Increase In Relative Density Research Articles

Microstructure and tensile properties of Ti-Mo alloys manufactured via using laser powder bed fusion

In this work, the dense Ti-7.5Mo sample (over 99.5%) was prepared by using laser powder bed fusion (L-PBF) from powder mixture of pure Ti and pure Mo. Through the use of mechanical mixture process, Mo particles present an uniform distribution. As the laser scanning speed decreases from 1700 mm/s to 1000 mm/s, the sample's relative density increases from 85.5% to 99.5%. The microstructural analysis indicates that Mo particle was mostly fully melted during laser melting. But, some large sized Mo particles were partial melted, which possesses gradient interface structure. Then, the tensile properties of as-fabricated samples under several laser scanning speed were determined. The results shows that the as-fabricated dense sample presents Young's modulus, ultimate tensile strength and strain at failure about of 70 GPa, 740 MPa and 9.2% respectively. Given to this low Young's modulus, which is approximate to bone of 30 GPa, the L-PBF processed Ti-7.5Mo shows great application potential in implant component.

Conductivity Characterizationof Iron Oxide Doped 8 mol% Yttria Stabilized Zirconia

A facile strategy was proposed to incorporate the dopant Fe into 8YSZ-based material, which can be potentially applied as solid electrode materials for Solid Oxide Fuel Cells (SOFC). In this study, 8YSZ powder was investigated in terms of densification, conductivity and thecrystal structure as a solid electrolytes. Therefore, varying mol% of Fe included 1, 2, and 3 were prepared for investigation. The crystalline structure of the pristine and Fe doped samples were characterized by X-ray diffraction (XRD) and the phase contents were evaluated by using the Rietveld method. Rietveld quantitative phase analysis demonstrates that the monoclinic-ZrO2phase increases (12.8 wt% to 39.7 wt%) as the concentration of Fe increases, while the amount of tetragonal-ZrO2 phase drop (40.4 wt% to 11.9 wt%) dramatically. Sintering activity was applied to improve incorporation of the 8YSZ powder and the dopant Fe where the relative density increases from 77% to 92%. Sample YSZ-2Fe has been fitted with CPE equivalent circuit and achieved 6.251 x 10-6S/cm at 300 °C in air. However, it was found that conductivity levels decreased as the mol% of Fe increased. In short, sample YSZ-2Fe ceramic demonstrated good results in terms of densification (92.09%), cubic ZrO2 phase (22 wt%) and conductivity 6.251 x 10-6 S/cm.

Fabrication of Cu Based Metallic Binder for Diamond Tools by Microwave Pressureless Sintering

Microwave pressureless sintering (MPS) method is successfully applied in the fabrication of Cu based metallic matrix for diamond tools. The main purpose of this work is to obtain better mechanical properties when the metal binder of the diamond tools was prepared by the MPS method. The orthogonal experimental method is adopted to design the sintering process parameters. The optimized experimental conditions are suggested as 880 °C of sintering temperature, 375 MPa of cold pressure, and 35 min of withholding time. The contrastive investigation of the MPS and conventional pressureless sintering (CPS) are performed under optimized conditions. The microstructures information are obtained by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and the necessary mechanical properties, such as relative density, hardness, and flexural strength are tested. Experimental results show that the MPS method, compared with CPS, can significantly improve the mechanical properties of the metallic matrix. The factors of relative density, hardness, and flexural strength increase 1.25%, 3.86%, and 6.28%, respectively. The possible sintering mechanism of the MPS method is also discussed. This work may provide a reference for the fabrication of metal-based diamond tools by microwave heating method.

Liquefaction of Level Ground Unsaturated Sand Deposits Using a Validated Fully Coupled Analysis Procedure

