Hot-press Sintering Process Research Articles

Hot pressing sintering process and sintering mechanism of W–La2O3–Y2O3–ZrO2

The W–La2O3–Y2O3–ZrO2 materials were prepared by vacuum hot pressing sintering process. The microstructure was characterized by scanning electron microscopy (SEM). The effects of sintering temperature, sintering pressure, holding time and heating rate on relative density, hardness and microstructure were studied. The sintering activation energy of the powder was calculated. Based on the result, the best sintering parameters by vacuum hot pressing sintering are as follows: sintering temperature of 1600 °C, sintering pressure of 60 MPa and holding time of 60 min. The heating rate is 10 °C·min−1 from room temperature to 1000 °C and 4 °C·min−1 from 1000 to 1600 °C. Using this process, the grain size is about 3 μm in diameter with relative density at 99.7%, and the hardness is HV 528.5. The sintering characteristic index (n) of the specimen is 4, and the sintering mechanism mainly depends on the diffusion from the surface to the intragranular in the volume diffusion. The sintering activation energy of W–La2O3–Y2O3–ZrO2 material is 286.2 kJ·mol−1, which indicates that the powder has higher activity in sintering process.

Mechanical durable ceria superhydrophobic coating fabricated by simple hot-press sintering

Mechanical durability is always a significant challenge in the application and research of superhydrophobic surfaces. In this work, a mechanical durable ceria (CeO2) superhydrophobic surface was fabricated by a facile hot press sintering process of CeO2 powders on the Cu substrate. Combustion synthesis is firstly adopted to fabricate CeO2 powders because powders with suitable micro-roughness for superhydrophobicity could be obtained by this method. In order to achieve hierarchical microstructures, stainless steel mesh is used to be the template in the hot press sintering process. After 90-day storage in air, the surfaces maintain superhydrophobic performance, indicating that the coating exhibits good long-term durability. The as-obtained superhydrophobic surface shows excellent mechanical stability after ultrasonic treatments of 120 min. The morphologies of the coatings before and after ultrasonic are observed. It is found that the microstructure is stable enough to resist severe mechanical damage, indicating the strong binding force between superhydrophobic coating and the substrate. This hot-press method has also been used to prepare superhydrophobic CeO2 surfaces on other different metal substrates, which shows broad application prospects.

텅스텐 제조를 위한 소결공정의 영향과 기계적 특성 평가

The monolithic tungsten materials were fabricated by a hot pressed sintering process using a chromium powder as an additive material in this study. Especially, mechanical properties of tungsten materials including the flexural strength and hardness were evaluated due to the sintering temperature and the effect of additive amount. SEM was also used to analyze the microstructural characteristics of the sintered tungsten material. It was found that both sintered density and flexural strength of tungsten materials increased with the increase in sintered temperature and additive Cr amount, accompanying to the grain growth in the microstructure. The relationship between microstructure and mechanical properties of flexural strength is discussed for producing the optimal fabricating condition of tungsten materials. The bending strength and Vickers hardness of tungsten sintered material increased with increasing sintering temperature. The bending strength of the tungsten sintered material was about 580 MPa and the Vickers hardness was about 470 Hʋ when 7 wt% of chromium powder was added at sintering temperature of 1,600℃. At the sintering temperature of 1,600℃, the sintering density of tungsten sintered material increased with promotion of microstructure densification as the content of chromium added to tungsten powder increased. In particular, it showed excellent sintered density of about 17.04 g/㎤ at a chromium content of 7 wt%.

The electrical and optical properties of Nb-doping PLZT (9/65/35) transparent ceramics

In the past few decades, transparent electro-optical ceramics PLZT (9/65/35) (Pb0.91La0.09(Zr0.65Ti0.35)0.9775O3) with special properties, particularly high transmittance in visible light, have gained much attention. However, restricted by the large ferroelectric hysteresis, the prospect is not optimistic. In this article, Pb0.91La0.09(Zr0.65Ti0.35)0.9775-5x/4NbxO3 (abbreviated as PLZTN) transparent ceramics with varying Nb content (x = 0.000, 0.005, 0.010, 0.015) were fabricated by hot press sintering process under oxygen atmosphere. Electrical and optical properties were systematically studied. The temperature dependence of the dielectric constant showed a diffuse phase transition indicated typical relaxor behaviour. Moreover, the temperature at maximum dielectric constant (Tm) are near about 63 °C, almost unchanged. Comparing with undoped samples, the PLZTN with x = 0.010 Nb doping shows a dramatic reduction of 162.5% in ferroelectric hysteresis, with only a slight decrease in the maximum polarization from 30.04 µC/cm2 to 28.53 µC/cm2. The quadratic electro optic coefficient experienced 54.8% reduction but still satisfy the application requirements. In terms of transmittance, the PLZTN samples kept a high value of transmittance (about 64%) along with increasing Nb content. Hence, the conclusion can be drawn that Nb doping in PLZT (9/65/35) is a novel strategy to reduce the ferroelectric hysteresis.

