Hot-press Sintering Research Articles

Improving the thermoelectric properties of septuple atomic-layer SnBi2Se4 by regulating the carrier concentration through Nb doping

Layered semiconductor materials have garnered significant attention in the thermoelectric field due to their excellent electrical property and intrinsically low lattice thermal conductivity. The septuple atomic-layered ternary compound SnBi2Se4 is reported as a promising thermoelectric material in both bulk and single-layer structures based on theoretical calculations, though experimental investigation remains unexplored. In this work, the melting and hot-press sintering methods were adopted to synthesize the septuple atomic-layered SnBi2Se4. Its unique layered crystal structure contributed to significant anisotropic transport properties and reduced thermal conductivity. However, its thermoelectric performance is constrained by a low carrier concentration that limits electrical conductivity. To solve this issue, the high-valent transition metal Nb was doped at Bi site to provide additional electrons. This doping resulted in a noticeable improvement in the performance of septuple atomic-layered SnBi2Se4 due to increased electrical conductivity and decreased thermal conductivity. Finally, a peak ZT ∼ 0.17 was obtained for SnBi1.97Nb0.03Se4 at 723 K, suggesting the effectiveness of Nb doping in enhancing the performance. These results indicate that septuple atomic-layered SnBi2Se4 is a highly promising thermoelectric material, though further performance improvements are needed.

Hot press sintering of Y2O3-Al2O3 glasses: Impact of particle size on thermal behaviour, sintering ability and mechanical properties of sintered bodies.

The impact of grinding on particle size, thermal behaviour, and sintering ability of yttrium aluminate glass microspheres with eutectic composition (76.8mol % Al2O3 and 23.2mol % Y2O3) was studied. The work was conducted with the aim of determining the optimal particle size and grinding conditions of glassy powder used for hot-pressing of ceramic and glass-ceramic materials with desired mechanical properties. The flame synthesis was used for the preparation of glass microspheres (diameter∼40μm). Ball milling procedure under different conditions was applied to adjust of size of prepared microbodies. The milled powders were subsequently hot pressed. The prepared samples (raw, milled microspheres and hot-press sintered bodies were characterised by X-ray powder diffraction, and scanning electron microscopy. Thermal analysis and particle size analysis in combination with X-ray powder diffraction and high temperature X-ray diffraction was used for detailed inspection of thermal behaviour and phase changes in raw and milled systems in the temperature interval 25-1200°C. The samples after flame synthesis and after milling were found to be X-ray amorphous. The particle size measurements showed that the systems with a smaller average size D [0.9]∼25μm and a monomodal particle size distribution were prepared after 6h of milling. Thermal analysis in combination with X-ray and high temperature X-ray analysis indicated a difference in the crystallization mechanism of the yttrium aluminate garnet phase depending on the milling time. The bulk glass ceramic with fine lamellar eutectic microstructure and interesting mechanical properties (Vickers hardness HV=17.6±0.2GPa, indentation fracture toughness KIC=4.3±0.3MPa.m1/2) resulted from the sintering of microspheres milled for 6h under the "gentlest" conditions (milling speed - 200rpm, and milling balls size - 5mm in diameter).

Examining the mechanical properties of B4C/SiC hybrid reinforced 7075Al matrix composites using fast hot pressure sintering technique

Examining the mechanical properties of B4C/SiC hybrid reinforced 7075Al matrix composites using fast hot pressure sintering technique

Study on Mg segregation, microstructure evolution and fracture behavior of hot-press sintered (TiC+B4C)/6061Al composites after T4 heat treatment

Study on Mg segregation, microstructure evolution and fracture behavior of hot-press sintered (TiC+B4C)/6061Al composites after T4 heat treatment

The high performance titanium suboxide ceramics prepared by a facile in-situ hot-pressed sintering

The high performance titanium suboxide ceramics prepared by a facile in-situ hot-pressed sintering

Novel insight into the microstructure evolution and defect formation of nano-polycrystalline CoCrFeNi HEA during vacuum hot-pressing sintering

Novel insight into the microstructure evolution and defect formation of nano-polycrystalline CoCrFeNi HEA during vacuum hot-pressing sintering

Rapid Sintering Method for Preparing Matrix-Matched Reference Materials in LA-MC-ICP-MS - An Example of Hafnium.

