolidated by both methods utilising optimised parameters, which led to very low porosity (∼0.3%) in the SLM material and unmeasurably low porosity in the SPS material. The main aim of the study was the thorough microstructure characterisation and interrelation between the microstructure and the functional properties, such as mechanical strength, deformability, and corrosion resistance. Both materials showed comparable strength of ∼110 MPa in tension and compression and relatively good deformability of ∼9% and ∼21% for the SLM and SPS materials, respectively. The corrosion resistance of the SPS material in 0.1 M NaCl solution was superior to the SLM one and comparable to the conventional extruded material. The digital image correlation during loading and the cross-section analysis of the corrosion layers revealed that the residual porosity and large strained grains have the dominant negative effect on the functional properties of the SLM material. On the other hand, one of the primary outcomes of this study is that the SPS consolidation method is very effective in the preparation of the W3 biodegradable alloy, resulting in material with convenient mechanical and degradation properties that might find practical applications.

Production of a Reinforced Refractory Multielement Alloy via High-Energy Ball Milling and Spark Plasma Sintering

Refractory high entropy alloys have shown potential to be developed as structural materials for elevated temperature applications. In the present research, the multielement alloy Fe2TiVZrW0.5 was produced by high-energy ball milling of elemental powders in the air to promote the formation of reinforcing oxide and nitride particles followed by spark plasma sintering consolidation. The sintering temperature was optimized to achieve a full-density material that was characterized from the microstructural and mechanical points of view. Hardness and KIC were measured in the as-sintered condition as well as after thermal treatment at 1100 °C. TEM observations showed the presence of a fine distribution of ZrO2 and Ti(V)-N in the microstructure mainly constituted by the bcc Fe-V and Fe-V-W phases. The fine distribution of ceramic particles in a metallic multielement matrix is responsible for the consistent hardness and thermal stability of this alloy.

Solidification of cesium containing magnetic zeolite sorbent by spark plasma sintering

The possibility of effective solidification of spent sorbents containing radioactive cesium by spark plasma sintering (SPS) technology for their safe and long-term disposal was studied. The kinetics of consolidation spent sorbent based on magnetic zeolite after adsorption saturation with cesium (∼23 wt %) under SPS conditions in the range of 700–950 °C was carried out. The structural, elemental and phase composition changes during high-rate (minutes) heating of zeolite powder saturated with Cs+ ions was studied by SEM, EDX and XRD methods. As a result, ceramic samples with mineral-like structure of Fe-substituted pollucite CsFeSi2O6 were successfully obtained. It was determined that the optimal temperature of SPS consolidation was 900 °C, at which the formation of CsFeSi2O6 ceramics with a relative density of 91.2%, compressive strength of 497.6 MPa, Vickers microhardness of 1019 HV, rate of cesium leaching of 2.33 × 10−8 g/cm2 × day was reached. It was found that the mechanism of cesium diffusion from the volume of ceramics corresponded to flushing from the available surface of the sample, the lowest diffusion coefficient was 2.71 × 10−16 cm2/s, as well as the lowest penetration depth of the solution into the volume of ceramics was 1.04 × 10−5 cm. The adsorbents prepared by SPS up to 900 °C retained the magnetization, and at higher temperature the magnetization decreased, which was caused by phase and structural changes of ceramics. The characteristics of ceramic obtained from spent adsorbent complied with the requirements of GOST R 50926–96 and ISO 6961:1982 for solidified Cs-containing radioactive waste.

Effect of Volume Fraction of Reinforcement on Microstructure and Mechanical Properties of In Situ (Ti, Nb)B/Ti2AlNb Composites with Tailored Three-Dimensional Network Architecture.

