Densification Characteristics Research Articles

Simulation of fast-firing densification by the discrete element method

The macroscopic behavior of powder compacts during the sintering process originates at the microscopic level. Despite the marked advance in analytical techniques, the characteristics of microscale densification, including heat transfer phenomena in particulate systems under fast firing, still need to be determined. Here, a numerical approach is used to explore macro and microscale densification gaps aiming to predict the behavior of parts consolidated by non-isothermal sintering. The model was built integrating concepts of heat transfer, transient temperature regime, sintering, and contact forces and implemented within the Discrete Element Method (DEM) framework. The scope of the article includes an alumina-based case study in which simulations were compared with the experimental investigation. The simulation results showed good agreement with the experimental data. Densification microkinetics depicted the evolution of densification gradients inside the sample. The model demonstrated its value for predicting high heating rate sintering features.

Spark plasma sintering of ceramic-reinforced binary/ternary nickel and titanium metal matrix composites: Mechanical properties, microstructure, and densification – A review

Spark Plasma sintering is an excellent technique for developing ceramic-reinforced binary/ternary nickel and titanium metal matrix composites (MMCs). This review analyzes the mechanical properties, microstructure, and densification characteristics of SPS-produced composites. Introducing ceramic reinforcement such as carbides, oxides, nitrides, or borides enhances the mechanical characteristics and functionality of MMCs. The SPS method has advantages such as high heating rates, low processing durations, and relatively low sintering temperatures, all of which assist in reducing reactivity concerns and retaining the desirable properties of the matrix and reinforcing materials. The impact of different process parameters such as temperature, pressure, heating rate, and holding time on the final microstructure and densification of the composites was discussed in this review. Additionally, it examined how different types, contents, and particle sizes of reinforcement affected the mechanical qualities, including hardness, tensile strength, fracture toughness, and wear resistance. Furthermore, the production of secondary phases and the interfacial bonding between the matrix and reinforcements are explored because they significantly affect the mechanical performance and behavior of the composites. This work contributes to an extensive understanding of the SPS procedure for ceramic-reinforced nickel and titanium MMCs, offering insightful information on processing parameters that enhance production and modify the characteristics of these technologically advanced materials for many applications in the aerospace, automotive, and structural industries.

The Densification Characteristics of Polished Fused Silica Glass and Its Scattering Characteristics

Optical surface scattering is an important subject in the field of optics. Previous studies of surface scattering mainly focused on the influence of surface topography and often ignored the influence of the mechanical property’s change caused by polished surface densification. In this paper, we study the mechanical property of fused silica glass in detail and analyze the scattering behaviour of actual fused silica glass’s surface with sub-angstrom roughness, considering the topography and the change of refractive index. Experimental results show that there is a negative correlation between the height and modulus on the surface of roughly polished fused silica glass, and the correlation coefficient γ = −0.29 was determined. After super−polishing, the mechanical properties of the sample surface become significantly uniform with a roughness of Rq = 0.06 nm and Ra = 0.05 nm, and the correlation coefficient becomes γ = −0.02. Moreover, the nanoindentation test proves that silica glass surfaces have been densified during polishing. Based on the densification characteristics, the bidirectional reflectance distribution function (BRDF) was simulated by the finite element method. The result indicates that the densification characteristics will increase the scattering intensity. This work not only deepens the understanding of the properties of polished optical surfaces but also the surface scattering characteristics of optical elements.

The Characteristics of Density Distribution and Densification on Medium and Small Indonesian Municipalities

While many studies on urban compactness measured built-up area (intensity), this study explored population density in forms of gradients. Also, medium and small cities (in this case, municipalities due to having autonomous economies), through inquiring their characteristics in common, could provide early insights for anticipating further growths. Density database was made, combined with cadastral data. Two kinds of urban growth pattern (i.e. concentric and linear) were comprehended to extract gradient patterns from the cities using three indices. Through assigning a time span (2010–2018), the densification rates were also derived. The results indicate that there was a transformation from linear to concentric pattern while populations increased, yet not rare to total sprawling. Besides, there were influences on the compactness states from how the cities are positioned among the others within their local clusters where, on one hand, being too close to large cities would promote sprawling in long term while, on the other hand, being surrounded evenly by other cities is likely advantageous. Nevertheless, the degree of these advantages was not prevailing fairly across the Indonesian regions. Given the complexity and multidisciplinary nature of urban form, these findings are considerable for further planning and studies.