Matrix effects can significantly bias Hf isotopic ratios in situ Hf isotope analyses using laser ablation (LA-) multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), necessitating the use of matrix-matched reference materials for accurate microanalysis. This work introduces a novel fast hot-pressing (FHP) sintering method to produce such reference materials efficiently for in situ analysis. By optimizing sintering temperatures, FHP technology enables the rapid preparation of in situ analysis reference materials with dense structures and homogeneous Hf isotopic compositions. The Hf isotope compositions of the FHP-sintered cassiterite and rutile were assessed using femtosecond LA-MC-ICP-MS, with results consistent with those determined by MC-ICP-MS. The homogeneity tests reveal minimal heterogeneity among the sintered sample tablets, suggesting their potential as reference materials for in situ Hf isotopic determination in cassiterite and rutile. The FHP method offers a rapid, cost-effective alternative to traditional preparation methods, producing large quantities of reference materials with compact structures. This procedure provides great promise for the synthesis of various isotope matrix-matched reference materials.

Improving the Fracture Toughness of Boron Carbide via Minor Additions of SiC and TiB2 Through Hot-Press Sintering.

Boron carbide (B4C) is an essential material in various high-performance applications due to its light weight and hardness. In this work, B4C-based composites were fabricated via a powder route consisting of powder mixing, precursor preparation, and hot-pressing under vacuum. The composites' mechanical properties and microstructure were analyzed to investigate the effect of adding minor second-phase particles. In addition to homogenizing the grain size, the addition of SiC (≤10 wt%) to B4C increased its strength and improved its fracture toughness, with values reaching 551 MPa and 3.22 MPa m1/2, respectively. Meanwhile, the addition of TiB2 (≤10 wt%) significantly improved the strength and fracture toughness only, with values reaching 548 MPa and 3.92 MPa m1/2, respectively, with only a minimal decrease in hardness. Microstructural analysis revealed that the second-phase particles were uniformly distributed and reduced the average grain size, contributing to the increase in strength. Additionally, the TiB2 particles impeded crack propagation and induced crack deflection at the interface, indicating the formation of an intergranular fracture mode. On the contrary, the addition of SiC primarily resulted in transgranular fracture behavior, though it still improved the toughness of the B4C. These results suggest that small amounts of SiC and TiB2 can effectively enhance the mechanical properties of B4C ceramics while maintaining the lightweight characteristics critical for military and aerospace applications.

Upcycling of waste diamond wire sawing silicon powders to prepare Al-50Si composite by hot-pressing sintering

The disposal of waste diamond wire sawing silicon powders (DWSSP) generated during solar-grade silicon wafer production is crucial for the sustainable development of the photovoltaic industry. To achieve the resourceful utilization of DWSSP, a method to prepare Al-50Si composite by upcycling DWSSP through hot-pressing sintering (HPS) was proposed. The effects of hot-pressing sintering temperature, pressure, and current on the densification of DWSSP and Al powders were investigated by finite element modeling analyses and experiments validation. The numerical simulation results showed that pressure-assisted sintering triggered the percolation effect of interparticle currents coupled with localized high Joule heat, accelerating the interfacial reaction between DWSSP and Al powders. It was found that the Vickers hardness and density of the prepared Al-50Si composite increased and then decreased at sintering temperatures of 450 to 500°C and showed a positive correlation at pressures of 50 to 200MPa. Optimal conditions of 475 °C sintering temperature, 150MPa sintering pressure, and 5min holding time yielded Al-50Si composite with a density of 2.36g/cm3 and a Vickers hardness of 201 HV0.1. The findings demonstrate the application of HPS method allows for the grave-to-cradle waste management of DWSSP and the preparation of recycled Al-50Si composite for its high value-added utilization.

