Densification Behavior Research Articles

Molten salt synthesis of Ti-Si-C coating on SiC particles and hot pressing of the prepared powders

SiC particles coated with Ti-Si-C layer were prepared by the molten salt synthesis method using NaCl-KCl eutectic mixture as the reaction medium and Ti metal powder as the Ti source. The synthesis was conducted under static argon atmosphere at 900 °C for 1–3 h. The post-synthesis treatment included dissolution of salts in hot water, followed by ultrasonic dispersion and sedimentation procedures. The thickness of the Ti-Si-C layer varied from 0.1 to 0.9 μm as the ratio of Ti to SiC components in the starting mixture changed from 0.05 to 0.4. The layer contained mainly nanocrystalline Ti5Si3, minor phases were TiC and Ti3SiC2. The as-prepared powders were hot pressed under 30 MPa at 1700 °C. The densification behavior of the samples during hot pressing as well as changes both in phase composition and in microstructure were studied. The flexural strength of the hot-pressed samples increased with an increase in the Ti:SiC molar ratio, giving the value as high as 213 ± 20 MPa for the sample with Ti/SiC = 0.4.

Compaction Behavior and Densification Mechanism of the TA15 Titanium Alloy in Electromagnetic Compaction Processing

Compaction Behavior and Densification Mechanism of the TA15 Titanium Alloy in Electromagnetic Compaction Processing

Influence of grading in compacted tailings behaviour: towards resilient design

The inherent variability of tailings is the main challenge in compacted filtered tailings stacks (CFTS) operation. Despite the advances in dewatering technologies, the filtration efficiency depends on the tailings’ gradation and mineralogy. A usual process is filtering materials separately, which can later be mixed and compacted. This paper studies two iron ore tailings (flotation and slime) from a unique mine and three mixtures (80/20, 70/30 and 60/40) produced from them to investigate the influence of grading on tailings’ compressibility, strength, stiffness, and state measures. The materials were thoroughly characterised and submitted to triaxial tests under low (50 kPa) and high (1,000 kPa) confinement levels and different moulding conditions (loose and dense). The results showed that the behaviour of the range of gradings investigated was similar in terms of compressibility, strength mobilisation (peak and M value), dilatancy and stiffness for similar compaction efforts. The packings produced seem to be affected mainly by the mineral composition and grading, while the mechanical procedures only change the magnitude of the state achieved, maintaining the proportion between them. Understanding how grading and mineralogy affect different geomechanical aspects of tailings is the first step towards resilient projects, which are essential to the mining industry’s future.

Explosive stress wave propagation and fracture characteristics of rock-like materials with weak filling defects

Filling-type defects have a non-negligible effect on the propagation of explosive stress waves in rock. Combined with the new dynamic caustics experimental system and ANSYS/LS-DYNA numerical simulation platform, the research on the propagation characteristics of explosive stress wave and fracture characteristics of rock-like materials containing weak filling defects with different ductility has been carried out. Firstly, we analyzed the influence of weak filling on the propagation of blast-induced cracks, explored the “guiding” and “stopping” effects of weak filling on cracks, and analyzed the mechanical characteristics of crack propagation. Secondly, the effect of planar weak filling ductility on the damage degree of blasted medium was quantitatively evaluated. Thirdly, the influence of weak filling on the fluctuation characteristics of explosive stress wave was investigated. Then, the mechanical response behavior of the specimens was analyzed, and the results showed that the compaction and slip behaviour characteristics of the weak filling have some variability in degree, some continuity in time, some correlation in space and are affected by the ductility of the planar weak filling. In addition, the stress wave and weak filling interaction mechanism was elucidated. The conclusions of the analysis have positive reference value for understanding the explosion mechanics mechanism of defective rock masses.

