Pressing Technique Research Articles

Fine-grained BCZT piezoelectric ceramics by combining high-energy mechanochemical synthesis and hot-press sintering

Different stoichiometries of lead-free BaZr0.2Ti0.8O3–Ba0.7Ca0.3TiO3 (BCZT) prepared by mechanosynthesis and sintered by either conventional sintering (CS) or hot pressing (HP) techniques were studied to establish the dependence of piezoelectric and dielectric properties on sintering parameters and microstructure. All synthesized stoichiometries showed a pseudocubic perovskite phase with homogeneously distributed A- and B-cations in the structure. The BCZT retained the pseudocubic symmetry after sintering and an average grain size <1.8 µm was obtained in all cases. HP sintering hindered the secondary phase segregation observed in the CS ceramics and increased the relative density. Piezoelectric coefficients (d33) ranging from 5.1 to 21 pC/N and from 10.0 to 88.0 pC/N were obtained for CS and HP ceramics, respectively, despite the pseudocubic symmetry and the fine grain size. The higher d33 values for the HP ceramics are a consequence of the higher density, better chemical homogeneity and lower sintering temperature and time required for the mechanosynthesized BCZT powders with high sintering activity.

Suppression of the sausaging effect in (Ba,Na)Fe2As2 round wires by using Ag1−zSnz/Cu double sheath

We report the fabrication of (Ba,Na)Fe2As2 round wires that are processed using the hot isostatic pressing (HIP) technique. We employed double sheaths composed of Cu and Ag1−zSnz alloy because they offer superior mechanical strength compared to pure Ag. The cross-sectional area of the wire core was measured using X-ray computed tomography. The findings of this study demonstrate that utilizing Ag1−zSnz alloy as the inner sheath material helps reduce the degree of the sausaging effect in the wire, resulting in a more uniform cross-sectional area of the wire core. However, transport critical current density (Jc) of the wires with the Ag1−zSnz alloy decreased gradually as the Sn content, z, increased, which may be attributed to the nonoptimized sintering temperatures during the HIP process. These results suggest that when heat-treated at an appropriate temperature during the HIP process, the use of Ag1−zSnz alloy holds great potential for use in high-performance applications.

Influences of binder phase and post-HIP treatment on tribological behavior of WC-based composite

In this study, WC-12Co and WC-12CoCrMo cemented carbides were prepared by the hot press sintering technique and subsequently post-treated by applying the hot isostatic pressing (HIP) technique. The effects of the binder phase and post-HIP treatment on the microstructures and mechanical and tribological properties of the two cemented carbides were investigated for ambient temperature use. The hardness and wear resistance of WC-12CoCrMo were increased by 87 % and two orders of magnitude compared to WC-12Co, respectively. The post-HIP did not affect the wear mechanism of cemented carbide. The binder phase was the fundamental factor in changing the wear mechanism. Post-HIP is a more viable option to enhance mechanical properties for complex carbide systems, as it promotes solid-state chemical reactions and results in an increased precipitation of secondary phases.

Effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite for engineered barrier system

This study aims to investigate the effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite buffer material for engineered barrier system. Highly instrumented unconfined compressive strength tests were performed on cylindrical specimens prepared using cold isostatic pressing (CIP) technique at varying testing conditions: (a) CIP pressures of 29.43 MPa, 39.24 MPa, and 58.86 MPa, (b) specimen sizes of 30 × 60mm, 40 × 80mm, and 50 × 100mm, and (c) loading rates of 0.5 %/min, 1.0 %/min, and 1.5 %/min. As CIP pressure increases, the unconfined compressive strength (qu), failure strain (εf), and elastic modulus (E) of Bentonil-WRK increase similar to Gyeongju compacted bentonite (KJ-II). Increase in diameter results in a decrease in qu and εf, and increase in E. Minimal effect of loading rate was observed on qu and εf. However, increasing loading rate tends to increase E. In addition, decrease in diameter increases the elastic threshold axial strain (εe,th). Increase in diameter and loading rate slightly increases Poisson's ratio. Prediction models are provided for assessing the effects of specimen diameter on qu and εf. Furthermore, correlation models of qu to ρd and E are proposed for Bentonil-WRK bentonite buffer material.

