High Relative Density Research Articles

Effects of raw powder characteristics on microstructure and mechanical properties of W[sbnd]20Cu composites manufactured by SLM

Selective laser melting (SLM) technique is a promising method to achieve near-net-shaping of WCu complex components. In this work, two types of raw powers were prepared, including spherical WCu composite powder and mixed WCu powder. Effect of the raw powder characteristics on the microstructure and mechanical properties of W20Cu alloy were investigated. The results show that the composite powder enables the WCu composites to possess a high relative density (95.1 %), homogeneous microstructure and super mechanical properties (204.40 ± 1.73 HBW for hardness and 500 MPa for tensile strength). Remarkably, compared to mixed powder, the tensile strength and hardness are increased by 37 % and 74.2 %, respectively. This good effect stems from the composite powder with good sphericity degree and uniform structure. As a result, a dense specimen with refined W particles (3.05 μm) evenly embedded in the Cu matrix phase, accompanied by dislocation structure and sub-grains within the Cu matrix are obtained, contributing to the superior mechanical properties of the composites. The present work offers a strategy for developing high-performance WCu composites using SLM technology.

Attenuating Cartilage Degeneration in a Low Mechanical Compression Rat Model Through Intra-Articular Injections of Allogeneic Bone Marrow-Derived Mesenchymal Stem Cells.

Mechanical stimulation significantly contributes to posttraumatic osteoarthritis (PTOA), a condition that impedes patient recovery following intra-articular injury. Effective treatment options for compression-induced injuries are limited. Bone marrow-derived mesenchymal stem cell (BMSC) implantation has emerged as a potential therapeutic breakthrough for joint diseases. The aim of this study was to attenuate the progression of PTOA induced by cyclic loading and demonstrate the potential effectiveness of BMSCs in a rat model of low mechanical compression. Using a rat model of compression-induced articular cartilage injury, assessments were conducted 2, 4, and 8 weeks after cyclic compressive loading. The expression of matrix metallopeptidase 13, transforming growth factor-beta 3 (TGF-β3), insulin-like growth factor 1 (IGF-1), and cleaved caspase-3 was evaluated through immunohistochemistry to investigate the mechanistic aspects underlying the prevention of compression-induced injury following BMSCs treatment. Intra-articular injections of BMSCs significantly improved scores in the OARSI (Osteoarthritis Research Society International) Osteoarthritis Cartilage Histopathology Assessment System and Histological-Histochemical Grading System. This treatment showed positive outcomes in maintaining high relative cell density and reducing proteoglycan loss after cyclic compression-induced injury. The expression patterns of IGF-1 and TGF-β3 provide valuable insights into the presence and distribution of these growth factors in healthy and injured cartilage. These findings highlight the efficacy of BMSCs treatment in attenuating the advancement of compression-induced injuries, albeit within a limited timeframe.

Investigation of Sr-substituted Ba1-xSrx(Zn1/3Nb2/3)O3 complex perovskites: Structural, electrical and electrochemical properties

Herein we report the structural, dielectric and electrochemical properties of Ba1-xSrx(Zn1/3Nb2/3)O3 (BSZN, 0 ≤ x ≤ 1) solid solution synthesised by solid-state reaction. A complete substitutional solid solution was obtained, wherein the BSZN cubic perovskites of the space group of Pm3‾m were obtained at x ≤ 0.6 while the pseudo-cubic phases were discernible at x > 0.6. The nano-sized crystallites, as determined by both Scherrer and Williamson-Hall analyses, supported the claim of large polyhedral grains of 0.1–0.3 μm by FE-SEM. Both ε′ and tan δ were found to vary consistently with increasing dopant concentration, except for an anomalous observation for the composition, x = 0.6 with the lowest tan δ of 0.0783 and the highest ε′ of 27.5. Such phenomenon could be attributed to the combined effects of larger grain size, higher relative density and stronger polarisation per molar volume. The impedance analysis revealed that these BSZN perovskites were of the negative temperature coefficient of resistance (NTCR) type. The combined plots of imaginary modulus (M″) and impedance (Z″) against frequency showed the short-range movement of localised charge carriers, suggesting a non-Debye-type relaxation process.

