Non-deformable Particles Research Articles

Hot extrusion of SiCp/Al-Cu composites: optimizing mechanical properties through microstructural control

The solid-state processing and utilization of light-metal-based composites align with green policies by reducing the weight of components and employing lower processing temperatures compared to traditional metallurgical methods. This study explores the incorporation of SiC particles at concentrations of 5 and 10 wt.% into an Al4Cu matrix through powder mixing, compaction at 235 MPa, hot extrusion, and sintering at 600 °C in a nitrogen atmosphere. The resulting microstructure, hardness, compressive strength, and flexural strength of the composites were evaluated. During extrusion, the composite underwent plastic deformation, leading to cracking and fragmentation of the SiC particles within the matrix. Therefore, evenly distributed reinforcing particles with a diameter much smaller than the originally introduced ceramic particles were observed. Recrystallization also occurred, with Al2Cu precipitates forming on grain boundaries and nanosized Al2O3 oxides observed in porous areas and at matrix-reinforcement interphase boundaries. The composite containing 5 wt.% SiC exhibited the highest compressive strength of 305 MPa, while the composite with 10 wt.% SiC achieved the highest flexural strength of 889 MPa. However, non-deformable SiC particles crack before reaching maximum strength due to stress concentration at their sharp edges, initiating microcracks in the matrix. Microstructural analysis further revealed that SiC particles tend to crack during hot extrusion, reducing their effectiveness in stress transfer. The hardness remained constant at 78 HV1, irrespective of SiC content. These findings demonstrate that the addition of SiC particles significantly enhances the mechanical properties of Al4Cu composites, making them promising materials for lightweight and high-strength applications.

Second phase strengthening mechanism of 2219 aluminum alloy

Second phase particles have a decisive role in strengthening 2219 aluminum alloy, so it is important to study its strengthening mechanism. The different characteristics of the second phase particles of 2219 aluminum alloy were summarized, and the strengthening mechanism of deformable second phase particles (strain strengthening, chemical strengthening, order strengthening, modulus strengthening) and non-deformable second phase particles was analyzed. The strengthening mechanism model was established, the main application of the two particles was explained, and the guiding significance of the second phase particles on the coarse residual crystal phase breaking and the grain microstructure refinement of aluminum alloy was pointed out.

Flow rate resonance of actively deforming particles

Lymphoid organs are unusual multicellular tissues: they are densely packed, but the lymphocytes trafficking through them are actively moving. We hypothesize that the intriguing ability of lymphocytes to avoid jamming and clogging is in part attributable to the dynamic shape changes that cells undergo when they move. In this work, we test this hypothesis by investigating an idealized system, namely, the flow of self-propelled, oscillating particles passing through a narrow constriction in two dimensions (2D), using numerical simulations. We found that deformation allows particles with these properties to flow through a narrow constriction in conditions when non-deformable particles would not be able to do so. Such a flowing state requires the amplitude and frequency of oscillations to exceed threshold values. Moreover, a resonance leading to the maximum flow rate was found when the oscillation frequency matched the natural frequency of the particle related to its elastic stiffness. To our knowledge, this phenomenon has not been described previously. Our findings could have important implications for understanding and controlling flow in a variety of systems in addition to lymphoid organs, such as granular flows subjected to vibration.

Stratified and gradient films by evaporation-induced stratification of bimodal latexes. Potential of confocal and scanning electron microscopy for compositional depth profiling

In the field of bimodal latex film's formation, finding methods to quantify particle concentration profiles within the film thickness is a challenge. Herein the advantages and limitations of confocal fluorescence microscopy (CFM) and scanning electron microscopy (SEM) are presented. Films are prepared from a bimodal fluorescent acrylic mixture of large non-deformable particles and small deformable particles having high Péclet numbers. A fixed volume fraction of large particles (ΦL) in the dispersion is used with increasing volume fractions of small particles latex (ΦS). At low ΦS, a surface stratification of large particles occurs with thicknesses up to several micrometers, allowing detection by both CFM and SEM. Small particles form a stratified surface layer above a threshold ΦS value. Its thickness of less than 500 nm is evidenced only by SEM due to the resolution limit of the confocal scan. SEM is also able to reveal concentration gradients of large particles below the “small-on-top” stratified layer.