Ultra-smooth surface with 0.4 Å roughness on fused silica

Ultra-smooth surface with sub-nanometer roughness is of great significance in various fields, including Ring Laser Gyro (RLG), high-power laser apparatus, ultraviolet optical systems, and the semiconductor industry. However, the mechanism of the ultra-smooth polishing process remains to be studied, which is of great value for understanding and optimizing optical-fabrication methods. This paper establishes a relationship between surface densification characteristics and surface roughness in conventional polishing. Moreover, we conclude that the densification process created by the longitudinal pressure, which avoids non-uniformity, is beneficial to forming super-smooth surfaces in the conventional polishing methods. Under this guidance, we can stably fabricate ultra-smooth surfaces on fused silica with 0.4 Å roughness. This result overturns the mainstream view that the longitudinal pressure in polishing should be minimized. This conclusion is meaningful for the understanding of the ultra-smooth surface formation not only in conventional polishing but also in other optical-fabrication technologies.

Coupling Relationship Between Densification Characteristics and Tight Oil Accumulation of the FGSR Reservoir: A Case Study of the Chang 7 Member of the Triassic Yanchang Formation in the Zhenyuan Area of the Southwest Ordos Basin, Central China

Fine-grained sedimentary rock (FGSR) reservoirs in a deep-water sedimentary environment from the Late Triassic Yanchang Formation in the Ordos Basin in central China have huge potential for tight oil production. According to the comprehensive research of fluid inclusion experiment, scanning electron microscopy, cathodoluminescence, thin section identification, and whole rock analysis, the petrographic characteristics, fluorescence spectrum parameters, and the homogenization temperature of oil inclusions and associated brine inclusions in the FGSR reservoir were analyzed to explore the coupling relationship between densification characteristics and tight oil accumulation of the FGSR reservoir. The results show the FGSR reservoir diagenesis has experienced compaction, cementation, and multiple stages of dissolution. A comprehensive analysis of burial history shows that the Chang 7 Member FGSR reservoir in the study area has three phases of oil charging, corresponding to the geologic time range of 132–124, 120–102, and 98–97 Ma. The organic acid produced by the first-stage oil charging accelerated the dissolution of feldspar and cuttings, and the dissolution pores increased significantly. Then, the organic acid in the second-stage oil charging accelerated the dissolution, and the abnormally high hydrocarbon expulsion pressure inhibited the damage of compaction on the pores of FGSR reservoir. Finally, the thermal evolution degree of source rocks reached the highest in the third-stage oil charging. The constructive effect of large-scale organic acids on pores and the protective effect of the chlorite membrane on pores inhibited the densification process of the FGSR reservoir. In short, the FGSR reservoir has experienced a cyclical reservoir densification process of “reducing porosity–increasing porosity–preserving porosity.” The coupling of pore evolution and oil charging of the FGSR reservoir is the key to the extensive accumulation and large-scale reservoir formation of tight oil in the Chang 7 Member of the Yanchang Formation in the Zhenyuan area, southwest Ordos Basin. The significance of the study may help to understand the process of the tight oil accumulation and predict the tight oil of the FGSR reservoir distribution.

Chemical vapor infiltration of additively manufactured preforms: Pore‐resolved simulations and experimental validation

AbstractThe densification of additively manufactured porous preforms by chemical vapor infiltration (CVI) is studied using pore‐resolved simulations and experiments. Experimentally, 3D printed silicon carbide (SiC) preforms are subject to CVI synthesis using methyltrichlorosilane (MTS) precursor to obtain high purity SiC/SiC composites. Optical images of the cross sections of the processed preforms are analyzed to obtain the spatial porosity distribution. The numerical method is based on a level set formulation to capture the spatial distribution and time evolution of the pore scale microstructural characteristics. The coupled transport and kinetic effects are represented using a dimensionless Thiele modulus. Simulations are initialized using representative synthetic preform geometries comprising of packed particles based on the size distribution of the powder used for 3D printing. The simulation results are validated against the experimental observations in terms of total density and the distribution of residual porosity. The densification characteristics, porosity classification, concentration profiles, and structure functions are analyzed as functions of processing temperature and Thiele modulus.

