Spark Plasma Sintering Technique Research Articles

Enhancing cutting tool durability: Exploration of Al2O3-SiCw-graphene composites fabricated by SPS for improved mechanical and scratch resistance

This study focuses on the fabrication and characterisation of Al2O3-SiCw-rGO composites sintered by spark plasma sintering (SPS) technique. The research is mainly focused on understanding the impact of varying graphene content (0.5, 1.0 and 1.5 vol %) on nanomechanical properties and scratch resistance. Among the compositions investigated, the composite containing 0.5 vol% graphene showed superior mechanical properties. Specifically, it exhibited a hardness of ∼30 GPa, a fracture toughness of 10.5 MPa m1/2 and a flexural strength of ∼920 MPa. In addition, this composite showed remarkable scratch resistance compared to composites with a higher or lower graphene content. In addition to mechanical properties, the fabricated composites also exhibited high electrical conductivity. This characteristic is especially advantageous for electrical discharge machining (EDM) processes. The high electrical conductivity enables efficient machining of complex shapes by EDM, thereby reducing machining costs while ensuring accuracy and efficiency.

Fe(Se,Te) Thin Films Deposited through Pulsed Laser Ablation from Spark Plasma Sintered Targets.

Iron-based superconductors are under study for their potential for high-field applications due to their excellent superconducting properties such as low structural anisotropy, large upper critical fields and low field dependence of the critical current density. Between them, Fe(Se,Te) is simple to be synthesized and can be fabricated as a coated conductor through laser ablation on simple metallic templates. In order to make all the steps simple and fast, we have applied the spark plasma sintering technique to synthesize bulk Fe(Se,Te) to obtain quite dense polycrystals in a very short time. The resulting polycrystals are very well connected and show excellent superconducting properties, with a critical temperature onset of about 16 K. In addition, when used as targets for pulsed laser ablation, good thin films are obtained with a critical current density above 105 A cm-2 up to 16 T.

Preparation of high-entropy nitride ceramics (TiVCrNbZr1-x)Ny by introducing nitrogen vacancies

ABSTRACT High-entropy ceramics have emerged as a research hotspot in the field of ceramics due to their single-crystal structure and excellent physicochemical properties. In this paper, an innovative approach is adopted to synthesize high-entropy nitride ceramics (TiVCrNbZr1-x)Ny. To achieve this, the non-stoichiometric compound TiN0.3 was introduced as a sintering additive and the Spark Plasma Sintering (SPS) technique was employed. By adding TiN0.3, successfully preparing high-entropy nitride ceramics at 1500°C, which introduces vacancy defects that provide additional space for the diffusion and migration of atoms, allowing for more efficient migration and diffusion within the crystal structure, thereby accelerating the sintering process. The (TiVCrNbZr1-x)Ny- xZrO2 samples achieved outstanding mechanical properties when sintered at 1700°C, owing to the mechanisms of solid solution strengthening and second-phase diffusion toughening. Specifically, the samples exhibited a hardness of 25.42 ± 1.58 GPa, a flexural strength of 888 ± 32 MPa, and a fracture toughness of 6.23 ± 0.27 MPa·m1/2. This innovative sintering route provides an efficient method for preparing high-entropy nitride ceramics at relatively low temperatures without sacrificing quality. This approach not only enhances production efficiency but also expands the potential practical applications of these ceramics.

Fabrication and characterization of in-situ Ti(C, N) – CoCrFeNi cermets via mechanical alloying and spark plasma sintering

Ti(C, N) cermets were prepared by adding CoCrFeNiTi to g-C3N4 and using mechanical alloying and spark plasma sintering techniques. The evolution of microstructure and the systematic analysis of the influence of different binder content on mechanical properties were investigated. This result demonstrates that with an increase in binder content, the grain size of Ti(C, N) in the cermets decreases, and the formation of spheroidal small grains becomes more prominent while the occurrence of large grains decreases. Additionally, the relative density and hardness of Ti(C, N) metal ceramics have slightly decreased. The fracture toughness of Ti(C, N)/HEA cermet is codetermined by the intrinsic sintering property and deformability of HEA binders. The Ti(C, N) cermets (CH3) exhibits excellently bending strength and fracture toughness，which are 1941 MPa and 11.2 MPa m1/2 respectively. The study aims to enhance the mechanical properties and toughness of Ti(C, N) and proposes a novel approach for the synthesis of Ti(C, N) cermet.

