High-pressure High-temperature Sintering Research Articles

Microstructure and mechanical properties of high-pressure sintered B6O-SiC nanocomposites

Boron suboxide (B6O) is recognized as a superhard material with a low mass density, high resistance to chemical wear, and excellent wear resistance. Despite its desirable properties, the limited fracture toughness of B6O restricts its application in industrial contexts. This study presents the structural and mechanical characterization of B6O-SiC nanocomposites, which were synthesized via a high-pressure high-temperature sintering process of B6O powders and SiC whiskers. The sintering process induced fragmentation of SiC whiskers, resulting in the homogenous distribution of SiC fragments within the B6O matrix. An increase in SiC content was observed to decrease the composite's hardness, while initially reducing then enhancing its toughness. The nanocomposites containing 20 wt% and 30 wt% SiC whiskers exhibited significant improvements in fracture toughness, averaging 6.5 MPa m1/2 and 7.0 MPa m1/2, respectively—approximately threefold the toughness of polycrystalline B6O—while sustaining high hardness values of 36.3 GPa and 35.6 GPa on average. Microstructural analyses revealed that the composites’ superior mechanical performance is due to the presence of strong grain boundaries, as well as a high density of nanotwins and stacking faults. The findings demonstrate a viable method for producing B6O-based nanocomposites with enhanced hardness and toughness, potentially expanding their industrial applicability.

Mechanical properties of a novel tungsten fiber-reinforced tungsten composite prepared through powder extrusion printing and high-pressure high-temperature sintering

Tungsten is one of the most promising candidate materials for plasma-facing materials (PFM) because of its high melting point, superior thermal conductivity, and low sputtering rate. However, its significant brittleness and high ductile-to-brittle transition temperature constrain its broader engineering applications. To address these limitations, we developed a novel tungsten fiber-reinforced tungsten (Wf//W) composite. This composite utilizes commercially available black tungsten wire mesh as the fiber reinforcement phase with a mass ratio of 1 %. The material was synthesized through a combined Powder Extrusion Printing and High-Pressure, High-Temperature sintering process, achieving a relative density exceeding 99 %. Additionally, the composite exhibits a maximum hardness of 589 ± 10 HV, attributable to the presence of high-density dislocations in the matrix. Its compressive strength reaches up to 1530 MPa, and the plastic deformation strain is as high as 15.8 %, both of which are outstanding compared to existing research. These findings offer an alternative route for producing high-density Wf//W materials, in addition to chemical vapor deposition method and powder metallurgy technique.

Half-Heusler phase TmNiSb under pressure: intrinsic phase separation, thermoelectric performance and structural transition

Half-Heusler (HH) phase TmNiSb was obtained by arc-melting combined with high-pressure high-temperature sintering in conditions: p = 5.5 GPa, T_{HPHT} = 20, 250, 500, 750, and 1000 ^{circ }C. Within pressing temperatures 20–750 ^{circ }C the samples maintained HH structure, however, we observed intrinsic phase separation. The material divided into three phases: stoichiometric TmNiSb, nickel-deficient phase TmNi_{1-x}Sb, and thulium-rich phase Tm(NiSb)_{1-y}. For TmNiSb sample sintered at 1000 ^{circ }C, we report structural transition to LiGaGe-type structure (P6_3mc, a = 4.367(3) Å, c = 7.138(7) Å). Interpretation of the transition is supported by X-ray powder diffraction, electron back-scattered diffraction, ab-initio calculations of Gibbs energy and phonon dispersion relations. Electrical resistivity measured for HH samples with phase separation shown non-degenerate behavior. Obtained energy gaps for HH samples were narrow (le 260 meV), while the average hole effective masses in range 0.8–2.5m_e. TmNiSb sample pressed at 750 ^{circ }C achieved the biggest power factor among the series, 13 upmuWK^{-2}cm^{-1}, which proves that the intrinsic phase separation is not detrimental for the electronic transport.

