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TiB 2 -B 4 C composites modified by SiC W with excellent mechanical properties were prepared using hot-press sintering. The effects of SiC W content on the microstructure, densification behavior and mechanical properties were investigated. The dynamic failure behavior was analyzed through the Hopkinson Bar (SHPB) testing. The results demonstrate that the addition of SiC W can effectively refine the microstructure and simultaneously improve the mechanical properties. The TiB 2 -B 4 C composite renforced with 6 wt% SiC W exhibits a nearly full-dense microstructure and excellent mechanical properties. The relative density, flexural strength, Vickers hardness and fracture toughness can reach to 99.95 %, 724 ± 61 MPa, 19.8 ± 0.7 GPa and 6.7 ± 0.3 MPa m1/2, respectively. The dynamic failure behavior exhibits that the damage degree increases with elevated loading speed. Moreover, the single-peak and double-peak of the waveform correspond to the two damage degrees of "broken" and "crushed". [ABSTRACT FROM AUTHOR]

Even though BiFeO3–BaTiO3 (BF–BT) with high Curie temperature and excellent piezoelectric properties is very suitable for high‐temperature applications, its rapid reduction in resistivity with temperature limits its further application. So far, there is no effective method to improve the resistivity of BF–BT at a high‐temperature state. In this work, hot‐press sintering combined with an oxygen atmosphere was used to prepare (1 − x)BF–xBT (x = 0.2–0.33) ceramics for the first time, which reduced the sintering temperature from 1000 to 920°C. The controllable grain size can be achieved by adjusting the sintering temperature and the applied pressure. The X‐ray photoelectron spectroscopy results confirmed that using hot‐press sintering effectively avoided the generation of heterovalent Fe ions, and the resistivity of BF–BT ceramics at the high‐temperature stage was improved by two orders of magnitude. It was found that hot‐press sintering can cause the oriented growth of the sample along the (1 1 0) direction, and further refined X‐ray diffraction was used to accurately analyze the changes in the lattice structure. The hot‐press sintered samples obtained larger polarization strength, especially the electro‐induced strain showed excellent temperature stability in the wide temperature range of 30–170°C. Hot‐pressing sintering combined with an oxygen atmosphere is more suitable for preparing high insulation and electrical breakdown resistance ceramics. [ABSTRACT FROM AUTHOR]

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples. [ABSTRACT FROM AUTHOR]

Infrared transparent Ce‐doped Y3Fe5O12 (Ce: YIG, CexY3‐xFe5O12, x = 0, 0.12, 0.24, 0.36) ceramics were successfully produced by the solid‐state reaction using a hot‐press sintering process from the Y2O3, Fe2O3, and CeO2 powders. The phase structure, microstructure, infrared transmittance, and magnetic and magneto‐optical properties of the Ce‐doped Y3Fe5O12 ceramics were measured and analyzed. The in‐line transmittances of the Ce‐doped Y3Fe5O12 ceramics with the x = 0, 0.12, 0.24 (L = 0.5 mm) at 1550 nm were about 72%, 66.5%, and 57.6%, respectively. In the state of saturation magnetization, the Faraday rotation angle per centimeter (θF) of CexY3‐xFe5O12 (x = 0, 0.12, 0.24) ceramics measured by the light extinction method was 182.5, −410.4, and −958.3 deg./cm, respectively. The change of the θF was about −142.5 deg./cm when per 1at.% Ce was substituted in the dodecahedral site of YIG materials. The (Ce0.24Y2.76)Fe5O12 ceramics were determined as the optimized composition for its excellent infrared optical and magneto‐optical properties. [ABSTRACT FROM AUTHOR]

Bi 4 Ti 3 O 12 (BIT) ceramic has great potential in high-temperature environment due to its high Curie temperature T C ~ 675 °C. In this work, hot press sintering (HPS) is applied on the 0.01 mol Ce and Nb/Cr co-doped BIT (BCTNC) ceramics to enhancing the low piezoelectric coefficient (d 33 < 7 pC/N) and resistivity. Extremely high d 33 (~39 pC/N) together with high T C (~672 °C) and high dc resistivity ρ (~1.49 ×107 Ω ∙cm at 500 °C) are obtained in HPS samples. The enhancement of piezoelectricity benefits from high density of domain and high poling electric field. Moreover, outstanding thermal stability of piezoelectric constant (d 33 ~ 35 pC/N after annealing at 650 °C) and low dielectric loss (tan δ ~ 3.8% at 500 °C) are observed as well. These findings are instrumental in understanding HPS and provide a possible manipulation of crystallized mechanism and domains growing kinetics to enhance piezoelectric performances of BIT based ceramics. [ABSTRACT FROM AUTHOR]