Microstructural evolution of nanodiamond-reinforced aluminum matrix composites during the process of hot extrusion

Nanodiamond (ND) has been recently considered to be an excellent reinforcement for strengthening metal matrix composites. However, most of the previous studies focused on manufacturing process, final structure, and mechanical properties. Systematic exploration of the microstructural evolution, which is critical to understand the effect mechanism of ND particles, still lacks. Herein, we seek to understand the effect of ND particles on microstructural evolution via comparative investigation of microstructures in different test points on extrusion remnant specimens of pure aluminum, 0.5 wt% and 1.0 wt% ND-reinforced aluminum composites prepared by powder metallurgy and hot extrusion. Finite element simulations were used to analyze the relative stress–strain states and deformation modes in different test points. Electron backscatter diffraction and transmission electron microscopy studies reveal that the mean grain size of ND-reinforced aluminum composite declined rapidly after entering the extrusion deformation zone. Microstructures in simple shear, tensile pure shear, and compressive pure shear deformation modes were quite different. The dispersed ND particles effectively promoted grain refinement and improved dislocation driving force with the increase in plastic strain. The large localized high-content ND clusters were broken into small ones, and small ones acted as non-deformable particles to stimulate nucleation and recrystallization under high dislocation driving force. Test results show that the hardness of 0.5 wt% and 1.0 wt% ND-reinforced aluminum composites was 1.9 and 2.1 times that of pure aluminum, respectively. The 0.5 wt% ND-reinforced aluminum composites exhibited optimal comprehensive mechanical properties with a tensile strength of 205 MPa and elongation of 18%, which were 115% and 91% of pure aluminum, respectively.

How Particle Deformability Influences the Surfactant Distribution in Colloidal Polymer Films.

The distribution of surfactants in waterborne colloidal polymer films is of significant interest for scientific understanding and defining surface properties in applications including pressure-sensitive adhesives and coatings. Because of negative effects on appearance, wetting, and adhesion, it is desirable to prevent surfactant accumulation at film surfaces. The effect of particle deformation on surfactant migration during film formation was previously investigated by Gromer et al. through simulations, but experimental investigations are lacking. Here, we study deuterium-labeled sodium dodecyl sulfate surfactant in a poly(butyl acrylate) latex model system. The particle deformability was varied via cross-linking of the intraparticle polymer chains by differing extents. The cross-linker concentration varied from 0 to 35 mol % in the copolymer, leading to a transition from viscoelastic to elastic. Ion beam analysis was used to probe the dry films and provide information on the near-surface depth distribution of surfactant. Films of nondeformable particles, containing the highest concentration of cross-linker, show no surfactant accumulation at the top surface. Films from particles partially deformed by capillary action show a distinct surfactant surface layer (ca. 150 nm thick). Films of coalesced particles, containing little or no cross-linker, show a very small amount of surfactant on the surface (ca. 20 nm thick). The observed results are explained by considering the effect of cross-linking on rubber elasticity and applying the viscous particle deformation model by Gromer et al. to elastically deformed particles. We find that partially deformed particles allow surfactant transport to the surface during film formation, whereas there is far less transport when skin formation acts as a barrier. With elastic particles, the surfactant is carried in the water phase as it falls beneath the surface of packed particles. The ability to exert control over surfactant distribution in waterborne colloidal films will aid in the design of new high-performance adhesives and coatings.