Effect of the Addition of Short Carbon Fiber on Thermal Insulation Properties of ZrB<sub>2</sub>- SiC Hot-Pressed Ceramics

Short carbon fibers reinforced ZrB2-SiC ceramics were prepared by hot pressing sintering process. The short carbon fibers with different volume fractions (0.2.4.6.8.10.20) were added for improving the thermal insulation properties of ZrB2-SiC ceramics. The experimental results showed that as the content of short carbon fiber increased, the thermal diffusivity decreased from 43.9m2/s to 32.9m2/s, the thermal conductivity decreased from 104.3 W/(m·K) to 72.9 W/(m·K) and thermal insulation performance reduced by 43.1%, respectively. The enhancement of the thermal insulation properties is mainly due to high interfacial thermal resistance of short carbon fiber and matrix.

In situ TEM observation of the microstructural characteristics and mechanical properties of vacuum hot-press sintered Co–30Cr–6Mo alloys

In this research, Co–30Cr–6Mo alloys were fabricated by vacuum hot-press sintering technique. The experiments utilized various hot-press sintering temperatures (1100 °C, 1150 °C, 1200 °C and 1250 °C) and hot-press pressures (20, 35 and 50 MPa) to find the optimal parameters for Co–30Cr–6Mo alloys, while simultaneously investigating the differences in microstructural characteristics and properties. The experimental results showed that the optimal hot-press sintering parameters of this sample were 1150 °C at 35 MPa for 1 h. Meanwhile, Co–30Cr–6Mo alloys possessed the optimal mechanical and electrical properties. Among them, the sintering density reached 8.13 ± 0.01 g cm−3, the hardness and TRS increased to 78.9 ± 0.2 HRA and 2672.2 ± 25.8 MPa, respectively, and the electrical conductivity was 3.11 ± 0.95 × 104 S m−1. TEM observation also identified the stacking faults, FCC and HCP structures of the Co phase, and the partial Cr23C6 carbides precipitated in the Co–30Cr–6Mo alloys, respectively. Consequently, the sintering characteristic of Co–30Cr–6Mo was effectively improved, and the mechanical properties were enhanced at a relatively lower sintering temperature by the vacuum hot-press sintering process.

Experimental study of hot pressed sintered modified materials

The PTFE/Cu composite powder was selected as the experimental raw material, and the modified material PTFE/Cu with dense structure was prepared by hot pressing sintering process. The morphology of the product before and after the test was compared and observed by SEM. The effect of different material ratios on the densification results of the powder was studied, and the difference between molding and hot pressing sintering was analyzed. The results show that hot-pressed sintering can produce modified PTFE/Cu with a density of up to 99.9%, which is higher than that obtained by molding under the same pressure. The SEM image shows that, unlike the molding, hot-pressing sintering makes the crystal grains of the two materials exist independently in the modified polymer, and makes the powder crystal grains gradually perpendicular to the hot pressing direction.

Table-like magnetocaloric effect and enhanced refrigerant capacity of HPS La(Fe,Si)13-based composites by Ce–Co grain boundary diffusion

The structure and magnetic properties of LaFe11.6Si1.4/Ce40Co60 bulk composites prepared by hot pressing sintering (HPS), followed by high-temperature diffusion annealing, were investigated. During the HPS process, the La(Fe,Si)13 alloy powder particles combined with Ce40Co60 binder and a porous structure with high mechanical strength were obtained. The addition of Ce40Co60 can also promote the peritectic reaction. Annealing has important effects on the magnetocaloric properties due to the diffusion of Ce and Co into the La(Fe,Si)13 phase during annealing. HPS samples were annealed at 1373 K for 24 h, and a table-like magnetocaloric effect, exhibiting a constant high magnetic entropy change (− ∆SM) of ~ 4.0 J/(kg K) in a commercially useful temperature region of 28 K (236–264 K), was obtained for a field change of 2 T. The values of full width at half maximum of (− ∆SM)–T plots (ΔTFWHM) and enhanced refrigeration capacity for the composites are 55 K and 173 J/kg, respectively, for a field change of 2 T. The composites exhibit high compressive strength of up to 312 MPa. The present results indicate that LaFe11.6Si1.4/Ce40Co60 bulk composites can meet the requirement of near room temperature magnetic refrigeration based on the Ericsson cycle.