The CrCuFeMnNiCox high‐entropy alloys (HEAs) were prepared by vacuum hot‐press sintering. The microstructure and atmospheric oxidation behavior at 800°C were studied. The phase structure of the Co0 alloy comprised the Cr‐rich FCC1 major phase, Cu‐rich FCC2 secondary phase, and a small amount of intermetallic compound ρ phase when x = 0. The bulk alloys comprised FCC2 major and FCC1 secondary phases when x ≥ 0.5. The oxidation kinetics curves approximately followed the parabolic law. A high Co content leads to a large oxidation weight gain of the alloys. The oxidation weight gain of the Co0 alloy was the smallest at approximately 4.46 mg cm−2 after atmospheric oxidation for 50 h, while the oxidation weight gain of the Co2.0 alloy was the largest at approximately 5.94 mg cm−2. The Co0 alloys exhibited the best oxidation resistance. Therefore, Co is not beneficial to the improvement of the oxidation properties of the CrCuFeMnNiCox HEAs. The main oxidation products of the HEAs mainly comprised MO, M2O3, M3O4, and (M,Cr)3O4 type metal oxides. The main oxidation mechanism was selective oxidation. [ABSTRACT FROM AUTHOR]

Grain size plays an important role in affecting the physical properties of ceramics. In this work, the effects of pre-sintering grain size G 0 of BaFe 12 O 19 (BaM) on the microstructure and magnetic properties of hot-press sintered BaM thick films were studied. Results show that reducing G 0 in submicron scale leads to notable decreases in grain growth activation energy and final sintered grain size. Smaller G 0 makes BaM grains easier to be aligned by magnetic field before sintering and less magnetic domain walls in the sintered film. This increases the c -axis orientation, out-of-plane remanence ratio SQ (>0.9) and coercivity of sintered film. Moreover, the zero-field ferromagnetic resonance linewidth ΔH decreases 54% as G 0 reduces from 1 μm to 0.3 μm. This is attributed to the increased film uniformity with larger SQ and film density D rel at smaller G 0. The above findings enable better understanding on the role of G 0 in improving the magnetic properties of hot-press sintered BaM and other hexaferrite thick films for self-biased microwave devices. [ABSTRACT FROM AUTHOR]

A machinable α-Al2O3/mica composite was prepared by hot-press sintering. In this experiment, a mica-contained glass ceramic in the MgO-Al2O3-SiO2-F glassy system was employed and the base glass powders were obtained by traditional melting-quenched method. Then, α-Al2O3 milling swarf was introduced by medium α-alumina milling ball to the glass powders. The test results indicate that the composites consist of mica crystal and mullite crystal, which are precipitated in the base glass. The α-Al2O3 shows an irregular polygon, which is inlayed in the base material. With the decrease of size of the base glass powders, the boundaries of composites among the sintered powders gradually vanish. The mica crystals in the composite also show an interlocking characteristic, which is a prerequisite of mica-contained glass ceramics with good machinability. Under different pressures, the tendency of preferred orientation is decreased with the reduction in grain size of glass powders, and the microstructure is proved to be consistent, significantly decreasing the composite’s hardness. Therefore, the machinability of the composite is improved.