The mechanical properties of (Ti, Nb)B/Ti2AlNb composites were expected to improve further by utilizing spark plasma sintering (SPS) and inducing the novel three-dimensional network architecture. In this study, (Ti, Nb)B/Ti2AlNb composites with the novel architecture were successfully fabricated by ball milling the LaB6 and Ti2AlNb mixed powders and subsequent SPS consolidation. The influence of the (Ti, Nb)B content on the microstructure and mechanical properties of the composites was revealed by using the scanning electron microscope (SEM), transmission electron microscopy (TEM) and electronic universal testing machine. The microstructural characterization demonstrated that the boride crystallized into a B27 structure and the α2-precipitated amount increased with the (Ti, Nb)B increasing. When the (Ti, Nb)B content reached 4.9 vol%, both the α2 and reinforcement exhibited a continuous distribution along the prior particle boundaries (PPBs). The tensile test displayed that the tensile strength of the composites presented an increasing trend with the increasing (Ti, Nb)B content followed by a decreasing trend. The composite with a 3.2 vol% reinforcement had the optimal mechanical properties; the yield strengths of the composite at 25 and 650 °C were 998.3 and 774.9 MPa, showing an 11.8% and 9.2% improvement when compared with the Ti2AlNb-based alloy. Overall, (Ti, Nb)B possessed an excellent strengthening effect and inhibited the strength weakening of the PPBs area at high temperatures; the reinforcement content mainly affected the mechanical properties of the (Ti, Nb)B/Ti2AlNb composites by altering the α2-precipitated amount and the morphology of (Ti, Nb)B in the PPBs area. Both the continuous precipitation of the brittle α2 phase and the agglomeration of the (Ti, Nb)B reinforcement dramatically deteriorated the mechanical properties.

Quartz, glass, and glass-ceramic matrix nanocomposites; containing carbon nanotubes: a review

Various concepts of techniques for incorporating carbon nanotubes in quartz, glass and glass-ceramic matrices are overviewed. Mechanical; in particular fracture toughness, hardness and strength, physical; density and microstructures, and functional; thermal and electrical conductivities of the fabricated CNT-loaded nanocomposites via different processing route and measuring techniques were compared and reported. Processing challenges such as the homogenous dispersion of the CNTs in the quartz, glass and glassceramic matrices and the loss of graphitic nanotubes during the consolidation process are still the major impending issues in CNT-quartz/glass/glass-ceramic matrix nanocomposites. There is need to explore in-situ production techniques, spark plasma sintering consolidation method, and controlled colloidal/sol-gel processes for CNTquartz/glass/glass-ceramic matrix nanocomposites.

Improved strength and conductivity of metallic-glass-reinforced nanocrystalline CuCrZr alloy

Metallic glass (MG)-particle-reinforced nanocrystalline CuCrZr alloys with ultrahigh strengths and good conductivities are designed and synthesized via mechanical milling and spark plasma sintering (SPS). The particle morphology and dispersion state of the CuZrAl MG reinforcement in the CuCrZr alloy matrix are optimized by regulating the milling time of the composite powders prior to SPS consolidation. Outstanding properties are achieved by 5 h and 10 h milling processes with ultimate compressive strengths of 1099 ± 33 and 1185 ± 29 MPa and high conductivities of 29.9 ± 0.8% IACS and 25.2 ± 0.6% IACS, respectively. According to the quantified results of strengthening and conductivity mechanisms, MG reinforcements and ultrafine grains are responsible for the balance of superior strength and conductivity of the composites.

Achieving high strength and high conductivity of bulk metallic glass composites by controlled milling process

Cu/Cu-Zr-Al metallic glass composites (C/CMGCs) are high-strength conductive materials that have been synthesized by a combination of ball milling (BM) and spark plasma sintering (SPS). This study investigated how the rotational speed of BM process before SPS consolidation affects the microstructure, mechanical properties and electrical properties of fabricated bulk C/CMGCs were investigated. Increasing the BM speed significantly enhanced the mechanical strength while maintaining a high electrical conductivity. However, when the speed exceeded 375 rpm, the high centrifugal force hindered effective impact between the balls and powder to impede further performance optimization. Using the grain boundary strengthening strategy, nanocrystalline copper was strengthened by tuning the milling parameters. The simultaneous achievement of high conductivity and superhigh strength in the C/CMGCs will prompt further explorations of functionalized bulk metallic glass composites with vast untapped potentials.