A V2X-Integrated Positioning Methodology in Ultradense Networks

Intelligent transport systems demand the provision of a continuous high-accuracy positioning service. However, a vehicle positioning system typically has to operate in dense urban areas where conventional satellite-based positioning systems suffer severe performance degradation. 5G technology presents a new paradigm to provide ubiquitous connectivity, where the vehicle-to-everything (V2X) communication turns out to be highly conducive to enable both accurate positioning and the emerging Internet of Vehicles (IoV). Due to the high probability of Line-of-Sight (LoS) communication, as well as the diversity and number of reference stations, the application of ultradense networks (UDN) in the vehicle-to-infrastructure (V2I) subsystem is envisaged to complement the existing positioning technologies. Moreover, the cooperative determination of location information could be enhanced by the vehicle-to-vehicle (V2V) subsystem. In this article, we propose a V2X-integrated positioning methodology in UDN, in which the V2I, V2V, and inertial navigation systems (INSs) are unified for data fusion. This formulation is an iterative high-dimensional estimation problem, and an efficient multiple particle filter (MPF)-based method is proposed for solving it. In order to mitigate the non-LoS (NLoS) impact and provide a relatively accurate input to the MPF, we introduce an advanced anchor selection method using the geometry-based <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> -means clustering (GK) algorithm based on the characteristics of network densification. Numerical results demonstrate that utilizing the GK algorithm in the proposed integrated positioning system could achieve 18.7% performance gains in accuracy, as compared with a state-of-the-art approach.

Influence of the sintering temperature on the microstructure, mechanical properties and densification characteristics of (TiB + TiC)/TC4 composite

A hybrid of TiB whiskers and TiC particles reinforced TC4 matrix composites were in situ synthesized by spark plasma sintering (SPS) using a TC4-0.6wt.% B4C powder mixture at temperatures range from 550 °C to 1150 °C. The effect of sintering temperature on microstructure, grain size, mechanical properties and densification process of the (TiB + TiC)/ TC4 matrix composites were investigated. The composite sintered at 1050 °C has the highest tensile strength (1129.0 MPa), yield strength (1077.8 MPa) and plasticity (7.1%). The aspect ratio of TiB whiskers increases almost linearly below 1050 °C and its highest value is 33.2. The grain size of TiC increases with the increase of sintering temperature, and rapid growth occurs in the range of 850 °C to 950 °C. The composite sintered body appears four shrinkage stages before applying sintering pressure. The corresponding peak temperatures are 663 °C, 758 °C, 840 °C and 994 °C, respectively.

Optimization of microwave processing parameters on powder-metallurgical 316L stainless steels

ABSTRACT Ultra-rapid microwave sintering of powder metals is recognized for better process advantages, namely less process time, uniform volumetric heating, and fine microstructural features that will improve mechanical and corrosion properties. In the present study, austenitic (316 L) stainless steel powder compacts were sintered using a multimode microwave hybrid heating system at solidus (1200°C and 1250°C) and super-solidus (1300°C) temperature with different holding times 30, 45 and 60 min. Mechanical as well as electrochemical responses were correlated with the microstructural features and densification characteristics. The samples sintered at 1300°C for 60 min have shown improved densification and higher tensile strength of 474.3 MPa with 22.1% ductility. It is also noted that an increase in sintering temperature resulted in excellent corrosion resistance in the order of ten times. The input process parameters and the output property responses are mathematically modeled with the help of RSM. The developed equations and experimental studies are in good agreement with output responses (sintered density, yield strength, %elongation, microhardness, corrosion rate) with 0.92 to 0.95 desirability. The validation of optimized output responses is evaluated by conducting confirmation tests at two conditions (1300°C for 60 min & 1300°C for 52 min) and are in line with regression model analysis.