Mathematical modelling of boundary layer flow over a permeable and time-dependent shrinking sheet – A stability analysis

Micropolar fluid is one type of non-Newtonian fluid which consists of non-deformable spherical particles that suspended in viscous medium. In this paper, the problem of two-dimensional boundary layer flow over a permeable shrinking sheet with time dependent velocity in strong concentration micropolar fluid is studied theoretically. The mathematical model is governed by continuity, momentum and microrotation equations. Similarity variables are introduced so that, after performing the similarity transformation on the governing equations, the resulting system of nonlinear ordinary differential equations is then numerically solved using the program bvp4c in Matlab software. The effects of the micropolar material parameter, the unsteadiness parameter, the shrinking parameter and the mass suction parameter to the skin friction coefficient, velocity profiles and microrotation profiles are investigated. It is found that triple solutions exist for some values of the parameters that were considered. Based on the stability analysis that was performed, it showed that only two branches of solutions are categorized as stable, whereas one solution branch is unstable.

Shear lid motion in DEM shear calibration and the effect of particle rearrangement on the internal friction angle

Shear cell tests are now commonly applied in particulate calibration procedures for the discrete element method. Usually, only the shear stresses at the shear plane in the particle bed are examined in short-time instances. This work aimed to find the regularities between the internal friction angle, the vertical position of the shear lid, and the rearrangements of particles in the layers during the shear test with the time instance duration of tens to hundreds of seconds. The Schulze RST Ring Shear Tester was used to compare real experiments to numerical DEM models of non-cohesive materials. The shear tests were investigated for different contact models and DEM input parameters. We also simultaneously monitored the overall specimen stiffness, material dilatancy during calibration, and shear stress. Particle bed stiffness increases with increasing shear modulus and coefficient of static friction for two contact models. The internal friction angle, which is a bulk property of the material determined by a set of particle properties, determines the ability (or resistance) to make displacements of rigid non-deformable particles in the shear testing process. The angle of the resultant of the vector of particle motion in space from the horizontal plane correlates with the angle of internal friction (at each location of the shear cell).

Droplet impact of blood and blood simulants on a solid surface: Effect of the deformability of red blood cells and the elasticity of plasma

The impact of blood droplets onto a solid wall is of great importance for bloodstain pattern analysis in forensic science. Previous studies suggest that the behaviour of impacting blood is similar to that of a Newtonian fluid, which has a shear viscosity equivalent to that of blood at high shear rates. To understand this important fact, we conducted comparative experiments of droplet impact on a glass surface using whole blood and three solutions with a shear viscosity similar to that of blood. Specifically, we used dog’s whole blood (deformable red blood cells dispersed in plasma, WB), plasma with non-deformable resin particles (PwP), glycerol and water with resin particles (GWwP), and a commercial blood simulant (hard particles dispersed in a water-based Newtonian solution, BS). Ranges of Reynolds and Weber numbers in our experiments were 550<Re<1700 and 120<We<860, respectively. Side and bottom views of droplet impact were simultaneously recorded by two high-speed cameras. The spreading radius of the impacting WB droplet in our experiments agreed well with that of Newtonian fluids with viscosity similar to that of WB at high shear rates. Splashing droplets of WB and Newtonian fluids form finger structures (finger-splashing). Although PwP has a viscosity similar to that of WB at high shear rates, an impacting PwP droplet exhibited typical characteristics of impacting suspension droplets, that is, a reduced spreading radius and splashing with ejection of particles. Such significant differences between impacting droplets of PwP and WB indicates that the high deformability of red blood cells in WB plays a crucial role in the Newtonian-like behaviour of blood droplets on impact. The finger-splashing of PwP and GWwP exhibited no significant difference, indicating that the effect of plasma elasticity on finger-splashing is negligible. Importantly, the impacting BS droplet behaved quite differently from WB in both spreading and splashing. Our results imply that the use of deformable particles rather than hard particles in a BS is essential for mimicking blood droplet impact.

How the spleen reshapes and retains young and old red blood cells: A computational investigation.