Study of powders for sintering SiC in the presence of a liquid phase

In this study, nanometric powders of silicon carbide (SiC), micrometric alumina (Al₂O₃) and yttria (Y₂O₃), with specific characteristics provided by the manufacturers, were used to investigate the compaction behavior and the resulting properties after sintering. The SiC used has a purity of over 99% and a particle size distribution with a d50 of 40 nm, while Al₂O₃ and Y₂O₃ have purities of 99.8% and 99.995%, respectively. The morphological evaluation of the powders was carried out using scanning electron microscopy (SEM), while the apparent density analysis was conducted using gas pycnometry. SiC mixtures with 1% and 5% Al₂O₃ and Y₂O₃ were prepared and subjected to uniaxial compaction tests to determine densification behavior under different pressures. The results of this study are relevant to the development of ceramic materials with optimized properties for a wide range of industrial applications. The addition of small amounts of oxides to SiC does not compromise its compaction properties, maintaining the effectiveness of the sintering process and resulting in materials with high density and improved mechanical properties.

Ultralow‐Temperature Sintering of Titanium Powder by Spark Plasma Sintering Under Cyclic Pressure

Spark plasma sintering (SPS) is a promising method for producing titanium components from powder but a limitation is that high sintering temperatures (>900 °C) are normally required to eliminate porosity. Herein, the SPS of commercially pure titanium powder is reported using both cyclic and constant uniaxial pressure and compare densification, microstructure, and mechanical behavior. The following parameters are varied: sintering temperature, TS, 400 to 900 °C; cyclic and constant pressures, 100 to 500 MPa; with and without an isothermal dwell of 60 min at TS. The mechanical behavior is determined by bend and tensile testing. It is demonstrated that the application of cyclic pressure (cyclic‐SPS) gives superior densification over the range of parameters investigated compared with a constant pressure. Bend testing reveals improved ductility after cyclic‐SPS compared with a constant pressure. The dwell at TS further improves mechanical properties, giving excellent tensile ductility and strength. Consequently, at the ultralow temperature of 500 °C, nearly fully dense, ductile, titanium is achieved. It is shown that cyclic pressure enhances the degree of powder compaction at room temperature, and mechanisms are proposed to rationalize the effect of cyclic‐SPS on enhancing the rates of densification and sintering as the temperature increases during processing.

Compaction behaviour of flax-preforms during forming for composites

Flax reinforced composites are becoming popular in automotive and civil industries due to their green production and recycling, and for good specific strength. To manufacture composites, firstly a multi-layer of flax preforms undergo compressive pressure before resin impregnation that causes nesting, wherein, fibres of one layer fit into the adjacent layers. This debulking of the preforms under compression is an important feature that determines the fibre volume fraction of composites. In this study, four flax structures such as: nonwoven tapes, unidirectional fabric, hopsack fabric, and nonwoven tape with glass veils were investigated for compaction behaviour under pressures between 1 and 10 bars, in single and multi-layer states, in dry and wet states, under different loading cycles, and in different ply orientations (0°/0° and 0°/90°). Nesting has been calculated for single- and multi-layer stacks. It was observed that the nonwoven structures shown greater thickness reduction compared to woven structures. Nesting factor was found to be higher than 1 for the nonwoven structures under compaction, indicating lower nesting, compared to the woven structures. In terms of thickness under repeated compaction, the reduction was the highest during first compressions, compared to the 2nd and 3rd compressions, for all the structures. When wettability was examined, thickness reduction for wet plies was higher for all the structures, compared to the dry phase. Finally, a comparative study was shown to evaluate fibre volume fractions of the composites.

Microstructure and mechanical properties of ZrB2 ceramic particle reinforced AlCoCrFeNi high entropy alloy composite materials prepared by spark plasma sintering

In this study, xZrB2-AlCoCrFeNi (x = 0,5,10,15) (wt%) based high entropy alloy (HEA) composites were prepared by Spark Plasma Sintering (SPS). The influence of ceramic particle ZrB2 content on the densification behavior, microstructural evolution, and mechanical properties of the composites was investigated through scanning electron microscopy, X-ray diffraction, and mechanical performance testing. The results indicate that the HEA composites undergo a phase transformation, from (FCC + BCC + B2) structure to (FCC + BCC + B2+Laves) structure with the addition of ZrB2. The incorporation of ZrB2 facilitates the emergence of the Cr precipitate phase, and the grain size of this phase enlarges as the ZrB2 content rises. Additionally, when the ZrB2 content is 10 %, the maximum compressive strength reached 2071 MPa. Furthermore, at the ZrB2 content of 15 %, the composite material achieves a maximum densification of 99.13 % and a maximum hardness of 1222.2 HV.

