Pressure Sintering Research Articles

Thermal creep and fatigue failure of the sintered silver solder in a SiC-IGBT module under power cycling

In this work, the creep samples of sintered silver were prepared by the chemical reduction method. According to the creep testing results, the Anand constitutive model was established to demonstrate the creep characteristics of sintered silver within a certain temperature range. According to the finite element electro-thermal–mechanical coupling analysis, the cyclic creep characteristics of sintered silver solder in the SiC-IGBT module under power cycling were simulated. The results shows that the sintering pressure and temperature can greatly promote the integrity of sintered silver by enhancing inert-particle bonding strength, and the established Anand model can effectively describe the creep behavior of sintered silver. The predicted results from electro-thermal–mechanical simulation were in good agreement with the power cycling testing results under the same condition. The finite element-based creep fatigue model is effective in predicting the creep fatigue life of sintered silver solders.

Rice-inspired oriented copper fiber wick with excellent capillary performance for ultra-thin vapor chamber

In response to the current trend of thermal management systems for microelectronic products, ultra-thin vapor chambers (UTVCs) have become an emerging hotspot. Currently, there is an urgent challenge to design of high-performance capillary wicks for use in limited spaces for UTVCs. In this study, an ultra-thin copper fiber wick (UTCFW), inspired by rice plants, was proposed and prepared by the limited fiber sintering and hydraulic pressure methods. By simply varying the fiber length in the mould, it was possible to prepare an UTCFW with ordered orientation similar to the developed root system of the rice plant. A chemical treatment was used to develop micro- and nano-scale structure on the surface of the UTCFW, similar to hairs on roots of the rice plant, which makes the UTCFW exhibit superhydrophilic properties. After optimization, the capillary factor M of the most ordered sample with 80 mm fibers (L80) was 1.254 μm, which was 567 % times that of the poorly ordered with 5 mm fibers (L5). In short, the bioinspired UTCFW had both excellent wettability and capillary performance. This study demonstrated the preparation of a high-performance and cost-effective UTCFW for improving the thermal performance of UTVCs.

High pressure sintering of fully dense tantalum carbide ceramics with limited grain growth

High pressure sintering of fully dense tantalum carbide ceramics with limited grain growth

Constructing a core-shell structure in Ti-based alloys with exceptional mechanical properties through semi-solid sintering

In this work, we developed a semi-solid sintering method for constructing a core-shell architecture in Ti68.8Nb13.6Co6.8Cr5.1Al6.5 alloy and revealed the underlying mechanism of microstructure evolution and deformation behavior. Fundamentally, the semi-solid state was achieved by sintering amorphous powders at temperatures between the melting point of the CoTi2 phase and the β-Ti matrix. During the process, the liquid CoTi2 phase was squeezed towards the β-Ti boundaries due to the sintering pressure and the growth of β-Ti grains. Subsequently, it transformed into a hard ultrafine CoTi2 phase distributed along the β-Ti boundaries, constructing a core-shell structure. The resulting core-shell structure exhibited a high compressive yield strength of 1560 MPa, an ultimate strength of 3006 MPa, and a remarkable compressive strain of 40.1%, surpassing typical Ti-based alloys under compressive loading. The high strength was attributed to dislocation-impeding effect of the CoTi2 phase, while the activation of multiple slip systems triggered by the CoTi2 shell contributed to plasticity. The results provide fundamental insights into the fabrication of Ti-based alloys with exceptional mechanical properties for structural materials applications.

Effect of the ratio of Y2O3 and MgSiN2 sintering additives on the microstructure, thermal and mechanical properties of Si3N4 ceramics

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si3N4) ceramics, Si3N4 ceramics were prepared by gas pressure sintering using different ratios of Y2O3/MgSiN2 as additives. Varying the ratio of Y2O3/MgSiN2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si3N4 ceramics, and ultimately changing their microstructure. The reduction in the Y2O3/MgSiN2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si3N4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si3N4/Si3N4. Therefore, Si3N4 ceramics with 1 wt% Y2O3 and 5 wt% MgSiN2 exhibited excellent properties after sintering at 1900 °C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm−1K−1, 776 MPa, and 11.66 MPa m1/2, respectively.

