Effect Of Second Phase Particles Research Articles

Wear behavior of self-lubricating Fe-Cr-C-Mn-Cu alloys: Smearing effect of second phase particles

Newly developed self-lubricating Fe-Cr-C-Mn-Cu cast composite alloys were investigated to study the role of Cu-rich second phase particles which smear on the wear surface during sliding. The wear resistance of the material was improved with an increasing copper concentration. The improved wear resistance was probably obtained by forming a protective tribofilm, which prevented metal-to-metal contact through smearing of the embedded Cu-rich second phase particles. This formation of protective oxide films during sliding is likely to improve the wear resistance of austenitic Fe-Cr-C-Mn-Cu cast composite alloys.

Pinning Effects on Grain Growth of Ferrite in an Fe–C–B Alloy

The pinning effects of second phase particles on the grain growth of ferrite were studied in an Fe–0.1C alloy containing 5 ppm boron (B). The number and size distribution of Fe3(CB) particles were measured at grain faces, edges and corners by serial sectioning. The particle size was determined from the number of consecutive sections on which the particle was observed. The proportion of particles at each grain boundary site was significantly greater than that of random distribution. The modified Zener theory which assumes that all grain boundaries are pinned by particles could explain the grain size very well, whereas the theory which considers that the pinning of grain boundary corners plays a major role gave a smaller grain size than experiment. Nishizawa et al.'s correlation model accounted well for the number of pinning particles on grain boundaries as well as the grain size. The Hunderi–Ryum's model which takes into accounts pinning of all grain boundary sites gave results close to experiment when a larger proportion of pinning particles at boundary sites than random distribution was incorporated.

A 3D Monte Carlo study of the effect of grain boundary anisotropy and particles on the size distribution of grains after recrystallisation and grain growth

The present paper considers 3D grain size distributions and how they evolve during and after recrystallisation and grain growth as investigated by a 3D Potts Monte Carlo (MC) model. Two particular cases have been studied: (i) the effects of anisotropy in grain boundary energy and boundary mobility on grain size distributions after recrystallisation and (ii) the effects of second phase particles on the size distributions after both recrystallisation and grain growth. The present 3D MC simulations have shown that anisotropy has a strong effect on the size distributions of grains after recrystallisation, however, mainly in terms of a large and increasing fraction of small grains with increasing anisotropy. After “correcting” for the unrealistic large number of small grains, the differences between the different cases become quite small, but based on an evaluation of the skewness in these “corrected” grain size distributions, a small shift from a normal towards a log-normal-like distribution is still indicated. Concerning the effect of particles, simulations have shown that for an increasing volume fraction of particles, the coarsened microstructures show a clear shift from a Gaussian like towards a log-normal-like distribution. This behaviour is observed both for grain growth alone and for recrystallisation and subsequent coarsening.

A micromechanics based damage model for composite materials

The predictive capacity of ductile fracture models when applied to composite and multiphase materials is related to the accuracy of the estimated stress/strain level in the second phases or reinforcements, which defines the condition for damage nucleation. Second phase particles contribute to the overall hardening of the composite before void nucleation, as well as to its softening after their fracture or decohesion. If the volume fraction of reinforcement is larger than a couple of percents, this softening can significantly affect the resistance to plastic localization and cannot be neglected. In order to explicitly account for the effect of second phase particles on the ductile fracture process, this study integrates a damage model based on the Gologanu–Leblond–Devaux constitutive behavior with a mean-field homogenization scheme. Even though the model is more general, the present study focuses on elastic particles dispersed in an elasto-plastic matrix. After assessing the mean-field homogenization scheme through comparison with two-dimensional axisymmetric finite element calculations, an extensive parametric study is performed using the integrated homogenization-damage model. The predictions of the integrated homogenization-damage model are also compared with experimental results on cast aluminum alloys, in terms of both the fracture strain and overall stress–strain curves. The study demonstrates the complex couplings among the load transfer to second phase particles, their resistance to fracture, the void nucleation mode, and the overall ductility.

Effect of particles on microstructural evolution during cold rolling of the aluminum alloy AA3104

The effect of second-phase particles on the evolution of the deformation microstructure during cold rolling of the particle-containing aluminum alloy AA3104 has been investigated using electron channeling contrast imaging and electron backscattered diffraction (EBSD). The results show that the influence of second-phase particles on the deformation microstructure depends on the particle size. Fine dispersoids present in the microstructure have no clear effect on the grain orientation dependence of the dislocation structures formed in the strain range examined. However, large scale structural heterogeneities, in the form of deformation zones, are formed near coarse constituent particles, leading to significant local distortions of the deformed microstructure. Analysis of EBSD data shows that significant orientation gradients are found in the vicinity of the coarse particles. Within the deformation zones the largest lattice rotations occur at the tips of plate-shaped constituent particles. A symmetrical pattern of TD-rotations of alternating sign is found in the deformation zones, with the magnitude of the lattice rotations increasing with increasing strain.