Formation mechanism of TiC twin during densification of SiCf/Ti2AlNb composites

SiCf/Ti2AlNb composites were fabricated using the magnetron sputtering precursor wires method in conjunction with the hot isostatic pressing (HIP) technique. The morphology, elemental distribution, and structural characteristics of the interfacial reaction layer (RL) were examined through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and wavelength dispersive spectroscopy (WDS). The results showed that the interface between SiC fibers and Ti2AlNb reacted to form TiC and α2. Due to the interdiffusion of elements at the interface, a small amount of Al atoms existed in the TiC layer. These Al atoms reduced the stacking fault energy (SFE) of TiC, which is beneficial for the formation and stability of Σ3{111} twin boundaries.

Thermal Conductivity of AlSi12/Al2O3-Graded Composites Consolidated by Hot Pressing and Spark Plasma Sintering: Experimental Evaluation and Numerical Modeling

Functionally graded metal matrix composites have attracted the attention of various industries as materials with tailorable properties due to spatially varying composition of constituents. This research work was inspired by an application, such as automotive brake disks, which requires advanced materials with improved wear resistance on the outer surface as combined with effective heat flux dissipation of the graded system. To this end, graded AlSi12/Al2O3 composites (FGMs) with a stepwise gradient in the volume fraction of alumina reinforcement were produced by hot pressing and spark plasma sintering techniques. The thermal conductivities of the individual composite layers and the FGMs were evaluated experimentally and simulated numerically using 3D finite element (FE) models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. The numerical models incorporated the effects of porosity of the fabricated AlSi12/Al2O3 composites, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The obtained experimental data and the results of the numerical models are in good agreement, the relative error being in the range of 4 to 6 pct for different compositions and FGM structure. The predictive capability of the proposed micro-XCT-based FE model suggests that this model can be applied to similar types of composites and different composition gradients.

Examination of the chemical composition and anti-diabetic activities of the oils of Abelmoschus esculentus, Peganum harmala, and Aquilaria agallocha cultivated in Muğla

In this study, the oils of Abelmoschus esculentus, Peganum harmala, and Aquilaria agallocha grown in different regions of Muğla, Türkiye were obtained using the cold pressing and maceration techniques. The oils were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS) to determine their fatty acid compositions. Thirty-seven fatty acids were detected. Palmitic acid (C16:0), linoleic acid (C18:2), and oleic acid (C18:1 cis-9) were the major components in all oils. Additionally, the anti-diabetic activity of the oils was screened against α-amylase and α-glycosidase, which are the related enzymes to diabetes mellitus. Promising results regarding anti-diabetic activity for Aquilaria agallocha oils were obtained.

Preparation of hierarchical microgroove textures on the surface of Al-based wicks by roller pressing and laser scanning irradiation

Fabrication of high-performance heat pipe wicks has become a major challenge due to the increase of heat dissipation requirements for electronic devices. In this paper, we propose a two-step method for the preparation of aluminum liquid-absorbing wicks with hierarchical groove structures by roller pressing and laser irradiation techniques. The effects of laser fluence and velocity on the groove morphology, wettability and capillary effect of the aluminum wicks with hierarchical grooves processed by laser scanning are investigated. The study demonstrates that sub-scale grooves with a period of 20 μm can be created on the surface of the aluminum wick using a laser fluence of 7.166 J/cm2, scanning velocities of 560 mm/s and 630 mm/s, and a pulse distance of 1 μm. The surface roughness of the irradiated aluminum wick was increased and energy dispersive spectroscopy tests showed an increase in the oxygen content of the machined surface, resulting in a surface amplification effect and the formation of a large number of hydrogen bonds in contact with the liquid. Capillary rise experiments demonstrate that hierarchical microgrooves enhance capillary action on the surface of the aluminum wick more effectively than single-scale grooves. This is due to the pumping effect in microgrooves and the diffusion effect in Ω-grooves. The hierarchical microgroove prepared under the above parameters had a capillary rise height of 88.5 mm and a capillary rise speed of 5.5 mm/s. This work proposes a method for producing high-performance wicks that are both efficient and cost-effective.