Design and optimization of stirrer and mixer design for the correct mixing of pharmaceutical powders through DEM

Mixing of granular materials is an important process for pharmaceutical industries. In this study, a quantifiable calculation method was suggested to determine the final mixing degree of the mixture. Based on that, the effect of the stirrer design, rotational speed, powder density, cohesivity, material ratios, and particle movement in the chamber guided through different designs of deflectors on the final mixing quality is examined. The results show that increasing the stirring speed, generates better mixing quality. However, introducing a varying rotational speed mode improves the mixing degree specially for binary mixtures with high relative densities. The improvement of the mixing with the number of contacting blades is observed. Finally, the introduction of a simple deflector drastically enhances the mixing quality and enables the feeding into the chamber, which is key for continuous operation with cohesive powders, making the process more stable and efficient by using more of the mixing volume.

Effect of grain size on mechanical properties and aging of yttria-stabilized tetragonal zirconia polycrystal fabricated by stereolithography-based additive manufacturing

The objective of this investigation was to comprehensively assess the impact of grain size on the mechanical properties and low-temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) fabricated by stereolithography-based additive manufacturing at the submicron scale. Four 3Y-TZP ceramics with high relative density (>98%), ranging in grain size from 0.2 μm to 1 μm, were successfully prepared and validated for studying mechanical properties (including Vickers hardness, fracture toughness, and flexural strength) as well as LTD progression. This study elucidates the mechanical behavior of zirconia ceramics at the submicron scale, focusing on fracture micromechanisms and the grain size dependence of transformation toughening. Additionally, it examines the influence of grain size on the hydrothermal aging behavior of zirconia ceramics at the submicron scale using Raman spectroscopy.

Cu/AlN composite and functionally graded materials with high strength and high electrical- and thermal-conductivity fabricated by spark plasma sintering

In this study, Cu/AlN composites and functionally graded materials (FGMs) were fabricated with the spark plasma sintering method. It was observed that a two-step sintering process, involving sintering under low pressure as the initial stage to remove adsorbed chemicals on the powder, was an effective method for producing sintering objects with high relative density. The hardness of the composites significantly increased with higher volume fraction of aluminum nitride (AlN) particles, while electrical- and thermal-conductivity decreased. Nevertheless, the advanse impact of AlN on thermal-conductivity was found to be minimal. Additionally during compression test, a crack was noted at the interface between Cu and Cu-5 vol%AlN region in two-layered FGMs after, whereas no such crack was observed in the three-layered FGMs. Therefore, it is confirmed that the concept of FGMs is useful in overcoming the shortcomings of mutually exclusiveness among high strength, high electrical- and high thermal-conductively.

Enhanced density and microstructural integrity of binder jetting manufactured ceramics through cold isostatic pressing

Binder jetting (BJ) is a type of additive manufacturing (AM) process that enables fabrication of complex zirconia (ZrO2) ceramic components. However, there are significant challenges in fabricating ceramic parts with high relative density and superior performance. In this study, cold isostatic pressing (CIP) process was integrated into BJ, successfully producing high-performance ZrO2 ceramics. Comprehensive study was conducted on ZrO2 granules, binder, and their interactions. In addition, effects of CIP process on relative density and mechanical properties of sintered samples were investigated. Results indicate that CIP process significantly enhances green body density and reduces spacing between particles, thereby facilitating subsequent densification during ceramic sintering. Moreover, debinding followed by CIP treatment yields superior mechanical properties compared to the methods where CIP was performed prior to debinding, as it prevents defect formation during debinding. Subsequently, differences in performance between ZrO2 ceramics treated with and without CIP were compared at various sintering temperatures. After sintering at 1400 °C, relative density and flexural strength of ZrO2 ceramics reached 98.75 ± 0.19 % and 1047.80 ± 88.45 MPa, representing significant improvements of 53.24 % and 100-fold increase compared to those without CIP treatment, respectively. These findings indicate that proposed method is highly promising for fabrication of high-density and high-performance ZrO2 components.