ODMR active bright sintered detonation nanodiamonds obtained without irradiation

We present the results of study the structure and composition of microcrystalline diamonds obtained by high-pressure high temperature sintering of detonation nanodiamond particles. Using optical detected magnetic resonance method, photoluminescence spectroscopy and Raman spectroscopy we found sintering of detonation nanodiamond significantly differ from initial detonation nanodiamonds and can be compared to high quality diamonds. Monocrystals of diamonds obtained by the method of oriented attachment have dimensions of up to tens of microns, possess the habitus of high-quality diamonds, and do not contain metal catalysts in the lattice structure. In those crystals, the presence of optically active nitrogen impurities in the crystal lattice is observed. In particular, there is a bright nitrogen-vacancy defects. They are characterized by optical detected magnetic resonance method, which shows that spin properties of the obtained single crystals correspond to high-quality natural diamonds and surpass synthetic diamonds obtained from graphite in the presence of metal catalysts, followed by irradiation and annealing to obtain nitrogen-vacancy defects optical defects in the diamond lattice. The presence of nitrogen-vacancy defects defects and the high-quality of the crystal structure of sintering of detonation nanodiamond allows us to consider them as potential candidates in quantum magnetometry. For this purpose, the possibility of a simple way to improve the AFM probe by fixing a microcrystalline sintering of detonation nanodiamond particle on its tip is demonstrated. Keywords: detonation nanodiamond, HPHT sintering, ODMR, single crystalline, photoluminescence, defects.

A Review of Binderless Polycrystalline Diamonds: Focus on the High-Pressure-High-Temperature Sintering Process.

Nowadays, synthetic diamonds are easy to fabricate industrially, and a wide range of methods were developed during the last century. Among them, the high-pressure–high-temperature (HP–HT) process is the most used to prepare diamond compacts for cutting or drilling applications. However, these diamond compacts contain binder, limiting their mechanical and optical properties and their substantial uses. Binderless diamond compacts were synthesized more recently, and important developments were made to optimize the P–T conditions of sintering. Resulting sintered compacts had mechanical and optical properties at least equivalent to that of natural single crystal and higher than that of binder-containing sintered compacts, offering a huge potential market. However, pressure–temperature (P–T) conditions to sinter such bodies remain too high for an industrial transfer, making this the next challenge to be accomplished. This review gives an overview of natural diamond formation and the main experimental techniques that are used to synthesize and/or sinter diamond powders and compact objects. The focus of this review is the HP–HT process, especially for the synthesis and sintering of binderless diamonds. P–T conditions of the formation and exceptional properties of such objects are discussed and compared with classic binder-diamonds objects and with natural single-crystal diamonds. Finally, the question of an industrial transfer is asked and outlooks related to this are proposed.

AB-stacked nanosheet-based hexagonal boron nitride.

Hexagonal boron nitride (h-BN) has been generally interpreted as having an AA stacking sequence. Evidence is presented in this article indicating that typical commercial h-BN platelets (∼10-500 nm in thickness) exhibit stacks of parallel nanosheets (∼10 nm in thickness) predominantly in the AB sequence. The AB-stacked nanosheet occurs as a metastable phase of h-BN resulting from the preferred texture and lateral growth of armchair (110) planes. It appears as an independent nanosheet or unit for h-BN platelets. The analysis is supported by simulation of thin AB films (2-20 layers), which explains the unique X-ray diffraction pattern of h-BN. With this analysis and the role of pressure in commercial high-pressure high-temperature sintering (driving nucleation and parallelizing the in-plane crystalline growth of the nuclei), a growth mechanism is proposed for 2D h-BN (on a substrate) as `substrate-induced 2D growth', where the substrate plays the role of pressure.

Impact of surface fluorination on phase stability of nanodiamond particles and inter-granular bonding in polycrystalline diamond under HPHT conditions

Polycrystalline diamond (PCD) compacts, made by conventional high pressure-high temperature (HPHT) technology, contain Co catalyst in inter-granular spaces causing degradation of PCD mechanical strength and thermal stability during rock cutting due to thermal expansion and graphitization. To solve this problem a catalyst-free synthesis of PCD based on HPHT sintering of fluorinated nanodiamond (FND) and submicron size aluminum mixtures was explored in the present work. The feasibility of using FND has been established by evaluation of phase stability of FNDs of 5, 10, and 90 nm sizes under industrially favorable P-T conditions (7.5–8 GPa, 1500–1700 °C) for PCD synthesis. It was found that surface fluorine slows down the graphitization of nanodiamond particles. Enlargement of diamonds from 5 and 10 nm up to a 10 μm has been observed for FND/Al systems. This phenomenon can be associated with the Wurtz-type reaction under the HPHT conditions leading to formation of inter-granular carbon‑carbon bonds between the nanoparticles and formation of the fluid Al-C-F phases in the samples volume, accelerating the mass transport and re-crystallization of nanodiamond. PCD samples sintered from mixtures of fluorinated micro-diamonds, nano-diamonds FND-90 and 3 wt% aluminum exhibited enhanced up to 1200 °C thermal stability and as high wear resistance as leached commercial PCD.