Heavy elemental compound addition enhancing thermoelectric performance of Chromium Silicide synthesized by Spark plasma sintering

Silicide-based materials drive great potential in developing mid-temperature range thermoelectric generators (TEGs) applications. However, realizing the efficient and stable silicide materials is still a constraint for its real potential device applications. Chromium silicide will likely become p-type thermoelectric materials in this direction for thermoelectric power generation applications. However, high thermal conductivity values impede the figure-of-merit (zT). The present work adopts the chromium silicide, adding different weight percentages of well-known ZrCoSbSn compounds employing the compaction spark plasma sintering (SPS) technique. By adopting these combinations, the thermal conductivity is significantly reduced by enhanced scattering of heat-carrying phonons by multiple interfaces. Also, the maximum power factor value of ≃ 2.1 × 10−3 W/mK2 is achieved by employing a CrSi2 -ZrCoSbSn compound addition. The enhanced figure-of-merit value (zT) ≃ 0.26 is realized in the temperature at 623 K for the CrSi2-5wt% ZrCoSbSn compound material.

Effect of grain size on the dielectric and magnetic properties of YFeO3 ceramics densified by microwave sintering and spark plasma sintering from powders synthesized via reverse chemical co-precipitation

YFeO3 (YFO) ceramics were synthesized by reverse co-precipitation at different pH values followed by microwave sintering (MS) and spark plasma sintering (SPS) techniques. Also, the effect of the grain size on the magnetic and dielectric properties of the sintered ceramics was examined using various characterization methods. Moreover, FESEM micrographs showed that the particle size of the calcined samples has declined by increasing the pH value. Furthermore, the magnetization curves exhibited weak ferromagnetic behavior in the pre-sintered powder samples. Besides, the Ms value was enhanced from 1.26emu/g to 2.3emu/g by an increase in pH from 8.5 to 10.5 owing to reducing the particle size and subsequently raising the amount of uncompensated surface spins. Furthermore, the powder samples showed an increase in the Hc and Mr values from 15Oe to 28Oe and 0.127emu/g to 0.296emu/g, respectively, with a reduction in particle size from 0.632 μm to 0.272 μm. Additionally, the specimens processed through the sintering techniques demonstrated a remarkable reduction in magnetic characteristics. Therefore, a decrease in magnetic saturation values from 2.3emu/g to 0.43emu/g for the MS sample and to 0.17emu/g for the SPS specimen was attributed to a marked reduction in the amount of free surfaces and subsequently uncompensated surface spins. At last, the observed dielectric characteristics of all the sintered pellets had a common dielectric behavior. This signifies that by increasing the frequency the ε′ and tanδ decline at lower frequencies and become frequency-independent at higher frequencies based upon the Maxwell-Wagner polarization theory. On the other hand, the ε′ value for the SPS sample produced at pH = 10.5 underwent a decline of 2.5 times at the low frequency of 200 Hz compared to the MS one due to the significant decrement of the grain boundaries on account of the coarsening of grains.

Joining of Cf/SiC composites using AlCoCrFeNi2.1 eutectic high‐entropy alloy filler by spark plasma sintering

AbstractAlCoCrFeNi2.1 eutectic high‐entropy alloy was introduced to join Cf/SiC composite by spark plasma sintering technique. The influence of holding times on microstructure, shear strength and fracture behavior of the joints was studied. When held for 7 min, the typical microstructure of the Cf/SiC‐AlCoCrFeNi2.1‐Cf/SiC joint was Cf/SiC composite → CrSi2 + FCC + Al8Cr5 + graphite → CrSi2 + FCC + Al8Cr5 → CrSi2 + FCC + Al8Cr5 + graphite → Cf/SiC composite. As the holding time extended, the Ni–Si and Fe–Si brittle phases in the joint gradually reduced, and the diffusion transition layer continued to thicken. The maximum joint strength was 23.9 MPa, which was obtained at 1450°C for 7 min. Analyzed by scanning electron microscopy and energy dispersive spectroscopy, the fracture modes of the joints joined at different holding times were all brittle fracture.

