Hot-press Sintering Method Research Articles

Mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks via the reduction of carbon contamination and agglomerations

Y2O3-MgO composites are promising for mid-infrared windows and domes in harsh environments. However, the insufficient transmittance range (the transmittance >30% only in ∼2-7 μm) and strong absorption peak (the transmittance <32% at 7.0 μm) of Y2O3-MgO composites severely limit their application range because of agglomerations and carbon contamination from organics in the raw materials, currently. In this study, utilizing carbon-free raw materials and high molecular motions, the reduction of carbon contamination and agglomerations within the as-synthesized nanopowers was achieved via the modified co-precipitation synthesis. A highly mid-infrared transparent (the maximum transmittance of 79% at 6.0 μm) Y2O3-MgO composite with wide transmittance range (the transmittance >30% in 2.2-9.7 μm) and weak absorption peaks (the transmittance ≈68.57% at 7.0 μm) was fabricated by the hot-pressing sintering method using the as-obtained nanopowders in the absence of exogenous dopants. And the modified co-precipitation synthesis is a method with great potential for the development of mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks.

Synthesis, microstructure, mechanical and tribological properties of high-entropy carbides (WZrNbTaTi)C-SiCw

In this work, composite high-entropy carbides (WZrNbTaTi)C-x SiCw (x = 0, 5 %, 10 %, 15 %, 20 %) are prepared using the two-step fast hot-pressing sintering (TSFHPS) method. The whiskers in the samples are evenly dispersed and well integrated with the ceramic matrix, forming high density materials. The mechanical properties and tribological properties at room temperature are studied, revealing that the addition of SiCw improves the performance of the materials. When the whisker content is 15 %, the hardness and fracture toughness of composite ceramics are the highest, which are 22.6 GPa and 6.8 MPa m1/2, respectively. The bending strength of the samples increases monotonically with the increase of whisker content, and reaches 639.2 MPa at 20 % content. At the same time, the addition of an appropriate amount of SiCw prevents the propagation of micro-cracks and the expansion of oxidative wear, thereby reducing the friction coefficient and wear rate, and improving the wear resistance of high-entropy carbides.

Arc erosion behaviour of Cu–diamond composites at different load voltages in air atmosphere

ABSTRACT To investigate the arc erosion performance of Cu–diamond composites, Cu–5vol.-% diamond composites were fabricated using the hot-pressing sintering method. Compared to pure copper, Cu–5vol.-% diamond composites exhibited improvements in Brinell hardness of 60.1 HB. The relative density and electrical conductivity of Cu–5vol.-% diamond composites were 97.54% and 83.29% IACS (International Annealing Copper Standard), respectively, with no significant decrease compared to pure copper. The thermal conductivity was 423.48 W·(m·K)−1, showing a slight enhancement. The effect of different load voltages on the arc erosion behaviour of Cu–5vol.-% diamond composites was investigated. Experimental results indicated that as the voltage rose from 3 to 7 kV, the breakdown strength decreased from 7.164 × 106 V m–1 to 2.535 × 106 V m–1, while the arc duration increased from 21.752 × 10−3 s to 28.864 × 10−3 s, and the breakdown current rose from 10.8 to 27.2 A. Additionally, the presence of diamond particles enhanced the viscosity of the molten pool, thus the splashing phenomenon of copper liquid during arc discharge was not obvious, indicating that the material loss was small. Few cracks and holes were detected. The Cu–5 vol.-% diamond composites possess good resistance to arc erosion.

Effects of adding Si3N4 whiskers to ZrB2–SiC ceramics on microstructure, mechanical properties and oxidation resistance

ZrB2–SiC–Si3N4w ceramics (ZSNw) were prepared via the hot-pressing sintering method. The bending strength and fracture toughness of ZSNw at room temperature reached to 520 ± 24 MPa and 5.2 ± 0.16 MPa m1/2, respectively. The enhancement in mechanical properties is attributed to the grain refinement and attenuation of grain boundary induced by the homogeneous distribution of Si3N4 whiskers. The oxidation resistance of ZSNw were conducted at 1500 °C in an air atmosphere. Remarkably, after 10 h of oxidation, ZSNw remained excellent strength and toughness reaching at 589 ± 26 MPa and 4.8 ± 0.12 MPa m1/2, respectively. This oxidation resistance of ZSNw was mainly attributed to the gain refinement induced by Si3N4 whiskers, which effectively reduced the voids within the ceramic matrix. Therefore, this process promoted the densification and homogenization of the SiO2 protective barriers, accompanied with hindering the inward permeation of oxygen and the outward release of oxides.

