Distribution Of Second Phase Particles Research Articles

The Recrystallization Behavior of AZ31 and WE43

The deformation and recrystallization behavior of two magnesium alloys, AZ31 and WE43, have been investigated. The cast alloys were heat treated to produce various distributions of second phase particles and deformed in a channel die at a strain rate of 10-4 s-1 at temperatures between 523 and 673 K. The alloys were subsequently annealed at temperatures between 708 and 798 K.The AZ31 and WE43 were extruded at 555 and 633 K, respectively. The microstructures were compared to those developed during channel die deformation. The tensile and compressive strengths and the texture of the alloys were determined in the as-extruded and recrystallised conditions.Optical microscopy and electron backscattered diffraction (EBSD) were used to characterize the microstructures of the alloys. The EBSD technique was used to determine the texture of the deformed and annealed samples.

Particle-Stimulated Nucleation of Dynamic Recrystallization in AZ31 Alloy at Elevated Temperatures

Particle-stimulated nucleation (PSN) was investigated in magnesium alloy AZ31 to study the effect of the evolution of second-phases during extrusion and other metal forming processes. Compression tests were carried out on samples taken from coarse-grained as-cast magnesium alloy billets containing a lamellar Mg17All2 eutectic phase and (Al, Mn) particles. These revealed that particle-stimulated DRX nucleation (PSN) was taking place during hot deformation and that this is facilitated by the fragmentation of the Mg17All2. When Mg17All2 dissolves into the matrix at about 350°C, the (Al, Mn) particles remain effective in producing PSN at temperatures up to at least 400°C. This suggests that alloy design leading to a suitable distribution of second-phase particles can improve the properties and formability of wrought magnesium alloys.

Application of the Evolution Strategy for Assessment of Deformation and Fracture Response of Ferritic Steel During Its Manufacturing

ABSTRACT In this article, the developed numerical techniques for assessment of deformation and fracture response of ferritic steel during its manufacturing are considered. Because microdefects of ferritic steel are thought to nucleate at second-phase particles, the formulated strategy for evaluating these particles uses standardized experimental fracture tests with micromechanical FEM simulations of microdefect evolution in the material. The evolution of the microdefects is described by an enhanced Gurson-type model incorporating effects of the microvoid aspect ratio. An estimate of the objective function for material parameters of the Gurson-type model is provided by the Kalman filtering technique. Their best fit set of the material parameters is established by the search scheme of the evolution strategy according to the density, size, and spatial distribution of second-phase particles in the material. Some examples are presented to demonstrate that the evolution strategy can be used to optimize important processes of steel manufacturing in the context of strength and toughness of critical parts.

Effects of friction stir processing on mechanical properties of the cast aluminum alloys A319 and A356

Abstract Surfaces of A319 and A356 castings were treated by friction stir processing to reduce porosity and to create more uniform distributions of second-phase particles. Dendritic microstructures were eliminated in stir zones. The ultimate tensile strengths, ductilities, and fatigue lives of both alloys were increased by the friction stir processing.

Tensile properties of Pb-Sn bearing alloy containing small amount of Sb

In this study, tensile tests of Pb–9.5Sn–0.5wt%Sb bearing alloy were investigated with respect to the effect of testing temperatures ranging from 393 to 473 K and strain rates ranging from 9.1 × 10–4 to 2 × 10–2 s–1. The tensile tests revealed that the solder alloy exhibits high ductility at 433 K and 5 × 10–3 s–1. Strain rate sensitivity parameter m and activation energy were determined to clarify the deformation mechanism. The effects of Sb-addition on the tensile properties of Pb–9.5Sn–0.5wt%Sb solder alloy were studied by comparing the tensile deformation behaviour of the two solders Pb–10wt%Sn and Pb–10Sn–1.5wt%Zn. Microstructural analysis confirmed that the mechanism controlling the tensile behaviour is a grain boundary sliding (GBS). This study revealed that the Pb–9.5Sn–0.5wt%Sb alloy shows a good combination of high strength and greater ductility by grain refinement. Also, the difference in the morphology and distribution of second phase particles caused by the Sb-addition resulted in better tensile properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An evaluation of global thresholding techniques for the automatic image segmentation of automotive aluminum sheet alloys

Digital image analysis is a valuable tool for the quantification of microstructural morphology, such as the size and clustering distributions of second-phase particles. However, the first step to such analysis is the segmentation of digital micrographs to identify the features of interest. Since the outcome of this step will have a significant influence on all subsequent processing, accurate segmentation is of the utmost importance. Grayscale images of the microstructures of three automotive aluminum alloys are used (AA5182, AA5754, and AA6111) to compare the abilities of several automatic global image thresholding techniques. The minimum cross-entropy method of Li and Lee [Pattern Recognit. 30 (1993) 617] was found to work well for all alloys when combined with the cost function of Yen et al. [IEEE T. Image Process. 4 (1995) 370].