Effect of hot isostatic pressing on microstructure and mechanical properties of TZM alloy formed by powder metallurgy

Abstract TZM alloy billets were fabricated using powder metallurgy (PM) and powder metallurgy + hot isostatic pressing (PM+HIP) techniques, and the influence of these two processes on the microstructure and mechanical properties of TZM alloy billets was compared. The experimental findings indicate that an enhanced hot isostatic pressing process effectively reduces the internal porosity of TZM alloy, leading to increased tensile strength and elongation at room temperature. However, there is no significant improvement in hardness and tensile strength at 600℃.

Steam explosion-treated mushroom substrate for robust and water-resistant wood composites

Despite its significant biomass content, mushroom substrate (MS) is often carelessly discarded as waste following the harvest of edible fungi. Therein, we harnessed the power of steam explosion (SE) to liberate fibers from discarded MS and substantially increase their surface area for improved binding. Consequently, we successfully fabricated robust and water-resistant wood composites via the hot pressing (HP) technique. Our research underscored the pivotal role played by the substantial lignin content (42.5 ± 2.1%) within waste MS, reinforcing the wood composites and endowing them with exceptional resistance to water-resistant properties. The wood composite derived from waste MS yielded outstanding outcomes in internal bond strength, static bending strength, and thickness swelling, registering at 4.9 MPa, 28.0 MPa, and 30.6%, respectively. These discoveries present a pioneering approach for efficiently utilizing a significant amount of MS.

Optimization of wear parameters for ECAP-processed ZK30 alloy using response surface and machine learning approaches: a comparative study

The present research applies different statistical analysis and machine learning (ML) approaches to predict and optimize the processing parameters on the wear behavior of ZK30 alloy processed through equal channel angular pressing (ECAP) technique. Firstly, The ECAPed ZK30 billets have been examined at as-annealed (AA), 1-pass, and 4-passes of route Bc (4Bc). Then, the wear output responses in terms of volume loss (VL) and coefficient of friction (COF) have been experimentally investigated by varying load pressure (P) and speed (V) using design of experiments (DOE). In the second step, statistical analysis of variance (ANOVA), 3D response surface plots, and ML have been employed to predict the output responses. Subsequently, genetic algorithm (GA), hybrid DOE–GA, and multi-objective genetic algorithm techniques have been used to optimize the input variables. The experimental results of ECAP process reveal a significant reduction in the average grain size by 92.7% as it processed through 4Bc compared to AA counterpart. Furthermore, 4Bc exhibited a significant improvement in the VL by 99.8% compared to AA counterpart. Both regression and ML prediction models establish a significant correlation between the projected and the actual data, indicating that the experimental and predicted values agreed exceptionally well. The minimal VL at different ECAP passes was obtained at the highest condition of the wear test. Also, the minimal COF for all ECAP passes was obtained at maximum wear load. However, the optimal speed in the wear process decreased with the number of billets passes for minimum COF. The validation of predicted ML models and VL regression under different wear conditions have an accuracy range of 70–99.7%, respectively.

Enhancing the degradation rate and biomineralization nature of antiferromagnetic Fe-20Mn alloy by groove pressing.