Synergistic toughening effect of SiC whiskers and particles in ZrO2–Al2O3–SiC ceramics

Zirconia ceramics have a good application prospect in the high-tech fields, whereas their potential utilization is highly limited by their mechanical properties. To fabricate zirconia based ceramics with superior mechanical properties, SiC whiskers (SiCw) and SiC particles (SiCp) were selected as the toughening phases for the preparation of ZrO2–Al2O3–SiC ceramics, and an advanced sintering technique called as oscillatory pressure sintering (OPS) was applied in the present work. The mechanical properties of such ceramics with 5 vol% SiCw and 10 vol% SiCp were significantly improved. The Vickers hardness increased to 15.26 GPa while the bending strength reached 917 MPa, and the fracture toughness rose to 6.83 MPa·m1/2. The toughness of the ceramics was improved by synergistic toughening effects including whisker toughening, stress-induced phase transformation toughening and particle dispersion toughening. Furthermore, SiCp and ZrO2, Al2O3 and SiCp, ZrO2 and SiCw as well as Al2O3 and SiCw formed a well-matched coherent phase boundary. The semi-coherent relationship was also generated at the phase boundary of SiCp and SiCw.

Impact of rare earth oxides metal (Dy, Tb, Er, Eu, Sm) admixtures on the structure, morphology, pinning centers and critical parameters of MgB2 materials manufactured by ambient pressure sintering and hot isostatic pressure processes

In our paper, we present the results of the structural, morphological and critical parameters of MgB2 cylindrical materials doped with Dy2O3, Tb2O3, Er2O3, Eu2O3 and Sm2O3. The materials were annealed under low and high isostatic pressures at 800 °C for 1 h in an argon atmosphere. Our results show that the HIP process significantly increases the density of MgB2 materials modified by the RE2O3 additive from 1.05 to 2.4 g/cm3. Scanning electron microscope (SEM) images indicate that the HIP process removes voids from the MgB2 material. The results indicate that the HIP process slightly affects the formation of REB4 and REB6 and does not affect the process of RE substitution for Mg. Further SEM results show that the morphologies of samples annealed at low isostatic pressure with Dy2O3, Tb2O3 and Er2O3 doping are completely different from those of samples with Eu2O3 and Sm2O3 doping. The magnetic measurements indicate that RE2O3 doping and annealing under low isostatic pressure slightly increases the critical temperature (Tc) and decreases the irreversible magnetic field (Birr). On the other hand, thermal treatment under high isostatic pressure with an admixture of RE2O3 lead to a greater increase in Tc and a decrease in Birr. Further magnetic measurements show that RE2O3 doping and annealing under low isostatic pressure mainly increase the magnetic critical current density (Jmc) at 4.2 K–30 K in low magnetic fields. Additional results indicate that high isostatic-pressure annealing of the RE2O3-doped MgB2 material significantly increases Jmc in low magnetic fields and decreases Jmc in high magnetic fields. Our results indicate that the Eu2O3 admixture most effectively increases Tc and Jmc and creates the large amount of the REB6 phase. It is as the only admixture that increases Birr after the HIP process and yields the smallest MgB2 grains.

