Homogeneous Particle Distribution Research Articles

Microstructural characterization and mechanical properties of in situ cast nanocomposites Al/TiC type

Al matrix nanocomposites reinforced with TiC particles have been successfully fabricated by self-propagating high-temperature reaction during casting from aluminium 1000 alloy and a mixture of powders of Ti, C and Al used as a moderator. The most important issue was to estimate the influence of moderator content on the microstructure. The microstructure of composites containing a lower amount of moderator (1% and 10%) consists of TiC particles, segregated mainly at grain boundaries of aluminium matrix, while a higher moderator content (>50%) allows to obtain materials with nearly homogenous distribution of TiC particles. Moreover, the elimination of brittle, additional phases e.g. TiAl3 and Al4C3, commonly observed in the Al/TiC composites, was evidenced. However, still small amounts of Ti3AlC and TiAl2.4Si0.6 phases that reduce the capacity of TiC were identified. The composites exhibit improved mechanical properties with regard to aluminium base alloy. The highest value of the relative increase of yield strength was found in the composite with 50% of moderator due to relatively small TiC particle size, well separated and uniformly distributed in the matrix.

Numerical analysis of dilute gas-solid flows in a horizontal pipe and a 90° bend coupled with a newly developed drag model

The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian Particle Tracking methods for the prediction of industrial type gas-solid flows. The Lagrangian approach is best suited to applications where the solids volume fraction is low, and the effect of particle concentration can be ignored. In the present work, a 3D time dependent numerical analysis is performed to study the effect of Lagrangian model improvements to replicate experimental studies of straight horizontal pipe flow and flow through a 90° horizontal-to-vertical bend. The present predictions are compared with published experimental data of Tsuji and Morikawa (1982), and Yilmaz (1997). Special attention is paid to influence of particle mass-flow rates and conveying velocity on the particle motion within the system. This study used a CFX-4 package, where the ability to modify the code was necessary to include particle model improvements. These improvements included implementing a newly drag force model developed as a part of this research work. Particle-wall collision and particle-particle collision models developed by Sommerfeld (1992), and Sommerfeld (2001) are also implemented in the CFD model. The standard k–ε dispersed turbulence model was utilized as the predictions for the gas phase only gave similar predicted axial velocity compared to the more computationally demanding Reynolds stress model. The results showed that the inclusion of the various improvements lead to reasonable predicted particle velocities in both the upper and lower regions of the straight horizontal pipe which denote the dilute and dense regions respectively. It was also found that the inclusion of the rough-wall particle wall collision model decreases the axial particle velocity in the lower region where the bulk of the particle wall collisions occur. While the inclusion of the particle collision models tends to disperse the particles away from the lower region resulting in a less dense lower section and a distinctly more homogenous particle distribution compared with the standard model predictions. Further, the increase in particle concentration leads to a reduction in axial velocity due to a loss of momentum through particle-wall and particle-particle collisions. Finally, the improved CFD model best predicted both the reduction and increase in the particle velocities in the different regions.

Cryogenic mechanical alloying of aluminum matrix composites for powder bed fusion additive manufacturing

Cryogenic mechanical alloying (cryomilling) was employed to fabricate aluminum matrix composite powder feedstock for additive manufacturing. The high energy milling of the powder system induces a homogenous distribution of reinforcement particles in the matrix powder by recurrent fracture and cold welding. In this study, aluminum matrix composite feedstock were produced via different cryomilling techniques at varying compositions, powder charges, and milling times. As-milled powders were characterized for particle size distribution, morphology, and homogeneity. Resultant powder demonstrated varying characteristics correlated to milling parameters. Powder metallurgy samples were also fabricated to understand as-sintered reinforcement distribution and the resultant strengthening. This research provides an indication of cryomilling capabilities to become an effective method for custom alloy powder production for powder bed fusion additive manufacturing.