Size and distribution of particles and voids pre-existing in equal channel angular pressed 5083 Al alloy: their effect on cavitation during low-temperature superplastic deformation

Abstract An ultrafine grained 5083 Al alloy was prepared by equal channel angular pressing with route Bc and an effective strain of ∼4 or ∼8. The changes of the size and distribution of second phase particles and voids pre-existing in the alloy during equal channel angular pressing (ECAP) were examined in detail. Under the present ECAP conditions, a portion of particles of 1.5–3.5 μm substantially increased. However, the further break-up of particles with these sizes became less significant and they were to be distributed more uniformly throughout the sample with increasing the ECAP pass from 4 to 8. In addition, these particles were likely to act as the preferential cavity nucleation sites during low-temperature superplastic deformation of the alloy. The population of voids with the size of 0.5–1.5 μm remarkably increased after ECAP. An analysis revealed that these voids were difficult to be sintered out at low-temperature superplastic deformation temperatures prior to deformation and might grow to larger size cavities. From the present results and analysis, it is suggested that the number of the ECAP pass less than that resulting the largest elongation may be preferable in the viewpoint of cavitation damage and commercial application of low-temperature superplasticity of ultrafine grained Al alloys, if moderate superplastic elongation is ensured.

Vapor pressure and void size effects on failure of a constrained ductile film

To achieve certain properties, semiconductor adhesives and molding compounds are made by blending filler particles with polymer matrix. Moisture collects at filler particle/polymer matrix interfaces and within voids of the composite. At reflow temperatures, the moisture vaporizes. The rapidly expanding vapor creates high internal pressure on pre-existing voids and particle/matrix interfaces. The simultaneous action of thermal stresses and internal vapor pressure drives both pre-existing and newly nucleated voids to grow and coalesce causing material failure. Particularly susceptible are polymeric films and adhesives joining elastic substrates, e.g. Ag filled epoxy. Several competing failure mechanisms are studied including: near-tip void growth and coalescence with the crack; extensive void growth and formation of an extended damaged zone emanating from the crack; and rapid void growth at highly stressed sites at large distances ahead of the crack, leading to multiple damaged zones. This competition is driven by the interplay between stress elevation induced by constrained plastic flow and stress relaxation due to vapor pressure assisted void growth. A model problem of a ductile film bonded between two elastic substrates, with a centerline crack, is studied. The computational study employs a Gurson porous material model incorporating vapor pressure effects. The formation of multiple damaged zones is favored when the film contains small voids or dilute second-phase particle distribution. The presence of large voids or high vapor pressure favor the growth of a self-similar damage zone emanating from the crack. High vapor pressure accelerates film cracking that can cause device failures.

Microstructure and tensile properties of Sn–9Zn– xAg lead-free solder alloys

Microstructural features and tensile properties of Sn–Zn eutectic alloys with varying Ag content were examined in this study. Results indicate that the main effects of Ag addition were reduced strength and greater ductility due to the differences in the morphology and distribution of second phase particles. Also, a modified structure caused by rapid solidification resulted in better tensile properties.

Adsorption of BTSE and γ-APS organosilanes on different microstructural regions of 2024-T3 aluminum alloy

The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and γ-aminopropyltriethoxysilane (γ-APS) has been studied on 2024-T3 aluminum alloy samples using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The thickness and coverage of the BTSE film formed on a mechanically polished sample was found to be strongly affected by the distribution of second-phase particles on the alloy surface. Specifically, although the adsorption occurs on the alloy matrix away from the particles, and on the particles themselves, the regions immediately surrounding the particles had less BTSE. The amounts of this adsorption on an air-oxidized sample is increased on average, although the coating is non-uniform with regions (∼100 μm) of higher and lower coverages. There appears to be a competition between the silane deposition and etching of the underlying oxide film for the initially oxidized sample. The adsorption of γ-APS is different with films of relatively even thickness formed over large areas of the polished sample; hydrogen bonding through the amino groups probably helps the distribution in this case.