Aluminum nitride (AlN) is used a ceramic heater material for the semiconductor industry. Because extremely high temperatures are required to achieve dense AlN components, sintering aids such as Y 2 O 3 are typically added to reduce the sintering temperature and time. To further reduce the sintering temperature, in this study, a low-melting-temperature glass (MgO–CaO–Al 2 O 3 –SiO 2 ; MCAS) was used as a sintering additive for AlN. With MCAS addition, fully dense AlN was obtained by hot-press sintering at 1500 °C for 3 h at 30 MPa. The mechanical properties, thermal conductivity, and volume resistance of the sintered AlN–MCAS sample were evaluated and compared with those of a reference sample (AlN prepared with 5 wt% Y2O3 sintering aid sintered at 1750 °C for 8 h at 10 MPa). The thermal conductivity of AlN prepared with 0.5 wt% MCAS was 91.2 W/m∙K, which was 84.8 W/m∙K lower than that of the reference sample at 25 °C; however, the difference in thermal conductivity between the samples was only 14.2 W/m∙K at the ceramic-heater operating temperature of 500 °C. The flexural strength of AlN–MCAS was 550 MPa, which was higher than that of the reference sample (425 MPa); this was attributed to the smaller grain size achieved by low-temperature sintering. The volume resistance of AlN–MCAS was lower than that of the reference sample in the range of 200–400 °C. However, the resistivity of the proposed AlN–MCAS sample was higher than that of the reference sample (500 °C) owing to grain-boundary scattering of phonons. In summary, the proposed sintering strategy produces AlN materials for heater applications with low production cost, while achieving the properties required by the semiconductor industry. [ABSTRACT FROM AUTHOR]

In this study, the surface of an AA-2024 alloy was covered with reinforced composite coating using hotpress sintering method. Al and B4C powders were synthesized through mechanical alloying technique and coated on the AA-2024 substrate at different rates. The microstructure of the intermediate transition region formed between the substrate (AA-2024 Al alloy) and the coating layer (Al/B4C MMCs), the microstructure of the Al/B4C metal matrix composites (MMCs) coating, the microhardness, and the adhesive wear resistance of the Al/B4C MMCs coating layer were investigated. It was observed that B4C powders homogeneously dispersed in the microstructure of the Al/B4C MMCs coating layer, moreover, the Al matrix and B4C reinforcement particles were bonded without a gap. It was also determined that an interface bonding occurred between Al/B4C MMCs coating layer and the AA-2024 substrate. Accordingly, it was determined that with the increase of B4C reinforcement particle ratio, the hardness of the coating layer, and the wear resistance increased. [ABSTRACT FROM AUTHOR]

In this current study, the impact of manganese addition to 93 W-4.9Ni-2.1Cu-xMn (where x = 1, 2, 3, and 4 Wt%) on the microstructure, texture development, and grain boundary character distribution of tungsten heavy alloy (WHAs) was examined. The samples were produced through a vacuum hot press sintering, with parameters 50 MPa pressure, 10 °C/min heating rate, and 1450 °C sintering temperature for 20 min holding duration. To study the influence of manganese on the texture development and microstructure in conventional WHAs, electron backscatter diffraction (EBSD) was employed. The important findings from the EBSD analysis reveal that fibre texture (001) 〈111〉 and a higher fraction of low-angle grain boundaries in the Mn unalloyed compact resulted from extensive atomic jumps between the particles at elevated temperatures. Further texture analysis on the Mn-added compacts reveals that manganese oxide (MnO) formation during liquid phase sintering led to lower densification and randomized weak fibre texture development in manganese-alloyed compacts. In addition, the texture degradation in Mn-added compacts is mainly caused by recrystallization followed by sub-structural recovery during liquid phase sintering. This study indicates that increasing manganese content in WHAs stoichiometry led to a heterogeneous distribution of binder matrix (Ni Cu) in the sintered compact. As a result, W-4.9Ni-2.1Cu-4Mn alloy revealed decreased relative density (90.70%), microhardness (389.5 HV 0.5), and electrical conductivity (15.74% of IACS). [Display omitted] • The formation of manganese oxide in Mn-added WHAs leads to a reduction in density and properties. • The addition of Mn into WHAs induces alterations in the texture orientation of Ʃ3 CSL and HAGBs. • The {111} 〈001〉 texture became weaker as the manganese stoichiometry in WHAs increased. • Hardness and conductivity showed the W-Ni-Cu alloy does not benefit from Mn. [ABSTRACT FROM AUTHOR]