Liquefaction of unsaturated sands has been observed in laboratory tests and in the field. A comprehensive investigation of unsaturated sand deposits subjected to seismic loading, especially using validated computational tools, is still lacking. This paper presents an analysis procedure to study the response of level ground unsaturated sand deposits subjected to seismic loading. The analysis procedure is a fully coupled flow–deformation finite element code with solid skeleton displacements, pore water pressure, and pore air pressure as nodal variables. The stress–strain behavior of unsaturated sands is described by a coupled hydro-mechanical elastoplastic constitutive model that includes the hysteretic model for soil water characteristic curves and the hydro-mechanical coupling mechanisms. The finite element code is first validated by comparing simulations with centrifuge test results. Reasonable comparisons of surface accelerations, ground settlements, and lateral deformations are obtained. A parametric study is then conducted to investigate the effects of initial degree of saturation, relative density, and effective overburden pressure on the seismic response of level ground unsaturated sand deposits. The results of the parametric study show that the thickness of the liquefied layer increases with an increase in degree of saturation. The potential for liquefaction reduced with increases in relative density and effective overburden stress. The results also reveal a drastic reduction in surface accelerations following liquefaction of a sand deposit.

Structure, morphology and electrical conductivity of Sm and Bi co-doped CeO2 electrolytes synthesized by co-precipitation method

In this paper, explain a new relationships between Bi3+ content, the phase crystal, microstructure and conductivity for Sm and Bi co-doped Ce0.8−xSm0.2BixO1.9−1/2x (x = 0, 0.05, 0.1, 0.15, 0.2) electrolytes prepared by co-precipitation method. The XRD patterns showed that this compounds exhibit a fluorite-type cubic structure after the samples calcined at 700 °C for 4 h and the cell volumes of increased when the Bi content increased. In addition, for the samples sintered at 1400 °C for 4 h, the Bi doping improves the relative density, the grain size and the average thermal expansion coefficient (TEC). More in details, the relative density and TEC increase with the Bi content. Form the AC impedance spectroscopy measurements, the conductivity of the sintered samples is found to improve with the increasing of Bi content (for x ≤ 0.15), which is ascribed to the increasing of the number of oxygen ion vacancies and the increase in the unit cell volume. However, the conductivity decreases when the Bi content is further increased (0.15 < x ≤ 0.2), which is ascribed the reduction of the number of free oxygen vacancies. The highest conductivity at 800 °C is 5.6 × 10−2 S/cm and the activation energy is 0.83 eV for Ce0.65Sm0.2Bi0.15O1.825, indicating that this would be a promising electrolyte for the intermediate temperature-solid oxide fuel cell applications.

High temperature deformation behavior of closed cell ZnAl27 hybrid foam made through stir casting technique

Closed cell ZnAl27 hybrid foam was synthesized through stir casting technique using CaH2 (0.5 wt%) as foaming agent and cenosphere particles were used as thickening agent and to create microporosity into the final structure. The relative density of the synthesized hybrid foam was found in the range of 0.20–0.30. Microstructural characterization was carried out to find distribution of cenosphere particles into the cell wall of hybrid foam. Compression tests were carried out to find out the effect of temperature, relative density and strain rate on the deformation behavior of the foam. It was found that each foamed sample displays three regions i.e., linear elastic, plateau and densification respectively. On the basis of stress-strain curves obtained at varying relative density, strain rate and temperature the values of plateau stress, energy absorption capacity and densification strain were calculated. It was found that according to the increase in relative density and strain rate the plateau stress and energy absorption capacity also increased. The effect of temperature on plateau stress and energy absorption capacity for lower relative density was more as compared to the higher relative density. The densification strain was almost invariant (0.02–0.03) on varying strain rate for the same relative density.

Controllable mesostructure, magnetic properties of soft magnetic Fe-Ni-Si by using selective laser melting from nickel coated high silicon steel powder

Fe-Ni-Si soft magnetic parts, using Ni coated high silicon steel powder, were manufactured by selective laser melting process. The type of defect changes from porosity to cracks and the relative density increases, from 50% to 99%, with the decreasing laser scanning speed. The microstructural analyses indicate that the low laser scanning speed fully melted the nickel coating and high-silicon steel core. The EBSD study showed that the separated island and lamellar mesostructures appeared on the top and side view respectively. Moreover, no apparent texture were observed. The magnetization saturation of SLM processed sample decreased, as the laser scanning speed was increased. Consequently, the magnetic properties of SLM processed Fe-Ni-Si alloy also showed anisotropic feature in building and scanning directions, which can be attributed to their different mesostructure.

