Volume Fraction Of Hard Particles Research Articles

Rheo-Squeeze Casting of High-Silicon Aluminium Alloy Pipes with Gradient Structures and Their Mechanical Properties

Three different compositions of high-Si Al alloy pipe, with a gradient structure, were produced through semi-solid rheological squeeze casting, the microstructural characteristics of which were investigated. The mechanism of gradient structure formation and the effect of acicular Fe-rich phases on liquid segregation were revealed. Meanwhile, the crystal structures of the Al4FeSi2 and Al15(Fe, Mn)3Si2 phase were elucidated. The relationship between the volume fraction of hard particles in the pipe wall and the macro-hardness was established. Wear resistance tests of the inner surfaces of the pipe walls, and tensile strength tests at different positions around the pipe walls, showed that the δ-Al4FeSi2 phase (acicular Fe-rich phases) reduced the wear resistance and the tensile strength of the alloy. In this study, the gradient distribution of the hard particles caused the outside of the pipe wall to have a higher tensile strength.

Characterization of Al-17wt.%Si Using Centrifugal Casting

Present work is focused on Horizontal centrifugal casting process, by which a wear resistant material with considerable strength can be designed. A material of heterogeneous microstructure designed in which a high volume fraction of hard particles is dispersed at the inner surface, where better wear properties are needed, and a gradually decreasing lower volume fraction of hard particles at the outer surface. By this, a better strength and ductility will be achieved at the desired surfaces. The present work is focused on the preparation of cylinder liners using centrifugal casting for Al-17wt%Si. These cylinder liners are characterized for Microstructure, Hardness, Tensile strength and Wear.

The Compressive Response of Idealized Cermetlike Materials

Metals reinforced with a high volume fraction of hard particles, e.g., cermets, have properties that are more akin to those of granular media than conventional composites. Here, the mechanical properties and deformation mechanisms of this class of materials are investigated through the fabrication and testing of idealized cermets, comprising steel spheres in a Sn/Pb solder matrix. These materials have a similar contrast in the properties of constituent phases compared to commercial cermets; however, the simpler microstructure allows an easier interpretation of their properties. A combination of X-ray tomography and multiaxial strain measurements revealed that deformation at large strains occurs by the development of shear bands similar to granular media, with the material dilating under hydrostatic pressure within these shear bands. Predictions of finite element models with a random arrangement of inclusions were in excellent agreement with the experimental results of idealized cermets. These calculations showed that at large inclusion volume fractions, composites with a random arrangement of inclusions are significantly stronger compared to their periodic counterparts, due to the development of a network of force chains through the percolated particles.

Effect of silicon content on hot working, processing maps, and microstructural evolution of cast TX32–0.4Al magnesium alloy

The effect of silicon (0.2–0.8wt%) addition on the hot working behavior and deformation mechanisms of the Mg–3Sn–2Ca–0.4Al (TX32–0.4Al) alloy has been evaluated by generating processing maps in the temperature and strain rate ranges of 300–500°C and 0.0003–10s−1. The processing map for the base TX32–0.4Al alloy exhibited two dynamic recrystallization (DRX) domains in the ranges (1) 300–360°C and 0.0003–0.001s−1 and (2) 400–500°C and 0.003–0.7s−1. While 0.2% Si addition did not result in any significant change in the processing map of the base TX32–0.4Al alloy, 0.4% Si addition has enhanced hot workability by widening the processing window(s) and by reducing flow instability. The rate controlling mechanism in Domain 1 is identified as climb, whereas it is cross-slip in Domain 2. When the Si content is increased to 0.6 and 0.8%, the volume fraction of hard intermetallic particles has increased nearly two fold. The processing map for the alloy with 0.6% Si addition exhibited an additional Domain 3 at higher temperatures and high strain rates (475–500°C and 0.01–10s−1). However, cracking has occurred in Domain 1 due to void formation at hard particles. In Domains 2 and 3, DRX occurred predominantly by basal slip with climb as a recovery process, as confirmed by the resulting basal texture and tilt type sub-boundary structure. This is attributed to the large back stress generated by the increased volume fraction of intermetallic particles due to which the extensive activation of basal slip required considerably high temperatures. Increase in the volume fraction of hard particles due to higher Si content reduces the flow instability by generating a high rate of entropy production through increasing the nucleation sites for power dissipation and enhances the occurrence of void formation and/or ductile fracture.