Microstructure and mechanical properties of Cu-ZTA cermet prepared by vacuum hot pressing sintering

In this paper, seven copper-zirconia toughened alumina (Cu-ZTA) cermets were prepared by vacuum hot pressing sintering (VHP). The effects of different binder content and different particle size of ZTA particles on the mechanical properties of Cu-ZTA cermets were investigated. The microstructure of the composites was studied by x-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The hardness of the material was measured by micro Vickers hardness tester. The results show that the solid solution strengthening occurs in the hot pressing sintering process, the formation of copper-based solid solution increases the hardness of the matrix, the highest is 192.04 HV0.1. The ZTA particles are uniformly distributed in the matrix, and the surface of the ZTA particles is surrounded by a continuous coppermatrix and second phase. Two interfaces are formed between ZTA particles and Cu matrix. One is the ZTA/Cu interface formed by the substitution of Cu atoms for Ni atoms, it is a mechanical meshing interface which extends the service life of cermet under mechanical stress and thermal stress. The other interface is the reaction bonding interface of Cu3Ti3O and TiOx. The friction and wear test results show that the use of low-diameter ZTA particles and increasing the content of Cu binder will improve the friction and wear properties of Cu-ZTAcermet. Under the action of stress, the fracture occurs at the interface of Cu/ZTA, and the wear, fracture and extraction of ZTA ceramics cause the failure of Cu-ZTA cermet.

Synthesis and Mechanical Characterization of a Ti(C,N)/Mo-Co-Ni/CaF2@Al2O3 Self-Lubricating Cermet.

In this paper, an Al2O3 coated CaF2 (CaF2@Al2O3) nanocomposite powder is used as the additive phase of a Ti(C,N)-based self-lubricating cermet material. A novel self-lubricating ceramic material with a multilayer core–shell microstructure was prepared using a vacuum hot-pressing sintering process. The results show that the surface of the CaF2 powder is coated with Al2O3, and when introduced into a Ti(C,N)–Mo–Co–Ni material system, it can utilize the high-temperature liquid phase diffusion mechanism of the metal Mo–Co–Ni phase in the sintering process. The CaF2@Al2O3@Mo–Co–Ni multilayer core–shell microstructure is formed in the material. Compared with the direct addition of CaF2 and Al2O3, the hardness and fracture toughness of the material are increased by 24.31% and 22.56%, reaching 23.93 GPa and 9.94 MPa·m1/2, respectively. The formation of the multilayer core–shell microstructure is the main reason for the improvement of the mechanical properties of the material.

Influence of aluminium addition on oxidation resistance of Ta-W alloy

ABSTRACT Alloys with composition of Ta-10 wt.% W and Ta-10 wt.% W-6 wt.% Al, respectively, were prepared by the hot-press sintering process. The oxidation behaviour at 900°C and 1000°C was studied. The oxidation weight gain curves of the Ta–10%W alloy followed the linear law and the final oxidation product was Ta2O5 solid solution. Meanwhile, due to the addition of Al, the oxidation weight gain curves of the Ta–10%W–6%Al alloy followed the parabolic law. The final oxidation products at 900°C formed a dense outer layer Al2O3 and an inner layer. However, after being oxidised at 1000°C, the oxidation products included Al2O3, AlTaO4 and Ta22W4O67. Since the dense Al2O3 oxide film was consumed by the generation of AlTaO4, the inward diffusion of oxygen cannot be prevented. The oxidation resistance degraded at 1000°C. The addition of Al significantly improved the oxidation resistance of the Ta-W-based alloy system.

In situ fabrication of Ti–Al/ Ti2AlC composite by hot-press sintering

Ti–Al/Ti2AlC (4, 8, 12, 16, and 20 wt%) composites were prepared in situ via the high-energy ball milling of TiH2, Al, and C powders, followed by hot-press sintering at 1473 K. The effects of ball milling time on average grain size and phase evolution were studied. Results showed that the average grain size of the powder first decreased and then increased with the increase in milling time. The nano-Ti2AlC reinforcement can be synthesized in situ during the hot-press sintering process. The effect of Ti2AlC contents on the microstructures and mechanical properties of the composite was further studied. The hardness and yield stress increased with the increase in the weight percentage of Ti2AlC. Grain refinement mechanism was the dominant strengthening mechanism of the Ti–Al/Ti2AlC composite.