Liana versus tree seedling responses to spatial and temporal variation in dry season severity

AbstractLianas are key components of tropical forests, particularly at sites with more severe dry seasons. In contrast, trees are more abundant and speciose in wetter areas. The seasonal growth advantage (SGA) hypothesis postulates that such contrasting distributions are produced by higher liana growth relative to trees during seasonal droughts. The SGA has been investigated for larger size classes (e.g., ≥5 cm diameter at 1.3 m, dbh), but rarely for seedlings. Using eight annual censuses of >12,000 seedlings of 483 tree and liana species conducted at eight 1‐ha plots spanning a strong rainfall gradient in central Panama, we evaluated whether liana seedlings had higher growth and/or survival rates than tree seedlings at sites with stronger droughts. We also tested whether an extreme El Niño drought during the study period had a more negative effect on tree compared to liana seedlings. The absolute density of liana seedlings was similar across the rainfall gradient, ranging from 0.32 individuals/m2 (0.20–0.49, 95% credible interval [CI]) at the driest end of the gradient and 0.27 individuals/m2 (0.13–0.51 95% CI) at the wettest end of the gradient. The relative density of liana seedlings compared to tree seedlings was higher at sites with stronger dry seasons (0.27, 0.21–0.33, 95% CI), compared to wetter sites (0.12, 0.04–0.20 95% CI), due to lower tree seedling densities at drier sites. However, liana seedlings did not grow or survive better than tree seedlings in drier sites compared to wetter sites. Tree seedlings were more negatively impacted in terms of mortality by the extreme El Niño drought than liana seedlings, with an increase in annual mortality rate of 0.013 (0.003–0.025 95% CI) compared to lianas of −0.009 (−0.028 to 0.008 95% CI), but not growth. Our results indicate that lianas do not have a SGA over trees at the seedling stage. Instead, higher survival of liana versus tree seedlings during severe droughts or differences in liana versus tree fecundity or germination across the rainfall gradient likely explain why liana seedlings have higher relative densities at drier sites.

The crystal structure, sintering characteristics and microwave dielectric properties of clinopyroxene SrBGe2O6 (B= Mn, Co) ceramics

Two novel low permittivity SrMnGe2O6 and SrCoGe2O6 ceramics with diopside structure were prepared by solid-state method, with their microwave dielectric properties reported for the first time. XRD and Rietveld refinement revealed that SrBGe2O6 (B = Mn, Co) ceramics belong to monoclinic system with C2/c space group. At lower sintering temperatures, SrBGe2O6 ceramics exhibit excellent relative density (> 94%). Compact SrMnGe2O6 and SrCoGe2O6 ceramics exhibit the best surface morphology, the highest relative density and the optimal microwave dielectric properties at 1100 °C and 1140 °C, respectively: εr = 8.71, Q×f = 30680 GHz, τf = − 60.32 ppm/°C; εr = 9.01, Q×f = 33335 GHz, τf = − 69.14 ppm/°C. The effect of intrinsic loss such as lattice vibration on the microwave properties of SrBGe2O6 ceramics was studied by Raman spectroscopy. An analysis based on lattice vibration elucidates the reasons behind the differences in microwave properties between the two ceramics. Furthermore, the correlation between Q×f value and sintering temperature was analyzed with covalent bond strength, and the relationship between structure and temperature stability was discussed by octahedral distortion. Study on these two novel ceramics not only broaden the system of microwave dielectric ceramics, but also provide new materials for the construction of communications technology.