Tailoring a Refractory High Entropy Alloy by Powder Metallurgy Process Optimization.

This paper reports the microstructural evolution and mechanical properties of a low-density Al0.3NbTa0.8Ti1.5V0.2Zr refractory high-entropy alloy (RHEA) prepared by means of a combination of mechanical alloying and spark plasma sintering (SPS). Prior to sintering, the morphology, chemical homogeneity and crystal structures of the powders were thoroughly investigated by varying the milling times to find optimal conditions for densification. The sintered bulk RHEAs were produced with diverse feedstock powder conditions. The microstructural development of the materials was analyzed in terms of phase composition and constitution, chemical homogeneity, and crystallographic properties. Hardness and elastic constants also were measured. The calculation of phase diagrams (CALPHAD) was performed to predict the phase changes in the alloy, and the results were compared with the experiments. Milling time seems to play a significant role in the contamination level of the sintered materials. Even though a protective atmosphere was used in the entire manufacturing process, carbide formation was detected in the sintered bulks as early as after 3 h of powder milling. Oxides were observed after 30 h due to wear of the high-carbon steel milling media and SPS consolidation. Ten hours of milling seems sufficient for achieving an optimal equilibrium between microstructural homogeneity and refinement, high hardness and minimal contamination.

Refractory TaTiNb, TaTiNbZr, and TaTiNbZrX (X = Mo, W) high entropy alloys by combined use of high energy ball milling and spark plasma sintering: Structural characterization, mechanical properties, electrical resistivity, and thermal conductivity

Refractory TaTiNb, TaTiNbZr, and TaTiNbZrX (X = Mo, W) high entropy alloys were synthesized by combined use of high energy ball milling (HEBM) and spark plasma sintering (SPS). Powders of predominantly bcc TaTiNbZrX (X = Mo, W) refractory high entropy alloys (RHEAs) were successfully prepared by short-term HEBM (60 min) and then SPS-consolidated at 1373 K for 10 min. TEM analysis of the TaTiNbZrW HEA powder obtained after 60 min of HEBM revealed its nanocrystalline structure with an average grain size of up to 50 nm and predominantly uniform distribution of the elements on an atomic scale. The SPS consolidation at 1300⁰C led to an increase in grain sizes up to 100–300 nm. Thus prepared bulk RHEA materials showed ultra-high Vickers hardness of 8.5 GPa and 13 GPa for TaTiNbZrMo and TaTiNbZrW alloys, respectively. The room-temperature compressive strength of TaTiNbZrW RHEA alloy sintered from HEBM powders attained a value of 2665 МPа, which is 30% higher than that for the same alloy produced from non-milled powders. Bulk samples of synthesized RHEA show a higher electrical resistivity (r) compared to the samples prepared from non-milled powder blends. Within the temperature range 298–573 K, the maximum r value for TaTiNbZrW RHEA alloy was found to vary between 132 and 143.6 Ω cm. A decrease in thermal conductivity was observed: (a) upon introduction of Zr, Mo, and W atoms to TaTiNb-based alloys due to additional phonon scattering on lattice distortions caused by different radius and mass of Zr, Mo, and W atoms and (b) for the HEBM-prepared bulk alloys because of additional phonon scattering on the surface of mechanocomposites.

New HfNbTaTiZr High-Entropy Alloy Coatings Produced by Electrospark Deposition with High Corrosion Resistance.

The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity powders in a planetary ball mill, achieving a good homogenization and a high alloying degree, followed by spark plasma sintering consolidation. The electrodes for electrospark deposition were cut and machined from the bulk material. Stainless steel specimens were coated and electrochemically tested for corrosion resistance in a 3.5% NaCl saline solution.