Analysis of the Microstructure and Mechanical Properties of a New Wrought Alloy Based on the ((Al) + Al4(Ca,La)) Eutectic

Abstract—This paper examines manufacturability problems of a new Al–Ca–La–Mn alloy in the process of pressure treatment. Electron microscopy and X-ray diffraction analysis were used to perform a detailed study of the structure of the alloy in the cast state and after thermomechanical treatment under different conditions. The cast structure of the alloy is shown to consist of the Al-based solid solution (Al) and Al4(Ca,La) eutectic phase, whose volume fraction is ~15%. The metallographic analysis of the alloys subjected to hot and cold rolling, as well as cold drawing, was performed; a substantial refining of eutectic intermetallics compared to that in the cast state was found. In particular, the homogeneous distribution of submicron spherical particles (300–500 nm in size) in the volume of composite material is observed, which are efficient stabilizers of the structure upon recrystallization. The obtained samples of rolled sheets demonstrate the high thermal stability of the structure and properties during long-term isothermal holding at 250 and 350°С. In particular, it has been shown that the 10-h annealing of cold-rolled sheet 1 mm thick at 250°С leads to a decrease in the hardness only by ~15%. The most favorable conditions for manufacturing the rolled sheets allow us to reach high mechanical properties (an ultimate strength of 240–290 MPa, a yield strength of 200–250 MPa, and a relative elongation of 5.5–15.5%).

Experimental Investigation of Mechanical Properties of Al6061 Reinforced with Iron oxide

The present work aimed at investigating the mechanical properties of the aluminum matrix composites. The aluminum 6061 alloy as a matrix reinforced with the weight fraction 2, 4 and 6% of particles of iron oxide (Fe2O3) of size 40µmis prepared using the stir casting technique. The prepared specimens are tested as per the standards for tensile, bending, impact and hardness properties of the composite. From the results it is observed that the mechanical properties of the said composite have increased with the increment in the weight percentage of iron oxide up to 4% of reinforcement. The significant reaction between the reinforcement and the matrix forms the better bonding between them. The enhanced mechanical properties of the aluminum-iron oxide composites are due to the fine, well bonded and homogeneous distribution of the iron oxide particles in the aluminum matrix. The maximum improvements were observed at 4 wt% of Fe2O3.

Processing of in situ Al3Ti/Al composites by advanced high shear technology: influence of mixing speed

High shear technology (HST) is an advanced melt stirring technology with the intensive shear effect and allows the production of particle-reinforced Al composites (PAMCs) with a homogeneous particle distribution. In the fabrication process, applying an appropriate mixing strategy to obtain the excellent microstructure and properties is crucial. In this work, Al3Ti/Al composites with different Al3Ti volume fractions were fabricated in situ by high shear technology at various mixing speeds. The effect of mixing speed on the microstructure and mechanical properties was investigated. The results show that the reaction rate and Al3Ti particle size increase with the increase of mixing speed. An intermediate mixing speed is appropriate for preparing the Al3Ti/Al composite with a homogeneous distribution of reinforcing particles and low porosity. A lower mixing speed leads to severe particle agglomerations, which deteriorates the ductility of Al3Ti/Al composites. A higher mixing speed results in high porosity within castings resulting from severe air entrainment, which significantly reduces mechanical properties. Young’s modulus improves with increasing the stiff Al3Ti particle content and matches well with the predicted results as well. Tensile and compression strength and hardness are enhanced due to generating the uniform distribution of reinforcing particles and the matrix grain refinement.