Towards homogeneous spark plasma sintering of complex-shaped ceramic matrix composites

Research laboratories worldwide use the spark plasma sintering (SPS) technique for sintering metallic and ceramic matrix composites. Typically, the SPS sintered parts are low circular cylinders (discs). The upscaling and industrialization of SPS technology face two challenges: the limitation of shaping non-cylindrical parts and the inhomogeneous sintering of large-sized products. This paper addresses these challenges in sintering axisymmetric shells within an SPS setup with improved thermal insulation. The paper considers the sintering of a 75 mm shell as a case study. The shell material is a zirconia-carbon nanotube composite. Finite element analysis revealed that homogeneous sintering of such a shell requires careful thermal insulation of the entire setup. Investigation of phases, microstructure, density, microhardness, and fracture toughness in the sintered shell showed a homogeneous structure and uniform properties.

Densification, hydrogen retention, microstructure, and mechanical properties of ε-ZrH2-x monolith fabricated by high-pressure spark plasma sintering

The sintering of zirconium hydride (ZrH2-x) without hydrogen atmosphere faces the challenge of thermal dehydrogenation problem, which is overcome by the high-pressure spark plasma sintering (HPSPS) technique in this study. The application of high pressure remarkably reduces the initial densification temperature and effectively restrains the thermal dehydrogenation of ZrH2-x in SPS. Under 500 MPa loading, ε-ZrH1.72 monolith with high densification (96.62 %) and high hydrogen density (6.04 × 10 22 atoms H/cm3) is sintered at a relatively low temperature of 700 °C for only 5 min. Meanwhile, the grain growth of ZrH2-x is very limited. The Young’s modulus and hardness of the sintered ε-ZrH1.72 are 58.68 GPa and 2.61 GPa respectively. Compared with the directly hydrided ε-ZrH2-x, the sintered ε-ZrH1.72 has a more uniform hardness distribution and improved fracture toughness of 3.19 MPa m1/2. This study provides a valuable reference for the sintering of other easily decomposable materials.

Anion/Cation Co-Doping to Improve the Thermoelectric Performance of Sn-Enriched n-Type SnSe Polycrystals with Suppressed Lattice Thermal Conductivity.

Enhancing the thermoelectric performance of n-type polycrystalline SnSe is essential, addressing challenges posed by elevated thermal conductivity and compromised power factor inherent in its intrinsic p-type characteristics. This investigation utilized solid-state reactions and spark plasma sintering techniques for the synthesis of n-type SnSe. A significant improvement in the figure of merit (ZT) is achieved through strategic reduction in Se concentration and optimization of crystal orientation. The co-doping with Br and Ge further improves the material; Br amplifies carrier concentration, enhancing electrical conductivity, while Ge introduces effective phonon scattering centers. In the Br/Ge co-doped SnSe sample, thermal conductivity dropped to 0.38Wm⁻¹K⁻¹, yielding a remarkable power factor of 662µWmK- 2 at 773K, culminating in a ZT of 1.34. This signifies a noteworthy 605% improvement over the pristine sample, underscoring the pivotal role of Ge doping in enhancing n-type material thermoelectric properties. The enhancement is attributed to Br doping introducing additional electronic states near the valence band, and Ge doping modifying the band structure, fostering resonant states near the conduction band. The Br/Ge co-doping further transforms the band structure, influencing electrical conductivity, Seebeck coefficient, and thermal conductivity, advancing the understanding and application of n-type SnSe materials for superior thermoelectric performance.

