Low Porosity Levels Research Articles

Antibacterial Ti-Mn-Cu alloys for biomedical applications.

Titanium alloys are common biomedical materials due to their biocompatibility and mechanical performance. However, titanium alloys are expensive and, unless surface treated, generally cannot prevent surgical infections related to bacteria which can damage the integrity of the implant. In this study, new titanium alloys were developed via powder metallurgy and the addition of manganese and copper, respectively, aiming to limit the manufacturing costs and induce new functionality on the materials including antibacterial response. The addition of manganese and copper to titanium significantly changes the behaviour of the Ti-Mn-Cu alloys leading to the successful stabilization of the beta titanium phase, great refinement of the typical lamellar structure, and achievement of materials with low level of porosity. Consequently, it is found that the mechanical performance and the antibacterial efficacy are enhanced by the addition of a higher amount of alloying elements. The manufactured Ti-Mn-Cu alloys fulfil the requirements for structural biomedical implants and have antibacterial response making them potential candidates for permanent medical implants.

Interfacial characterisation of multi-material 316L stainless steel/Inconel 718 fabricated by laser powder bed fusion

In this study, the interfacial region of multi-material 316L stainless steel/Inconel 718 (316L SS/IN718) fabricated by laser powder bed fusion (L-PBF) is investigated in detail for the first time. The interfacial region consists of a fusion zone (FZ) with intermixed fused Fe and Ni, and individual 316L SS and IN 718 regions. Solid metallurgical bonding is achieved, as evidenced by the low porosity level (~0.27%) and absence of cracks. Microhardness measurements show an average of ~265 HV at the interfacial region, and ~304 HV and ~223 HV at the individual IN 718 and 316L SS regions, respectively.

Effect of Graphene Additive on Flexural and Interlaminar Shear Strength Properties of Carbon Fiber-Reinforced Polymer Composite

Composite materials are widely used in various manufacturing fields from aeronautic and aerospace industries to the automotive industry. This is due to their outstanding mechanical properties with respect to their light weight. However, some studies showed that the major flaws of these materials are located at the fiber/matrix interface. Therefore, enhancing matrix adhesion properties could significantly improve the overall material characteristics. This study aims to analyze the effect of graphene particles on the adhesion properties of carbon fiber-reinforced polymer (CFRP) through interlaminar shear strength (ILSS) and flexural testing. Seven modified epoxy resins were prepared with different graphene contents. The CFRP laminates were next manufactured using a method that guarantees a repeatable and consistent fiber volume fraction with a low porosity level. Short beam shear and flexural tests were performed to compare the effect of graphene on the mechanical properties of the different laminates. It was found that 0.25 wt.% of graphene filler enhanced the flexural strength by 5%, whilst the higher concentrations (2 and 3 wt.%) decreased the flexural strength by about 7%. Regarding the ILSS, samples with low concentrations (0.25 and 0.5 wt.%) demonstrated a decent increase. Meanwhile, 3 wt.% slightly decreases the ILSS.

Comparative study of eutectic Al-Si alloys manufactured by WAAM and casting

Wire and arc additive manufacturing (WAAM) of metallic materials is expected to become part of the new industrial revolution. The possibilities for complex designs and superior mechanical properties can in many cases replace traditional manufacturing processes such as casting. In order to benchmark the properties of aluminium WAAM components, a comparative study was performed with two different casting techniques: permanent casting with steel mould and sand mould casting. Aluminium-silicon alloys with near eutectic composition were used for the comparison. Porosity levels, secondary dendrite arm spacing, grain size distribution, tensile strength and microhardness were considered for the comparison. The WAAM material exhibited superior mechanical properties originating from a finer dendritic and eutectic microstructure compared with the castings. A slight anisotropy in tensile ductility was observed in the WAAM material, probably due to a coarse microstructural zone between individual beads. All investigated materials had low levels of porosity, < 1% by area fraction. The comparative study has shown that WAAM of aluminium-silicon alloys is well suited for high-integrity applications.