A comparative study between friction stir processing and friction stir vibration processing to develop magnesium surface nanocomposites

Friction stir processing (FSP) can be used to improve surface composites. In this study, a modified method of FSP called friction stir vibration processing (FSVP) was applied to develop a surface composite on AZ91 magnesium alloy. In this technique, the workpiece is vibrated normal to the processing direction. The results illustrated that compared with the FSP method, the FSVP caused a better homogeneous distribution of SiC particles in the microstructure. The results also showed that matrix grains of friction stir vibration processed (FSV-processed) samples ((26.43 ± 2.00) µm) were finer than those of friction stir processed (FS-processed) specimens ((39.43 ± 2.00) µm). The results indicated that the ultimate tensile strength (UTS) of FSV-processed specimens (361.82 MPa) was higher than that of FS-processed specimens (324.97 MPa). The higher plastic strain in the material during FSVP, due to workpiece vibration, resulted in higher dynamic recrystallization, and consequently, finer grains were developed. The elongation and formability index of the FSV-processed specimen (16.88% and 6107.52 MPa%, respectively) were higher than those of the FS-processed sample (15.24% and 4952.54 MPa%, respectively). Moreover, the effects of FSVP were also found to intensify as the vibration frequency increased.

Thermomechanical treatment of A380 aluminum alloy for globular thixo feedstock

AbstractThe main aim of this paper is to present and evaluate thermomechanical treatment for semi‐solid feedstock production of A380 (AlSi9Cu3(Fe)) aluminum alloy. Equal channel angular pressing (ECAP) is used to heavily deform and refine as cast dendritic microstructure with needle like eutectic appearance. The deformed microstructure is easily changed to globular microstructure by recovery and recrystallization mechanisms during heating at the semi‐solid temperature range which is a crucial factor for quality semi‐solid feedstock preparation. The microstructural evolutions investigations during semi‐solid heating at different holding times is carried out utilizing optical microscope and scanning electron microscope accompanied by energy dispersive x‐ray spectroscopy. Homogeneous distribution of the silicon particles and intermetallic compounds around globular primary aluminum phase is observed. The used approach is appropriate and seems highly promising for preparation of the quality semi‐solid feedstock.

Fabrication of Al Alloy-Based Metal Matrix Composites and Use the Interpolation Approach for Mechanical Properties Estimation

Aluminum alloy-based metal matrix composites (AMMCs) are extensively utilized due to their distinctive mechanical properties. Al-6%Si alloy was reinforced with different contents of alumina (Al2O3) particles (0, 1.5, 3, 4.5, 6, 7.5, 9, 10.5 and 12% wt.) and the MMCs were prepared by stir casting at 800°C. Microstructural characterization of AMMCs was studied using optical microscopy, to emphasize the homogeneous distribution of the reinforcement particles (Al2O3) in the Al alloy matrix. Hardness and wear tests were used to study the influence of Al2O3 addition on the mechanical properties of the prepared composites. The interpolation method is applied as a perfect alternative approach for saving the consumed time during the experimental work. The used mathematical expression can be utilized for an early prediction of the mechanical properties of AMMCs at different contents of Al2O3 particles without carrying out much experimental analysis. The current study shows that the linear interpolator is the optimal one where it achieved Mean square error (MSE) equals 0.1875, and 0.0119 for hardness and wear loss tests, respectively.

DEM simulation of particle segregation in filling of vibratory dies

The homogeneity of the metal powder in the dies is a primary factor affecting the quality of the product obtained by powder metallurgy manufacturing routes. Hence, a desirable goal during die filling is to achieve a homogeneous distribution of particles. However, the presence of particles of different shapes and sizes in metallic powders may give rise to inhomogeneous distribution leading to the segregation of particles. In addition to segregation, the presence of cavities or gaps in the dies with sharp features can affect the quality of final products. In this work, discrete element simulations are carried out to study the die filling of an axisymmetric die with internal stepped features which led to the formation of gaps in the die as it is filled with particles. The die is subjected to vertical vibratory motion and the effect of vibration parameters on the size segregation of particles and the compaction characteristics of the metallic powder are studied. At higher amplitudes, a cluster of coarse particles was observed at the center near the base of the die. At higher vibrational frequencies out of phase, flows were observed in the stepped regions of the die which led to the formation of surface waves.