Interfacial behavior and damage mechanism of Al-B4C/Al laminated composites under ballistic impact

The present study involved the fabrication of Al-B4C/Al laminated composites with a strong bonding interface using an integrated (or one-step) hot-pressed sintering method followed by hot rolling. A comprehensive analysis of the mechanical properties and interface behavior of Al-B4C/Al laminated composites under various loading conditions, particularly focusing on ballistic impact. Findings indicate that the laminated composite exhibits a high-strength interface bonding (greater than 318 MPa) facilitated by the continuous Al matrix, with no interlayer delamination occurring even after Charpy impact failure and ballistic penetration. The integrated interface promotes coordinate deformation between different component layers, enhancing the comprehensive mechanical performance of the Al-B4C/Al laminated composites. Moreover, the integrate interface of the Al-B4C/Al laminated plate enables a higher absorption of impact energy from projectiles, increasing by 10% and 70% compared to the monolithic and unbonded stacked plates, respectively.

Improvement in the thermal conductivities and bending strengths of graphite film/Cu composites by matrix alloying with Zr

Graphite film/Cu composites were fabricated by the hot-pressing sintering method. The thermal conductivities and bending strengths of the composites were improved by matrix alloying with Zr. By sanding the surface of the graphite film, carbides were easily generated at the interface. The presence of carbides at the interface transformed the interfacial bonding characteristics from mechanical to physical-chemical bonding. Enhanced interfacial bonding could improve the thermal conductivity of the composites. The optimum Zr addition amount was 1.5 wt%, and the thermal conductivity of the composites was 725 W/mK. The enhanced interfacial bonding improved the composite bending strength. When the Zr concentration was 2 wt%, the composite bending strength was 34 MPa, which was an increase of 100 % compared with that of the absence of Zr.

Hot-pressing of BeO ceramics and its thermal conductivity and flexural strength

Due to its excellent strength and high thermal conductivity, beryllium oxide (BeO) is widely used as a fuel matrix material and neutron moderator in nuclear reactors. In the preparation of bulk BeO materials, previous research on the hot-pressing sintering methods is insufficient. This paper mainly introduces the process of hot-pressing sintering, and uses orthogonal experiments with different process parameters to explore their influences on the grain size and porosity of the products, and how to affect their flexural strength and thermal conductivity as well. Molecular dynamics simulations have also been used to study the growth of the amorphous phase in BeO ceramics. In addition, a relatively optimized preparation scheme, that is, holding at 1500 °C for 30 min and pressure of 20 MPa can be obtained. Under the optimized parameter, the flexural strength of the product can reach 244.74 MPa, and its thermal conductivity can reach 179 W/(m*K) at 200 °C, and 31 W/(m*K) at about 1000 °C. It provides a reference for the preparation of high performance BeO ceramics.

Enhancement of thermoelectric performance by stacking fault control in (GeTe)1-x(Bi2Te3)x compounds, synthesized by hot press sintering method

We investigated the thermoelectric (TE) properties of GeTe by incorporating Bi2Te3 in the GeTe system. The addition of Bi2Te3 into the GeTe matrix leads to phonon scattering caused by stacking fault or structural defect, resulting in a substantial reduction in lattice thermal conductivity κlat. We observed a significant decrease in total thermal conductivities in the vertical and horizontal pressing directions, respectively. The optimized carrier properties and low thermal conductivity in the composites have led to a remarkable improvement in the dimensionless figure of merit (zT) 1.26 at 650 K. This study highlights the potential for creating high-performance thermoelectric materials through GeTe-Bi2Te3 compounds, emphasizing the importance of defect engineering and stacking faults in reducing thermal conductivity and improving thermoelectric efficiency.

A novel wear-resistant and corrosion-resistant Mo2NiB2–Ni cermet coating prepared using fast hot pressing sintering

A new fast hot pressing (FHP) sintering method was used to prepare Mo2NiB2–Ni cermet coating to solve the problems of small scale and high energy consumption in the production. The synthetic phase and microstructure of the Mo2NiB2–Ni cermet coating were studied, and friction and wear as well as electrochemical corrosion performance were also tested. The results indicated that the Mo2NiB2–Ni cermet coating was composed of two phases, the Mo2NiB2 hard phase and the Ni metal-bonded phase. A metallurgical bond interface resembling interlocking teeth was formed between the Mo2NiB2–Ni cermet coating and the stainless steel substrate, thereby enhancing the bonding strength of the interface. Compared with the Mo2FeB2–Fe cermet coating, the Mo2NiB2–Ni cermet coating had certain wear resistance and excellent corrosion resistance. The high hardness of the Mo2NiB2 hard phase, the low mutual solubility between the Ni metal-bonded phase and the Si3N4 balls, and the generated mechanical mixing layer reduced the friction coefficient and the adhesive wear, which improved the wear resistance. The higher open circuit potential and the formation of the passivation film during the corrosion process enhanced the corrosion resistance of the Mo2NiB2–Ni cermet coating.