Multiphysics Simulation and Experimental Investigation of the Densification of Metals by Spark Plasma Sintering

Multivariant experimental investigations and multiphysics microstructural modeling of the spark plasma sintering process of metallic powders have been performed up to a relative density of approximately 80%. In comparison, the effect of sintering temperature, pressure, and particle size on the interparticle contact area growth and axial shrinkage of cylindrical specimens of copper and nickel particles is measured in laboratory scaled tests. Herein, for the first time all relevant for sintering phenomena are considered simultaneously: the fully coupled thermo‐electro‐mechanical modeling of the spark plasma sintering processes, additionally taking into account for lattice, grain boundary, surface diffusion, electromigration, and thermomigration, has been carried out. The computational analysis of various physical phenomena allows to identify dominant and insignificant mechanisms. The two‐level numerical simulation includes the modeling of the sintering setup at the macroscopic level and the neck formation process in particle chain systems at the microscopic level. The results of the numerical simulations show a very good agreement with the experimental data. Therefore, the impact of electrical and mechanical loads as well as of particle size on microscopic distribution of temperature, inelastic strain, and on densification has been studied by the finite element simulations.

Optimization of Spark Plasma Sintering Technology by Taguchi Method in the Production of a Wide Range of Materials: Review.

This paper reviews the production of sinters using the spark plasma sintering method. SPS (spark plasma sintering) technology has been used for several decades, mainly in laboratories, to consolidate a huge number of both new and traditional materials. However, it is now more often introduced into practical industrial use, with equipment as early as the fifth generation capable of producing larger-size components at competitive costs. Although the mechanism of sintering with the use of this method is not yet understood, the effectiveness of the SPS process for the rapid and efficient consolidation of a wide range of materials with novel micro-structures remains indisputable. With a relatively wide variation in chemical composition, the structure allows the selection of appropriate consolidation parameters for these materials. The influence on the values of apparent density and mechanical properties depends on the parameters of the spark plasma sintering process. In order to achieve a density close to the theoretical density of sinters, optimization of the sintering parameters, i.e., sintering temperature, heating rate, sintering time, pressing pressure and protective atmosphere, should be carried out. In this paper, the optimization of spark plasma sintering of Si3N4-Al2O3-ZrO2 composite was carried out using the Taguchi method. The effects of four sintering factors, namely heating rate, sintering time, sintering temperature and sintering pressure, on the final density were investigated. Optimal sintering conditions were proposed and a confirmation experiment was conducted. The optimal combination of sintering conditions for spark plasma sintering (SPS) of Si3N4-Al2O3-ZrO2 composite for high apparent density was determined as A3-B3-C3-D2. Based on ANOVA analysis, it was found that the apparent density of sintering was significantly influenced by sintering temperature, followed by pressing pressure, sintering time and heating rate. Validation of the developed mathematical model predicting the apparent density of sinters showed close agreement between the predicted response results and experimental results.

Copper-graphite-TiC composites-synthesis and microstructure investigation

Copper-graphite-TiC composites were prepared by gas pressure sintering, using copper-coated graphite, pure copper, and Ti3AlC2 as the raw materials. The phase composition and microstructure of copper-graphite-TiC composites have been studied. The results indicate that a strong interdiffusion occurred between the copper matrix and Ti3AlC2 during the sintering process. Ti3AlC2 was completely decomposed into TiC, and a TiC interface transition layer was formed to enhance the bonding strength between the copper matrix and graphite.

Microstructure and performance optimization of Al2O3/TiC/TiB2/h-BN@Al2O3 self-lubricating ceramic tool materials

Based on the classical Monte Carlo (MC) model and grain growth theory, the model of h-BN@Al2O3 coated solid lubricant was designed and introduced into the simulation system. The Al2O3/TiB2/h-BN@Al2O3 self-lubricating composite ceramic tool model was designed, and the microstructure evolution of tool materials during hot pressing sintering was simulated. The effects of TiB2 and h-BN@Al2O3 content on the microstructure of ceramic materials were studied, and finally the optimized composition parameters were obtained. The effects of sintering temperature and sintering pressure on the microstructure of tool materials were studied, and reasonable sintering parameters were obtained. The experimental results show that under the sintering temperature of 1650℃ and sintering pressure of 32Mpa, the ceramic material with 10%volTiB2 and 5%volh-BN@Al2O3 has the best mechanical properties, that is, the bending strength is 610MPa, the hardness is 17.9GPa, and the fracture toughness is 5.17 MPa·m1/2. SEM analysis shows that the grain growth of the material is uniform, the solid lubricant is well combined with the matrix, and the material has a good microstructure. Comparing the simulation results with the previous experimental results, it is found that the results are in good agreement, which indicates that the designed MC model reliably reflects the physical process of material grain growth, and has certain guiding significance for further research on the mechanism of grain growth.