Microstructure, mechanical and tribological properties of cold sprayed Ti6Al4V–CoCr composite coatings

Metal-matrix composite (MMC) coatings are advanced materials, composed of two or more phases that can be tailored based on the industrial needs such as lightweight and wear-resistance. Cold spray (CS) technology is highly suitable to develop these MMC coatings as it is a low temperature deposition method, which does not involve particle melting, hence retaining the original properties of the materials. Ti–6Al–4V (Ti64) is a common alloy used in aerospace applications owing to its lightweight and high yield strength. Recently, cold sprayed Ti64 coatings have shown promise to repair damaged or enhance surfaces of Ti components. However, there are still several issues with cold sprayed Ti64 coatings, such as relatively high porosity level and low wear-resistance. To solve these, a novel approach is to incorporate CoCr (ASTM F75) as reinforcing metal alloy particles into the Ti64 matrix to form a Ti64–CoCr composite coating. Pure Ti64 and pure CoCr coatings were also deposited as a comparison. The Ti64–CoCr composite coating achieved low porosity level (0.9%), high hardness (434 HV) and high wear resistance (1.7 × 10−4 mm3/Nm) compared to the Ti64 coatings. These properties were obtained while maintaining the original phases of the feedstock Ti64 and CoCr powders and achieving adhesion strength above 60 MPa. A 20 nm thick Ti–Co interdiffusion layer was also observed at the interface of CoCr and Ti64 particles under TEM. These results showed that Ti64–CoCr composite coating is a promising lightweight and wear resistant metallic coating for aerospace application.

Effect of Ti on microstructure, mechanical properties and corrosion resistance of Zr-Ta-Ti alloys processed by spark plasma sintering

The microstructure, mechanical properties and corrosion resistance of Zr-30%Ta and Zr-25%Ta-5%Ti alloy prepared by spark plasma sintering (SPS) technology were investigated. The experimental results showed that the Zr-Ta-Ti alloys made by the SPS processing have a low level of porosity with the relative density of 96%–98%. The analyses of XRD and TEM revealed that the Zr-30Ta alloy consists of α+β phase, and the Zr-25Ta-5Ti alloy belongs to the near β type alloy containing a small amount of α and ω phases. With the addition of Ti, the elastic modulus of the alloys was decreased from (99.5±7.2) GPa for Zr-30Ta alloy to (73.6±6.3) GPa for Zr-25Ta-5Ti alloy. Furthermore, it is shown that, in comparison to CP-Ti and Ti-6Al-4V alloy, the Zr-Ta-Ti alloy produced in this work offers an improved corrosion resistance due to the more stable ZrO2 and Ta2O5 generated in the passivation film on the surface of the alloys. This study demonstrates that Zr-Ta-Ti alloys are a promising candidate of novel metallic biomaterials.

Effect of Nano-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; on Characteristics of Aluminium A356 Matrix Composite Produced by Stir Casting Route

Aluminium Matrix Composites (AMCs) made by A356 as matrix and nanoAl2O3 as reinforced are widely used for high performance application because of light weight and alumina has good performance at high temperature. In this study, the nanoAl2O3 used varied from 0.1 vf-% to 1.2 vf-%, which subsequently determined the optimum point. In addition, the magnesium with 10% are added as a wetting agent between aluminium and nanoAl2O3 as reinforced. Stir casting process is carried out for 2 minutes and 4 minutes for the degassing process using argon gasses then pouring molten metal in to the mold at 800°C. The effect of nanoAl2O3 on the mechanical properties and microstructure of the composites was investigated. The result showed that the tensile strength decreased with the addition of nanoAl2O3 but the hardness increased. Increasing of hardness mainly caused by grain refinement, and particle strengthening which act as obstacles to the motion of dislocations. Addition of nanoAl2O3 as reinforced also tend to form microporosity and agglomeration which would decrease the tensile strength of composites. The optimum strength was reached by 0.5 %Vf nanoAl2O3 with the value of 140 MPa and hardness of 46 BHN which was supported by low porosity level. Keyword : Al A356, Al2O3, nanoComposite, Stir Casting