Performance improvement of radiata pine wood by combining impregnation of furfuryl alcohol resin and densification for making fretboard materials

The fast-growing plantation radiata pine wood has undesirable intrinsic properties, which cannot meet the physical and mechanical performance requirements of string instrument fretboard materials. In this study, the synergistic modification technology of FA impregnation treatment and densification treatment was proposed to improve the density, dimensional stability, and mechanical properties. In addition, its surface color of radiata pine wood was deepened to imitate precious tropical hardwood (e.g., ebony, Indian rosewood, and African blackwood) that are commonly used in the fretboards of string instruments. This technology combined the characteristics of the wood densification and FA impregnation treatment, that is, the densification treatment can improve the mechanical strength of low-quality wood and FA can fix the deformation of the densified wood, preventing treated wood from spring back. The performance differences between the fretboard wood and FA-densified-wood with compression rates (CRs) of 17 %, 33 %, and 50 % were analyzed, and the optimal CR was determined. The fretboard wood has high density (> 800 kg/m3), dimensionally stable, and red brown or jet-black surface color. The modulus of rupture (MOR), modulus of elasticity (MOE), compression strength (CS), Brinell hardness (BH), and impact bending strength (IBS) of the fretboard wood are higher than 140.0 MPa, 13.0 GPa, 120 MPa, 7.9 N/m2, and 17 kJ/m2, respectively. The fretboard wood also has good abrasion resistance. The FA-modified wood with a CR of 50 % had a high density (> 1000 kg/m3), superior dimensional stability, excellent mechanical properties, and its surface color was jet black, which was the same as those of the fretboard wood. The FA-modified wood with a CR of 50 % met the performance requirements of wood for fretboards, and has the potential to replace the fretboard wood for string instrument fretboard manufacturing. It breaks through the restriction that fast-growing plantation wood cannot be used for musical instruments, alleviating the shortage of the resources of commonly used tropical hardwood for fretboards and providing new insights for the high-value utilization of plantation radiata pine wood.

Asynchronous densification of zirconia ceramics formed by stereolithographic additive manufacturing

Stereolithography has been proven as a feasible approach to make crack-free ceramic macrostructure with customized designs, but the microstructure, especially pore structure remains to be tailored more precisely for better performance, where the sintering protocol and related densification characteristics could play a vital role as the slurry preparation and debinding protocol do. Herein we report a phenomenon named “asynchronous densification”, that is, the surface region of zirconia ceramics formed by stereolithographic additive manufacturing would be densified prior to the bulk at 1200°C during the conventional pressureless sintering in air. The cause of this asynchronism is unclear but supposed to be correlated with low packing density, high sintering activity, poor thermal conduction of ceramics and impurities. Early densification of the surface may have negative effects towards ceramic components with more homogeneous microstructure, suppressed pore coalescence and limited grain growth, and therefore needs to be better controlled through optimization in sintering protocol.

Effect of Ti and its compounds on the mechanical properties and microstructure of B4C ceramics fabricated via pressureless sintering

The addition of Ti and its compounds particles has the potential to effectively enhance the fracture toughness of B4C ceramics. However, the influence of different Ti-based compounds on B4C ceramics has not been extensively studied. In this work, B4C–TiB2 multiphase ceramics were prepared by adding 5% Ti or its compounds (TiO2, TiB2 or TiC) in B4C and the effects of the additives on the B4C ceramics were studied. For this purpose, we adopted a sintering process carried out in situ in the absence of pressure at a temperature of 2250 °C for 1 h. It was evident from the results that the additives are capable of enhancing the sintering densification characteristics and the properties exhibited by B4C, as opposed to single-phase B4C ceramics. Additionally, different additives have varied effects on the microstructures and mechanical properties of B4C–TiB2 multiphase ceramics. The results of the study indicate that the TiC-added sample exhibits the most optimal mechanical properties, with 4.52 MPa m1/2 fracture toughness, 344.0 MPa flexural strength, 26.2 GPa hardness, and 516.0 GPa elastic modulus.