Machine learning for predicting ZT values of high-performance thermoelectric materials in mid-temperature range

Machine learning (ML) is increasingly being adopted to accelerate the development of materials research. In this work, we applied the ML approach to predict the figure-of-merit (ZT) of thermoelectric (TE) materials. The experimental datasets were gathered from 150 published articles for five high-performance TE groups in the mid-temperature range, i.e., PbTe, Co4Sb12, Mg2Si, BiCuSeO, and Cu2Se, resulting in 1563 data points in total. The chemical formulas of individual compounds, including the dopant types and concentrations, were extracted as ML features using the Magpie software. The ZT value was set as the target value. The model was built based on different regression algorithms, and its accuracy for predicting ZT was evaluated using the coefficient of determination (R2) and the root mean squared error (RMSE). It was found that the model’s accuracy increased with increasing datasets and by incorporating features from experimental parameters (measurement temperature, sintering temperature, and sintering pressure). The final ML model showed relatively high accuracy, with an R2 of 0.859 and an RMSE of 0.156 for a test set. It means that the model can confidently predict the ZT of specific doped compounds in the selected TE groups. To utilize the model effectively, it is implemented as a webpage application with a user-friendly interface so that researchers without ML expertise can explore the ZT values of the doped TE materials. It will certainly be beneficial for experimentalists as a guideline for designing their experiments.

Influence of bismuth oxide as a sintering aid on the densification of cold sintering of zirconia

In the past decades, Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high temperature structural material and electrolyte for fuel cells, etc. The traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually requires a sintering temperature as high as 1200 °C. General interest in lowering the sintering temperature to reduce energy consumption and thermal stresses has led to research on two promising routes – cold sintering via temperature-dependent chemical reactivity and sintering aids, which facilitates mass transport and improves densification. Here we combine both by developing a single-step sintering process benefitting from both water vapor through the in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering aid. The resultant ZrO2 has a relative density above 80% with a sintering temperature as low as 900 °C, significantly higher than that of ZrO2 without sintering aids, which had a relative density of 54%, both sintered at 50 MPa. The dependence of porosity of sintered samples as a function of sintering pressure (range: 50 MPa–300 MPa) and temperature (range 400 °C–1200 °C) is mapped out as guidance for further material property design. A linear relationship between hardness and relative density was found, with a maximal hardness of 6.6 GPa achieved in samples with 30% porosity. In addition to sintered density, phase stabilization of tetragonal ZrO2 is enhanced at sintering temperature of 900 °C with water vapor and Bi2O3, respectively.

High transport Jc in 7-filament Cu/Ag sheathed Ba0.6K0.4Fe2As2 tapes manufactured by ambient pressure sintering

In regard to iron-based superconductors (IBS), the multi-filament Cu/Ag composite sheathed Ba-122 tape is particularly attractive for industrial high-field applications owing to its prominent properties. By a cost-effective and scalable way, ambient pressure sintering, a high transport critical current density (Jc) of 7-filament Cu/Ag sheathed Ba-122 tapes reached 4.5 × 104 A cm−2 at 4.2 K and 10 T, whose corresponding engineering critical current density (Je) has achieved to 104 A cm−2. An optimized powder-in-tube (PIT) method was adopted aiming at overcoming the difficulty of ambient pressure sintering to obtain high-density superconducting core and grain alignment. Improvements in the manufacturing process, such as drawing without intermediate annealing and rolling from larger initial diameter to thinner tapes, have resulted in high grain connectivity and good c-axis texture, which are the major factors contributing to high Jc. Our results demonstrate that the ambient pressure sintering process is a viable method to fabricate long-length multifilamentary Cu/Ag composite sheathed IBS tapes with high Jc for practical high-field applications.