Multiscale micromechanical analysis of alkali-activated fly ash-slag paste

Current demand for highly sustainable concrete, e.g. alkali-activated fly ash-slag (AAFS) concrete, urges understanding the links between microstructure and micromechanical properties of this binder. This paper presents a systematic investigation into the microstructure and micromechanical properties of AAFS paste from nano-scale to micro-scale. Nanoindentation was used to evaluate the micromechanical properties, while the microstructure was characterised using 29Si nuclear magnetic resonance, Fourier transform infrared spectroscopy, backscattered electron microscopy, and mercury intrusion porosimetry. The results indicate that N-A-S-H gels have a relatively low elastic modulus due to their high level of structural disorder and gel porosity, while the C-A-S-H gels and N-C-A-S-H gels with a low level of structural disorder and gel porosity have a relatively high elastic modulus. The elasticity of reaction products and their relative volumetric proportions mainly determine the macroscopic elasticity of AAFS paste, while the porosity and pore size distribution primarily condition its macroscopic strength.

Thermal conductivity of porous Alumina-20 wt% zirconia ceramic composites

Effect of porosity and temperature on thermal conductivity of the porous Alumina-20 wt% Zirconia (3 mol.% Y2O3) ceramic composites with and without niobia were investigated. The ceramic powders were synthesized by the sol-gel route using alkoxide precursors. The porosity in the composites was maintained in the range of 9.5–65 vol% using starch as a space holder material. After processing, samples were compacted uniaxially and sintered at 1873 K for 3 h. The thermal conductivity of porous ceramic composites with and without niobia dopant was measured at three different temperatures of 300, 473, and 673 K using laser-flash technique. The thermal conductivity of the samples was reduced with increasing temperature and porosity. At temperature of 300 K, the thermal conductivity value of 11 W/m.K was obtained for the undoped sample S0 with 17 vol% residual porosity, dropped to 2 W/mK for the sample S40 containing 65 vol% porosity, and for the same sample it was further reduced to the lowest value of 0.68 W/m.K at 673 K. The measured conductivity values were used to determine the grain boundary thermal resistance value (R) of the samples which exhibited an ascending trend with the porosity. The obtained thermal conductivity for the different porous composites was verified and formulated with the Maxwell-Eucken and Ticha models. The results showed that the experimentally measured conductivity values follow a descending order with the models while at the higher-porosity level (57–65 vol%), it fits well with the Ticha equation with only 9% and 4.6% deviation for undoped and doped samples, respectively. Results also revealed that the addition of niobia significantly reduced thermal conductivity at the lower porosity levels, but at higher porosity level the effect of porosity was more dominant.

Dynamics of Necking and Fracture in Ductile Porous Materials

AbstractThe onset of necking in dynamically expanding ductile rings is delayed due to the stabilizing effect of inertia, and with increasing expansion velocity, both the number of necks incepted and the number of fragments increase. In general, neck retardation is expected to delay fragmentation as necking is often the precursor to fracture. However, in porous ductile materials, it is possible that fracture can occur without significant necking. Thus, the objective of this work is to unravel the complex interaction of initial porosity and inertia on the onset of necking and fracture. To this end, we have carried out a series of finite element calculations of unit cells with sinusoidal geometric perturbations and varying levels of initial porosity under a wide range of dynamic loading conditions. In the calculations, the material is modeled using a constitutive framework that includes many of the hardening and softening mechanisms that are characteristics of ductile metallic materials, such as strain hardening, strain rate hardening, thermal softening, and damage-induced softening. The contribution of the inertia effect on the loading process is evaluated through a dimensionless parameter that combines the effects of loading rate, material properties, and unit cell size. Our results show that low initial porosity levels favor necking before fracture, and high initial porosity levels favor fracture before necking, especially at high loading rates where inertia effects delay the onset of necking. The finite element results are also compared with the predictions of linear stability analysis of necking instabilities in porous ductile materials.