Effect of mechanical alloying on the microstructural evolution of a ferritic ODS steel with (Y–Ti–Al–Zr) addition processed by Spark Plasma Sintering (SPS)

The high-energy milling is one of the most extended techniques to produce Oxide dispersion strengthened (ODS) powder steels for nuclear applications. The consequences of the high energy mill process on the final powders can be measured by means of deformation level, size, morphology and alloying degree. In this work, an ODS ferritic steel, Fe–14Cr–5Al–3W-0.4Ti-0.25Y2O3-0.6Zr, was fabricated using two different mechanical alloying (MA) conditions (Mstd and Mact) and subsequently consolidated by Spark Plasma Sintering (SPS). Milling conditions were set to evidence the effectivity of milling by changing the revolutions per minute (rpm) and dwell milling time. Differences on the particle size distribution as well as on the stored plastic deformation were observed, determining the consolidation ability of the material and the achieved microstructure. Since recrystallization depends on the plastic deformation degree, the composition of each particle and the promoted oxide dispersion, a dual grain size distribution was attained after SPS consolidation. Mact showed the highest areas of ultrafine regions when the material is consolidated at 1100 °C. Microhardness and small punch tests were used to evaluate the material under room temperature and up to 500 °C. The produced materials have attained remarkable mechanical properties under high temperature conditions.

Comparison of Conventional and Flash Spark Plasma Sintering of Cu–Cr Pseudo-Alloys: Kinetics, Structure, Properties

Spark plasma sintering (SPS) is widely used for the consolidation of different materials. Copper-based pseudo alloys have found a variety of applications including as electrodes in vacuum interrupters of high-voltage electric circuits. How does the kinetics of SPS consolidation for such alloys depend on the heating rate? Do SPS kinetics depend on the microstructure of the media to be sintered? These questions were addressed by the investigation of SPS kinetics in the heating rate range of 0.1 to 50 K/s. The latter conditions were achieved through flash spark plasma sintering (FSPS). We also compared the sintering kinetics for the conventional copper–chromium mixture and for the mechanically induced copper/chromium nanostructured particles. It was shown that, under FSPS conditions, the observed maximum consolidation rates were 20–30 times higher than that for conventional SPS with a heating rate of 100 K/min. Under the investigated conditions, the sintering rate for mechanically induced composite Cu/Cr particles was 2–4 times higher compared to the conventional Cu + Cr mixtures. The apparent sintering activation energy for the Cu/Cr powder was twice less than that for Cu–Cr mixture. It was concluded that the FSPS of nanostructured powders is an efficient approach for the fabrication of pseudo-alloys.

Synthesis and Spark Plasma Sintering of Microcrystalline Thorium Dioxide for Nuclear Fuel Products

Thorium dioxide represents a future of the world market of nuclear fuel for fourth generation nuclear reactors. In this regard, the problems of technologies for thorium separation from irradiated fuel, its conversion into fuel raw materials, and fabrication of required quality fuel products need effective solutions. In this work the synthesis of microcrystalline mesoporous ThO2 powders through the deposition of the oxalate complex from nitrate solutions, and its consolidation by spark plasma sintering (SPS) technology has been studied. The influence of the SPS temperature ranging within 1000–1600°С on the ThO2 powder shrinkage dynamics, phase composition, microstructure, and density of pelletized ceramic products has been studied. Vickers microhardness parameters of samples have been determined. The results show that high-speed (minutes-taking) SPS consolidation of powders at 1600°C and 80 MPa can provide ThO2 ceramics with 92.5% theoretical density. Microcrystalline powders with particle sizes averaging 3-4 µm can be used as raw materials instead of less accessible nanoscale materials. The study shows the expediency and prospects of further studies with the view of SPS technology adaptation for the needs of the nuclear industry.