The effect of the addition of 2-dimensional manganese-oxide to ceria on density and electrical conduction

Gadolinium-doped ceria (GDC), a prominent solid electrolyte for solid oxide fuel cells, is known to have poor sinterability and requires high temperatures for densification. To address this issue, transition-metal oxides have frequently been used as sintering aids to enhance the sinterability of ceria. In this study, a two-dimensional (2D) sintering aid, distinct from conventional three-dimensional structures, was used. Specifically, 2D MnO2 with nanometer-thickness, produced by a chemical exfoliation method, was utilized to improve the sinterability of GDC. GDC with the sintering additive (2D MnO2) was sintered at various temperatures (800–1200 °C). The addition of 2D MnO2 successfully reduced the sintering temperature. As a result, the sample with high relative density demonstrated high oxygen ionic conduction, even though it was sintered at a lower temperature.

Corrosion behavior of magnesium-aluminum spinel in low-temperature electrolytes

Magnesium-aluminum spinel composite is a novel material designed for low-temperature aluminum electrolytic baths without a ledge profile. In this study, multi-doped magnesium-aluminum spinel was successfully prepared, and its corrosion behavior in low-temperature aluminum electrolytes was investigated. The multi-doped magnesium-aluminum spinel exhibited high relative density and homogeneous grain structure. The addition of lithium fluoride and potassium fluoride altered the physical structure of the aluminum electrolytes. A corundum phase was observed on the surface of the corroded multi-doped magnesium-aluminum spinel. The average corrosion depth and static corrosion rate were found to be related to the electrolyte composition and liquidus temperature. Notably, the corrosion rate decreased as the exposure time increased.

Laser Directed Energy Deposition Additive Manufacturing of Al7075 alloy: Process Development, Microstructure, and Porosity

7xxx series aluminum alloys are priority materials adopted in aerospace because of their lightweight property and excellent mechanical performance. The combination of lightweight material and additive manufacturing techniques can significantly promote lightweight design in many industries. This study developed the optimal process for manufacturing Al7075 alloy by laser-aided directed energy deposition and revealed the material properties of the as-deposited Al7075 specimens. Firstly, single-track experiments were conducted by varying laser power, printing speed, and powder delivery rate in broad ranges. Results indicated that the printing speed and powder delivery rate impact the surface finish and shape of single-track beads considerably. Block specimens printed with the optimal parameters selected from the single-track experiments present crack-free quality and have a high relative density of up to 99.89%. Second phases with rich Cu, Mg, and Zn elements along the inter-dendritic regions and grain boundaries were observed from the microstructure inspection. The composition of zinc in the deposited samples is lower than usual, which leads to a relatively low microhardness.

Flash Sintering of Bimetallic Assemblies for Turbine Disks in Next‐Generation Jet Engines

René 77 and another advanced powder metallurgy nickel‐based superalloy are flash‐sintered and joined to produce a dual‐alloy assembly. This innovative process allows for the sintering of powders to achieve high relative densities or the formation of solid joints in a shorter time than is feasible with conventional diffusion bonding techniques. Examination of the microstructure after heat treatments reveals that diffusion and recrystallization phenomena can modulate the transition zone. The creep properties of both alloys, evaluated using stress relaxation tests, do not seem to differ by more than an order of magnitude, while the higher thermal stability of René 77 compared to Alloy B at 800 °C tips the scales. In tension, base materials show very high properties, while bimetallic specimens exhibit at least higher properties than René 77. However, failure occurs at the bond at high temperatures due to the formation of an oxide film during the bonding process. These encouraging results illustrate the potential and constraints of the flash‐sintering process for producing dissimilar assemblies, which may enhance the properties of next‐generation aero‐engine turbine disks.