Novel insight into the microstructure evolution and strengthening mechanism of nanocrystalline copper prepared by hot-pressing sintering: A molecular dynamics study

An integrated strategy is proposed for the design and performance evaluation of nanocrystalline (NC) copper prepared by using the hot-pressing sintering process (HPS). Molecular dynamics (MD) simulation is employed to investigate the microstructure and performance of the prepared NC copper. The merging of nanoparticles (NPs) during HPS is influenced by the initial surface area of NPs. A higher surface area corresponding to a smaller size of NPs will promote the merging of NPs by providing more interface for the diffusion of atoms. The designed grain size can be obtained by adjusting the initial size of NPs. The mechanical properties of NC copper do not present a liner correlation with the grain size. With the grain size increasing from 1.51 to 4.10 nm, the strength and ductility of NC copper first increase but then decrease. The cooperating influence of the grain boundaries with high strength and the matrix with high ductility on the mechanical properties is revealed. This study highlights the relationship between microstructure evolution and mechanical properties in NC metals, offering insights into designing high-performance NC materials. The MD model can be extended into another case with a larger size and time scale.

In situ synthesis of Si3N4/h-BN composites by hot-pressed sintering

Various methods have been implemented to deal with the problem of the aggregation of h-BN in the Si3N4 matrix, thereby improving the machinability of Si3N4 ceramics. In this paper, the in-situ phase transformation of c-BN was introduced to prepare hot-pressed Si3N4/h-BN composites. Results show that compared with the direct addition of h-BN, the h-BN generated by the phase transformation of c-BN was more homogeneously disperse in Si3N4 matrix. Meanwhile, the phase transition (c→h-BN) enhanced the densification process, and the retarding effect of BN on the α→β-Si3N4 phase transformation and the Si3N4 grain growth was weakened. Thereby, the interlocking microstructure of elongated grains was greatly improved, and the fracture toughness and flexural strength of Si3N4/h-BN composites increased by 9.2 % and 11.5 %, respectively, after the addition of 5 vol.% c-BN. The proposed method provides a new idea for the preparation of composite ceramics.

Tailoring structural and mechanical properties of Cf/SiC ceramic matrix composites with BN/SiAlC interphases

In this work, we studied the effects of protective boron nitride/silconaluminocarbide (BN/SiAlC) interphases on the structural and mechanical properties of fabricated stacked carbon fiber-reinforced SiC ceramic matrix composites (Cf/SiC CMCs) via the hot-press sintering route. The structural analyses were carried out by X-ray diffraction and scanning electron microscopy (SEM), while mechanical properties were elucidated by employing universal testing machine. The observed sharp diffraction peaks indicate excellent crystallization, and the formation of 4H-SiC polytype was attributed to the partial transition of β-SiC phase during high-temperature sintering. The composite with single BN interface layer revealed enhanced bending strength of up to 364 ± 39.46 MPa (↑40 %), while composite with double layered interface showed optimal strength of 436 ± 33.54 MPa, and toughness of 6.11 ± 0.74 MPa.m1/2, with increments of 67.7 % and 128.8 %, respectively, compared to the composite without interphase layer. In the composite with duplex interfacial layer (3BN/SiAlC), the microcracks generated during fracture propagated into the BN layer, deflected through both the sublayers and at the fiber-BN interface, resulting in fiber pull out using fracture energy, leading to the enhanced strength and toughness of the composite. The load-displacement curve revealed that the stacking Cf/SiC CMCs with weak interlayer binding owing to the BN/SiAlC coating treatment possesses significant toughness to the SiC ceramics.

Effect of Si Gradient Pattern on the Microstructure and Properties of Laminated Electrical Steel Composites Prepared by Hot-Press Sintering