Mechanical properties and tempering resistance of an ultrafine grained Tool Steel-PSZ composite fabricated by high energy mechanical milling and spark plasma sintering

The mechanical properties and tempering resistance of a powder metallurgical (PM) tool steel (AISI H13) reinforced with partially stabilized zirconia (PSZ) were investigated. The choice of particles reinforcement was made in view to the well-known phase transformation toughening effect in PSZ. Composite powders were produced by high energy mechanical milling and subsequently consolidated by spark plasma sintering (SPS). An ultrafine grain microstructure was achieved showing a homogenous distribution of refined PSZ particles within the severely deformed matrix. Thanks to the fast SPS consolidation, a small amount (less than 2 vol%) of reaction products were formed. The hardness of the composites was significantly higher than the unreinforced counterpart, due to the microstructural refinement, increased dislocation density, and dispersion hardening. Tempering resistance at 550 °C and 650 °C was also significantly improved. The hot compressive yield strength of the composites measured 650 °C and 450 °C was increased up to 1.8 times compared to unreinforced steel. PSZ phase transformation during hot compression contributed to increased work hardening. Fracture toughness was significantly decreased compared to the base material. However, compared to a TiC reinforced H13 with the same hardness, a marginal increase in apparent fracture toughness was observed.

Spark plasma sintering (SPS) densified U3Si2 pellets: Microstructure control and enhanced mechanical and oxidation properties

Dense U3Si2 pellets with controlled grain structure and enhanced thermal-mechanical and oxidation properties are synthesized with spark plasma sintering (SPS). Microstructure and phase composition of the SPS densified pellets are characterized systematically using SEM, EDS, and XRD. Thermal-mechanical properties and oxidation behavior of the sintered silicide fuel pellets are analyzed by laser flash, indentation, and dynamic thermogravimetric analysis. Dense U3Si2 pellets are consolidated by combining high energy ball milling and rapid sintering by SPS, and the microstructure structures are controlled from micron-sized (∼5.7 μm grain size) for conventional silicide to a nanocrystalline matrix with an average grain size of ∼280 nm. A dominant phase of distorted U3Si2 was identified with lattice expansion due to residual thermal stress upon SPS consolidation and rapid cooling processes. Both micron-sized and nano-sized pellets show exceptional thermal transport properties, consistent with monolithic silicides reported in literature. The SPS-densified pellets possess simultaneously high hardness and fracture toughness. The SPS-densified silicide pellets also demonstrate exceptional oxidation performance with extended onset oxidation temperature above 500 °C and reduced oxidation kinetics, particularly for nano-sized pellets. A strong strain effect was proposed in which compressive stress in nano-sized pellets enhances the oxidation resistance of silicide fuels, as evidenced by the degradation of oxidation performance upon strain relaxation by isothermal annealing. The correlation among the sintering process – microstructure control – physical properties and fuel behavior is established. A new concept of strain engineering is proposed further properties optimization, enabling the development of potential oxidation and corrosion-resistant silicides with extended performance, the key technological challenge of U3Si2 as the leading concept of accident tolerant fuels.

Influence of Heat Treatment on Microstructure and Properties of NiTi46 Alloy Consolidated by Spark Plasma Sintering.

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating high-temperature synthesis, milling, and spark plasma sintering consolidation at three various temperatures. The compacted samples were subsequently heat-treated at temperatures between 400 °C and 900 °C with the following quenching in water or slow cooling in a closed furnace. The influence of the consolidation temperature and regime of heat treatment on the microstructure, mechanical properties, and temperatures of phase transformation was evaluated. The results demonstrate the brittle behaviour of the samples directly after spark plasma sintering at all temperatures by the compressive test and no transformation temperatures at differential scanning calorimetry curves. The biggest improvement of mechanical properties, which was mainly a ductility enhancement, was achieved by heat treatment at 700 °C. Slow cooling has to be recommended in order to obtain the shape memory properties.