The Fe-Mn alloys are potential candidates for biodegradable implant applications. However, the very low degradation rates of Fe-Mn alloys in the physiological environment are a major disadvantage. In this study, the degradation rate of a Fe-20Mn alloy was improved using the groove pressing (GP) technique. Hot rolled sheets of 2 mm thickness were subjected to GP operation at 1000°C. Uniform fine-grained (UFG) Fe-Mn alloys were obtained using the GP technique. The influence of GP on the microstructure, mechanical properties, degradation behavior in simulated body fluid (SBF), surface wettability, biomineralization, and cytocompatibility was investigated and compared to the annealed (A Fe-Mn) and rolled (R Fe-Mn) sample. The groove-pressed Fe-Mn (G Fe-Mn) alloy had a grain size of approximately 40 ± 16 μm whereas the A Fe-Mn and R Fe-Mn samples had grain sizes of 303 ± 81 and 117 ± 14.5 μm, respectively. Enhanced strength and elongation were also observed with the G Fe-Mn sample. The potentiodynamic polarization test showed the highest Icorr, lowest polarization resistance, and lowest Ecorr for the G Fe-Mn sample among all other samples indicating its higher degradation rate. The weight loss data from immersion tests also shows that the percentage of weight loss increases with time indicating the accelerated degradation behavior of the sample. The static immersion test showed an enhancement in weight loss of 0.46 ± 0.02% and 1.02 ± 0.05% for R Fe-Mn and G Fe-Mn samples, respectively, than A Fe-Mn sample (0.31 ± 0.03%) after 56 days in immersion in SBF. The greater biomineralization tendency in UFG materials is confirmed by the G Fe-Mn sample's stronger hydroxyapatite deposition. When compared to the A Fe-Mn and R Fe-Mn samples, the G Fe-Mn sample has a better wettability, which promotes higher cell adhesion and vitality, showing higher biocompatibility. This study demonstrates that Fe-20Mn processed by GP has potential applications for the manufacture of biodegradable metallic implants.

Overview of clinical and laboratory evaluation results of the effectiveness of digital methods for knowledge-based fabrication of complete removable acrylic dentures

This article provides an overview of the conceptual studies of modern digital technologies for the fabrication of complete removable acrylic dentures. Analysis of data of subtractive and additive methods of digital manufacturing shows the advantages of digital CAD/CAM methods over traditional methods. The use of known prepolymerized acrylic blocks in the subtractive milling method has enabled achieving high physical and mechanical properties, optimal spatial accuracy, and minimal thickness of the fabricated dentures. Moreover, residual monomer volume reduction in solid polymer blocks has allowed the high biological inertness and safety of the fabricated structures for prosthetic bed tissues and the patient’s body. Layer-by-layer printing of removable dentures by fused polymer deposition modeling technology results in high spatial accuracy of constructing structures of any degree of complexity and reduced total production time of removable dentures.&#x0D; Despite the intensity of implementation of digital CAD/CAM technologies in the practice of complete removable denture manufacturing, the search for alternative methods of modernization of the known traditional means and methods continues. However, we believe that automation and digitalization of the clinical and laboratory manufacturing of complete removable acrylic dentures has clear prospects for the total replacement of compression pressing and hot polymerization techniques of acrylates. In summary, the potential prospect in the future is a global reassessment of traditional concepts for the fabrication of complete removable dentures, considering the formation of an innovative digital CAD/CAM philosophy and the introduction of computer intelligent systems.

Stretchable electronic facial masks for photodynamic therapy

In this paper, we introduce a novel stretchable electronic facial mask for photodynamic therapy (SEFMPT) integrated with red-blue-green LED arrays, which realizes several favorable characteristics such as portability, uniformity of illuminance on the human face, and hands-free for personal long-time use. To achieve high mechanical, thermal and electrical performances of the SEFMPT, an unusual design of thick multilayer organic-inorganic composite (TMOIC) serpentine interconnects and a new piecewise single-side soft pressing (PSSP) technique for encapsulation are developed, which could also be extended to the design and fabrication of other stretchable electronics. By integrating the tri-color LEDs that could independently irradiate red, blue, and green lights, the multifunctional therapeutic purpose is realized, including skin anti-aging, treatment of Propionibacterium acnes (P. acnes) and skin whitening. The exploitation of the SEFMPT provides a distinct opportunity for new developments in both photodynamic technology and wearable electronics.