Inconel 718 produced by hot pressing: optimization of temperature and pressure conditions

This paper aims to act as a useful engineering tool for researchers who are studying the production of well-densified IN718 parts by uniaxial vacuum hot pressing. To the best of the authors’ knowledge, there is no relevant information on literature about densification of IN718 parts by this technique. This work is focused on understanding the influence of uniaxial vacuum hot pressing sintering conditions (temperature and pressure) on Inconel 718 (IN718) powder densification, microstructural, fracture mode, and hardness properties. The optimization of temperature and pressure sintering conditions are presented as well as its influence on the densification, microstructural features, and hardness properties. The sintering conditions included temperatures of 1000, 1068, 1150, and 1200 °C; pressures of 50 and 60 MPa; and a dwell time of 60 min.The results showed an increase in the grain size (GS) of the compacts with the processing temperature and a change on the fracture mode from intergranular dominant fracture to fully dimple ductile fracture. Regarding the microstructural properties, the results showed that γ′(Ni3(Al, Ti)) intermetallic precipitate originated from IN718 powders was retained in the sintered specimens. The hardness results revealed that the sintering temperature of 1000 °C is not enough to promote accurate densification. The optimum hardness results were achieved at 1200 °C (327 HV) with high levels of densification and pure intragranular fracture mode. In future studies, shear and tensile strength test should be performed in order to properly evaluate the mechanical behavior of hot-pressed IN718 specimens.

Enhancement of the upper critical field in disordered nanocrystalline MgB2 bulks

Nanocrystalline superconducting MgB2 bulks were prepared by high pressure sintering of ball milled MgB2 powders. The disorder produced in these nanocrystalline materials shows a significant improvement in the upper critical field Hc2(0) of 38 T without severe suppression the superconducting transition temperature Tc. The band gap Δσ(0) decreases from 6.3 ± 0.1 meV to 5.4 ± 0.1 meV, while Δπ(0) keeps nearly fixed with the decrease in grain size to 20 nm. The ratios of the mean free path to the BCS coherence lengths li/ξ0,i(i = σ, π) turn out to be far less than 1, confirming that the two bands of the nanocrystalline bulks are both in the dirty limit. Strong intraband scatterings are responsible for the enhancement of Hc2(0).

Sintering evolution monitoring of ultra‐high‐molecular‐weight polyethylene

AbstractUHMWPE nascent powders have been commercially processed by sintering for decades although key aspects of the mechanisms and kinetics of this process are not fully understood. Herein, the volume change during each stage of the sintering is monitored by in‐situ measurements with other characterization methods. Results indicate that the α‐transition plays a crucial role in the early stages of the sintering process. Without pressure during sintering, a large expansion is observed during heating through the α‐transition well before melting and this apparent volume change is also related to the residual stress resulting from the compaction. However, the application of a moderate pressure during heating leads to a significant densification. Specifically, five distinct processes are identified from the in‐situ measurements via customized pressure sintering apparatus. These include room temperature densification, subsequent densification while heating through the α‐transition, process of melt explosion that involves the enthalpic process of crystal melting and the entropic process density changes during the isothermal sintering of non‐equilibrium melt, and the subsequent recrystallization under pressure. The density evolution offers a comprehensive understanding of the intricate processing of UHMWPE nascent powder and this can be effectively employed to investigate the impact of various processing parameters on the sintering process.