Investigating the valence balance of adding Nano SiC and MWCNTs on the improvement properties of copper composite using mechanical alloying and SPS techniques

This study presents a comprehensive investigation of copper-based nanocomposites reinforced with silicon carbide (SiC) nanoparticles and multi-walled carbon nanotubes (MWCNTs). The manufacturing procedure involved powder metallurgy techniques followed by spark plasma sintering (SPS). Microstructural analysis revealed a notable reduction in particle size (from 23.72 μm to 18.31 μm) and crystallite size (from 104.32 nm to 87.36 nm) with the addition of reinforcements. The bulk microstructure exhibited a reduction in grain size by approximately 13.1 %. XRD analysis confirmed the absence of new phases. Evaluation of SPS parameters demonstrated varying density and porosity, with the highest relative density of 99.96 % observed in pure copper composites. Hardness measurements indicated that surface hardness surpassed cross-sectional values, with the lowest recorded value being 64.79 HV for composite Cu-5%SiC-1%MWCNTs (S4). Wear rate analysis revealed an increase, with pure copper composites exhibiting a wear rate of 1.78 × 10^-4 mm3/m, while composite S4 displayed a rate of 3.25 × 10^-4 mm3/m under a load of 5 N. Coefficient of Friction (COF) exhibited significant fluctuations, influenced by the applied load and composite composition. Thermal conductivity decreased with higher SiC and MWCNT content, with sample S1 exhibiting the highest thermal conductivity among reinforced composites. Electrical conductivity trends were influenced by the type and concentration of reinforcing particles, resulting in an increase of approximately six times in composite S4 compared to the pure sample.

Effect of Nitrogen Atmosphere Annealing of Alloyed Powders on the Microstructure and Properties of ODS Ferritic Steels.

Oxide Dispersion Strengthened (ODS) ferritic steels are promising materials for the nuclear power sector. This paper presents the results of a study on the sintering process using the Spark Plasma Sintering (SPS) technique, focusing on ODS ferritic steel powders with different contents (0.3 and 0.6 vol.%) of Y2O3. The novelty lies in the analysis of the effect of pre-annealing treatment on powders previously prepared by mechanical alloying on the microstructure, mechanical, and thermal properties of the sinters. Using the SPS method, it was possible to obtain well-densified sinters with a relative density above 98%. Pre-annealing the powders resulted in an increase in the relative density of the sinters and a slight increase in their thermal conductivity. The use of low electron energies during SEM analysis allowed for a fairly good visualization of the reinforcing oxides uniformly dispersed in the matrix. Analysis of the Mössbauer spectroscopy results revealed that pre-annealing induces local atomic rearrangements within the solid solution. In addition, there was an additional spectral component, indicating the formation of a Cr-based paramagnetic phase. The ODS material with a higher Y2O3 content showed increased Vickers hardness values, as well as increased Young's modulus and nanohardness, as determined by nanoindentation tests.

Combined Effect of Particle Reinforcement and T6 Heat Treatment on the Compressive Deformation Behavior of an A357 Aluminum Alloy at Room Temperature and at 350 °C

Solid state sintering of cast aluminum powders by resistance heating sintering (RHS), also known as spark plasma sintering or field-assisted sintering technique, creates a very fine microstructure in the bulk material. This leads to high performance material properties with an improved strength and ductility compared to conventional production routes of the same alloys. In this study, the mechanical behavior of an RHS-sintered age-hardenable A357 (AlSi7Mg0.6) cast alloy and a SiCp/A357 aluminum matrix composite (AMC) was investigated. Aiming for high strength and good wear behavior in tribological applications, the AMC was reinforced with a high particle content (35 vol.%) of a coarse particle fraction (d50 = 21 µm). Afterwards, separated and combined effects of particle reinforcement and heat treatment were studied under compressive load both at room temperature and at 350 °C. At room temperature compression, the strengthening effect of precipitation hardening was about twice as high as that for the particle reinforcement, despite the high particle content. At elevated temperatures, the compressive deformation behavior was characterized by simultaneously occurring temperature-activated recovery, recrystallisation and precipitation processes. The occurrence and interaction of these processes was significantly affected by the initial material condition. Moreover, a rearrangement of the SiC reinforcement particles was detected after hot deformation. This rearrangement lead to a homogenized dispersion of the reinforcement phase without considerable particle fragmentation, which offers the potential for secondary thermo-mechanical processing of highly reinforced AMCs.