In this study, electrical steel laminated composites with positive Si gradient (PO-G), counter Si gradient (CO-G), and cross Si gradient (CR-G) were fabricated by hot-press sintering, cold rolling and annealing. The microstructure evolution during processing, as well as the magnetic and mechanical properties were investigated. The results indicate that the microstructure of the high-silicon layer and medium-silicon layer in the hot-pressed composites featured columnar grains throughout the thickness. The microstructure of the low-silicon layer in the hot-pressed CO-G sample consisted of equiaxed grains. However, a mixed structure dominated by columnar grains with some equiaxed grains was observed in the inner low-silicon layer of the PO-G and CR-G samples. Following cold rolling, the thickness ratio of each layer remained largely unchanged. After annealing, the microstructure of each layer transformed into columnar grains. The average grain size of the high-silicon layer, medium-silicon layer, and low-silicon layers in the three composites were approximately 20–23 μm, 33–38 μm, and 42–49 μm, respectively. Compared with the CO-G and CR-G samples, the annealed PO-G composite exhibited lower core loss at 400–1000 Hz and superior tensile strength. Furthermore, the core loss of the three composites was greater than that of the initial medium-silicon and high-silicon materials. This can be attributed to the increased hysteresis loss due to the existence of multi-layer interface.

Influence of rare earth second phases on the salt spray corrosion and electrochemical corrosion properties of FeCrAl-Gd-Sc alloys

FeCrAl alloys have excellent oxidation and corrosion resistance and have been widely used in cladding materials and structural components. In this study, Fe-21Cr-4Al-xGd-xSc (x=0, 0.5, 1, 2 wt%) alloys were prepared by the vacuum hot press sintering method. The corrosion properties of the Fe-21Cr-4Al-xSc-xGd alloy have been investigated by salt spray and electrochemical corrosion methods. The results show that Sc and Gd doped FeCrAl alloys form nanoscale cubic phase ScAlO3, Gd monomer and intermetallic compounds between Gd and Fe as the second phase. The Sc and Gd doped FeCrAl alloy forms a corrosion film on the surface during the corrosion process. It can effectively hinder the erosion of corrosive ions on the alloy, thus improving the corrosion resistance of the FeCrAl alloy. The second phase (Gd monomer, Fe5Gd, Fe9Gd, ScAlO3) effectively prevents micro galvanic corrosion of inclusions when the addition of Sc and Gd is less than 1 wt%. When the content of Sc and Gd reaches 2 wt%, the role of the second phase tends to accelerate the corrosion of the alloy by acting as the cathode of micro galvanic corrosion. Therefore, FeCrAl-1wt%Sc-1wt%Gd alloy has a better corrosion resistance, and the corrosion rate is only 1.37 mm/year.

Effects of alloying elements on microstructure evolution, interfacial structure, and mechanical properties of Al/Cu laminate

Hot press sintering process was employed to fabricate the Al/Cu laminates with pure Al or 6061Al as interlayer, and the effects of alloying elements on microstructure evolution, interfacial structure, and mechanical properties were clarified. A good metallurgical bonding was achieved and intermetallic compounds layers consisting of Al4Cu9, Al2Cu, and AlCu phases formed at the Al/Cu interface. Mg element facilitated the enrichment of Cu atoms and provided the nucleation sites for Al2Cu, resulting in a thicker Al2Cu phase and numerous dispersed Al2Cu particles in 6061Al/Cu laminate. MgAl2O4 phase distributed along 6061Al/Al2Cu interface, and it exhibits a coherent relationship with both 6061Al and Al2Cu, which contributed to enhancing the resistance of dislocation movement and the effectiveness of load transfer. During the tensile deformation of Al/Cu laminate using pure Al as the interlayer, the cracks were more likely to propagate across the Al/Al2Cu interface into the Al layer. When 6061Al was used as interlayer, the overall higher tensile strength was achieved, and the tensile curves showed two distinct stress drops. Moreover, the cracks faced greater resistance when traversing the 6061Al/Al2Cu interface during the expansion, and they tended to extend along the 6061Al/Cu interface, showing a distinct delamination fracture morphology.