The spleen, the largest secondary lymphoid organ in humans, not only fulfils a broad range of immune functions, but also plays an important role in red blood cell’s (RBC) life cycle. Although much progress has been made to elucidate the critical biological processes involved in the maturation of young RBCs (reticulocytes) as well as removal of senescent RBCs in the spleen, the underlying mechanisms driving these processes are still obscure. Herein, we perform a computational study to simulate the passage of RBCs through interendothelial slits (IES) in the spleen at different stages of their lifespan and investigate the role of the spleen in facilitating the maturation of reticulocytes and in clearing the senescent RBCs. Our simulations reveal that at the beginning of the RBC life cycle, intracellular non-deformable particles in reticulocytes can be biomechanically expelled from the cell upon passage through IES, an insightful explanation of why this peculiar “pitting” process is spleen-specific. Our results also show that immature RBCs shed surface area by releasing vesicles after crossing IES and progressively acquire the biconcave shape of mature RBCs. These findings likely explain why RBCs from splenectomized patients are significantly larger than those from nonsplenectomized subjects. Finally, we show that at the end of their life span, senescent RBCs are not only retained by IES due to reduced deformability but also become susceptible to mechanical lysis under shear stress. This finding supports the recent hypothesis that transformation into a hemolyzed ghost is a prerequisite for phagocytosis of senescent RBCs. Altogether, our computational investigation illustrates critical biological processes in the spleen that cannot be observed in vivo or in vitro and offer insights into the role of the spleen in the RBC physiology.

Stress relaxations during cyclic loading-unloading in precipitation hardened Mg-4.5Zn

The impact of aging on cyclic loading-unloading responses of extruded Mg-Zn alloys was investigated in compression. In-situ Synchrotron transmission X-ray diffraction and electron backscatter diffraction post-mortem analysis were performed. To aid interpretation additional tests were performed on tensile samples and on samples with lower levels of Zn. The effect of aging is seen to be complex. During initial loading, aging clearly promotes twinning over slip. However, twins in the aged sample are thinner than those in the non-aged material. Upon unloading, additional ‘forward’ twinning occurs in the aged samples and this then is followed by de-twinning. Non-aged samples display de-twinning but no additional forward twinning. With subsequent re-loading, non-aged samples display a re-loading yield effect while the aged samples do not. Aging also leads to a noticeable ratchetting strain. It is proposed that understanding these disparate phenomena requires consideration of the dislocation activity that relaxes the stresses within the highly stressed zones that surround twins and precipitates. Precipitation retards the relaxation of slip events occurring in the highly stressed zone at the twin periphery. At the same time, slip activity in the stressed regions surrounding non-deforming particles is proposed to lead to a creep-type phenomenon that redistributes load and creates the ratchetting effect seen during cyclic loading of aged samples. To model the cyclic response of aged magnesium alloys will require consideration of these complex relaxation effects.

Microstructure characterization and mechanism of fatigue crack propagation of 6082 aluminum alloy joints

In this research the metal inert gas (MIG)welding was applied on 8.6 mm thick 6082-T6 aluminum alloy. It was found that the hardness of the 6082 high-strength aluminum alloy weld center is the lowest, the hardness is 84 HV, and the hardness of the softened zone is 100 HV. In the fatigue crack stability propagation stage, when the crack between the fatigue strips encounters the non-deformable second phase particles, the non-deformable second phase particles continue to propagation forward under the action of dislocations, and the deformable second phase particles have an effect on the crack and the crack does not expand. The crack between the fatigue strips is mainly caused by the tear propagation and propagations in a "Z" shape.