Synergistic effect of YAG particulate reinforcement on microstructural and thermo-mechanical properties of pressureless sintered MgAl2O4 spinel ceramic composites

Yttrium aluminum garnet (YAG) powders, synthesized through a partial wet chemical process, exhibit controlled morphology, high phase purity, and uniform homogeneity etc. This process involves the precipitation of aluminum ions onto Y2O3 particles. The transformation process of the Al-compound/Y2O3 precursor structure leads to the direct crystallization of pure YAG at 900 °C, passing through an intermediate stage where hexagonal YAH phase forms. A comprehensive study was conducted on the impact of preformed YAG as a reinforcing phase on the densification, mechanical, and thermo-mechanical properties of MgAl2O4-YAG composite, sintered under pressureless sintering in temperature range of 1500 °C–1600 °C. The inclusion of YAG particulate up to 5.0 wt% significantly enhances the densification, hardness, fracture toughness, flexural strength and high-temperature mechanical behavior of magnesium aluminate spinel (MAS) ceramics, however, increasing the YAG content beyond 5.0 wt% causes a reduction in these properties. The optimized addition of YAG particulate contributes to reducing the average grain size and refining the microstructure of the spinel ceramic matrix.

Temperature dependences of phase composition, densification, and thermal/chemical stability of Sr0.5Zr2(PO4)3-Nd0.5Sm0.5PO4 composite ceramics for nuclear waste form

A kind of Sr0.5Zr2(PO4)3-Nd0.5Sm0.5PO4 (hereinafter SrZP-Nd0.5Sm0.5PO4) composite ceramics was prepared through a one-step microwave sintering technique, where Sr, Nd, Sm were simulated for fission products and minor actinides (MA). The crystal structure and morphology of constituent phases were systematically characterized by XRD, TEM, and SEM techniques. The temperature dependent phase analysis results of SrZP-Nd0.5Sm0.5PO4 composite ceramics illustrate that with evaluating temperature monazite structure formed primarily, and the SrZP phase formed subsequently. With the temperature rising further, the monazite phase finally transformed into Nd0.5Sm0.5PO4 monazite solid solution. XRD refinement and TEM measurements are used to verify the crystal structures of the as-prepared SrZP and Nd0.5Sm0.5PO4 phases in the composite ceramics. The dependence of densification behaviors on temperature shows that the distinct densification of the SrZP-Nd0.5Sm0.5PO4 composite ceramics occurs in the temperature range of 950 °C to 1000 °C, and the relative density reaches 97.7 % at 1050 °C. TG-DSC tests show that the SrZP-Nd0.5Sm0.5PO4 composite ceramics exhibit excellent thermal stability at high temperatures. And SrZP-Nd0.5Sm0.5PO4 composite ceramics possess outstanding chemical stability, whose normalized leaching rate of Sr, Nd, and Sm is 10−4 g·m−2·d−1, 10−7 g·m−2·d−1, and 10−7 g·m−2·d−1 order of magnitude, respectively.

Investigation on selective laser-melted AlSi10Mg micro-struts: influence of processing parameters on dimensional accuracy, molten pool morphology and microhardness

PurposeThis study aims to address the limited understanding of the complex correlations among strut size, structural orientation and process parameters in selective laser melting (SLM)-fabricated lattice structures. By investigating the effects of crucial process parameters, strut diameter and angle on the microstructure and mechanical performance of AlSi10Mg struts, the research seeks to enhance the surface morphologies, microstructures and mechanical properties of AM lattice structures, enabling their application in various engineering fields, including medical science and space technologies.Design/methodology/approachThis comprehensive study investigates SLM-fabricated AlSi10Mg strut structures, examining the effects of process parameters, strut diameter and angle on densification behavior and microstructural characteristics. By analyzing microstructure, geometrical properties, melt pool morphology and mechanical properties using optical microscopy, scanning electron microscope, energy dispersive X-ray spectroscopy and microhardness tests, the research addresses existing gaps in knowledge on fine lattice strut elements and their impact on surface morphology and microstructure.FindingsThe study revealed that laser energy, power density and strut inclination angle significantly impact the microstructure, geometrical properties and mechanical performance of SLM-produced AlSi10Mg struts. Findings insight enable the optimization of SLM process parameters to produce lattice structures with enhanced surface morphologies, microstructures and mechanical properties, paving the way for applications in medical science and space technologies.Originality/valueThis study uniquely investigates the effects of processing parameters, strut diameter and inclination angle on SLM-fabricated AlSi10Mg struts, focusing on fine lattice strut elements with diameters as small as 200 µm. Unlike existing literature, it delves into the complex correlations among strut size, structural orientation and process parameters to understand their impact on microstructure, geometrical imperfections and mechanical properties. The study provides novel insights that contribute to the optimization of SLM process parameters, moving beyond the typically recommended guidelines from powder or machine suppliers.