Thermal conductivity and thermal expansion of few-layer h-BN/Cu composites

Few-layer h-BN/Cu composites are successfully synthesized by solvothermal method and subsequently vacuum hot-pressing sintering process, and the influence of h-BN content on the thermal physics properties of composites is investigated. The thermal conductivity of the composites initially increase with increasing h-BN content, reaching a maximum of 428 W/(m·K) at 6 wt% h-BN. As the content of h-BN content further increased, the thermal conductivity decrease, which can be explained by the anisotropic thermal conductivity of h-BN and its distribution in the composites. The introduction of h-BN reduces the thermal expansion coefficient of the composites because of its low thermal expansion coefficient. These composites have potential applications in the field of electrical packaging.

Elaborating highly thermal-conductive diamond/Cu composites by sintering intermittently electroplated core-shell powders

Actuated by the needs of high power electronic devices heat dissipation, diamond/Cu composites with excellent thermal dissipation properties have been considered as the next generation of thermal management material. Herein, an easy-to-operate intermittently electroplated method is developed for coating micro-sized particles and successfully applied to prepare Cu-coated diamond powders for the first time. The Cu coating is covered evenly and densely on the diamond particles surface, and its volume fraction in diamond/Cu composite powders could be precisely controlled by adjusting the plating time. The dense diamond/Cu composites bulks with varied Cu volume fractions were obtained by hot-press sintering process. The as-sintered microstructures of diamond/Cu bulks present that diamond particles are bonded strongly by Cu shell layer, which is conducive to promoting densification capacity. The maximal diamond/Cu composite bulk possesses high thermal conductivity of 638 W/(m·K) and low coefficient of thermal expansion (CTE) of 4.11 × 10−6/K at 55 vol% diamond. The bending strength of 45 vol% diamond/Cu composite reaches 276 MPa. The combination of these excellent thermal and mechanical properties, coupled with the simple, efficient powder-preparation process, demonstrate the large potential of intermittently electroplated method applying in the development of thermal management material.

Enhancement of Thermal Conductivity and Mechanical Properties of Cu-Reduced Graphene Oxide Composites by Interface Modification

Copper matrix composites reinforced with reduced graphene oxide (rGO) were fabricated via charge adsorption process, thermal reduction, and hot-press sintering process. We investigated the effect of rGO on the thermal conductivity, electrical conductivity, mechanical properties, and microstructure of the composites. By controlling the reaction process, copper on the rGO surface was oxidized to form Cu2O. The presence of Cu2O at the interface enhanced interfacial bonding strength and reduced the interfacial thermal resistance, thus improving the thermal conductivity and mechanical properties. This enhancement occurred at low rGO contents. By contrast, excessive amounts led to rGO agglomeration and a degradation of the performance. At the optimum rGO content of 0.6 wt.%, the composites had a 10% increase in thermal conductivity and a 46% increase in yield strength (σ0.2), while maintaining high electrical conductivity.

Tin Acceptor Doping Enhanced Thermoelectric Performance of n-Type Yb Single-Filled Skutterudites via Reduced Electronic Thermal Conductivity.

Although introducing more fillers in nanocages is beneficial to gain low lattice thermal conductivity within filling fraction limit, accompanying high electronic thermal conductivity usually results in an unsatisfactory figure of merit ZT in CoSb3. In this work, Sn is adopted to tailor the electronic transport behavior for a high-filled Yb0.3Co4Sb12 alloy through rapid melt spinning combined with hot-press sintering processes. In spite of the reduced electrical conductivity, the power factors are scarcely influenced due to improved Seebeck coefficients by the reduced carrier concentration and moderate ionized impurity scattering. However, the lower total thermal conductivity is synergistically tuned by the effective suppression of electronic thermal conductivity and the low lattice thermal conductivity. As a result, both the high maximum ZT value of 1.4 at 823 K and the average ZT value of ∼0.98 between 300 and 850 K can be achieved in the Yb0.3Co4Sb11.85Sn0.15 sample. This work illustrates a promising approach for improving thermoelectric properties by largely tuning the electronic thermal conductivity.