Impact of Gamma Radiation and Rice Husk Nanosilica on the Physico-Mechanical Properties of Styrene Butadiene Rubber/Natural Rubber Blend

Silica is the major inorganic constituent of the rice husk. High-surface area amorphous silica, Extracted Nanosilica (ENS), was developed by washing out the rice husk, followed by combustion and finally chemically treated. ENS was characterized by FTIR, XRD and TEM techniques. Reinforcement of natural rubber (NR)/styrene butadiene rubber (SBR) blend with varying ratio of ENS, namely 5, 10 and 20 phr, and separately with 20 phr Hisil (commercial silica) was established. Vulcanization of the produced composites was applied by gamma irradiation at a total dose range from 50 to 200 kGy. The radiation-cured nanocomposites were examined via mechanical, physical and thermal investigations. The SEM micrographs affirmed the homogenous distribution of silica particles throughout the polymer matrices. The results ensured noticeable enhancement in the investigated properties of the nanocomposites.

Performance of Coconut Shell Activated Carbon in LiMn<sub>0.7</sub>Fe<sub>0.3</sub>PO<sub>4</sub>/CNT/C Composite for Lithium Ion Battery Cathode

Synthesis and characterization of LiMn0.7Fe0.3PO4/CNT/C composite used as lithium ion battery cathode has been carried out. The active materials of LiMn0.7Fe0.3PO4 was synthesized via hydrothermal method from the precursors of LiOH, NH4H2PO4, FeSO4.7H2O and MnSO4.7H2O. The activated carbon was pyrolyzed from coconut shell whereas the carbon nanotube (CNT) was commercially available in the market. The composite was prepared using a ball-mill to mix the components homogeneously. Simultaneous thermal analysis STA was used to determine the formation temperature of LiMn0.7Fe0.3PO4 to which the sintering process was conducted at 700 °C. After sintering, the materials in powder forms were characterized using scanning electron microscope (SEM) to examine the morphology, whereas X-ray diffraction (XRD) was used to identify the phases formed. The performance of the composite as lithium ion battery cathode was characterized using electrochemical impedance spectroscopy (EIS) and battery analyzer. Secondary electron image from SEM showed that the samples have homogeneous particle distribution. Examination result from X-ray diffraction indicated that LiMn0.7Fe0.3PO4 phase has been successfully synthesized with small impurities from a secondary phase. Performance analysis showed that the presence of activated carbon and CNTs in LiMn0.7Fe0.3PO4 to form LiMn0.7Fe0.3PO4/CNTs/C gives significant improvement in the conductivity; however, some more improvement is still needed for the capacity.

Viscoelasticity, mechanical properties, and in vivo biocompatibility of injectable polyvinyl alcohol/bioactive glass composite hydrogels as potential bone tissue scaffolds

An injectable composite hydrogel composed of polyvinyl alcohol (PVA) and bioactive glass (BG) particles were synthesized by a physical crosslinking approach. The morphology, mechanical properties, and viscoelasticity of the PVA/BG composite hydrogel were characterized. Scanning electronic microscopy (SEM) showed uniform and homogeneous distribution of BG particles throughout the composite hydrogel. The incorporation of 2.5 wt% of BG particles in the composite hydrogel formulations, enhanced the static compressive strength and static elastic modulus by 325% and 150%, respectively. The storage molds (G′) was greater than the loss modules (G′′) at all the frequency range studied, which revealed a self-standing elastic composite hydrogel with a smooth injectability. The PVA/BG composite hydrogel was also implanted subcutaneously in the dorsal region of adult male rats. After 4 weeks of implantation, no inflammatory cells were seen within and around the implant, which indicated that the composite hydrogel was biocompatible. The properties of the synthesized injectable PVA/BG composite hydrogel demonstrate its capability toward bone regeneration.