Transition mechanism and thermokinetic analysis of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics for nuclear waste forms based on in-situ synthesis

In this study, the novelly designed Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics were utilized as nuclear waste form to simultaneously immobilize simulated fission products Sr and actinide nuclides. The phase transition mechanism, thermokinetics and densification behavior of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics based on in-situ synthesis were systemically analyzed by XRD, in-situ XPS, TG-DSC, SEM and density measurements. The results demonstrate that the formation of Ce0.5Sm0.5PO4 solid solution phase preceded that of Sr0.5Zr2(PO4)3 phase, of which there is a valence change of Ce from Ce4+ to Ce3+ before 1023 K. Additionally, as for the exothermic crystallization enthalpy, change of exothermic crystallization enthalpy and activation energy, the values of Sr0.5Zr2(PO4)3 and Ce0.5Sm0.5PO4 phases in composite ceramics are 286.17 – 515.61 mJ, 19.11 – 35.38 J/g, 702.45 kJ/mol and 145.21 – 232.44 mJ, 9.26 – 15.44 J/g, 450.04 kJ/mol, respectively. It is then indicated that the formation of Ce0.5Sm0.5PO4 phase is definitely more favorable than that of Sr0.5Zr2(PO4)3 phase. Simultaneously, the relative densities of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics are more than 95 % when the sintering temperature exceeds 1273 K.

Pressureless sintering of HfC-HfB2-SiC-HfSi2 ceramics and their ultra high-temperature ablation resistance

HfC-HfB2-SiC-HfSi2 nanocomposites were synthesized by pressureless sintering with varying quantities of the HfSi2 additive. The morphology and densification behavior of HfC-HfB2-SiC-HfSi2 were investigated, and the results indicated that the sintering aid generated silicides to fill the grain gap. Plasma ablation tests investigated the ablation properties at 2700 °C, and the HfC-HfB2-SiC-HfSi2 nanocomposites exhibited excellent ablation resistance. The incorporation of the HfSi2 additive (4–7 wt%) not only improves the densification of the ceramic composite but also significantly promotes the mass ablation rate from -0.41mg∙cm−2s−1 to -0.048mg∙cm−2s−1. This was mainly attributed to the forming of a dense oxidation layer consisting of the Hf-Si-O phase, which acted as an excellent barrier to prevent the diffusion of O into the ceramic matrix.

Microcrystalline Cellulose-A Green Alternative to Conventional Soil Stabilizers.

Biopolymers are polymers of natural origin and are environmentally friendly, carbon neutral and less energy-intense additives that can be used for various geotechnical applications. Biopolymers like xanthan gum, carrageenan, chitosan, agar, gellan gum and gelatin have shown potential for improving subgrade strength, erosion resistance, and as canal liners and in slope stabilization. But minimal research has been carried out on cellulose-based biopolymers, particularly microcrystalline cellulose (MCC), for their application in geotechnical and geo-environmental engineering. In this study, the effect of MCC on select geotechnical properties of kaolin, a weak, highly compressible clay soil, like its liquid and plastic limits, compaction behavior, deformation behavior, unconfined compression strength (UCS) and aging, was investigated. MCC was used in dosages of 0.5, 1.0, 1.5 and 2% of the dry weight of the soil, and the dry mixing method was adopted for sample preparation. The results show that the liquid limit increased marginally by 11% but the plasticity index was nearly 74% higher than that of untreated kaolin. MCC rendered the treated soil stiffer, which is reflected in the deformation modulus, which increased with both dosage and age of the treated sample. The UCS of kaolin increased with dosage and curing period. The maximum UCS was observed for a dosage of 2% MCC at a 90-day curing period. The increase in stiffness and strength of the treated kaolin with aging points out that MCC can be a potential soil stabilizer.