Mechanical characteristics and crystallographic texture of AA5083 during Equal Channel Angular Pressing Technique

AA5083 bars processed by four pass ambient Equal Channel Angular Pressing were subjected to intersection annealing, where time and temperature were varied after each pass. The microstructures, texturing and compressive characteristics of the samples were meticulously examined. Due to the high annealing temperatures, both ultimate tensile strength and compressive stresses decreased with increasing grain size. However, intersection annealing at room temperature resulted in the best compressive yield strength. The deformation behavior of AA5083 billets was investigated using finite element analysis. Electron back scatter diffraction was employed to examine the texture of the Equal Channel Angular Pressed billet crystals. Extensive research was conducted on the tensile properties and Vickers microhardness. The finite element simulations revealed that the 900 die exhibited a significantly more uniform dispersion of plastic strain compared to the 1200 die. The renewal of additional slip mechanisms during the four Pass process was attributed to the grain refining that occurred after the 1-Pass and 2-Pass stages. Equal Channel Angular Pressing successfully produced a homogeneously ultra-fine grained microstructure. The increase in strength was attributed to grain refining and dislocation strengthening. Molecular dynamics simulations were employed to study the ECAPed approach of AA5083 providing insights into the deformation behavior and polycrystal formation.

Strategy and mechanism to improve the fatigue properties of Ti6Al4V ELI alloy by microstructure modulation combined with surface strengthening process

The hot isostatic pressing (HIP) technique allows obtaining powder metallurgy Ti6Al4V parts with high densities, but its microstructure is not ideal, resulting in a lower fatigue life than expected. In this work, the ideal microstructure was obtained by heat treatment, but this process produces thermally induced porosity (TIP). After heat treatment, the fatigue strength of the bimodal Ti6Al4V alloy reached 680 MPa at 107 cycles, whereas the HIP Ti6Al4V alloy with a fully equiaxed microstructure was lower than 590 MPa. This is because the bimodal Ti6Al4V alloy has better resistance to fatigue crack initiation. This result confirmed that TIPs do not have a significant negative impact on fatigue properties. To further improve the fatigue performance, this study induced gradient nanostructured (GNS) in Ti6Al4V alloy by ultrasonic surface rolling process (USRP), and the fatigue strength of the USRP-treated specimen reached 750 MPa at 107 cycles. Combining microstructure observations and theoretical analysis, the surface hardening mechanism of the USRP-treated Ti6Al4V alloy was quantitatively described. The results showed that the plastic deformation layer is approximately 130 μm, but grain boundary strengthening maintained its effect to a depth of about 200 μm whilst dislocation strengthening maintained its effect to a depth of approximately 350 μm. Under the comprehensive effect of surface hardening and compressive residual stress field, the fatigue crack initiation period of the USRP specimen was significantly extended. This may be the primary reason behind the enhanced fatigue performance obtained through USRP treatment.

Study on the effect of the ECAP deformation on the organization and properties of the extruded Mg-Sn-Al alloys

In order to refine the grain and the second phase size of the Mg-Sn-Al alloys further, as well as enhance the alloy's strength-ductility performance match, the alloy was deformed by equal-channel angular pressing (ECAP) technique after conventional extrusion. After ECAP (180℃), the microstructures and mechanical properties of the alloy were observed. The results show that the average grain size of the alloy reduced from 23.3 μm to 1.25 μm, and the percentage of the high-angle grain boundaries rise to 71 %. The texture of the ECAPed alloy on TD direction shows a typical fiber (10 1¯ 0) < 11 2¯ 0>, with an intensity of 12.016. The mechanical properties of the ECAPed alloy were tested after aging at 240℃ for 192 h, and the results show that the ultimate tensile strength of the aging alloy was 415 MPa, the yield strength was 324 MPa and the elongation was 10.5 %.