Spark plasma sintering-densified vanadinite apatite-based chlorine waste forms with high thermal stability and chlorine confinement

Effective management of the long-lived radioactive 36Cl is necessary for the development of pyrochemical reprocessing of used fuels and also the molten salt reactors in which a large quantity of Cl-containing waste is encountered. Significant challenge exists in developing advanced waste form matrix with high Cl confinement capability and fabrication technology with minimized loss of Cl. In this work, Cl-bearing vanadinite apatite (Pb5(VO4)3Cl) powder samples are synthesized by solid state reaction at room temperature using high energy ball milling (HEBM), and dense pellets above 99% theoretical density can be consolidated by spark plasma sintering (SPS) at a temperature as low as 450 °C for 3 min. The effects of various sintering temperatures (300–800 °C) on physical density, microstructure, thermal stability and mechanical properties of the SPS densified pellets are investigated. Microstructure analysis shows that the average grain size of nanocrystalline ceramic is less than 190 nm when sintered at 450 °C, and the sintered microstructure is dominated by grain growth at higher sintering temperatures. No phase decomposition and significant chlorine loss can be identified during HEBM and low temperature SPS consolidation processes. Thermal gravimetric analysis (TGA) test indicates that the phase decomposition and chlorine loss occur only at an elevated temperature 830 °C for both HEBM-prepared powders and SPS densified pellets. Vanadinite pellets densified at 450 °C possess the maximum hardness of 4.6 GPa. The SPS-densified Cl-bearing vanadinite apatite displays high confinement of chlorine and a good thermal stability, and thus could be used as a potential nuclear waste form for the immobilization of the long-lived and highly volatile 36Cl.

Synthetic CaSiO3 sol-gel powder and SPS ceramic derivatives: “In vivo” toxicity assessment

The paper presents template strategy using siloxane-acrylate latex and its modified form to prepare nanostructured calcium silicate (wollastonite) containing nanosized gold and regular porosity. Optimal conditions for the annealing of silicate xerogel were outlined leading to nanoporous wollastonite with minimal porous defects (pore size corresponds to latex particles 150–200 nm). The fabrication of nanostructured wollastonite ceramics was suggested to use spark plasma sintering (SPS). The formation of porous ceramic framework (compressive strength ∼ 120 MPa) via SPS consolidation of silicate xerogel (xonotlite) contained latex template (poreformer), a feature of the method for wollastonite template synthesis. The ceramic wollastonite samples have been implanted into ICR/CD1 mice to test the toxicity of the material “in vivo”. The results are of great interest for the preparation of high-quality biomaterials for modern medicine using simple technological approaches and available raw materials.

Thermal analysis and microstructure of oxide dispersion strengthened ferritic steels produced by ball milling with different amounts of process control agent

Fe–14Cr–3 W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of elemental powders with various amounts of process control agent (PCA), ethanol (0.25 mass%, 2.5 mass%, 4 mass% and 20 mass%) under an Ar atmosphere and spark plasma sintering (SPS) consolidation at 1070 °C. The influence of the quantity of PCA on the properties (microstructure, density and Vickers hardness) of the as-milled powders and of the consolidated steels was investigated. X-ray diffraction shows a bcc–α-phase with fine crystallite size, 6.7–11 nm, for all powders. The particle size and the lattice constant of α-ferrite of the as-milled powders decrease as the amount of PCA increases. The powder milled with the highest amount of PCA, 20 mass%, contains carbides (M3C) and oxides ((Fe,Cr)2O3). The thermal analysis shows that as the amount of PCA increases, (1) the Curie temperature, Tc, increases, (2) the temperature of α → γ transition, Tα→γ, decreases, (3) the mass loss with CO/CO2 degassing increases, and (4) the milling with PCA hinders the nitrogen incorporation from milling media and air. The density and Vickers hardness of the SPS-consolidated and post-SPS annealed steels show an increasing trend with the increase in the amount of PCA. Carbides and oxides were detected in the post-SPS annealed steels derived from the powders milled with 2.5 mass% PCA and 4 mass% PCA (M23C6 and (Fe,Cr)2O3), and 20 mass% PCA (M3C and (Fe,Cr)2O3). The obtained results were discussed in terms of: (1) dissolution into the alloy matrix of carbon and oxygen released after the disintegration of PCA, (2) carbides and oxides precipitation during milling and/or upon heating and (3) promotion of thermally activated processes (such as carbothermal reaction) upon heating which can develop as well at the contact points/particle surfaces during SPS consolidation and can influence the process of densification.