Atomization of Ti-64 alloy using the EIGA process: comparison of the characteristics of powders produced in labscale and industrial-scale facilities

Titanium alloy powders, mostly the Ti-64 alloy with composition Ti-6Al-4V (wt.%), are extensively used for biomedical and high-demanding applications, e.g. in aeronautics. Advanced powder metallurgy processes like additive manufacturing are strong drivers for the production of high quality powders, insuring a good rheological behavior, a low porosity level in the parts and an adequate roughness. Ideally, fine spherical particles with no volume and surface defects are aimed at. Inert gas atomization is a process that is able to produce clean powders for such applications, especially for AM. To avoid the chemical reaction of titanium with the commonly used alumina crucibles, a crucible-free configuration has been designed in the EIGA process (Electrode induction melting Inert Gas Atomization). Two EIGA facilities are currently available in France for R&amp;D purposes: a one-liter (nominal rod diameter/length (mm): 50/500) labscale facility at ONERA and an eight-liter capacity (100/1000) industrial-scale facility at the MetaFensch Institute. Using the smaller facility to screen and optimize atomization parameters and transfer them to the bigger facility is a tempting approach. This communication will show the characteristics of Ti-64 powders produced in both facilities, in terms of particle shape, particle size distribution, presence of satellites and porous particles.

Application of Image Processing in Detection of Bone Diseases Using X-rays

This study compares published algorithms for the detection of bone diseases particularly osteoporosis (which is characterized by low level of bone mineral density and porosity due to microarchitectural deterioration) with claimed accuracy on based on the author selected dataset. In this study common dataset is used to verify accuracy and performance of the published algorithms by comparing the output results published by the authors and the results gathered and compiled by this study. Features like contrast, correlation, homogeneity, entropy, energy along with standard deviation, range, skewness are calculated from Gray-Level Co-occurrence Matrix (GLCM) technique. Study also implement all algorithms published by the authors and tested with common dataset containing digital images of X-ray femur (left and right leg femur; both). The research concludes that the standard deviation, image contrast and specifically energy with entropy plays a vital role in determining the disease by performing Haralick features textural analysis on plain (Non-DEXA) radiographs.

Effect of porosity on dielectric properties of ZnO ceramics

In this study we investigated the effect of porosity level on the dielectric properties and conductivity of ZnO ceramic samples sintered by pressure-less solid-state reaction method. The relative permittivity (εr′) and, tangent loss value decreased gradually with increasing porosity, being 1.9 × 105 and 35.6 × 103 for sample with low porosity and high porosity level, respectively at room temperature. Also the tangent loss decreases with increasing porosity level being quite high (∼102) at low frequencies and, low (∼10−1) at high frequencies. The complex part of the relative permittivity results could be fitted to the Maxwell-Wagner (MW) model suggesting a poly-dispersive relaxation time. The frequency dependence-ac conductivity determined by means of dielectric data was strongly dependent of the porosity level. It decreases sharply with increasing porosity level is frequency independent- up to ∼104 − 105 Hz followed by an abrupt increase at higher frequencies. These data were discussed in terms ZnO defects such as Zn interstitial and oxygen vacancies present in the grain boundaries.

Microscopic pore structures of tight sandstone reservoirs and their diagenetic controls: A case study of the Upper Triassic Xujiahe Formation of the Western Sichuan Depression, China