Defects control of silicon nitride ceramics by oscillatory pressure sintering and consequent hot isotropic pressing

Micro-pores and micro-cracks inhibit the enhancement in strength and toughness of structural ceramics. Among various processing procedures, sintering is the key stage to control microstructure and then enhance mechanical performances of ceramics. Here, we reported the consolation of silicon nitride ceramics with high strength and toughness by defects control, using oscillatory pressure sintering (OPS) followed by hot isostatic pressing (HIP) techniques. The introduction of oscillatory pressure and isostatic pressure may enhance grain sliding and grains deformation of during sintering, thus removed the trapped pores at grain boundaries and accelerated growth of β-Si3N4 grains. Because of the microstructure evolution, the Si3N4 ceramics exhibited flexural strength of 1630 ± 21 MPa and fracture toughness of 7.1 ± 0.6 MPa m1/2 when sintered at 1750 °C. Thus, this work provides a path to prepare ultra-strong and tough ceramics by controlling various micro-defects.

Effect of the Equal Channel Angular Pressing on the Microstructure and Phase Composition of a 7xxx Series Al-Zn-Mg-Zr Alloy.

A supersaturated Al-4.8%Zn-1.2%Mg-0.14%Zr (wt%) alloy was processed by the equal-channel angular pressing (ECAP) technique at room temperature in order to obtain an ultrafine-grained (UFG) microstructure having an average grain size of about 260 nm. The hardness and microstructural characteristics, such as the phase composition and precipitations of this UFG microstructure were studied using depth-sensing indentation (DSI), transmission electron microscopy (TEM), as well as non-isothermal scanning of differential scanning calorimetry (DSC), and compared to the properties of the un-deformed sample. Emphasis was placed on the effect of the UFG microstructure on the subsequent thermal processes in DSC measurements. It has been shown that the ECAP process resulted in not only an ultrafine-grained but also a strongly precipitated microstructure, leading to a hardness (2115 MPa) two and a half times higher than the initial hardness of the freshly quenched sample. Because of the significant changes in microstructure, ECAP has also a strong effect on the dissolution (endothermic) and precipitation (exothermic) processes during DSC measurements, where the dissolution and precipitation processes were quantitatively characterized by using experimentally determined specific enthalpies, ΔH and activation energies, Q.

Optimization of lithium disilicate glass-ceramic crowns: finish line, scanning and processing methods.

To investigate the optimal combination of factors (finish line, scanning, and ceramic processing) to achieve the best values of both adaptation and fracture load of lithium disilicate (LD) crowns. Abutment preparations, chamfer (C) and rounded shoulder (S), were produced with a dentin analog material and scanned with extraoral (E) or intraoral (I) scanners. The captured images were processed using CAD software to design a premolar. Blocks of LD were milled using a CAD/CAM system (Cad). For the pressing technique (Pre), crowns were first 3D printed using a polymeric material, and a heat-pressing protocol was performed. The design of experiments was used to plan four experimental groups (n = 10): (1) CadCI; (2) CadSE; (3) PreCE; and (4) PreSI. Two dependent variables were analyzed: (1) adaptation, measured using the replica technique; and (2) fracture load of the cemented crowns. Fractographic analysis was performed. Data were analyzed using ANOVA and regression statistical analyses. There was no significant effect of scanning method or finish line for the gap thickness in the different regions. For the processing method, Cad resulted in larger gap thickness in the occlusal, axial angle, and marginal areas and smaller gap in the axial area (P < .001). There was no effect of the investigated factors on the fracture load. However, PreCE was considered to be the optimal design, as it achieved 100% of the desired fracture load (> 1,000 N) and 40% of the adaptation (< 200 μm). The optimal combination of factors for all-ceramic crowns is chamfer abutment preparation, extraoral scanning, and the press technique (combined with 3D printing).