Deterministic reversible model of non-equilibrium phase transitions and stochastic counterpart

N point particles move within a billiard table made of two circular cavities connected by a straight channel. The usual billiard dynamics is modified so that it remains deterministic, phase space volumes preserving and time reversal invariant. Particles move in straight lines and are elastically reflected at the boundary of the table, as usual, but those in a channel that are moving away from a cavity invert their motion (rebound), if their number exceeds a given threshold T. When the geometrical parameters of the billiard table are fixed, this mechanism gives rise to non-equilibrium phase transitions in the large N limit: letting T/N decrease, the homogeneous particle distribution abruptly turns into a stationary inhomogeneous one. The equivalence with a modified Ehrenfest two urn model, motivated by the ergodicity of the billiard with no rebound, allows us to obtain analytical results that accurately describe the numerical billiard simulation results. Thus, a stochastic exactly solvable model that exhibits non-equilibrium phase transitions is also introduced.

Towards Raman Automation for Microplastics: Developing Strategies for Particle Adhesion and Filter Subsampling.

Automation and subsampling have been proposed as solutions to reduce the time required to quantify and characterize microplastics in samples using spectroscopy. However, there are methodological dilemmas associated with automation that are preventing its widespread implementation including ensuring particles stay adhered to the filter during filter mapping and developing an appropriate subsampling strategy to reduce the time needed for analysis. We provide a solution to the particle adherence issue by applying Skin Tac, a non-polymeric permeable adhesive that allows microplastic particles to adhere to the filter without having their Raman signal masked by the adhesive. We also explore different subsampling strategies to help inform how to take a representative subsample. Based on the particle distributions observed on filters, we determined that assuming a homogenous particle distribution is inappropriate and can lead to over- and under-estimations of extrapolated particle counts. Instead, we provide recommendations for future studies that wish to subsample to increase the throughput of samples for spectroscopic analysis.

Mechanical and Tribological Behavior of Mg-Matrix Composites Manufactured by Stir Casting

In the recent decades, magnesium matrix composites present a plenty of applications in automotive, marine and aerospace industries. In this work, AZ31B is selected as Mg matrix material and hard Tungsten carbide (WC) particles as reinforcement material. Mg/WC composites are reinforced with different weight proportions (0, 5, 10 and 15% wt.) using stir casting method. The worn surface of manufactured Mg/WC composites and base Mg material were examined by scanning electron microscope (SEM). The wear test results denote that AZ31B/15% wt. WC composites have excellent tribological behaviour when compared to the base magnesium matrix AZ31B alloy. The yield tensile strength, flexural strength, ultimate tensile strength and micro-hardness of the manufactured composites are improved by increasing the WC content. Further, SEM analysis revealed the homogeneous distribution of WC particles throughout the Mg matrix.

Pd-NCQD composite confined in SBA-15 as highly active catalyst for aqueous phase catalytic hydrodechlorination of 2,4-dichlorophenoxyacetic acid

A composite consisting of Pd particles and N-doped carbon quantum dots (NCQDs) confined in mesoporous SBA-15 (Pd-NC@SBA-15) was prepared. For comparison, Pd catalysts supported on SBA-15 (im-Pd/SBA-15), NCQDs modified SBA-15 (im-Pd/NC-SBA-15) and N-doped carbon nanotubes (Pd/NCNTs) were prepared using the impregnation method. The catalysts were characterized and the aqueous phase catalytic hydrodechlorination (HDC) of 2,4- dichlorophenoxyacetic acid (2,4-D) was investigated. Characterization results showed that Pd-NC@SBA-15 had a higher Pd dispersion and more homogeneous Pd particle distribution than other catalysts. Additionally, the presence of NCQDs led to increased content of positively charged Pd in Pd-NC@SBA-15. As a result, Pd-NC@SBA-15 exhibited a much higher catalytic activity. Furthermore, the turnover frequency value of the Pd-NC@SBA-15 catalyst increased with Pdn+ content and remained identical at Pdn+/Pd0 ratio above 1.20. The HDC of 2,4-D on Pd-NC@SBA-15 proceeded via both stepwise and concerted pathways and the stepwise dechlorination pathway was predominant. The present study highlights that substantial enhancement of the catalytic activity can be achieved by rational NCQDs modification of Pd based catalysts for the aqueous phase catalytic removal of pollutants.