Superconducting properties of NaCl doped MgB2 bulks fabricated by hot pressed sintering

MgB2 bulks with NaCl doping amount ranging from 0–30 at% have been prepared by hot pressed sintering process. With the increase of NaCl doping amount, the c axis lattice parameter of MgB2 monotonously increases, indicating the substitution of Mg atoms by larger Na atoms. Meanwhile, the intensity of diffraction peaks of both NaCl and impurity phase of MgO increases. More compact morphology was found in the NaCl doped MgB2 samples. The critical transition temperature (Tc) decreases from 38.2 K to 36.8 K with the increase of NaCl doping amount from 0 to 30 at%, and the corresponding transition width of Tc (ΔTc) increases from 0.5 K to 1.8 K. When the doping amount of NaCl is not exceeding 10 at%, the Jc value is about 106 A/cm2 at 4.2 K, 3 T, and 5 × 105 A/cm2 at 10 K, 3T. Jc performance of the 5 at% NaCl doped MgB2 sample (NC05) reaches 6.8 × 105 A/cm2 at 20 K, 2T, which improves approximately 20% compared to the pure one, attributing to the better grain connectivity of MgB2 and enhancement of flux pinning force by NaCl doping.

Effects of barium substitution on the optical and electrical properties of PLZT transparent electro-optical ceramics

Abstract Transparent electro-optic (EO) ceramics Pb0.91-xLa0.09Bax(Zr0.65Ti0.35)0.9775O3 (PLBZT x/9/65/35) with the amount of x = 0, 0.01, 0.02, 0.04 barium substitution for Pb at A-site were fabricated by hot pressing sintering process. The effects of barium substitution on the micro structure, ferroelectric, dielectric, optical and electro-optic birefringence properties were systematically studied. XRD result shows a typical ABO3 perovskite structure and no second phase observed within the detection limit, which clarifies the entry of Ba2+ ions into PLZT that caused the expansion of the crystal lattice. Due to the mixing ion effect of Pb2+, Ba2+ and La3+ at A-site, both coercive field (Ec) and remnant polarization (Pr) show reducing tendency with increasing doping. And the temperature of the dielectric maximum (Tm) was decreased almost linearly with increasing barium modifying amount. Especially, the reduction of the ferroelectric hysteresis was observed, which may reveal the Ba doping a new method to solve the problems faced now in device designing. In summary, the easily tuned Tm and slim hysteresis loop may prove PLBZT a promising candidate for optical modulator, light switch, energy storage and other relevant applications.

The Study on Sintering Capabilities of High Purity Metal Vanadium Powder

High purity metal vanadium powder was milled by high energy ball milling, and the grain size and morphology of vanadium powder was observed by electron probe, and the stress-strain curve was measured by CMT5305 universal testing machine for research of the mechanical property. In order to investigate the effect of sintering process on the property of product, the vanadium powder was sintered by the hot pressing sintering process and the cold isostatic pressing with vacuum sintering process respectively. The experimental results show that for the cold isostatic pressing with vacuum sintering process, the density of raw compact increases with the increase of pressing pressure. When the pressure increases to 280 MPa, the density and relative density of raw compact are 3.99 g·cm-3 and 66.94% respectively, the density and relative density of product after sintering are 5.28 g·cm-3 and 88.59% respectively. With the pressure increasing from 80 MPa to 200 MPa, the compressive strength increases significantly from 0.4 MPa to 6.0 MPa, the pressure increases to 280 MPa, the compressive strength slowly increases to 7.4 MPa. For the hot pressing sintering process, the relative density of product is higher than that of cold isostatic pressing with vacuum sintering process, and the density and relative density reach to 5.51 g·cm-3 and 92.91% respectively under 280 MPa pressure.

Enhanced Mechanical, Tribological, and Thermal Properties of Fe3Al Composites with Carbon Nanotubes

In this work, Fe3Al-based composites reinforced with carbon nanotubes were fabricated by a hot-press sintering process under various sintering pressures. The effects of sintering pressure and additives (alumina and lanthanum) on both the physical and the mechanical properties were systematically investigated. Results showed that with the sintering pressure of 15 MPa and incorporation of carbon nanotubes (CNTs), the microhardness of Fe3Al composite exhibited a peak value at 1038.1 HV, which was ~ 60% higher than those without the addition of carbon nanotubes (644.9 HV). Also, both the compressive yield strength and the thermal conductivity of Fe3Al composite were also significantly improved. Results of wear test showed the Fe3Al composite exhibited a low wearing rate (10−6-10−5 order of magnitude) and a friction coefficient (0.53-0.67).