Tungsten copper composite fabricated by compound plastic deformation technologies

In this study, compound plastic deformation technologies including canned extrusion and rotary swaging were developed to produce W-40 wt.% Cu composite. The relative density increases from 98.4% of as-extruded composite to 99.1% after swaging at 1223 K. The as-extruded composites have conductance of 67% IACS and hardness of 155 HV. But the as-extruded composites swaged at 1173 K ∼ 1323 K have higher hardness and lower specific conductance with accumulated deformation amount ∼72.30%. After heat treatment at 973 K ∼ 1273 K, the deformed material obtained a better match between the hardness and the conductivity. After compound plastic deformation, homogeneous microstructure of W and Cu phases for W-40 wt.% Cu composite can be acquired. All results indicate that W-40 wt.% Cu composite with high performance can be fabricated by compound plastic deformation technologies.

Liquefaction behavior of dredged silty-fine sands under cyclic loading for land reclamation: laboratory experiment and numerical simulation

Medium-coarse sands (CS) were dredged and exhausted in land reclamation. However, the remaining silty-fine sands (FS) were wasted. The liquefaction behavior of dredged silty-FS and the possibility of utilizing the remaining silty-FS as dredger fill source for land reclamation should be investigated. Cyclic consolidation-undrained triaxial tests were performed to investigate the liquefaction resistance of dredged silty-FS under different influencing factors. The cyclic stress ratio (CSR) of dredged silty-FS increased with the increase in initial relative density and consolidation stress ratio and decreased with the increase in silt content and consolidation stress. The CSR first decreased with the increase in clay content up to a threshold value and increased with the increase in clay content. A regression model was created to estimate the relationship between CSR and silt content, clay content, initial relative density, consolidation stress, consolidation stress ratio, and cyclic resistance ratio. Response surface methodology (RSM) was employed to investigate the mutual influence among the five independent variables. On the basis of cyclic triaxial tests, particle flow code models were introduced to investigate the microscopic internal fabric changes of dredged silty-FS and the influence of extended factors on liquefaction. The average microscopic contact force and coordination number between particles controlled the macroscopic mechanical behavior of sands. Sand liquefaction was due to the cumulative loss of coordination number under cyclic loading. The average contact force between particles was linearly decreased to 0 and the coordination number sharply decreased when the sample reached initial liquefaction. On the basis of numerical tests, CSR increased with the increase in D50 and vibration frequency. The influence of vibration frequency was relatively small. In addition, the CS–FS and CS–FS–CS combination layers showed greater liquefaction resistance than the FS layer. In the filling process, the interbed of FS and CS improved the liquefaction resistance of dredged silty-FS to a certain extent.

Synthesis, microstructure, and mechanical behaviour of a unique porous PHBV scaffold manufactured using selective laser sintering.

Selective Laser Sintering (SLS) is a promising technique for manufacturing bio-polymer scaffolds used in bone tissue engineering applications. Conventional scaffolds made using SLS have complex engineered architectures to introduce adequate porosity and pore interconnectivity. This study presents an alternative approach to manufacture scaffolds via SLS without using pre-designed architectures. In this work, a SLS process was developed for fabricating interconnected porous biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds with large surface areas and relative porosities of up to 80%. These characteristics provide great potential to enhance cell attachment inside the scaffolds. The scaffold microstructure was dependent on the laser energy density (LED) during the SLS process. An increase in LED led to scaffolds with higher relative densities, stronger inter-layer connections, and a reduced quantity of residual powder trapped inside the pores. An increase in relative density from 20.3% to 41.1% resulted in a higher maximum compressive modulus and strength of 36.4 MPa and 6.7 MPa, respectively.

Dynamic compressive response of additively manufactured AlSi10Mg alloy hierarchical honeycomb structures