A study of compaction of composite particles by multi-particle finite element method

We study the compaction of composite mixture of soft and hard micro-/nano-size particles using multi-particle finite element method. In this method, each particle is fully discretized into finite element mesh. Local non-uniform contact deformation and non-uniformity stress chains transmitted through the composite are well illustrated. In this work, we focus on the effect of inter-particle friction and volume fraction of hard particles on compaction pressure. Results of closed die compaction of 400 two-dimensional monosize spherical particles of zero and 40% volume fraction hard particles are presented. The results show that compaction pressure increases with inter-particle friction and volume fraction of hard particles. The predicted compaction pressure curves are in good agreement with experimental data and other models.

Influence of the Particle Size and Particle Size Ratio on the Morphology and Viscoelastic Properties of Bimodal Hard/Soft Latex Blends

The morphology and viscoelastic properties of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles were investigated as a function of the particle sizes and the particle size ratio (soft particle diameter/hard particle diameter). Minimum film formation temperature (MFT) measurements were associated with transmission electron microscopy (TEM) to emphasize the particle size ratio dependence of the film formation properties. A significant increase of the MFT values with the soft/hard particle size ratio was observed. As long as the particle size ratio was low, TEM micrographs showed that the film forming soft particles, undergoing complete coalescence, clearly act as the continuous phase where the non film forming hard particles are found evenly dispersed while keeping their initial spherical shape. At higher values of the particle size ratio, TEM micrographs pointed out that the soft particles are prevented from coming into contact with each other by the surrounding hard particles, therefore dramatically increasing the MFT of the sample and resulting in a non film forming latex blend. The existence of a critical volume fraction of hard particles that is directly related to the soft/hard particle size ratio was then established on the basis of geometrical arguments involving the percolation theory. The higher the particle size ratio, the lower the critical volume fraction of hard particles that leads to a macroscopic phase inversion resulting in a non film forming bimodal latex blend. Subsequently, the mechanical film properties were investigated by solid-state dynamic mechanical analysis. The size of the dispersed hard phase was found to affect the final viscoelastic film properties. The smaller the size of the hard particles, the better the mechanical enhancement of the mechanical film properties. Last, the experimental viscoelastic thermograms were compared with some theoretical predictions based on self-consistent mechanical modeling. The final film properties of the bimodal hard/soft latex blends were then directly connected to the film formation properties.

Volume fraction of hard particles from small-angle scattering experiments

The paper deals with possibilities for the calculation of the total volume fraction, c, of a single phase of hard, disconnected particles from scattering data. The diversity of particle arrangements is far reaching. Explicit formulas demand special assumptions. One case was selected and analyzed more in detail: Hard particles, the centres of which are described by a pair correlation function g( r). It is proved, for any isotropic arrangement of hard particles, that c can be detected based on the relative scattering intensity I( h) from the small-angle scattering correlation function γ( r) operating with the first derivative in the origin. Let γ 0 ′(0) be the first derivative of the correlation function of the single particles. Then c is given by c=1− γ 0 ′(0)/ γ ′(0). This is explained for a so-called dead leaves model, where γ( r) is known analytically, and for experimental examples.