In the present research an Al–7.7%Mn–4.9%Zr–3.2%Cu (wt%) alloy was processed by mechanical alloying (MA) followed by hot press sintering. The microstructure, phase composition, and mechanical properties of the MA granules and sintered samples were investigated. The dissolution of Mn, Zr, and Cu with further precipitation of the Al6Mn phase were observed during high-energy ball milling. In the alloy processed without stearic acid after milling for ~10 h, an Al-based solid solution with ~4.9 wt%Zr, ~3.2 wt%Cu and a ~5 wt%Mn with a grain size of ~16 nm and a microhardness of ~530 HV were observed. The addition of stearic acid facilitated Mn dissolution and precipitation of the Al6Mn phase during milling but led to the formation of the ZrH2 phase that decreased the Zr solute and the microhardness. Precipitation of the Al6Mn, L12–Al3Zr, and Al2Cu phases during annealing and sintering of the MA granules in the temperate range of 350–375 °C was observed, and an additional Al20Cu2Mn3 phase was precipitated at 400–450 °C. Hot-press sintering at 450 °C provided a low fraction of cavities of ~1.5%, the yield strength of 1100 MPa, ultimate compressive strength of 1200 MPa, strain at fracture of 0.5% at room temperature, the yield strength of 380 MPa, ultimate compressive strength of 440 MPa, and strain at fracture of 3.5% at 350 °C. The microstructural evolution during high-temperature deformation on the sample surface was studied and the differences in deformation behavior for the alloys sintered at different temperatures were discussed. [ABSTRACT FROM AUTHOR]

Dense lead-free ceramics K 0.5 Na 0.5 NbO 3 were prepared via hot-press sintering in a relatively wide temperature window. Mean grain sizes of the ceramics increase from 160 nm to 720 nm due to changing the sintering parameters. All ceramics exhibit single orthorhombic phase, different domain sizes and domain morphology. Microstructure, dielectric, ferroelectric, and piezoelectric properties of the ceramics were studied systematically. For the ceramics with the mean grain size of 160 nm, the highest maximum polarization (P m) of 30.8 μC/cm2, dielectric constant (ϵ r) of 7119, piezoelectric constant (d 33) of 151 pC/N, and converse piezoelectric constant (d 33 *) of 291 p.m./V under the very low measurement electric field of 30 kV/cm were obtained. The excellent electrical properties are related to nano-scale fine domain configuration in fine-grained ceramics. [ABSTRACT FROM AUTHOR]

Boron nitride-barium aluminosilicate (BN-BAS) composite ceramics were fabricated by the sol-gel method and hot-pressed sintering. The effects of the introduction method of BAS and sintering temperature on the phase assemblage, density, apparent porosity, mechanical properties and microstructures of the h-BN composite ceramics were investigated. The following two introduction methods were adopted: (A) BAS gel powder was prepared by the sol-gel method and then mixed with h-BN for hot pressing sintering, and (B) the BN-BAS composite powder was first prepared by the sol-gel method and then hot-pressed and sintered. The results indicate that the density, bending strength and fracture toughness of the latter are higher than those of the former when other conditions are the same. In the gel step of Group B, BAS has been coated on the surface of BN particles in dots, chemical bonding has existed, the distribution of BAS is more uniform, and it can better serve as a sintering aid. The BN-BAS composites prepared by both methods achieved the maximum mechanical properties at a sintering temperature of 1700 °C, and the density, apparent porosity, bending strength and fracture toughness of Group A were 2.40 g/cm3, 1.82%, 132.8 MPa and 2.3 MPa m1/2, while those of Group B were 2.42 g/cm3, 1.45%, 162.9 MPa and 2.7 MP m1/2. [ABSTRACT FROM AUTHOR]

This study examines the effect of cobalt on the crystallographic texture and grain boundary evolution of hot-press sintered tungsten heavy alloy (W-4.9Ni-2.1Cu). Traditional tungsten heavy alloy with a Ni:Cu ratio of 7:3 has cobalt added (i.e., cobalt content increased from 0 to 1 wt% with a 0.25 wt% interval). The samples were produced using the hot press sintering method with the following parameters: 50 MPa pressure, 10 °C/min heating rate, 1450 °C temperature, and a 20-min hold time. The unalloyed cobalt WHA compact has a fibre texture in the (001) plane that is aligned in the 〈111〉 orientation. In addition, the cobalt-alloyed WHAs compacts exhibit a lower proportion of grain boundaries with low angles. Enhanced solid solution formation between cobalt and WHAs during liquid phase sintering led to increased compacts densification and randomised weak fibre development in cobalt-alloyed compacts. Texture deterioration (001) <111> in cobalt-added WHAs is caused predominantly by substructural recovery during liquid phase sintering. This study indicates that the addition of cobalt to the stoichiometry of WHAs resulted in the homogenous distribution of binder matrix within the compact during sintering. As a result, the W-4.9Ni-2.1Cu-1Co alloy exhibited improved microhardness (429.5 HV0.5), electrical conductivity (23.34% of IACS), and relative density (98.10%). • The use of ball milling results in higher densification, faster solution re-precipitation kinetics during sintering. • Weakness in (001) <111> texture was attributed from the increase of cobalt stoichiometry in WHAs (W-4.9Ni-2.1Cu). • Enrichment of cobalt at the tungsten-binder matrix interface results in textural anisotropy in cobalt added WHAs. • Cobalt is an effective alloying addition for strengthening the WHA as evidenced by an increase of hardness and conductivity. [ABSTRACT FROM AUTHOR]