Densification, mechanical properties, and oxidation behavior of spark plasma sintered TaB2-SiC-BN composites

TaB2-30 vol% SiC binary and TaB2-SiC-BN ternary composites with varying hexagonal boron nitride (BN) ratios (1–3–5–7–10 vol%) were consolidated by spark plasma sintering at 1650℃ under 40 MPa for 5 min. The densification characteristics, phase formation, mechanical properties, and oxidation behavior of both the TaB2-SiC and TaB2-SiC-BN composites were investigated. No new peaks other than the characteristic peaks associated with the starting materials were observed. Among all compositions, that containing 27 and 3 vol% of SiC and BN, respectively, exhibited the highest densification, ∼99.9 %. Homogeneous heating during sintering due to the thermal conductivity of hexagonal BN, along with the reduction in porosity by BN entering between TaB2 and SiC grains improved the densification behavior of the ternary composites. Besides, the incorporation of BN led to significant improvements also on the fracture toughness, which increased by ∼46 %. In ternary composites, crack deflection and branching were identified to be effective toughening mechanisms. The addition of BN had a negligible effect on Vickers hardness when agglomeration was minimal. The oxidation resistance at 1100 and 1200 °C increased with the addition of BN.

Microstructure and performance of carbon fiber reinforced aluminum matrix composites with molybdenum carbide coating on carbon fibers

In this work, a molybdenum carbide coating on the surface of short carbon fibers prepared using molten salt method was proposed to ameliorate the interfacial bonding and improve the performance of carbon fiber/Al composites. The carbon fiber/Al composites were produced using vacuum hot pressing. The characteristics of molybdenum carbide coating were analyzed. Besides, the microstructures, bending strength and thermal properties of the carbon fiber/Al composites were explored. Furthermore, the interfacial thermal resistance of the composites was investigated in relation to theoretical evaluations derived from the combined Maxwell-Garnett effective medium approach and acoustic mismatch model schemes. The results indicated that a homogeneous Mo2C coating with a thickness of 0.5 μm was obtained by proper molar ratio of carbon fibers, MoO3 and chloride salts mixture and heated at 1000 °C for 60 min. The Mo2C coating greatly enhanced the bond between the aluminum matrix and carbon fiber, leading to improvements in the densification behavior and bending strength of the coated composites. The enhanced thermal properties including improved thermal conductivity and reduced coefficient of thermal expansion (CTE) were also achieved by the Mo2C coating. The in-plane thermal conductivity of 60 vol.% Mo2C-coated carbon fiber/Al composite was 221 W·m−1·K−1 enhanced by 92% compared to that of uncoated composite and the CTE was 6.0 × 10–6 K−1 which was suitable for electronic packaging materials.

Compaction Creep and Evolution of Transport Properties of Carbonate Fault Gouges During the Percolation of CO2‐Rich Fluids

AbstractTo investigate the impact of CO2‐rich fluids on compaction behaviors and transport properties in carbonate fault zones, we conducted compaction‐coupled fluid flow experiments with CO2‐rich fluids percolating precompacted calcite aggregates. Our findings reveal distinct responses among samples subjected to different fluid conditions. Specifically, samples exposed to dry conditions exhibited negligible compaction strain, while those under wet‐closed conditions displayed relatively minor strain. In contrast, samples subjected to flow‐through conditions demonstrated significant compaction strain, with strain rates higher by 2–3 orders of magnitude than closed conditions due to enhanced pressure solution, subcritical cracking, and chemical dissolution. Strain rate, permeability, and grain size distribution exhibited spontaneous variations in response to fluid flow and compaction. Microstructures and mechanical and transport data suggest that deformation during the initial infiltration of CO2‐rich fluids was dominated by subcritical cracking, followed by pressure solution as grain size evolved, which resulted in compaction and reduced permeability. The persistent infiltration of CO2‐rich fluids further enhanced inhomogeneous dissolution‐precipitation with preferred dissolution channels serving as fluid pathways. The re‐precipitations may cement fault rocks and form low permeability seals, resulting in anisotropic fluid flow and localized fluid pressure in fault zones. As applied to nature, our results provide experimental evidence for the evolution of internal structures and transport behaviors, shedding important light on the mechanisms and sealing potential of carbonate faults in response to the infiltration of CO2‐rich fluids during the post‐seismic and inter‐seismic processes.