Adhesive and mechanical properties of soft nanocomposites: Model studies with blended latex films

AbstractWe used a unique approach based on contact mechanics to quantify the adhesive and linear viscoelastic properties of latex films approximately 100 μm thick. The latex films were formed from a mixture of two particle types and form stable films consisting of rigid and compliant regions. We used atomic force microscopy to verify that these regions remained well dispersed on the length scale of the original particle size. The properties of the films were determined by ϕh, the volume fraction of the stiffer component. For ϕh < 0.45, the films were quite adhesive, with viscoelastic properties determined by the compliant matrix material. Adhesive interactions between the film and indenter enabled us to oscillate the indenter in the direction normal to the film surface while maintaining a constant contact area, allowing us to determine the frequency dependence of the dynamic moduli of the films. Stiffer films with higher volume fractions of hard particles were characterized by indentation measurements, from which we were able to determine the time dependence of the relaxation modulus of the latex films. All results were consistent with a power‐law form of the relaxation modulus with an exponent of 0.25. The magnitude of the relaxation modulus increased by a factor of 3000 as the volume fraction of hard particles increased from 0 to 0.89. For low values of ϕh, the composition dependence of the film stiffness was similar to the concentration dependence of the viscosity of spherical particle suspensions. A much weaker concentration dependence was observed for the highest values of ϕh, where the properties of the films were dominated by the stiffer component. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3090–3102, 2001

The role of heterogeneity on the flow and fracture of two-phase materials

The mechanical behavior of two-phase alloys containing a high volume fraction of hard particles is sensitive to effects such as particle clustering and damage. Models for such behavior are necessarily complex. However, recent progress is such that global effects (e.g. the decrease of work hardening capacity due to continuum processes during compressive flow) can be predicted with reasonable accuracy. Parameters involving localized processes such as ductility are more difficult to predict. In this paper we review and extend models for the role of particle clustering and damage (in the form of particle cracking) on deformation. Further understanding of this problem will rely on a combination of critical experiments on materials with well controlled microstructures, and on models which synthesize the results of detailed FEM calculations and large scale continuum mechanics approaches.

Elevated temperature erosion of range of composite layers of Ni–Cr based functionally graded material

AbstractFunctionally graded materials can be used in aggressive environments at elevated temperature because they provide the possibility of minimising wastage of materials. Gradation of the volume fraction of hard particles through the layers means that thermal cycling effects are less severe than for many conventional metal–substrate systems. Because such materials may provide resistance to wear and corrosion (by using a corrosion resistant matrix), it is thought that they may have applications to environments at elevated temperatures, in which materials selection involves a compromise between corrosion resistance and high yield strength. The object of the present study was to investigate the erosion resistance of the various layers of a candidate functionally graded material which consisted of WC particles in a Ni–Cr matrix. The performances of the various composite layers were considered separately in order to establish the variation of erosion rates through the graded structure. The effects of temper...

Creep of amorphous Fe 40Ni 40P 14B 6

The steady-state creep rate, ϵge, of amorphous Fe 40Ni 40P 14B 6 has been measured under stresses, σ, ranging between 0.12 GPa and 1.41 GPa at temperatures between 524 and 646 K (corresponding to 0.80 and 0.99 of the absolute glass transition temperature). The creep rates were found to satisfy the equation ϵ ̇ geασ (2,00 ± 0,15) t a (0,54 ± 0,05) at any particular temperature other than the highest temperature, for finite values of the pre-annealing time t a (the time spent by the specimen at temperature before the application of stress). At the highest temperature of 646 K creep tests were prolonged to study the effect of crystallization on ϵge. The variation of ϵge with volume fraction of crystal was found to be in excellent agreement with Einstein's predictions for the viscosity of a slurry containing a known volume fraction of hard particles.

Yield points and strain aging in hexagonal-based particulate composites

Initial and strain-aging yield points have been observed and studied for three hexagonal-based particulate composites: Cd-30 vol pct B, Mg-25 vol pct B, and Zn-15 vol pct A12O3. The strain-aging yield points begin to appear at 0.5 to 0.6Tm and persist up to the melting temperature. These effects are associated with the large volume fraction of hard particles, which are considered to be a primary source of dislocations and vacancies; strain aging yield points are attributed to the resulting decrease in mobile dislocation density, by annihilation or interaction with imperfections other than impurity atoms, which occurs during aging after straining.