Influence of Cobalt content on the microstructure and texture evolution of hot-press sintered Tungsten nickel copper Alloy (W-Ni-Cu)

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%).

Biocompatibility study of Fe-doped zirconia-toughened alumina ceramic for artificial joints

Fe-doped zirconia toughened alumina (Fe: ZTA) ceramic is a promising material for artificial joint implants because of high density, good mechanical properties and excellent wear resistance. To evaluate its use in biological implants, Fe: ZTA ceramics with different Fe contents (0–5 wt.%) were fabricated using the fast hot pressed sintering method, and the biocompatibility of Fe: ZTA ceramics and the biotoxicity of wear debris from Fe: ZTA were systematically studied. The additive Fe element mainly exists in the form of FeAl2O4. The addition of Fe results in the increase of surface hydrophobicity and the decrease of surface energy and polar component, improving the protein absorption on Fe: ZTA surface. According to the culture results with osteoblasts and macrophages, Fe doping can increase the osteoblast activity and does not cause significant macrophage activation on the surface of Fe: ZTA ceramics. Particularly, the 1.5 wt.% Fe: ZTA ceramic can significantly improve the cytocompatibility of osteoblasts and reduce the inflammatory reaction. On this basis, 1.5 wt.% Fe: ZTA ceramic with the best biocompatibility was used to prepare the wear debris, and the biotoxicity of wear debris was further studied. The result confirms that wear debris of Fe: ZTA ceramic (50–1000 μg/ml) does not cause the significant decrease in osteoblast activity and has no significant effect on the osteoblast morphology, without distinct cytotoxicity. The wear debris of Fe: ZTA (≤ 200 μg/ml) will not cause significant inflammatory response. This study can provide guidance for the application of Fe: ZTA ceramic in biological implants.

Influence of Ti2SnC content on arc erosion resistance in Ag–Ti2SnC composites

Abstract In this work, an Ag–Ti2SnC composite was fabricated by the hot-pressing sintering method, and the erosion behavior of Ag–Ti2SnC with volume percentages of 10–40% was studied at a load voltage of 10 kV. The arc life and breakdown current were observed at about 31–36 ms and 39 A, respectively. The cathode spot traveled the fastest on the surface of the Ag–40 vol% Ti2SnC composite. Due to emission center model, the temperature of the minor protrusions on the cathode surface increased, resulting in Ag ions, Ti ions, and Sn ions being generated. Combining with the ionized oxygen, Ag2O, AgO, TiO2, and SnO2 were formed on the eroded Ag–Ti2SnC surface after arc erosion. The research results will broaden the application range of Ag–Ti2SnC electrical contact material and enrich the arc erosion mechanism.

Effect of particle volume fraction on wear behavior in Al–SiC MMC coated on DIN AlZnMgCu1.5 alloy

Abstract In this study, DIN AlZnMgCu1.5 alloy surface (Al + SiC) was coated with metal matrix composite (MMC) by using hot press sintering method (HPSM). Al was used as matrix material and SiC powders were used as reinforcing material in the coating process on DIN AlZnMgCu1.5 alloy surface. Al/SiC MMC coating was produced at 600 °C under 120 MPa pressure and with varying SiC content (5, 10 and 15 vol.%). Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to examine the microstructure, elemental analysis and phase structure of both the coating zone and the transition zone between the substrate and the coating. The hardness was measured and a dry sliding linear reciprocating wear test was run to determine the mechanical properties of the coating layer. Consequently, the coefficient of friction (COF) and wear volume were determined. OM and SEM images showed a homogeneous distribution of SiC particles and a less porous structure. The hardness of the MMC coating increased with increasing SiC content. Also, the numerical analysis of the wear test simulation was done based on Archard’s law. The results of both wear tests showed that the volume loss values were consistent with each other and the amount of wear significantly reduced by increasing the rate of SiC reinforcement.