Ultrafast pressure sintering: A one-step route to dense high-entropy carbide from precursors

Bulk high-entropy carbide ceramics (HECs) possess exceptional properties, but their fabrication typically involves energy-intensive and complex processes. This study introduces a novel ultrafast pressure sintering (UPS) method for the one-step synthesis and densification of HECs. Utilizing a custom-designed apparatus, this approach leverages the synergistic effects of direct Joule heating, reaction-released heat, and precisely controlled pressure to fabricate dense, single-phase, and homogeneous (Cr0.2Nb0.2Ta0.2Mo0.2W0.2)C0.83 HEC with a fine-grained microstructure at a relatively low temperature of 1800 °C and a short dwell time of 3 min. Compared to conventional techniques such as hot-pressing and spark plasma sintering, UPS offers significant advantages, including reduced energy consumption, simplified processing, lower equipment costs, and enhanced scalability. This novel approach not only presents a promising route for the efficient fabrication of HECs, but also elucidates the underlying mechanisms governing their synthesis and densification, opening the way for broader applications in the development of advanced materials.

Effect of hot-pressing sintering temperature and pressure on the densification and properties of Ti-TiB composites

Ti/TiB composites exhibit promising potential for applications in the automotive, aerospace, and biomedical sectors. Hot pressing coupled with in situ reaction synthesis is a commonly employed technique for fabricating discontinuously TiB-reinforced titanium matrix composites. Despite its efficacy, comprehensive research investigating the influence of hot-pressing process parameters on the densification and properties of these composites remains scarce. This study systematically examined the effects of pressure (16–48 MPa) and temperature (1250 °C to 1350 °C) on the density, microstructure, and mechanical properties of Ti/TiB composites produced through hot pressing. By analyzing densification curves and rate curves, the densification behavior under varying processing conditions was elucidated. The results indicate that elevated sintering temperatures and pressures correlate with increased densification rates, reduced porosity, and enhanced sample density. A strong relationship between relative densities and hardness was observed. This research contributes to a deeper understanding of the hot-pressing sintering process for Ti-TiB composites and facilitates the optimization of processing conditions.

Neutron shielding performance of polyethylene-7% B and Al-30 wt% B4C composites fabricated via hot-press sintering

The current research aims to investigate the neutron shielding features of polyethylene-7% B and Al-30 wt% B4C composites that are fabricated via the hot-press sintering. The practical analysis was conducted via Neutron radiography and simulation through MCNP code. The results illustrated the Al-30 wt% B4C with 5 mm thickness has equivalent neutron absorption properties with 14 mm thickness of PE-%7 B. Composites with higher density and homogenous distribution of B4C have a better neutron shield property. Al-30 wt% B4C Composite fabricated at 650 °C has a higher neutron absorption property. Experimental and simulation findings confirmed each other at the lower thicknesses and Al-30 wt% B4C has better neutron shielding than PE-7% B. At thicknesses over 1 cm, the amount of cross-sectional area of polyethylene-7% B and Al-30 wt% B4C composites are near to each other. By increasing the thicknesses of composites, the relative total dose reduction and the shield properties of composites are enhanced.

Correction: Effect of MgO Content on the Microstructure and Properties of Zirconia-Toughened Alumina (ZTA) Ceramics by Hot Pressure Sintering

Correction: Effect of MgO Content on the Microstructure and Properties of Zirconia-Toughened Alumina (ZTA) Ceramics by Hot Pressure Sintering

Bionic structural design and model calculation for high toughness Si3N4f/BNi fibrous monolithic ceramic: A strategy from the fibrous cell and interface

Preeminent mechanical and dielectric performances are demonstrated by covalently bonded Si3N4 ceramics, yet their application range is still challenged because of limited toughness and sintering density. In this work, the Si3N4f/BNi fibrous monolithic ceramic with uniaxially arranged Si3N4 fibers cells separated by BN interfaces were successfully synthesized via hot-pressed sintering based on bionic structural design. The Si3N4f/BNi fibrous monolithic ceramics with bionic structure exhibited flexural strength, fracture toughness, and density of up to 501 MPa, 10.99 MPa m1/2, and 3.43 g/cm3, respectively. The results revealed that bionic structural design enables to significantly increase the toughness of the ceramic without sacrificing its strength. Furthermore, an original model for determining the flexural strength of fibrous monolithic ceramics was proposed, which can account for various shapes of fibrous cells. The findings of this research open up new prospects for achieving competitive mechanical performance of ceramics.