Periodic honeycombs have been used for their high strength, low weight and multifunctionality. The quasi-static and dynamic compressive responses of three types of additively manufactured AlSi10Mg honeycomb structures, specifically a single-scale honeycomb and two hierarchical honeycombs with two and three levels of hierarchy, respectively, have been investigated using experimental measurement and finite element (FE) simulations. The validated FE simulation has been employed to investigate the effects of relative density of the honeycombs and the key experimental parameters. The following failure modes of the three types of honeycombs have been observed both under quasi-static and dynamic compression: (1) the single-scale honeycomb experienced a transition of failure mechanism from local plastic buckling of walls to local damage of the parent material without buckling with the increase of the relative density of the honeycomb; (2) the hierarchical honeycombs all failed with parent material damage without buckling at different relative densities. For both quasi-static and dynamic compression, the hierarchical honeycombs offer higher peak nominal wall stresses compared to the single-scale honeycomb at low relative density of ρ¯=0.19; the difference is diminished as relative density increases, i.e. the three types of honeycombs can achieve similar peak wall stresses when ρ¯⩾0.26. Numerical results have suggested the hierarchical honeycombs can offer better energy absorption capacity than the single-scale honeycomb. The two-scale and three-scale hierarchical honeycombs achieved similar peak nominal wall stresses for both quasi-static and dynamic compression, which may suggest that the structural performance under out-of-plane compression is not sensitive to the hierarchical architecture. This work indicates that the structural advantage of hierarchical honeycombs can be utilised to develop high performance lightweight structural components.

Extremely dense microstructure and enhanced ionic conductivity in hot-isostatic pressing treated cubic garnet-type solid electrolyte of Ga2O3-doped Li7La3Zr2O12

A large number of pores and a low relative density that are frequently observed in solid electrolytes reduce severely their ionic conductivity and thus limit their applicability. Here, we report on the use of hot isostatic pressing (HIP) for ameliorating the garnet-type lithium-ion conducting solid electrolyte of Ga2O3-doped Li7La3Zr2O[Formula: see text] (Ga-LLZO) with nominal composition of Li[Formula: see text]Ga[Formula: see text]La3Zr2O[Formula: see text]. The Ga-LLZO pellets were conventionally sintered at 1075[Formula: see text]C for 12[Formula: see text]h, and then were followed by HIP treatment at 120[Formula: see text]MPa and 1160[Formula: see text]C under an Ar atmosphere. It is found that the HIP-treated Ga-LLZO shows an extremely dense microstructure and a significantly enhanced ionic conductivity. Coherent with the increase in relative density from 90.5% (untreated) to 97.5% (HIP-treated), the ionic conductivity of the HIP-treated Ga-LLZO reaches as high as [Formula: see text][Formula: see text]S/cm at room temperature (25[Formula: see text]C), being two times higher than that of [Formula: see text][Formula: see text]S/cm for the untreated one.

Microstructure and mechanical properties of hot pressed submicron TiB2 powders

This paper studies the microstructure and mechanical properties of hot pressed submicron TiB2 powders obtained from a special carbon coated precursors method. With the hot press temperature increasing from 1500 °C to 1800 °C, the relative density increases and the sample maintains a single TiB2 phase. The powders are able to be sintered to a relative density of ~94.5% at the temperature of 1800 °C. For the first time, unique elongated platelike grain structure, which has only been observed from transient liquid phase or reaction sintered borides, also forms at the sintering temperature of 1800 °C. In addition, the sample sintered at 1800 °C has a fine microstructure (elongated grain of ~0.3–3 µm) and high mechanical properties (hardness of ~27.6 ± 2.3 GPa, flexural strength of ~560 ± 49 MPa, and fracture toughness of ~6.5 ± 0.2 MPa m−1/2). Correlations between mechanical properties and microstructure are further discussed.

Influence of TiO2 contents and sintering temperature on the microstructure and mechanical properties of WC-Al2O3 cemented carbide reinforced by multi-wall carbon nanotubes

WC-30 vol% Al2O3-0.5 wt% CNTs (WAC) cemented carbides with TiO2 as additives were consolidated by high energy ball milling and hot pressing the as-milled composite powders. The effects of TiO2 contents on the microstructure and mechanical properties of the obtained WAC cemented carbides were investigated. The presence of moderate TiO2 refined the grain sizes of WC, which contributed to the increase of relative density, hardness and fracture toughness. However, excessive TiO2 (surpassed 2 wt%) leaded to the increase of grain sizes and the production of new tialite (Al2TiO5) phase, which deteriorated the properties like relative density as well as hardness. While, the fracture toughness values still increased from 7.41 MPam1/2 (0 wt%TiO2) to 7.85 MPam1/2 (3 wt%TiO2) owing to the presence of second phase Al2TiO5. Furthermore, the effect of sintering temperature on microstructure and mechanical properties of WAC cemented carbides with different contents of TiO2 were also examined. Results showed that by increasing TiO2 contents, sintering temperature of the WAC with optimum hardness and fracture toughness shifted to low values. And the maximum values of hardness and fracture toughness for the component of WAC-6 wt% TiO2 sintered at 1440 °C was comparable to the optimal hardness and fracture toughness for WAC-2wt% TiO2 sintered at 1540 °C. According to the investigation results of the selected WAC-6wt% TiO2 composites, the grain growth of WC particles was hindered by the decrease of sintering temperature, resulting in the enhancement of mechanical properties despite of the slightly decreased relative density.