Cr-rich structure evolution and enhanced mechanical properties of CoCrFeNi high entropy alloys by mechanical alloying

Mechanically-alloyed CoCrFeNi high entropy alloys (MA-HEAs) show better mechanical properties than as-cast HEAs. However, the limited amount of powder milled in one-milling cycle creates a challenge in larger-scale applications. The low ball-to-powder ratio (BPR) milling used to increase powder yield resulted in the formation of Cr-rich second phases in the face-centered cubic matrix. To overcome the above issues, in this work, with a low BPR of 5:1, four different processes were analyzed: quicker milling intervals, higher milling speed, and the pre-alloying of Cr and Ni. All parameters mentioned before were used and tested together in the fourth sample. Samples were consolidated by spark plasma sintering technique. Microstructural characterization was made on a Scanning Electron Microscope equipped with EDS and EBSD detectors and a Transmission Electron Microscope. X-ray diffraction was employed to develop the structural evolution of powders sintered and annealed samples. The global hardness was measured using microhardness tests, while the nanohardness tests helped us correlate the evolution of secondary phases with their mechanical properties. The results show that pre-alloying elements with the lowest diffusion coefficient before the main milling process might be an attractive strategy to improve productivity and optimize microstructure without limiting the efficiency of low BPR MA-HEAs. The results described below demonstrate the promising perspective for the implementation of powder metallurgy techniques in a mass scale production as low BPR is essential for numerous applications like aerospace industry, car engines and medicine, where improved productivity of powder mixing is mandatory.

Enhanced thermoelectric properties of Mg2Si0.3Sn0.7 via Bi-doping under high pressure

A series of n-type Mg2(Si0.3Sn0.7)1-xBix compounds with 0≤x≤0.02 were successfully synthesized through a combined approach involving solid-state reaction, high-pressure synthesis, and spark plasma sintering techniques. The method yielded homogeneously distributed single-phase materials at the micron scale, although minor compositional variations were detected within nanoscale precipitates embedded in the grains. The sample with Bi content of 0.01 exhibited enhanced thermoelectric properties, reaching a peak thermoelectric figure of merit (ZT) of 1.45 at 700 K while maintaining an average ZT of about 1.1 over the temperature range of 300−773 K. The enhancement in thermoelectric performance is ascribed to the optimized carrier concentration, band convergence, and refined microstructure. The findings suggest a simplified approach to doping that could be beneficial in creating high-performance thermoelectric materials for energy conversion.

Microstructural design to Al-6Mg-5Gd alloy for the unification of structural and neutron shielding properties

Design of composition and microstructure can effective improve the structural and neutron shielding properties of neutron shielding materials. Based on the shielding standard of 30%B4C/Al, an Al-6Mg-5Gd (wt%) alloy was designed by Shmakov-Yamamoto model and successfully fabricated by Powder Metallurgy-based routines (e.g., powder fabrication, spark plasma sintering and hot extrusion techniques). By the rapid solidification in the atomization process, the submicron cell structures were formed in powders. Due to the difference in the original powder size, the as-sintered alloys had heterogeneous microstructures, leading to the bimodal grain structures of as-extruded alloys. During these processes, the formation of nano-sized τ(C15) (Al4MgGd) phase in combination with its firstly observed transformation behavior showed the great impacts on microstructure evolutions. Therefore, the as-extruded alloy exhibited the superior yield strength (335±7 MPa), ultimate tensile strength (462±5 MPa) and elongation (10.2±0.3%). Through the neutron absorption test, the as-extruded alloy showed the comparable of macroscopic transmission cross section with 30%B4C/Al. In comparison with the available Al-based neutron shielding materials, our report exhibited the best unification of mechanical and functional properties. The underlying mechanisms for synergic strength-ductility behavior were discussed on the nano-sized phase strengthening, α-Al/τ interface modulation, and bimodal grain features. Critically, this work designed and studied a high-performance neutron shielding material, shedding light on the advanced structural-functional integrated materials.

Using the Spark Plasma Sintering System for Fabrication of Advanced Semiconductor Materials.