Compaction and Densification Characteristics of Iron Powder/Coal Fly Ash Mixtures Processed by Powder Metallurgy Technique

The present work elucidates the compaction and the densification behavior of iron powder and coal fly ash (CFA) mixtures during powder metallurgy (P/M) processing. The flowability and the compressibility characteristics of the starting materials were exhibited through Hausner ratio and Carr’s index. Morphological, elemental and crystallographic characterizations of the starting materials were carried out using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy and x-ray diffraction investigations, respectively. The CFA of 0, 5, 10 and 15 wt.% was mixed with the iron powder through ball milling. Further, the cold compaction of the mixtures containing iron/CFA was performed in the hardened steel die using a uniaxial hydraulic press at pressures of 91 MPa, 138 MPa and 185 MPa, respectively. Subsequently, the preforms were sintered at 950, 1050 and 1150 °C in a tubular furnace under an inert atmosphere. The density of the preforms and the sintered pallets was estimated using weight to volume ratio and Archimedes method, respectively. The obtained mineralogy, morphology and physio-mechanical properties of the CFA are in good agreement with the ASTM standards. Further, the flowability and the compressibility characteristics of the starting materials rendered them suitable for processing through the P/M process. SEM analysis of the sintered pallets exhibited uniform distribution of CFA particulates in the iron matrix with clear and strong interfaces. An inverse effect of an increased amount of CFA inclusion has been observed on the green and sintered density of the composite. However, a linear influence of increased compacting pressure and sintering temperature has been observed on green and sintered densities, respectively. The magnitude of the green density achieved during cold compaction is considerably higher than that achieved during the sintering process. The obtained compaction data were successfully fitted using the Ge compaction equation.

Formability and densification behavior of two-layered structure powder metallurgical hot-pressed Al-Cu/Al composites during hot-upsetting

An experimental investigation has been performed on the hot formability and densification characteristics of Al-Cu/Al two-layered structure composites. The two-layered composites having different Cu compositions in the Al-Cu layer such as (Cu: 5wt. %, 10wt. %, and 15wt. %) were prepared using the powder metallurgy (P/M) route. The composites were hot-pressed as layer by layer in a steel cylindrical die at 550°C temperature with 0.9 initial relative density (IRD) and 0.1 s−1strain rate. The preforms were hot deformed between two flat dies with a capacity of 50-ton hydraulic press machine at a temperature range of 150°C – 450°C under triaxial stress state condition. The hot-upsetting behaviour of preforms was analyzed until the cracks begin on the cylindrical preform at the outer surface. The effect of different Cu composition and various deformation temperatures on two-layered preforms were discussed. Results revealed that the (10wt. %Cu) preform achieved good cooperative deformation behaviour between Al-Cu and Al layers at the interface region. The relationship between the process parameters was discussed such as the effect of axial stress ([Formula: see text]), relative density ( R) on axial strain ([Formula: see text]) and formability stress index ( β), different stress ratio parameters ([Formula: see text], [Formula: see text]) on relative density ( R).

Densification characteristics, microstructure and wear behaviour of spark plasma sintering processed titanium-niobium pentoxide (Ti-Nb2O5) based composites

The present study investigated the densification behavior, microstructure and wear properties of Ti-Nb2O5 based composites processed by spark plasma sintering (SPS). The SPS process was performed using sintering temperature of 1000 °C, holding time 10 min, heating rate 100 °C/min and applied pressure 50 MPa, as sintering process parameters. Optical and Scanning electron microscopy, X-Ray diffractometry, Relative density and hardness measurement, coefficient of friction and wear rate evaluation were used to characterize the composites produced. The CpTi and Ti-Nb2O5 composites attained full densification (relative densities ranged from 99.57 to 99.94%), and the total sintering times and densification stages were independent of the Nb2O5 reinforcement. However,the sinterability of the composites improved with increase in Nb2O5 content. The punch displacement curve of the Nb2O5 reinforced CpTi composite grades were higher compared to the CpTi. Also, the hardness values increased progressively with increase in Nb2O5 content. The microstructures that the addition of Nb2O5 resulted in structural transformation from lamellar (α) in the Cp Ti to bimodal (α + β) structures in the Ti-Nb2O5 composites accompanied with decrease in average grain size with increase in Nb2O5 content. The steady-state friction coefficients for all the composite samples ranged from 0.3 to 0.6. However, there was largely progressive increase in friction coefficient with Nb2O5 content. Generally, the wear resistance increased with increase in Nb2O5 content with the wear mechanism of the composites from wear track assessment, established to be mixed mode of adhesive and abrasive wear.