PREPARATION AND THERMOELECTRIC PROPERTIES OF rGO/Bi2Te3/PEDOT:PSS COMPOSITE BLOCK

Reduced graphene oxide/bismuth telluride (rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt;) bulk composite materials containing the poreforming agent, sodium chloride (NaCl), were prepared by a hot-pressing sintering method after mixing rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt; nanopowders with NaCl powders. Three-dimensional connected holes formed in the bulk composite materials after removing the NaCl pore-forming agent. Next, rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt;/poly(3,4-ethylen edioxythiophene):poly(styrene sulfonate (PEDOT:PSS) nanocomposite bulk materials were prepared by filling PEDOT:PSS into the as-prepared three-dimensional connected holes in the rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt; bulk composite skeletons. The effects of the PEDOT:PSS filling procedure on the compositions and microstructures of the rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt;/PEDOT:PSS nanocomposite bulk materials were studied. The influence of the contents of NaCl and measurement temperatures on the thermal electrical properties of the bulk composite materials was investigated. A power factor of 560 &amp;mu;W/(m&lt;sup&gt;-1&lt;/sup&gt;&amp;#183;K&lt;sup&gt;-2&lt;/sup&gt;) was obtained at 400 K for the rGO/Bi&lt;sub&gt;2&lt;/sub&gt;Te&lt;sub&gt;3&lt;/sub&gt;/PEDOT:PSS nanocomposite bulk materials.

Fabrication of Al/Al-TiB2 laminate composites via hot press sintering process: An insight into the mechanical properties and fracture behavior

The Al/Al-TiB2 laminated composites with different numbers of layers was fabricated by hot press sintering method. The results show that Al/Al-TiB2 interface is well bonded without obvious micropores, cracks, or other defects, while the stacking faults and dislocation loops are observed at the interface. The average grain sizes of Al and Al-TiB2 layers are 45.17 and 5.51 μm in the composite with 3 layers, while they greatly increase to 80.07 and 6.51 μm in the composite with 5 layers. The hardness increases gradually along Al layer, Al/Al-TiB2 interface, and Al-TiB2 layer. TiB2 particles mainly contributes to the enhancement of bending strength, and the maximum strength of 110.0 MPa is achieved in the composite with 3 layers due to the fine grain size, small particle spacing, and more geometrically necessary dislocations in Al-TiB2 layer. During bending deformation, Al layer exhibits ductile fracture with shear lip, slip band, fatigue striation and dimple, while Al-TiB2 layer shows typical brittle fracture with micro-voids and cleavage. The stress concentration and crack always appear in Al-TiB2 layer, while Al layer can transfer strain and inhibit strain localization. An increasing ductility of the laminated composites is achieved due to crack deflection, interfacial delamination, and strain transferring.

Effect of texture on the thermal conductivity and mechanical properties of silicon nitride ceramic

In this study investigated the texture, microstructure, and mechanical behavior of silicon nitride (Si3N4) ceramics were investigated using various techniques, including the orientation distribution function, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The orientation distribution of c-axis of the β-Si3N4 phase derived from the hot-press sintering method, where the considerable orientation arrangement of grains was perpendicular (SPE sample) and parallel (SPA sample) to the hot-pressed direction. XRD analysis showed that the SPA sample had stronger {0001}<10-10> and {0001}<2-1-10> textures than those of the SPE sample. For these reasons, the SPE sample exhibited a lower thermal conductivity of 54 W (m K)−1 than that of the SPA sample (91 W (m K)−1). The mechanical behavior of the Si3N4 ceramics was affected by the orientation arrangement of the grains. Analysis of the cracks on the surface of the Si3N4 ceramics at different indentation angles (0°, 22.5°, 45°, and 67.5°), revealed a rising tendency of fracture toughness in the Si3N4 ceramics, with values of 3.6 MPa m1/2, 4.1 MPa m1/2, 5.5 MPa m1/2 and 6.1 MPa m1/2, respectively. These results were attributed to the texture and close-packed hexagonal structure.

High temperature oxidation behavior and oxide film properties of IN718 alloy after heat treatment by hot pressing sintering

The IN718 superalloy was prepared by hot pressing sintering method, and the IN718 alloy blocks under different sintering pressures were obtained. The hot-pressed IN718 superalloy(HPS IN718) prepared by the optimum sintering pressure was treated by solid solution and aging. The high temperature oxidation behavior and the properties of oxide film of HPS IN718 at 850 °C in air were studied. The microstructure of HPS IN718 was characterized by optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM), and energy dispersive spectrometer(EDS). The morphology and microstructure of the oxide film of HPS IN718 at 850 °C for different oxidation times were analyzed. The adhesion and wear resistance of the oxide film was tested by an automatic scratch tester and a pin-on-disc friction and wear tester. The results show that the IN718 alloy prepared by sintering pressure 30 MPa has good density, and more uniform structure. The results of the oxidation test show that with the increase in oxidation time, the weight of the sample increases parabolically. The oxidation rate was 3.84 × 10−3 mg/(cm2·h1), which belongs to the complete oxidation resistance level. The oxides gradually aggregate and grow from small particles and clusters in the early stage of oxidation. After 125 h oxidation, the thickness of the oxide layer is 3–4 µm. The outermost layer of the oxide film is composed of TiO2, Fe2Cr2O4, and Fe0.7Cr1.3O3, the subsurface layer is dense Cr2O3, and the inner oxide is Al2O3. As the oxidation time increases, the adhesion between the oxide film and the substrate increases. The surface friction coefficient of the sample is reduced. It is found that after oxidation for 125 h, the adhesion between the oxide film and the substrate is 15 N, the surface friction coefficient is 0.08, the friction coefficient is reduced by 0.37 compared with the substrate, and the wear resistance is the better.