In this research, Co-30 mass% Cr alloys were fabricated by a vacuum hot-press sintering process. Different amounts of submicron cobalt and chromium (the mean grain size is 800 and 700 nm, respectively) powders were mixed by ball milling. Furthermore, this study imposed various hot-press sintering temperatures (1100, 1150, 1200 and 1250°C) and pressures (20, 35 and 50 MPa), while maintaining the sintering time at 1 h, respectively. The experimental results show that the optimum parameters of hot-press sintered Co-30 mass% Cr alloys are 1150°C at 35 MPa for 1 h. Meanwhile, the sintered density reaches 7.92 g·cm-3, the closed porosity decreases to 0.46%, and the hardness and transverse rupture strength (TRS) values increase to 77.2 HRA and 997.1 MPa, respectively. While the hot-press sintered Co-30 mass% Cr alloys at 1150°C and 20 MPa for 1 h, the electrical conductivity was slightly enhanced to 1.79 × 104 S·cm-1, and the phase transformation (FCC → HCP) of cobalt displayed a slight effect on sintering behaviors of Co-30 mass% Cr alloys. All these results confirm that the mechanical and electrical properties of Co-30 mass% Cr alloys are effectively improved by using the hot-press sintering technique. [ABSTRACT FROM AUTHOR]

In the present research, two different compositions of submicron-structured cobalt (800 ± 45 nm) and chromium (700 ± 50 nm) powders are mixed to fabricate Co-50 mass% Cr alloys by the vacuum hot-press sintering technique. This study imposes various hot-press sintering temperatures (1150, 1200, 1250 and 1300°C) and pressures (20, 30, 40 and 50 MPa) while maintaining the sintering time at 1 h, respectively. The experimental results show that the optimum parameters of hot-press sintered Co-50 mass% Cr alloys are 1200°C at 50 MPa for 1 h. Meanwhile, the sintered density reaches 7.73 g cm−3, the closed porosity decreases to 0.31%, and the hardness and transverse rupture strength values increase to 80.6 ± 0.3 HRA and 1052.9 ± 17.5 MPa, respectively. Grain growth is not obviously generated after 1200°C hot-press sintering at 50 MPa for 1 h. Consequently, the optimal solid-phase sintering process effectively improved hot-press sintered Co-50 mass% Cr alloys, which resulted in the good properties. [ABSTRACT FROM AUTHOR]

Sintering is a critical process for the preparation of metallic matrix diamond tools. The purpose of this work aims to propose a novel microwave hot-press sintering (MHPS) method for the improvement of mechanical properties for Fe-Cu-W-Sn matrix diamond tools. The samples were prepared by MHPS and conventional hot-press sintering (CHPS), respectively. The microstructures of samples were characterized using XRD, EMPA, and SEM tests. The mechanical properties of samples, such as relative density, hardness, bending strength, and impact toughness were also investigated. Experimental results show that the samples by MHPS method has obvious advantages with shorter sintering time, lower sintering temperature, more uniform element diffusion, and better holding situation of diamond abrasives in the alloyed matrix. The optimal mechanical properties of samples sintered by MHPS at 850 °C, to be specific, including relative density, hardness and flexural strength reach 97.8%, 99.2 HRB and 986 MPa, respectively. The possible mechanism of MHPS is discussed. This work can provide a reference for microwave sintering of metallic matrix diamond tools. [ABSTRACT FROM AUTHOR]