The effect of spark plasma sintering parameters on the densification and mechanical properties of TiB2‐TiC‐TiB composites

AbstractSpark plasma sintering (SPS) tests were designed using the Taguchi method to create high‐performance composites consisting of 60 wt% TiB2, 30 wt% TiC, and 10 wt% Ti. The effects of SPS parameters on the microstructure and mechanical properties of TiB2‐TiC‐TiB composites were systematically investigated. Additionally, the evolution of phase and microstructure during the densification of the composites was analyzed in detail. It has been demonstrated that composites can achieve a high relative density of 99.8%, a hardness of 22.2 GPa, a strength of 739 MPa, and a fracture toughness of 7.07 MPa m1/2, as well as a dense structure and small grain size. These properties can be obtained by sintering at a temperature of 1500°C, a pressure of 50 MPa, and a holding time of 5 min. Sintering temperature is the primary factor that promotes the densification of the composite and influences its relative density, grain size, and morphology. Holding time and sintering pressure are relatively minor factors, but they play important roles at different stages of the sintering process.

Review on the thermal characteristics and applications of silicon nitride ceramics

As the heat generation problem is predicted to intensify due to the trend of integration and high density of the power semiconductor power module responsible for the electric drive of the electric vehicle, which has recently been in full swing, high-reliability materials and It is essential to secure large-area heat dissipation substrate manufacturing process technology, and technical obstacles to maintain reliability even in environmental changes such as severe cold/excessive heat are becoming issues.In the case of silicon nitride ceramic material, which is in the spotlight as a heat dissipation substrate material, a balance that meets the user’s needs is required. In order to realize excellent heat dissipation performance, it is necessary to reduce the thickness of the silicon nitride substrate, increase the thickness of the metal junction, and improve the thermal conductivity of the silicon nitride material. Therefore, the task of technological progress beyond the complementary relationship between heat conduction-intensity still remains.In this paper, various technical considerations for increasing the thermal conductivity of silicon nitride ceramics are described, and the direction of technological progress is described along with detailed examples. In order to improve thermal conductivity, it is necessary to minimize the inflow of impurities into the raw material powder, appropriately select sintering additives required for liquid phase sintering, and optimize the microstructure through minimization of the amorphous glass phase and control of grain growth by the gas pressure sintering process.

A relationship of porosity and mechanical properties of spark plasma sintered scandia stabilized zirconia thermal barrier coating

Porous ceramic materials are popularly accepted as thermal barrier coatings (TBCs) in insulating gas turbine parts working at high temperatures. In this research, three different types of Scandia stabilized zirconia (ScSZ) systems, a nanometric 10 mol% ScSZ (10-ScSZ), a micrometric 8 mol% ScSZ (8-ScSZ) and a combination of these two powders (10-8-ScSZ) have been developed by Spark Plasma Sintering (SPS) process. Varying SPS parameters, for instance, temperature, pressure and dwell time were applied to develop the different volumes of porosity in the materials. Subsequently, the microstructure of the materials has been studied and mechanical properties have been evaluated. All three materials demonstrate a reduced porosity level at high sintering temperature and pressure. However, the nanometric 10-ScSZ material shows a higher reduction of porosity from 51.8% to 11.1% at 30 MPa pressure and 40.2%–8.5% at 60 MPa pressure within the temperature range of 1000–1200 °C. Besides, the 10-8-ScSZ composite exhibits substantially increased porosity in comparison to its constituent parts. The results also show that the nanometric 10-ScSZ material exhibits a greater mechanical strength including Vickers microhardness of 81 HV, flexural strength of 361 MPa and elastic modulus of 187 GPa at 5% porosity level, as compared to the other two materials. Additionally, it is observed that all the mechanical properties for all three materials consistently decrease with the increase in porosity levels. While compared with the traditional atmospheric plasma spray (APS) processed ceramic coating, the porous ScSZ coating materials exhibit a larger elastic modulus. Therefore, the porous ScSZ developed by the SPS process could be a prospective alternative thermal barrier coating (TBC).