Two-phase flow simulation for distinguishing deformable particles with a LiMCA system

In the metallurgical industry, Liquid Metal Cleanliness Analyser (LiMCA) commercial equipment cannot distinguish between hard particles (e.g., oxides, borides) and deformable particles (e.g., bubbles, molten salts). Therefore, hard particle concentrations can sometimes be grossly overestimated, which reduces the measurement accuracy. However, the method could potentially discriminate between deformable particles and hard particles by evaluating the particle's ability to deform. In this work, the coupled multiphysics problem of a particle deforming within current-carrying aluminium metal passing through the electric sensing zone (ESZ) is simulated using the conservative level-set (CLS) method. An emphasis is placed on understanding the transient deformation history, and the effect of the capillary number, Reynolds number, and confinement ratio on deformation are studied. Furthermore, a computational basis is given to estimate the influence of particle deformation on electrical resistance pulses (ERP). It is found that ERP features of deformation particles, including the peak magnitude and the pulse width, are different from those of hard particles. Based on the results, the effect of a particle's deformation and the feasibility to discriminate it from non-deformable particles in the LiMCA system is evaluated.

Effects of hot extrusion on microstructure and mechanical properties of Mg matrix composite reinforced with deformable TC4 particles

Abstract Mg matrix composites were often reinforced by non-deformable ceramic particles. In this paper, a novel Mg matrix composite reinforced with deformable TC4 (Ti–6Al–4 V) particles was fabricated and then extruded. The evolutions of microstructure and mechanical properties of the composite during hot extrusion were investigated. Hot extrusion refined grains and eliminated the segregation of TC4 particles. TC4 particles, as deformable particles, stimulated the nucleation of dynamic recrystallization during extrusion. However, since the deformation of TC4 particles partly released the stress concentrations around them, the recrystallized grains are just slightly smaller around TC4 particles than that away from them, which is evidently different from the case in Mg matrix composites reinforced by non-deformable ceramic particles. Compared with AZ91 matrix composites reinforced by SiC particles, the present composite possesses the superior comprehensive mechanical properties, which are attributed to not only the strong interfacial bonds between TC4p and matrix but also the deformability of TC4 particles.

Spontaneous shrinking of soft nanoparticles boosts their diffusion in confined media

Improving nanoparticles (NPs) transport across biological barriers is a significant challenge that could be addressed through understanding NPs diffusion in dense and confined media. Here, we report the ability of soft NPs to shrink in confined environments, therefore boosting their diffusion compared to hard, non-deformable particles. We demonstrate this behavior by embedding microgel NPs in agarose gels. The origin of the shrinking appears to be related to the overlap of the electrostatic double layers (EDL) surrounding the NPs and the agarose fibres. Indeed, it is shown that screening the EDL interactions, by increasing the ionic strength of the medium, prevents the soft particle shrinkage. The shrunken NPs diffuse up to 2 orders of magnitude faster in agarose gel than their hard NP counterparts. These findings provide valuable insights on the role of long range interactions on soft NPs dynamics in crowded environments, and help rationalize the design of more efficient NP-based transport systems.

Unique defect evolution during the plastic deformation of a metal matrix composite

During the plastic deformation of a metal matrix composite (MMC) containing non-deformable particles, high dislocation density and strong back stresses are expected because the particles help with blocking and accumulating dislocations. Here we report that the MMC has lower, instead of higher, dislocation density than the corresponding monolithic matrix material when they are deformed to high plastic strains, because smaller sub-grains in the MMC lowered dislocation generation rate and meanwhile promoted the dislocation interaction and annihilation in the matrix. This unique defect density evolution is a hitherto unknown but important factor affecting the mechanical properties of MMCs.

Mechanical and Microstructural Characterization of AF955 (UNS N09955) Nickel-Based Superalloy After Different Heat Treatments