Compressive Deformation Behavior of Open-Cell Cu-Zn-Al Alloy Foam Made Through P/M Route Using Mechanically Alloyed Powder

Cu-Zn-Al foams of varying porosity fractions using mechanical alloyed powder have been made through powder metallurgy route. Here, NH4 (HCO3) was used as a space holder. Mechanically alloyed Cu-Zn-Al is made using a planetary ball mill taking the ratio of Cu/Zn/Al = 70:25:5 (by weight ratio). The ball/powder ratios were varied in the four ranges 10:1, 15:1, 20:1, and 25:1. Green compacts of milled powder and space holder samples were sintered at three stages at three different temperatures 350, 550, and 850 °C for 1 h at each stage. The crystalline size and particle size as a function of ball/powder ratios were examined. The compressive deformation responses of foams are varied with relative density and the ball/powder ratio. The plateau stress and energy absorption of these foams increase with an increase in relative density but decreases with increase in ball/powder ratio, even though crystalline size decreases. This has further been explained on the basis of particle morphology as a function of ball/powder ratio.

Compressive behavior of a rolled open-cell aluminum foam

In this paper, we investigate compressive behavior of an open-cell 6101 aluminum foam in as-cast and as-rolled conditions. The as-cast foam with a relative density of ρ* = 7% was rolled to create two distinct as-rolled conditions with relative densities of ρ* = 29% and ρ* = 42%, respectively. The quasi-static and high strain rate compressive behavior was studied over a range of strain rates 10−4 /s ≤ ε̇ ≤ 5 × 103/s. It was found that the internal structure of as-rolled foams significantly differs from as-cast foams. Rolling causes plastic bending, stretching, and buckling of individual struts and ligaments, resulting in reduced pore size and an increase in relative density. In as-rolled condition, compressive plateau strength increased with increase in ρ*; it was up to 26 times higher as compared to the as-cast condition. In the range of strain rates considered here, strain rate sensitive compressive behavior was not observed; instead, the intrinsic strain rate sensitivity of parent material governed the compressive behavior in all conditions. Our results demonstrate the feasibility of using conventional rolling as a simple way to modify internal structure and relative density of as-cast foams, thereby enabling mechanical properties more attractive for various structural applications.

A curtain traveling pluviator to reconstitute large scale sand specimens

The preparation of repeatable and uniformly reconstituted soil specimens up to the specified conditions is an essential requirement for the laboratory tests. In this study for large samples replication, the simultaneous usage of the traveling pluviation and curtain raining technique is used to develop a new method, called the curtain travelling pluviator (CTP). This simple and cost effective system is based on the air pluviation approach, whilst reducing the sample production time, can reproduce uniform samples with relative densities ranging from 25% to 96%. In order to investigate the resulting suitability and uniformity from the proposed method, a series of tests is performed. The effect of curtain traveling velocity, curtain width, drop height, and flow rate on the parameters of the sample is thoroughly investigated. Increase in the curtain velocity and drop height leads to the increase in relative density for the sand specimen. Increase in curtain width typically resulted in the reduction of relative density. Test results reveal that the terminal drop height for the sand specimen in this study is more than 500 mm. Relative density contour lines are presented that can be utilized in optimizing the drop height and curtain width parameters. Sample uniformity in the vertical and horizontal orientation is investigated through the sampling containers. Increasing relative density tends to result in the higher sample repeatability and uniformity.