Abstract The study of microscopic pore structures is of central significance to the evaluation of the reservoir quality and well productivity of tight gas sandstone. The second and fourth members (abbreviated as T3x2 and T3x4, respectively) of the Upper Triassic Xujiahe Formation of the Western Sichuan Depression were used as cases to analyze microscopic pore structures and diagenetic controls in consideration of the disparities in reservoir quality and well productivity. Optical microscopy of thin sections, Micro-CT Scanning, scanning electron microscopy (SEM), High Pressure Mercury Injection (HPMI) and apex methods based on the HPMI results were used to determine the pore and throat geometries and the types and pore size distributions in terms of the quantity and levels of pore connectivity. Tight sandstone reservoirs of the study area are characterized by poor physical properties, with the T3x2 reservoirs presenting relatively higher levels of permeability and lower porosity levels than those of the T3x4 reservoirs. The pore spacing configurations, sizes and distributions and throat geometries reveal significant disparities. Primary pores and micro-fractures were found to be more developed in the T3x2 reservoirs with bending and narrow pore throats measured as smaller than 0.5 μm. Compared to those of the T3x2 reservoirs, secondary pores including moldic and intracrystalline pores were more developed in the T3x4 reservoirs with relatively larger, straighter and wider throats of 0.5–1.0 μm. An evaluation of the pore connectivity levels shows that only 26.86% and 28.90% pores are closely connected to the whole for T3x2 and T3x4 reservoirs, respectively. Four major diagenetic processes were found to control reservoir quality and the microscopic pore structure. Mechanical compaction is the primary cause of the densification of reservoirs in the study area. Compared to that observed in the T3x4 reservoirs, more intensive mechanical compaction was observed in the T3x2 reservoirs, changing the configuration of the throats present, reducing the pore throat radii, and ultimately lowering the porosity of T3x2 reservoirs as a whole. Quartz overgrowth and late period carbonate cements were observed in partly filled pore spaces, narrowing throats and reducing pore connectivity, but eogenetic cementation and chlorite cements can increase the pressure-resistance of sandstone and inhibit compaction quartz overgrowth. Thus, T3x4 reservoirs are relatively more porous as a result of eogenetic calcite cementation, and primary pores are more developed in T3x2 reservoirs with chlorite cements. Dissolution is a major factor that improves the tight sandstone reservoir quality because it generates a large volume of secondary pores. The more intensive levels of dissolution in T3x4 reservoirs not only creates more intergranular, intragranular, moldic and intracrystalline pores but also further increases the porosity of T3x4 reservoirs. Fracturing effects have developed in the study area to improve pore connectivity levels and thus the permeability of tight sandstone reservoirs, potentially explaining the pore connectivity and permeability of certain T3x2 reservoirs. This work may be able to be used as a useful reference for the reservoir quality evaluation and exploration of tight gas sandstone reservoirs for similar oil fields worldwide.

Study of the suitability of unfired clay bricks with polymeric HDPE & PET wastes additives as a construction material

Under the framework of the Moroccan circular economy 2030 strategy, this study investigates the use of solid polymeric wastes as an alternative additive material in the construction sector. Polymeric waste additives improve both the bulk density and thermal conductivity of clay bricks; unfortunately, this comes at the expense of their mechanical properties. This paper presents an innovative way to improve the performance of unfired clay bricks with polymeric, HDPE and PET, additives to meet the Moroccan testing standards in the building sector, without using expensive organophilic and stabilizing treatments. X-ray Diffraction and Fluorescence analysis show that the used extracted clay is of an Illite type with non-swelling characteristics. Three different additive grain-sizes (δ ≤ 1 mm; 1 mm<δ ≤ 3 mm and 3 mm<δ ≤ 6 mm) with different percentages (0%, 1%, 3%, 7%, 15% and 20%), by weight, are investigated. The microscopic snapshots and experimental measurements reflect a low porosity level when using the smallest polymeric grain additive size (δ ≤ 1 mm), which results in improving the brick sample's performance. In fact, bulk density measurements show that the prepared specimens can be classified as lightweight bricks, as their density does not exceed the 1.75 g/cm3 mark. Besides, capillary water absorption coefficient and compressive strength properties are also improved by almost 17% and 28%, respectively, when using the smallest polymeric-grain additives of size (δ ≤ 1 mm) if compared to the largest ones of size (3 mm<δ ≤ 6 mm).

Effect of extrusion ratio on the microstructure and property of the Al–Zn–Mg–Cu alloy prepared by spray conform

The commercial Al-5.72Zn-2.36Mg-1.66Cu (7075) alloys were prepared by the spray Conform (SC) technique consisting of the spray forming and Conform extrusion. The extrusion ratio (ER) was selected as the variable parameter to study the influence mechanism on the microstructures and properties while keeping the other parameters unchanged. The microstructures and properties were investigated by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and tensile tests. Concretely, the changing rules of the grains, second phases, tensile strength and elongation with ER were researched respectively. Results indicate that a fine equiaxed grain microstructure with low level of segregation and porosity was achieved by SC. And the intergranular and intragranular phases were fine and homogeneous before and after retrogression and re-aging (RRA). The dispersion and tensile strength are positive to ER, but the grain size (GS) is inverse. Meanwhile, the elongation increases firstly and then decreases with increasing ER.