Novel Recycling System of Aluminum and Iron Wastes-<I>in-situ</I> Al-Al<SUB>3</SUB>Fe Functionally Graded Material Manufactured by a Centrifugal Method-

In this study, the concept of novel recycling system using waste Al and Fe is described. Taking advantage of the fact that due to its cyclic usage, aluminum scrap unavoidably contains iron and steel wastes, an in-situ Al-Al3Fe functionally graded material (FGM) is planned to be fabricated. A centrifugal method is applied to a model master alloy, Al-10 mass% Fe, obtained from virgin materials, the content of which is decided from the liquidus temperature. The resulting product is a thick-walled tube having a graded distribution of second phase particles in the Al matrix. It has been established that the shape of the particles varies depending on their position along the radial direction. The second phase is confirmed to be a stable Al3Fe intermetallic compound. Thin plates of Al-Al3Fe having homogeneously distributed Al3Fe particles, considering both the composition gradient and the particle morphology, were machined from the thick-walled Al-Al3Fe FGM tube and their mechanical properties measured. Based on the experimental observations, the potential and the advantages of the Al-Al3Fe alloy as a recyclable eco-FGM are discussed.

Deconvolution of morphological texture from crystallographic texture data

The physical properties of composite materials reinforced with fibres usually depend significantly on the orientation distribution of these fibres. The goal of this study is to develop a technique to measure the orientation distribution of second-phase particles which in themselves have a strong crystallographic texture. This permits the well known methods of pole-figure measurements to be used and the deconvolution of the `morphological texture function' from these data. In the current paper, the deconvolution procedure is presented and validated by simulations. Finally, the procedure is applied to an experimental system, which further confirms the validity of the approach. The simulations convoluted a morphological texture function with a crystallographic texture using a discrete representation of the orientation distribution function (ODF). After the convolution, the resulting ODF was converted to a series-expansion representation, which then permitted the deconvolution by an independent method. The results of the deconvolution return the original MTF, hence validating the procedure derived. The experimental system measured the crystallographic texture of 316L stainless-steel yarns woven into a fabric. The crystallographic texture obtained from straight yarns was used as the reference texture. The X-ray diffraction measurements reveal the weave pattern but with some ghosting errors. These are attributed to an insufficient measurement volume, which could be overcome by using radiation with a greater penetration, such as neutrons.

Computational Characterization of Micro- to Macroscopic Mechanical Behavior and Damage of Polymers Containing Second-Phase Particles

To clarify the mechanical characteristics and damage of polymers containingsecond-phase particles, i.e., blended polymers, a homogenization method has been developed which can handle the large deformation problems, including onset and propagation of instability, and completely reproduce the periodic feature of the distribution of second-phase particles under any macroscopically homogeneous loading condition. The parametric study has clarified the characteristic features of polymers containingperiodically distributed soft cylindrical particles of different volume fractions and sizes subjected to macroscopically homogeneous stress in different directions. The results indicate that, dependingon the tensional direction with respect to the unit cell, different types of shear bands are observed, and that the shear band connectingthe particles that appeared in the early stages of deformation is responsible for the reduction of the macroscopic yield stress. Increasingthe volume fraction of particles causes a decrease of the macroscopic yield stress and of the directional dependence of the macroscopic stress–strain relation. The size difference of particles causes very complicated and different types of shear bands, however, due to the high stress concentration caused by the presence of small particles, the onset and propagation of shear bands are promoted, and the macroscopic deformation behaviors become essentially isotropic. The maximum mean stress appears in the small particle, which suggests that the blending of particles of different sizes promotes the onset of cavitation, which suppresses the maximum mean stress in the matrix and results in additional shear deformation and in preventing onset of damage in matrix caused by crazing. The location of maximum normal stress on the boundary surface between particles and matrix moves with the propagation of the shear band. The magnitude of maximum normal stress increases with the increase of the size difference between the particles and with the decrease of the volume fraction within the present simulation.