Characterization of nanoporous silver mechanical properties by molecular dynamics simulation

Nanoporous metals (NPMs) have great potential applications in many technological areas, such as catalysis, sensing, actuation, and fuel cells, because of their unique physical and chemical properties. The cognition of related mechanical properties is one of the important bases for achieving functionalized applications. A series of large-scale molecular dynamics (MD) simulations is performed to study the mechanical properties of nanoporous sliver (NPS) under uniaxial tension. Three different topology architectures of NPS, including cube, gyroid and diamond structures, are constructed and investigated. The effects of topology architecture and relative density on the mechanical properties are discussed. The LAMMPS is used to perform MD simulations and the embedded atom method potential is utilized to describe the interatomic interactions. The applied strain rate is 109 s-1 and the applied strain increment is 0.001 in each loading step. The results show that the plastic properties of NPS mainly depend on those of ligaments and the breakage of NPS mainly occurs in ligament areas. Meanwhile, the gyroid structure has better plasticity than other structures, due to the existence of ligament in spiral form. For one structure, the ultimate strength and the Young's modulus increase with the increase of relative density. Analysis shows that the basic mechanical properties of NPS largely depend on the relative density, similar to those of porous materials. The modulus as a function of relative density displays a power-law relation and the exponents depend on the topology architectures. The exponents of three structures are in a range between 1 and 2, showing that the bending of ligament and the tension of ligament are both included during the deformation. The variation trends of modulus of diamond and gyroid structures are similar to the variation of relative density, whose possible reason is that diamond and gyroid structures are both constructed by triply periodic minimal surfaces. With the same relative density, the modulus of diamond structure is in good agreement with that of gyroid structure, and the modulus of cube structure is the minimum. The strength shows a linear relation with the relative density, indicating that the yielding behavior of NPS is dominated by the axial yielding of ligament. When three types of NPSs have the same relative density, the strength of diamond structure is the maximum, cube structure second, and gyroid structure is the minimum. In diamond structure NPS, the structure of triangular framework is formed between ligaments, resulting in a relatively higher strength. The present study will provide an atomistic insight into the understanding of deformation mechanisms of nanoporous metals, and it will provide data support for designing NPMs with optimal mechanical properties by controlling geometric structure.

Experimental study on pull-out response of geogrid embedded in sand

Geosynthetics have been widely employed to reinforce the soils over the last two decades. Pullout resistance and interface friction resistance of the geogrids are crucial design parameters for some geotechnical applications. In this study, the effects of pull-out resistance of geogrid material embedded in sand soil was examined by using simple shear test set-up with a little modification. Thus, a series of experiments carried on sand soil with different relative densities and gradations. In the tests, poor graded sand was reinforced with geogrid. The reinforcement material has 0.85 mm thickness and 1 cm grid aperture. It can be inferenced from experiments that behavior of pull-out resistance had resemblance to classical load–displacement behavior of soil. Classically when displacement increases pull-out resistance increases until a certain displacement but after a certain pull-out resistance when displacement increases pull-out resistance decreases. The tests showed that, the increase in relative density leaded to increase in pull-out load. Due to the interlocking of soil grains with geogrid gaps, interface friction between soil and geogrid was also observed greater than internal friction of soil.

Sorption behavior and microcellular foaming of low-density polyethylene/clay nanocomposites by gas dissolution under sub-critical conditions

Two of the most interesting properties of polymer composites are their improved gas barrier properties, which make them useful for packaging and protective applications and their ability to generate microcellular structures with interesting applications in the construction sector. In this paper, the batch gas dissolution method has been employed to analyze both the sorption behavior and the microcellular foamability of different formulations based on blends of low-density polyethylene, polyethylene grafted with maleic anhydride, and layered clays. Blends of low-density polyethylene and polyethylene grafted with maleic anhydride have been also produced with the aim of clearly distinguish the role played by the clays. The batch gas dissolution process, employing CO2 as gaseous phase, has been intensively used for the foaming of amorphous polymers; however, it is not common in the case of semi-crystalline polymers like low-density polyethylene. Results indicate that the presence of clays reduces slightly the diffusivity. However, the reduction in diffusivity when the clay content increases from 3 wt.% to 5 wt.% is not as high as expected. The existence of an interface between the clays and the polymer, which allows gas molecules to find faster ways across the composite, could be the reason of this behavior. Regarding the cellular materials, in general the relative density increases when adding nanoparticles and also a deterioration of the cellular structure is observed. The slight improvements in the sorption behavior have not been high enough to overcome the effects related to the worsening of the extensional rheological properties of the polymer composites.