The study of composition, structure and cathodoluminescent features of YAG:Eu3+ nanoceramics. Excitation capture efficiency of Eu3+ energy levels

The focus of this research paper is upon cathodoluminescent features of YAG:Eu3+ nanoceramics. The concentration series of samples was synthesized from nano powders using low temperature high pressure sintering technique. The composition of the samples has been studied using electron-probe microanalysis. The structure and the grain size of the samples have been studied by X-ray diffraction, scanning electron microscopy and electron backscattered diffraction. Cathodoluminescent study of the samples has been performed. The concentration dependence of cathodoluminescence intensity and kinetic dependencies of CL bands have been obtained. The excitation capture efficiency of the radiative energy levels was estimated based on cathodoluminescence intensity rise rate dependence on electron beam current density. Energy transfer mechanism between the energy levels will be discussed hereinafter.

Вплив температури спікання на фазовий склад та механічні властивості композитів на основі $c$BN з добавками сполук ванадію

The influence of the sintering temperature on the mechanical properties of cBN-based ceramic composites with binders in form of vanadium compounds is investigated by methods of physical material science. Two compositions are selected for the study cBN–VC–Al and cBN–VN–Al with 60% vol. of cBN. Samples are obtained by high pressure high temperature sintering (HPHT) in toroid type apparatus with central hole 30. Sintering is conducted in temperature range of 1600–2450°C under pressure of 7.7 GPa. Sintering in the temperature range of 1600–1850°C induces the beginning of the interaction between components of the mixture and significant change in the elastic properties of the samples in both systems. As found, the maximum values of microhardness are achieved at 2150°C—40 GPa for a system with a carbide binder and 30 GPa in a system with vanadium nitride. The highest level of tool wear resistance during high-speed machining of steels is shown the samples of both groups sintered in the temperature range of 2000–2150°С. (Less)

Effect of N, N′-m-phenylene bismaleimide on mechanical performance of waste rubber powder sintered by high-pressure high-temperature method

Waste rubber with three-dimensional structure is insoluble and non-melting, which creates recycling problem. The technique called “high-pressure high-temperature sintering” (HPHTS) can convert vulcanized rubber powder into usable rubber products. However, reversion occurs when vulcanizates are exposed to a prolonged treatment at high temperature. This reversion results in the decrease of mechanical properties of sintered waste rubber powder (WRP) samples. To address this problem, a method of enhancing the mechanical properties of sintered WRP by incorporating different content of maleic anhydride (MA) and N, N′-m-phenylene bismaleimide (BMI) is discussed in this paper. The results show that BMI and MA can slow down the formation of the conjugated double bonds. Through Diels–Alder reaction, BMI inhibits conjugated double bonds formation and improves the adhesion between particles and particles, which is beneficial to improvement of final properties. Therefore, BMI improves the mechanical properties of sintered WRP greatly.

“Frozen” pressure effect in GGAG:Ce3+ white light emitting nanoceramics

Nanocrystalline powders of Ce3+ doped Gd3Ga3Al2O12 (GGAG) with the size of tens nanometers were prepared using modified Pechini method. Low Temperature High Pressure sintering method was used for the fabrication of the translucent nanoceramics using as starting materials nanocrystalline GGAG:Ce3+ powders. For growth of GGAG:Ce single crystal the Czochralski method was utilized. XRD measurement was used in order to characterize the grain size of the GGAG:Ce3+ nanostructures. Excitation and emission and luminescence decays measurements were done to observe impact of the grain size and applied pressure on the spectroscopic properties of crystallites and ceramics. It was observed that for the smallest grains both spectra are significantly changed. The spectroscopic properties of the nanopowders were compared to the GGAG:Ce3+ ceramics made from them as well as to the single crystal. It was found that is possible to modify permanently the crystal field in the nanocrystals by applying the pressure during sintering.