Processing and microstructure of single grain, uranium-doped Y–Ba–Cu–O superconductor

Large grain Y–Ba–Cu–O (YBCO) superconductor doped with various amounts of depleted UO2 and containing excess Y2BaCuO5 (Y-211) and Y2O3 have been fabricated by top seeded melt growth (TSMG). The effect of depleted UO2 on the large grain microstructure has been studied systematically in samples with and without added Pt. It is found that UO2 refines the size of the second phase particles in the superconducting YBa2Cu3O7−δ (Y-123) matrix to dimensions of a few hundred nanometres with an approximately spherical morphology. Addition of Y2O3 to the uranium-doped precursor powder, rather than Y-211, yields a significantly finer distribution of second phase particles and an associated higher critical current density Jc at increased magnetic field.

Effect of particle distribution on deformation and damage of two-phase alloys

The effect of an inhomogeneous distribution of second phase particles on strength and damage has been studied here using a model system based on rapidly solidified Al–Cu alloys which result in Al–CuAl 2 composites, Materials with both a homogeneous and bimodal distribution of the CuAl 2 particles have been produced. When tested in compression (i.e. little or no damage) the clustered materials are significantly stronger than homogeneous alloys containing the same overall CuAl 2 volume fraction. These results are consistent with a previously published self-consistent model.

Mecanismos de desgaste en materiales compuestos de matriz acero rápido fabricados por técnicas pulvimetalúrgicas

The development of metal matrix composites has a major interest for automotive and cutting tools industries since they possess better mechanical properties and wear resistance than corresponding base materials. One of the manufacturing methods for these materials includes processing by powder metallurgy techniques. In this case, blending of both, base material and reinforcement powders constitute the most important process in order to achieve a homogeneous distribution of second phase particles. In the present work, composite materials of M3/2 tool steel reinforced with 2.5, 5, and 8 vol% of niobium carbide have been prepared. In order to ensure a homogeneous mix, powders of both materials were mixed by dry high-energy mechanical milling at 200 r.p.m. for 40 h.. After a recovering annealing, two routes for consolidate were followed: (1) die pressing and vacuum sintering, and (2) hot isostatic pressing (HIP). Pin-on-disc tests were carried out to evaluate wear behaviour in all the materials. Results show that ceramic particles additions improve wear resistance of base material.

Multi-scale characterization of spatially heterogeneous systems: implications for discontinuously reinforced metal–matrix composite microstructures

A new multi-scale technique is presented for characterizing the spatial distribution of second-phase particles in two-dimensional distributed multi-phase systems. The implications for the characterization of reinforcement distributions in discontinuously reinforced metallic matrix composite microstructures are discussed, along with results of the analysis both for simulated and experimental discontinuously reinforced aluminum (DRA) materials. A systematic variation in the degree of spatial heterogeneity is observed with increasing length scale. This result leads to the definition of the parameter L H or homogeneous length scale. The relevance of L H measured for a real DRA microstructure is then discussed in the context of statistical variations in mechanical properties such as tensile strength, ductility, and fracture toughness.

Random dispersion model of two-dimensional size distribution of second-phase particles

A simulation model of the discrete two-dimensional size distribution (2-DSD) has been proposed based on a probability density function (PDF) of the three-dimensional size distribution (3-DSD) for spherical particles which are randomly dispersed in space. The mono-dispersed system, as well as the exponential, the Rayleigh, the log-normal, and the pseudo-normal distributions are chosen as the PDF of the 3-DSD. The proposed 2-DSD model is applied to the estimation of the mean value and volume fraction of particles with a hypothetical microscopic analysis. The estimated values of the mean value and the area fraction are assessed as a function of the area of the limited field of view and the measured number of sections.

Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al 3 Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al 3 Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al 3 Zr particles and found to be rod shaped and identified to be cubic ordered L 1 2 phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al 3 Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al 3 Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.

Study of the Damage of AA 8006 Twin-Roll Cast Thin Sheets during Forming of Heat Exchanger Fins

A study of typical cracks which occur during forming operations of heat exchanger fins from strip-cast Al-Fe-Mn-Si (AA 8006) alloy sheets is presented. A number of failed heat exchanger lamellae, 0.10 to 0.25 mm thick, were examined by light and electron microscopy. Formability of the material correlates rather well with the grain structure and the distribution of second phase particles in the matrix. Sheets having good formability usually contain coarser intermetallic particles when compared with sheets torn during deep drawing operations. It was found that failure was due to surface grain size inhomogeneity in many cases, therefore a uniform grain structure is also favorable for improved formability.