Novel insights into PLMN-13PT ceramics: impact of spark plasma sintering on compositional and dielectric properties

AbstractThis study investigates the effects of Spark Plasma Sintering (SPS) on the physical, structural, microstructural, dielectric, and optical properties of on 87[Pb(1−y)Laₓ(Mg1/3Nb2/3)O3]-13PbTiO3, (PLMN-13PT) ceramics. The primary objective was to evaluate how SPS influences the densification, grain growth, and compositional variations of these ceramics, which are critical for electronic device applications. The results demonstrate that SPS effectively achieves high relative density while suppressing grain growth, leading to a more homogeneous microstructure. However, the rapid densification process also induces compositional variations that significantly impact the dielectric properties, including the reduction of undesirable phases like pyrochlore, which are detrimental to performance. These findings highlight the potential of SPS for optimizing PLMN-13PT ceramics, enhancing their suitability for the miniaturization of multifunctional electronic devices.

Improving Bulk and Interfacial Lithium Transport in Garnet-Type Solid Electrolytes through Microstructure Optimization for High-Performance All-Solid-State Batteries.

Garnet-type Li6.4La3Zr1.4Ta0.6O7 (LLZTO) is regarded as a highly competitive next-generation solid-state electrolyte for all-solid-state lithium batteries owing to reliable safety, a wide electrochemical operation window of 0-6 V versus Li+/Li, and a superior stability against Li metal. Nevertheless, insufficient interface contacts caused by pores, along with Li dendrite growth at these voids and grain boundary regions, have hindered their commercial application. Herein, we suggest a method to produce high-quality LLZTO using LiAlO2 (LAO) as a chemical additive that leads to an improved microstructure with larger grain size (∼25 μm), a high relative density (∼96%), lower porosity (∼3.7%), and continuous secondary phases in grain boundary regions. This improved structure results in (i) improved Li-ion conductivity and enhanced interfacial resistance between Li metal and LLZTO by a denser structure with fewer pores and (ii) suppression of Li dendrite penetration in the electrolyte by secondary phases in grain boundary regions.

Effects of carbon on the synthesis and densification of tantalum carbide powder

Tantalum carbide (TaC) powder was synthesised at 1500 ºC by sol-gel and carbothermal reduction processes using tantalum pentachloride (TaCl5) and phenolic resin as the starting materials. The effects of the C/Ta ratios in the Ta-containing precursor on the reaction yield, microstructure, chemical composition, and sinterability of the powders were investigated. The results showed that a high C/Ta ratio was favourable for the formation of TaC powder. With an increase in the C/Ta ratio, the oxygen content of the powder decreased, whereas the free carbon content increased. Consolidated TaC ceramics with high relative density (> 97 %) were obtained at 1900 ºC for 5 min under 80 MPa after sintering the powder synthesised at C/Ta ratios of 4.00 and above. However, the hardness and fracture toughness of the TaC ceramics were slightly reduced when the C/Ta ratio exceeded 4.00, owing to weak interface bonding caused by excessive free carbon in the powder. It was found that sintering TaC powders prepared at a C/Ta ratio of 4.00 produced dense TaC ceramics, with a Vickers hardness and fracture toughness of 16.54 GPa and 3.72 GPa∙m1/2, respectively.

Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.

A comprehensive study of the effect of scanning strategy on IN939 fabricated by powder bed fusion-laser beam

This study provides a comprehensive investigation into the effects of different scanning strategies on the material properties of IN939 fabricated using the PBF-LB process. The scanning strategies examined included alternating bi-directional scanning with rotation angles of 0°, 45°, 67°, and 90° between adjacent layers (named as shown), as well as alternating chessboard scanning with rotation angles of 67° and 90° (named as Q67° and Q90°). The results revealed that the 45° and 67° samples had the highest relative density, while the 0° and Q67° samples showed the highest average porosity. Moreover, various types of cracks, including solidification, solid-state, and oxide-induced cracks, were observed. Among the bi-directional scan samples, the 0° sample displayed the most extensive cracking and the highest σmax residual stress values in both XZ and XY planes. Conversely, the 45° and 67° samples exhibited fewer cracks. Notably, the lowest σmax residual stress in the XZ planes among the bi-directional scan samples was observed in the 67° sample. Additionally, microstructural analyses indicated differences in grain size and morphology, among the samples. Texture analysis indicated that the 0° and 90° samples exhibited strong cube textures, whereas the texture intensity weakened for the 45° and 67° samples. Moreover, the alternating chessboard scanning strategy led to rougher surfaces (higher Sa and Sz values) compared to the alternating bi-directional scanning strategy, regardless of the rotation angles. Furthermore, the microhardness values among the samples showed minimal variance, ranging between 321 ± 14 HV and 356± 7 HV.