Effect of the number of layers on surface topography of bismuth-titanium coatings

The objective of this research is to perform a topographic characterization by atomic force microscopy of the surface of bismuth titanate (Bi/Ti) coatings varying the number of layers deposited on the substrates, considering that there were not results of reported studies in which these precursors were used. It is important to analyze the surface behavior of these coatings as a first phase of future researches to establish the viability of possible uses and applications in biomedical industry. The films were synthesized by the sol-gel method from bismuth nitrate pentahydrate and titanium tetrabutoxide. Subsequently, by means of the spin- coating technique, the coatings were deposited on 316L stainless steel in monolayer and bi- layer, as this type of steel has been widely used for medical applications due to its good compatibility. The roughness values of each of the coatings were also determined. It is concluded that there is a relationship between the topography of the surface and the roughness values of the films with respect to the concentration of the precursors, the number and the speed of centrifugation of the layers deposited on the substrate. High concentrations of titanium tetrabutoxide effect on the good densification characteristics of the coatings.

Reaction sintering behavior and electrical properties of a Ga-doped ITO system

In this study, we investigated the characteristics of densification, phase formation, and electrical properties during reaction sintering when a Ga-doped ITO, with 10 at% Sn, served as the target material. Results showed that Ga doping enhanced the densification of ITO at a relatively low sintering temperature. Interestingly, the 1 at% Ga- and 20 at% Ga-doped samples showed shrinkage values of 19.5% and 23.0%, respectively, despite the fact they both starting shrinking at the same temperature. In addition, the second phase Ga3-xIn5+xSn2O16 was formed at 5 at% Ga-doped ITO. Moreover, the ITO lattice parameters decreased up to 40 at% Ga doping, since the ionic radius of Ga3+ is smaller than that of In3+. Furthermore, as the Ga concentration increased, the carrier concentration and mobility decreased and resistivity increased. These modifications are thought to result from an increasing quantity of the Ga3-xIn5+xSn2O16 s phase and the corresponding resistivity increase, both of which occur as a function of increasing Ga concentration.

Role of surfactant-induced chromia barriers on performance characteristics of Pd composite membranes

The article elaborates upon the optimality of electroplating and surfactant coupled electroplating based chromium oxide barriers on the process and product characterization variables of Pd electroless plating during dense Pd composite membranes fabrication. Porous stainless steel discs with 100 nm pore size were deployed to fabricate Pd composite membranes on chromium oxide diffusion barriers prepared with electroplating (7.8 and 20 µm thickness) and surfactant assisted electroplating (7.1 and 12.5 µm thickness). These diffusion barrier films were obtained by subsequent oxidation of chrome plated films at 700 °C. Eventually, palladium films were achieved using rate enhanced Pd electroless plating associated with coupled surfactant and sonication under dropwise addition mode of reducing agent. The surfactant inclusion during chrome plating enabled higher Pd metal film thickness and plating rates but could not provide better pore densification characteristics of dense Pd-chromia-PSS membranes.

Microstructural evolution and sintering kinetics during spark plasma sintering of pure tantalum powder

Spark plasma sintering (SPS) technology can significantly inhibit grain coarsening due to its characteristics of rapid sintering and densification, and obtain a material with high density and uniform microstructure. We completed the SPS sintering of tantalum powder, and characterized the microstructure and mechanical properties of the samples at different sintering temperatures. The results show that during the pure tantalum sintering process, the rapid densification temperature range is 800 °C–1300 °C, and the maximum shrinkage rate of the sample is 1100 °C. A creep model was applied to determine the densification mechanisms involved in the densification stage, which can be elucidated by evaluating the stress exponent (n) and the apparent activation energy (Qd) from the densification rate law. It shows that a series of interfacial reactions and grain boundary diffusions govern the densification process at low effective compaction stresses (n = 1.6, Qd = 107.01 kJ/mol), while dislocation climbing operate at higher effective compaction stresses (n = 3.1 and n = 4.1), which is confirmed by TEM. When the sintering temperature of tantalum powder increased from 1500 °C to 1700 °C, the density and grain size of the sample increase gradually, the tensile strength and flexural strength also increase. The surface hardness of the sample increases gradually. Moreover, surface hardness is much higher than core hardness. The fracture mode of the specimen changes from brittle fracture to ductile fracture. This study has enabled the selection of high quality tantalum alloy sintering routes and optimization of the sintering process.