Crystallographic texture and grain boundary character development of hot-press sintered tungsten heavy alloy: The effect of rhenium concentration

In this study, the effects of rhenium on the evolution of microstructure and texture in hot press sintered tungsten heavy alloy (93W-4.9Ni-2.1Cu) is examined. Rhenium is added (i.e., increased rhenium from 0 to 1 wt % with interval of 0.25 wt %) to a conventional tungsten heavy alloy while maintaining a constant Ni: Cu (7:3) ratio. The samples were prepared using a vacuum hot press sintering method with parameters including 50 MPa pressure, 10 °C/min heating rate, and 1450 °C temperature for a 20-min holding time. The impact of rhenium on densification, crystallographic texture development, and grain boundary features of Re alloyed WHA was studied using electron backscattered diffraction (EBSD). The development of grain boundary texture was the result of a Ʃ3 CSL increase in sintered compact. The base alloy exhibits fibre texture in the (001) plane with the <111> direction and a higher proportion of low-angle grain boundaries. Reduced kinetics of grain growth during sintering led to a higher degree of densification and randomised weak fibre texture in rhenium-alloyed samples. The deterioration of texture in the (001) <111> direction in rhenium-added alloys was caused by recrystallization following recovery during sintering. Metallographic studies reveal that an increase in rhenium in the WHA's stoichiometry resulted in particle refinement during sintering, thereby enhancing the WHA's properties. Maximum micro-hardness (432 HV0.5), electrical conductivity (23.74 % of IACS), and relative density (99.90 %) were observed in a 93W-4.9Ni-2.1Cu (Re 1 wt% alloy).

Effect of CeO2@GNPs on the Corrosion Properties of 2024 Alloy

The nanocomposites of 2024 Al reinforced with CeO2@GNPs (graphene) nanoparticles were fabricated using the hot-press sintering method. With the addition of 0.5 wt% CeO2@GNPs, the YS and UTS of the fabricated nanocomposites increased by 21.1% and 24.7%, respectively. The load transfer effect and optimization of the interfacial bonding were the main factors to improve the mechanical properties of the composites. The effect of the surface modification of GNPs on the corrosion resistance of the composites was investigated, demonstrating that the addition of GNPs weakened the corrosion resistance of the fabricated nanocomposites. Meanwhile, the corrosion current density (2.776 × 10−3 A·cm−2) and polarization resistance (13,971.37 Ω cm2) of the prepared composites with CeO2 nanoparticle-layered GNPs exhibited a significant decreasing trend compared with the composites without a CeO2 nanoparticle layer (3.540 × 10−3 A·cm−2, 10,199.72 Ω cm2). Optimizing the dispersion of GNPs and their interfacial bonding with the aluminum matrix promoted the reduction in the corrosion area and the possibility of micro-couple formation, leading to an effective enhancement of the corrosion resistance of the nanocomposites.

Effects of TiB2 content and gradient structure on microstructural characterization and mechanical properties of TiB2/Al7050 composites

TiB2 particle reinforced Al7050 matrix homogeneous composites (HC), TiB2/Al7050 three-layer conventional linear gradient functionally gradient materials (TFGM), and TiB2/Al7050 five-layer functionally gradient materials with a bionic structure (FFGM) were successfully prepared using vacuum hot-pressed sintering (VHS) method. The effects of gradient structure and TiB2 particle content on the microstructural characterization and mechanical properties of these composites were investigated. The results demonstrate that the bending strength of all composites improves with the increase in TiB2 content. Comparatively, the bending strength of functionally gradient materials (FGM) are generally superior due to a combination of the interlayer strength of each layer, heterogeneous deformation-induced strengthening, strength-plasticity synergy of the whole material, and synergistic interlayer strengthening under strong bonding. Notably, the enhancements in bending strength and strain exhibited by FFGM are more pronounced, highlighting its "soft-hard interleaved" and "strong-tough complementary" structural pattern. The research provides valuable insights for the application and further development of FGM.