Understanding the microstructural role of bio-sourced 3D printed structures on the tensile performance

This study aims at revealing the role of microstructural arrangement on the mechanical behaviour of printed PLA-Hemp using Fused Deposition Modelling (FDM). 3D printing is performed by varying the printing temperature. The laying down process is monitored using infra-red measurement. X-ray micro-tomography is used to acquire the 3D microstructure of printed PLA-Hemp. Tensile performance is determined by testing neat and notched specimens. Finite element modelling based on microstructure implementation is conducted to reveal the deformation mechanisms associated with the tensile loading. The results show a wide temperature range for printability of PLA-Hemp but overheating effects characterises the printing using large temperatures (>220 °C). The tensile performance is found dependent on the printing temperature, a modified filament morphology, and an imperfect nature of the hemp-PLA interface within the filament. Finite element results reveal particular characteristics of stress fields that superpose with underlined microstructure of filament arrangement. Despite this correlation, the low porosity level and the brittle nature of the filament do not allow strong dependence of the crack propagation on the raster orientation.

Reliability Analysis of Brinell Hardness Results for Aged Alumix321/SiC Composites

Aluminum/SiC composites are widely employed in the automotive industry. Aluminum composites can be produced by hot pressing which forms a final product with a low porosity level and a denser structure. Homogeneous distribution of reinforcement particles, the level of porosity, and heat treatment not only affect the mechanical properties of the composites but also the reliability of their mechanical test results. In this study, Brinell hardness test reliability analyses of the hot-pressed Alumix321/SiC composites were carried out. The effects of increasing SiC amount and aging treatment on the reliability of hardness test results were discussed. Reliability analysis revealed that the aging treatment and increasing amount of SiC reinforcement decreased the reliability of the hardness test results. The reason for this was researched and resulting cases were discussed.

Combustion synthesis of SiC-MoSi2-Al2O3 composites

Abstract Combustion synthesis of SiC-MoSi2-Al2O3 composites by using highly exothermic reactive system of MoO3-Al-Si-SiO2 was investigated. It has been shown that, by using the combustion synthesis method, it is feasible to prepare, at 1500 °C, an electrical heating element with room temperature resistivity and element watt loading of 12 Ω cm and 20 W/cm2 respectively. The colloid containing nano-sized material 30 wt% SiO2, was used as the plasticizer medium as well as combustion source. The β-SiC functioned as a filler material to control the combustion reaction and also constituted part of the final product. The amount of SiC additive varied in the range from 45% to 65% wt. and was optimized with respect to porosity level, reaction conversion and net-shape quality of the heating elements. The element containing about 60% wt. SiC reveals low porosity level, with full conversion for the reaction and superior net-shape quality. However, despite the relatively high level of porosity present in the final synthesized product, it can be used as an electrical heating element in accordance with the investigation at the element temperatures up to 1500 °C.

Study on the optimizing mechanisms of superior comprehensive properties of a hot spray formed Al-Zn-Mg-Cu alloy

In this study, the microstructure of a hot spray formed Al-Zn-Mg-Cu alloy was observed, and the effects of ageing treatment parameters on the precipitation, the mechanical properties and corrosion behavior of the alloy were investigated. The as-deposited Al-Zn-Mg-Cu alloy had a fine equiaxed grain structure with low level of segregation and porosity. After hot extrusion and solution treatment, most of the coarse phases were dissolved, providing a favorable condition for subsequent ageing strengthening. The alloy was subjected to three different ageing treatments: peak-aging, over-aging, and non-isothermal retrogression and re-ageing (NRRA). Results showed that the alloy in peak-ageing condition possessed much better mechanical properties, but poorer corrosion resistance than that in the over-ageing condition. After NRRA treatment, however, great comprehensive performance was achieved for the alloy. In NRRA condition, the optimum combination of the size and number of strengthening phases was responsible for the high mechanical properties, whilst the separated grain boundary precipitates (GBPs) and the higher Cu content of the GBPs contributed to the better corrosion resistance.