The mechanical and strain-hardening behaviors of the new AF955 nickel-based superalloy were investigated through two different heat treatments. The first consisted of a solubilization with a subsequent precipitation heat treatment at 746 °C for 4 hours, while the second included an additional precipitation treatment at 621 °C for 8 hours, which further increased the AF955 yield stress by about 15 pct and the ultimate stress by about 9 pct. However, through analyzing the true stress and true strain flow curves, the Considere’s stresses of AF955 after the heat treatments were similar and the strain-hardening behaviors at high stresses were surprisingly comparable. The AF955 microstructures were observed after the two different heat treatments through transmission electron microscopy. The dimensions and volume fractions of the strengthening γ″ and γ′ particles were quantified through the imaging analysis technique, finding that there were only γ″ particles in AF955 with heat treatment at 746 °C, while with the additional heat treatment at 621 °C, there was a higher total volume fraction of the γ″ + γ′ phases. The microstructure quantification allowed modeling of the different yield behaviors of the alloy after the heat treatments through the Orowan model for nondeformable particles and the weak coupled dislocation (WCD) and strong coupled dislocation models for deformable particles. The WCD model for deformable particles described the yield behaviors of AF955 very well after both heat treatments. Moreover, the deformability of the γ″ and γ′ particles also explained the comparable strain-hardening behaviors at high stresses of AF955 after the two different heat treatments. Although mechanical properties are correctly assumed to be key parameters for classifying materials, the analysis of true stress and true strain flow curves always should be performed to properly rationalize the mechanical behaviors of metallic alloys.

Evaluation of Particle Resuspension and Single-layer Rates with Exposure Time and Friction Velocity for Multilayer Deposits in a Turbulent Boundary Layer

The present work deals with the resuspension of small nondeformable particles from multilayer deposits in a turbulent boundary layer. A kinetic force-balance approach was adopted to model particle motion at the point of detachment, whereby intermolecular interactions were modeled by the Lennard-Jones potential. The rate of change of the number of particles was estimated for each discrete layer based on existing kinetic models. In particular, the kinetic equations of Lazaridis and Drossinos (1998), LD, and Friess and Yadigaroglu (2001), FY, were implemented and compared using lattice arranged deposits. The influence of exposure time and friction velocity was investigated through the obtained resuspension rates. It was found that the single-layer resuspension rates were substantially affected by the layer position within the deposit as well as considerably influenced by both the exposure time and the friction velocity. Moreover, the numerical results demonstrate that the LD kinetic estimates higher resuspension rates compared to the FY kinetic only for short exposures to the flow, predominantly due to a different expression for the fraction of exposed particles. In addition, the present study recognized the time dependence (i.e., a short-term vs. long-term regime) of the resuspension rate observed both experimentally (Wu et al., 1992; Wang et al., 2012) and by model predictions (Lazaridis and Drossinos, 1998; Friess and Yadigaroglu, 2001; Reeks and Hall, 2001) and confirmed the inverse dependence of the resuspension rate with time in long-term regime. Two regimes were also identified while evaluating the resuspension rate for a range of friction velocities, viz., a low-friction regime in which the resuspension rate increases with friction and a high-friction regime in which the opposite behaviour was observed.

Mathematical model and software for investigation of internal ballistic processes in high-speed projectile installations

This paper describes a software package that allows to explore the interior ballistics processes occurring in a shot scheme with bulk charges using propellant pasty substances at various loading schemes, etc. As a mathematical model, a model of a polydisperse mixture of non-deformable particles and a carrier gas phase is used in the quasi-one-dimensional approximation. Writing the equations of the mathematical model allows to use it to describe a broad class of interior ballistics processes. Features of the using approach are illustrated by calculating the ignition period for the charge of tubular propellant.

The Effect of Submicron Second-Phase Particles on the Rate of Grain Refinement in a Copper-Oxygen Alloy During Cold Spray

The effect of non-deformable submicron second-phase particles (d = 200-500 nm) on microstructural refinement during cold spray was examined. Using single particle impact testing, two types of splats were fabricated using two different feedstocks: a Cu-0.21wt.%O powder containing Cu2O second-phase particles and a single-phase Cu. Microstructural evolution analysis using high-resolution electron backscatter diffraction shows grain refinement occurred at a higher rate in the Cu-0.21wt.%O powder. That was due to dynamic recrystallization initiated by particle-stimulated nucleation (PSN). High-strain-rate deformation of cold spray was found to be the key to activate PSN. The present study suggests cold spray is a possible technique to fabricate ultrafine-grained materials by using feedstock containing second-phase particles.