Design and Fabrication of a C-Band Patch Antenna with Low Loss BaM4Si5O17 Microwave Dielectric Ceramics.

Single-phase BaM4Si5O17 (M = Yb, Er, Y, Ho) ceramics have been investigated for their crystal structures, microwave dielectric properties, flexural strength, and potential applications in dielectric antennas. Rietveld refinement and TEM analysis revealed that the BaM4Si5O17 ceramics exhibit a monoclinic structure (space groups: P21/m). The εr of the BaM4Si5O17 ceramics was dominated by ionic polarizability and ρrel. The Q × f values were considerably larger at BaM4Si5O17 (M = Yb and Y) ceramics with the high Utotal and low intrinsic dielectric loss. The τf values were controlled by the MO6 octahedron distortion and -VBa. The flexural strength was mainly dominated by pores and average grain size and reached the maximum value (156 MPa) at BaY4Si5O17 ceramic with small average gain sizes and high relative density. Additionally, a patch antenna was fabricated using high-performance BaY4Si5O17 ceramic characterized by a εr value of 9.02, a Q × f value of 60620 at 12.30 GHz, and a τf value of -37.65 ppm/°C. This design achieved a high simulated radiation efficiency of 82.70% and a gain of 5.60 dBi at 6.97 GHz. indicating potential applications of BaY4Si5O17 ceramic because of its low dielectric loss and high flexural strength.

Laser powder bed fusion of SiC particle-reinforced pre-alloyed TiB2/AlSi10Mg composite with high-strength and high-stiffness

Recently, laser powder bed fusion (LPBF) of particle-reinforced aluminum matrix composites (PAMCs) with high-strength and high-stiffness have attracted extensive attention in aviation and aerospace. However, performance improvement of single or dual PAMCs using traditional mechanical mixing method is still limited. Therefore, this study innovatively employed pre-alloyed ∼6.5 wt% TiB2/AlSi10Mg composite as the matrix and mechanically mixed SiC particles with different contents (5 vol% and 10 vol%) to fabricate dual PAMCs with high particles content through LPBF. The results indicated that the 5 vol% SiC+TiB2/AlSi10Mg composite revealed relatively weak agglomeration effect of SiC particle and highest relative density (∼99.1 %), thus exhibiting optimal processability. Using this composition material as the research object, it was found that the microstructure maintains the basic features of pre-alloyed TiB2/AlSi10Mg composite except for the slight grain coarsening. However, SiC particles react with α-Al matrix and Al3Ti. Then Al4C3 and TiC enhancement phase were formed, and micron-sized Si particles precipitated within the Al cells surrounded by the eutectic Al-Si. More importantly, due to novel preparation method of dual PAMCs powder, simultaneous enhancement in ultimate tensile strength (∼554.0 MPa), yield strength (∼376.0 MPa), and elastic modulus (∼97.4 GPa) was achieved. Total particle content (∼14.0 wt%) and tensile property were higher than those of reported other PAMCs processed by LPBF. Finally, expect for the fracture characteristics inherent to the pre-alloyed TiB2/AlSi10Mg composite, new fracture mechanism for the tearing of SiC particles was exhibited. This work provides new insights into the preparation of high-strength and high-stiffness PAMCs processed by LPBF.