The interest in the Spark Plasma Sintering (SPS) technique has continuously increased over the last few years. This article shows the possibility of the development of an SPS device used for material processing and synthesis in both scientific and industrial applications and aims to present manufacturing methods and the versatility of an SPS device, presenting examples of processing Arc-Melted- (half-Heusler, cobalt triantimonide) and Self-propagating High-temperature Synthesis (SHS)-synthesized semiconductor (bismuth telluride) materials. The SPS system functionality development is presented, the purpose of which was to broaden the knowledge of the nature of SPS processes. This approach enabled the precise design of material sintering processes and also contributed to increasing the repeatability and accuracy of sintering conditions.

Effects of thermal, stress, and electric fields on microstructure and ion distribution of (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 spinel ferrites

In this work, conventional sintering, hot-pressing sintering, and spark plasma sintering techniques were utilized to simulate the thermal field, thermal-stress field, and thermal-stress-electric field, respectively. The effects of these fields on the microstructure and cation distribution of the (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 ferrite (HEF) material were comprehensively analyzed. The results indicate that in the temperature range of 1000–1100 °C, the thermal field provides the driving force for sintering, promotes grain growth (average particle size: 2→7 μm), and increases crystallinity degree. The stress field brings the particles into close contact with each other, facilitates diffusion, and delays grain growth (0.5→5 μm). The electric field reduces grain boundary energy, causes mass transfer, and makes the grains finer (0.5→0.7 μm) and more uniform. Mathematical model analysis reveals that the thermal field is beneficial to the random distribution of cations, which yields an inversion degree (γ) of about 2/3 and increases the configuration entropy of HEF. The stress field leads to lattice distortion, permits ions with larger radius to occupy tetrahedral positions, and changes the cell parameters and oxygen position parameter of HEF. Finally, the interaction between electric field and crystal charges increases the electrostatic field energy, which promotes the formation of positive spinel structure and maximizes the crystal field stability energy. X-ray photoelectron spectra, Raman spectra, and change in lattice constant confirm the rationality of the mathematical model, and can be used to establish the model of the crystal structure under field effects.

Friction and wear behaviors of boron-containing high entropy alloy/diamond composites

In present work, FeCoCrNiB0.15 high-entropy alloy (HEA) with its diamond composite were prepared by spark plasma sintering (SPS) technique at 950 °C. FeCoCrNiMo0.15 and its diamond composite samples were prepared for comparison. The phase composition and microstructures of FeCoCrNiMo0.15 and FeCoCrNiB0.15 HEAs and diamond composite samples were investigated, and the friction and wear behaviors of the HEAs and diamond composites against Si3N4 balls under dry sliding condition in ambient air were compared on a ball-on-disk tester. The results showed that, Cr-rich phase precipitated from the metastable FCC matrix was observed in both HEAs. The relative density of the FeCoCrNiMo0.15 and FeCoCrNiB0.15 alloy samples was ∼93.1 % and ∼ 98.4 %, respectively, while the Vickers hardness of the samples was 309.7 ± 10.6 HV1 and 317.5 ± 8.4 HV1, respectively. The wear resistance of FeCoCrNiB0.15 was higher than that of FeCoCrNiMo0.15 alloy, and the grinding rate of FeCoCrNiB0.15/diamond composite against Si3N4 was higher than that of the FeCoCrNiMo0.15/diamond composite. With detailed microstructural analyses, the possible friction and wear mechanism were discussed. Present study shows that the boron-doped HEA matrix in diamond composites is a promising candidate for fabricating diamond tools with long service life and high processing efficiency.

Phase Prediction, Microstructure, and Microhardness of Sintered Nickel-Based Superalloy

In this study, the phase formation, microstructure and microhardness of nickel-based superalloy fabricated using a spark plasma sintering technique were evaluated. The microstructure and microhardness of the nickel-based superalloy were explored at diverse sintering temperatures (600 °C - 1050 °C). The phase formations and volume fraction with respect to temperature were predicted by using CALPHAD-based software. The microstructure, phase constitution, and microhardness were evaluated via scanning electron microscope (SEM), X-ray diffraction (XRD), and Vickers hardness tester. The findings indicated that the spark plasma sintering technique enables the development and growth of the necking of particles, enhancing elemental bonding and alloy densification as the temperature increases. The hardness value increases at increasing temperatures, with a maximum value of 353 HV attained at a temperature of 1050 °C.