Densification, microstructure, and wear properties of TiB2-TiC-GNP and TiB2-TiC-BN composites

In this study, TiB2–TiC, TiB2–TiC-GNP, and TiB2-TiC-BN composites were produced via spark plasma sintering (SPS). The densification and sintering behavior, phase and Raman spectroscopy analyses, microstructural properties, Vickers microhardness, and wear behavior of the binary and ternary composites were investigated. The addition of various amounts of TiC to TiB2 resulted in nearly complete densification. The TiB2–TiC-GNP specimens exhibited a relative density of more than 99 %; in contrast, the addition of BN did not contribute to the densification. The Vickers hardness of the GNP-added composites was ∼25 GPa, whereas hBN addition to the matrix decreased the hardness to ∼22 GPa (∼9 % decrease). According to the wear test, the addition of GNPs did not result in a significant change in the TiB2–TiC matrix; however, the addition of hBN increased the specific wear rate of the matrix by ∼100 %. The GNPs did not have a negative effect on the densification, microstructural, or mechanical properties, such as the Vickers hardness and wear resistance. Hence, they were determined to be a more suitable sintering aid for matrix composition than hBN.

Trifluoromethylation Enables Compact 2D Linear Stacking and Improves the Efficiency and Stability of Q‐PHJ Organic Solar Cells

AbstractCompared to the bulk heterojunction (BHJ) devices, the quasiplanar heterojunction (Q‐PHJ) exhibits a more stable morphology and superior charge transfer performance. To achieve both high efficiency and long‐term stability, it is necessary to design new materials for Q‐PHJ devices. In this study, QxIC‐CF3 and QxIC‐CH3 are designed and synthesized for the first time. The trifluoromethylation of the central core exerts a modulatory effect on the molecular stacking pattern, leveraging the strong electrostatic potential and intermolecular interactions. Compared with QxIC‐CH3, the single crystal structure reveals that QxIC‐CF3 exhibits a more compact 2D linear stacking behavior. These benefits, combined with the separated electron and hole transport channels in Q‐PHJ device, lead to increased charge mobility and reduced energy loss. The devices based on D18/QxIC‐CF3 exhibit an efficiency of 18.1%, which is the highest power conversion efficiency (PCE) for Q‐PHJ to date. Additionally, the thermodynamic stability of the active layer morphology enhances the lifespan of the aforementioned devices under illumination conditions. Specifically, the T80 is 420 h, which is nearly twice that of the renowned Y6‐based BHJ device (T80 = 220 h). By combining the advantages of the trifluoromethylation and Q‐PHJ device, efficient and stable organic solar cell devices can be constructed.

Exploring co-processing strategies for multi-material spark plasma sintering of pure Cu with AlSi10Mg by master sintering curves

Manufacturing complex multi-material metallic components without assembly operations is currently being explored using novel additive manufacturing techniques. For materials combinations that are difficult to process via melting-based processes, multi-material spark plasma sintering (SPS) appears as a promising alternative. However, due to different sintering kinetics, materials with very different melting points might have to be co-sintered at non-optimal conditions. In this work, the potential to improve the co-sinterability of dissimilar materials, namely pure copper and AlSi10Mg, is evaluated by altering the sintering kinetics of copper using different particle size distributions (PSD). Using the master sintering curve (MSC) approach, the densification behaviour of spherical pure copper powder during SPS is evaluated systematically to study the influence of PSD, uniaxial applied pressure, and isothermal holding temperature. An intermediate-sized monomodal and close-to-optimal bimodal PSD are compared for processing at lower sintering temperatures. It was observed that, compared to an intermediate monomodal PSD, a near-optimal bimodal powder mixture yields fully dense Cu–AlSi10Mg components at lower temperature and shorter process times. Therefore, the use of a bimodal mixture enables multi-material sintering, offers energy and cost savings to produce multi-material components, and improves compatibility between materials with very different melting points.