Influence of secondary phase particles Al2O3/SiC on the microstructure and tribological characteristics of AA7075-based surface hybrid composites tailored using friction stir processing

Recently, cylinder liners of automotive and aircraft engines are encountered severe wear due to piston slap occurred by the repeated sliding stroke of piston. This research focuses on providing an alternative material for cylinder liners, which can be obtained through friction stir processing on AA7075 with different weight ratios of reinforcements like Al2O3 and SiC. Friction stir processing is executed with a tool rotational speed of 1000 r/min and traveling speed of 56 mm/min at 2° tool tilt angle. The images of optical microscopy reveal the fine-grains with a homogeneous distribution of secondary phase particles and also offer decrement in particle clustering except at some localized regions. It is identified that addition of 3.7 wt.% Al2O3 + 3.0 wt.% SiC in AA7075 enhanced the microhardness about 33.96% higher than base matrix. Hence, wear resistance of the specimen is improved. Dry sliding wear behavior of specimens is analyzed using pin on disc at 20, 40, and 60 N load conditions to create the actual sliding behavior of piston on cylinder wall. Increasing the wt.% of Al2O3 particles enhanced the wear resistance of AA7075 surface hybrid composites at 20 N load due to the formation of protective tribofilm. Specimen with 3.7% Al2O3 + 3.0% SiC has better lubrication and load-bearing capacity that exhibits superior tribological behavior at 40 and 60 N. Higher Fe content of 5.44 wt.% has been obtained through spectroscopy analysis in S5, which is 8% and 6% higher than S3 (7.5% of Al2O3) and S7 (6% of SiC), respectively. The scratching action of this hard specimen on the counterpart brings more Fe content. Increase of Al2O3 particles paved the way for tribofilm formation and identified through scanning electron microscopy micrographs. The observation from worn specimens shows that finer wear debris had increased by adding more quantity of SiC particles due to abrasive wear mechanism.

Study of the microstructure and mechanical characteristics of AZ91–SiCp composites fabricated by stir casting

In recent years, the composite materials have been very desirable by researchers for many engineering applications such as aviation and biomedical because of the tremendous characteristics of magnesium matrix metal composite. This current investigation aims to develop the AZ91/SiCp composites with various weight fractions (0, 2.5, 5 and 10 wt%) of silicon carbide particles via the stir casting method. The effect of SiC particles content on microstructure, mechanical and wear behaviour was investigated. The optical microscope, scanning electron microscopy and EDX analyses were utilized to detect the distribution of hard particles as well as the interface between the alloy and particles. Based on the findings, the homogeneous distribution of particles, refinement of grains in addition to good bonding between AZ91 alloy and particles have been achieved in produced composites. Therefore, the mechanical characteristics and wear performance are improved in composites compared with the unreinforced alloy. Moreover, these results suggest that for applications demanding high mechanical properties and wear resistance the AZ91/SiCp will be effective composites.

Microstructure and Electrical Property of Ex-Situ and In-Situ Copper Titanium Carbide Nanocomposites

In this study, ex-situ Cu-TiC nanocomposites of 1, 3 and 5 vol. % TiC and in-situ Cu-TiH2-C nanocomposites (corresponding to 5 vol. % TiC) were prepared using ball milling and spark plasma sintering methods. Powder mixtures were milled for 4 h at 400 rpm. As-milled Cu-TiC composite powders were consolidated under an applied pressure of 70 MPa. The phase composition, and microstructure of the composite samples were characterized by X-ray diffraction, and scanning electron microscope and transmission electron microscope techniques, respectively. With the increasing TiC content from 1 to 5 vol. %, the hardness of the ex-situ composites when sintered at 600 °C changed between 161.4 and 178.5 HV and the electrical conductivity decreased from 52.1 to 47.6% IACS. In-situ Cu-TiH2-C nanocomposite sintered at 950 °C had higher hardness and electrical conductivity than ex-situ Cu-TiC composite due to having a homogenous distribution of nano reinforcement particles and dense structure.