Assessment of the performance of TiB2 nanoparticles doped cBN-TiN-Al-Co composites by high temperature high pressure sintering

In this study, cBN composites incorporating TiN–Al–Co were synthesized via high temperature and high pressure (HPHT) methods. TiB2 nanoparticles were employed to optimize cBN cutting tools capacity for precise cutting. The effects of TiB2 nanoparticles on the preparation and properties of cBN composites were comprehensively investigated. The results show that the presence of TiB2 nanoparticles uniformly distributed in the interface not only promotes the formation of AlCo but also inhibits crack propagation, which contributed to the enhanced mechanical properties. With the appropriate addition of TiB2 nanoparticles, cBN composites obtained the compact and fine microstructure and presented better mechanical properties. Consequently, cBN composites incorporating 6 wt% TiB2 nanoparticles exhibited excellent relative density of 99.81%, bending strength of 731 MPa, hardness of 49.5 GPa, fracture toughness of 7.4 MPa⋅m1/2, and abrasive ratio of 2.1. Such composites with outstanding mechanical properties might be promising for cutting tools.

Enhanced thermoelectric power factor of half-Heusler solid solution Sc1-xTmxNiSb prepared by high-pressure high-temperature sintering method

Abstract In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc1-xTmxNiSb (x = 0.0, 0.25, 0.5, 0.75, 1.0) was synthesized by arc melting and subsequent high-pressure high-temperature sintering. The products were examined by means of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The crystal structure of each sample was established to be of the MgAgAs-type, and the cubic lattice parameter was found to behave in accordance to the Vegard's law. The electrical transport properties of the Sc1-xTmxNiSb alloys were determined via resistivity and thermoelectric power measurements performed at temperatures 2–950 K. For each sample a semiconducting-like behavior was found with rather small values of the room-temperature resistivity (ρ = 10–50 μΩm), and fairly large positive Seebeck coefficient (Smax = 80–136 μV/K). For the alloy Sc0.75Tm0.25NiSb, combination of relatively small ρ (similar to that of TmNiSb) with rather high S (comparable to that of ScNiSb) yielded the thermoelectric power factor PF = 1.2 × 10 mW/(m K2) at 650 K, which is about twice larger than that found for ScNiSb. Increasing the amount of Tm in Sc1-xTmxNiSb brings about significant reduction in the thermal conductivity at 350 K from about 6 W/(m K) to ca. 3 W/(m K), and consequently leads to sizable enhancement of the thermoelectric figure of merit.

Особливості формування структури та фазового складу в процесі реакційного спікання кубічного нітриду бору зі сполуками Ti, Cr, V

Influence of sintering temperature on both phase composition and structure of ceramic matrix composites based on cubic boron nitride with binders in a form of Al and the Ti, Cr, V carbides are investigated by methods of physical materials science. As the object of study, three cBN–TiC–Al, cBN–Cr3C2–Al, cBN–VC–Al compositions containing 60% vol. cBN are selected. The composites are obtained by high-pressure high-temperature (HPHT) sintering in high-pressure apparatus AVTT-30 in the temperature range of 1600– 2450°C under pressure of 7.7 GPa. In the process of HPHT sintering of composites in the cBN–TiC–Al and cBN–Cr3C2–Al systems, the formation of titanium and chromium diborides is found at the temperatures of sintering Тsint ≥ 1850°С and Тsint ≥ 2150°С, respectively, simultaneously with the formation of alu-minium nitride. (Less)

Consolidation of nanocrystals of detonation diamonds at high-pressure high-temperature sintering

The process of consolidation of nanocrystals of detonation nanodiamond (DND) into polycrystalline aggregates during their annealing at high pressures and temperatures (HPHT) was studied. The experiments on HPHT annealing of DND powder were carried out using a high pressure apparatus BARS at 5GPa and 1100, 1200°С. It was established that after HPHT annealing the microhardness of sintered DND samples had a value of 14GPa. It was proposed that HPHT annealing of DNDs leads to deep purification of nanoparticle surface, resulting in formation of strong nanodiamond polycrystalline aggregates. The observed growth can be a result of interaction of neighboring DND nanocrystals along the contact areas that are purified of impurities during the HPHT annealing.

Identification of paramagnetic nitrogen centers (P1) in diamond crystallites synthesized via the sintering of detonation nanodiamonds at high pressure and temperature

Diamond single crystals synthesized from powder detonation nanodiamonds (DNDs) by means of treatment at high pressures (P ~ 7 GPa) and temperatures (T > 1300°C) have been studied by electron paramagnetic resonance (EPR). A key feature of treatment (high-pressure high–temperature (HPHT) sintering) is the use of low molecular weight alcohols in the process. The appearance of a hyperfine EPR signal structure due to “paramagnetic nitrogen” (P1 centers) is explained by the growth of submicron and micron diamond single crystals from DND nanocrystals by the oriented attachment and coalescence mechanism. Such growth and coarsening of crystals appreciably decreases the concentration of paramagnetic centers, the presence of which hinders the detection of a hyperfine structure in the EPR signal from P1 centers, in the near-surface areas of coalesced and grown together DND particles. It has been shown that the concentration of paramagnetic defects of all types decreases to ~3.1 × 1018 g–1 (~60 ppm) during HPHT treatment at T = 1650°C. This causes the successful identification of P1 centers, whose fraction is no less than ~40% of the total amount of paramagnetic centers in microcrystals synthesized by HPHT sintering.

Study HTHP Sintered WC/Co Hardmetal

WC/Co is widely used as cutting tools, because has a unique combination of high strength, hardness, toughness, and moderate stiffness, especially with fine grained WC and finely distributed cobalt. WC/Co powder mixture sinters by different methods such as vacuum sintering, microwave sintering and SPS. High pressure high temperature (HPHT) sintering is a proposed method that can result in better distribution of cobalt and avoid undesirable phases by using high pressure, high temperature and very short sintering time. In this study, a powder mixture of WC- 10 wt% Co was sintered by HPHT at 1500 to 1900oC under a pressure of 7.7 GPa for 2 minutes. Microstructural/structural analyses were performed by SEM/EDS. Hardness and compression test were also done to obtain the effect of sintering parameters. It was found that HPHT sintering method can be used to produce WC/Co hardmetal with low sintering time and high production rate. It was realized that increasing sintering temperature in HTHP sintering method results in increasing density but hardness and compression strength increase by increasing sintering temperature up to 1800 oC and then decrease.

Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering

Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering

Structural and magnetic properties of ceramics prepared by high-pressure high-temperature sintering of manganese-doped gallium nitride nanopowders

A precursor system made of Ga(NMe2)3 and Mn[N(SiMe3)2]2 (Me=CH3, initial Mn-contents 5, 10, 20at.%) upon ammonolysis in refluxing ammonia afforded Ga/Mn amide-imide precursors. The 10at.% Mn-precursor was nitrided at 500, 700, and 900°C. The 5 and 20at.% Mn-precursors were nitrided only at 900°C. All nanopowders were characterized by XRD, FT-IR, SEM/EDX, whereas some by Raman spectroscopy and XRF. Magnetization measurements were performed with a SQUID magnetometer. Each nanopowder was subjected to no additive high-pressure high-temperature sintering, 7GPa, 1000°C, 10min, affording ceramic pellets. Their structural and magnetic properties were examined to appraise an extent of Mn-incorporation into GaN under sintering conditions. In all samples, the paramagnetic phase of (Ga, Mn)N was accompanied by an antiferromagnetic residue, the latter resulting from oxidation of air sensitive Mn-excess by-products. (Ga, Mn)N in the ceramics showed increased Mn-contents about 1.6 times higher than in the parent nanopowders.

Comprehensive study of photoluminescence and cathodoluminescence of YAG:Eu3+ nano- and microceramics

The nanosized YAG particles doped with Eu3+ as the luminescent probe, were prepared by the modified Pechini method. The series of samples with various Eu3+ concentrations in the range of 0.1% up to 4% and the different average grain size from 31 to 75nm were obtained. YAG:Eu3+ nanoceramics were fabricated by the low temperature high pressure sintering technique (LTHP). Comprehensive studied with microsized grains ceramic as a reference were performed. The photoluminescence and cathodoluminescence properties of YAG:Eu3+ nanoceramic were performed at room temperature. In particular, the influence of dopant concentration and grain size of nanocrystals on the cathodoluminescence and photoluminescence properties was analyzed. The changes of the luminescent asymmetric ratio associated with the change in local symmetry for nanocrystals, nanoceramics and microceramics was investigated.