Influence of Second Phase Particle on Fatigue Crack Growth Behavior in Ferrite Matrix Steels

Fatigue crack growth tests of two ferrite-pearlite and two ferrite-bainite steels with different size and spacing of particle, where pearlite/bainite (hard) particles were uniformly distributed in the ferrite matrix, were carried out to investigate effect of second phase particle on fatigue crack growth behavior in Paris regime. The fatigue crack growth curves for the four materials did not coincide each other, even when the crack growth curves were arranged by the effective stress intensity factor range. From the in-situ observations, crack tip stress shielding phenomena, such as interlocking, branching, etc were found on the crack wake, which enhanced fatigue crack growth resistance. Small size and spacing of pearlite/bainite particle seemed to induce small but frequent crack deflections, which resulted in crack closure phenomena. On the other hand, large size of pearlite/bainite particle seemed to induce stress shielding phenomena and then contribute to high crack growth resistance, which was the main reason for lower fatigue crack growth rate of the large size and spacing of hard particle compared the small size of hard particle.

Numerical Modeling of Second-Phase Particle Effects on Localized Deformation

A new finite element analysis based on rate dependent crystal plasticity theory has been developed to investigate the effects of second-phase particles on the initiation and propagation of localized deformation in the form of shear bands. The new model can incorporate electron backscatter diffraction data into finite element analyses. The numerical analysis not only accounts for crystallographic texture (and its evolution) but also accounts for grain morphologies. A unit-cell approach has been adopted where an element or a number of elements of the finite element mesh are considered to represent a single crystal within the polycrystal aggregate. Second-phase particles in the form of finite elements with stiff elastic properties are randomly distributed within the unit cell. Numerical simulations of unixial tension, in-plane plane strain tension, and balanced biaxial tension have been performed by models with and without second-phase particles for a direct chill-cast AA5754 aluminum alloy sheet. The effects of various parameters, such as second-phase particle distribution, texture evolution, and strain paths on particle induced localized deformation patterns, are also investigated.

Effect of Second Phase Particles on Phase Stability of Zirconia in Hot Water

The effect of second phase particles on tetragonal to monoclinic (t-m) phase transformation of zirconia is examined, which causes the degradation of zirconia in vivo. Silica is selected as the second phase particles and dispersed 0.1 to 10mol% into 3mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP). As the result, phase transformation is promoted in all the samples examined in comparison with 3Y-TZP. Non-dispersed specimen exhibits better phase stability than that in silica doped one. Since the thermal expansion coefficient is smaller in order of silica and zirconia, the residual stresses induced during cooling from the sintering temperature must be the dominant factor to determine the phase stability in these materials.

Phase-Field Modeling of Recrystallization - Effects of Second-Phase Particles on the Recrystallization Kinetics

The effects of second-phase particles on the recrystallization kinetics in two-dimensional polycrystalline structures were investigated. Numerical simulations of recrystallization were performed by coupling the unified subgrain growth theory with a phase-field methodology. Simple assumptions based on experimental observations were utilized for preparing initial microstructures. The following results were obtained: (1) The presence of second-phase particles retarded recrystallization speeds. (2) If the mean subgrain size was small enough recrystallized region covered whole system for various values of the particle fraction, f. (3) On the other hand, if the mean subgrain size was not small enough the progress of recrystallization was frozen at some point.

Effect of Second-Phase Particles on Grain Refinement of Mg-Al-Zn Alloy during ECAE

The effect of second-phase particles on the grain refinement of AZ61 and AZ91 Mg-Al-Zn alloys with different volume fractions of β-Mg17Al12 phase particles during equal channel angular extrusion (ECAE) has been investigated. The microstructure were observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed that grain refinement was enhanced by second phase particles at initial stage of ECAE. And finer grains with the high angle grain boundaries (HAGBs) and disperse second-phase particles could be obtained in AZ61 and AZ91 after 8 passes of ECAE.

Effect of second-phase particles on shape memory in Fe–Mn–Si-based alloys

The shape memory behaviour of two Fe–Mn–Si-based alloys has been investigated. One alloy was a reference alloy, and the other alloy was similar in composition except that it contained 0.55 wt% Ti. Following solution treatment and quenching, strip samples were subjected to three types of treatments; isothermal holding, cold rolling followed by isothermal holding, and hot rolling followed by isothermal holding. These treatments resulted in the formation of intermetallic precipitates in the Ti-containing alloy, while the reference alloy remained precipitate-free. In comparing the shape memory of the reference and the particle-containing alloy after identical heat treatments, it was found that the formation of precipitates had a beneficial effect on the shape memory in all cases. In general, the larger precipitates caused a larger increase in the shape memory. The effect of particle size on shape memory has been analysed using the current data and published results for a range of precipitate types.

Effect of Second Phase Particles on Ultra-Fine Grain Evolution during Multi-Directional Forging of Austenitic Stainless Steel

Effect of Second Phase Particles on Ultra-Fine Grain Evolution during Multi-Directional Forging of Austenitic Stainless Steel

Discussion on the Rate Controlling Process of Coarsening of Niobium Carbonitrides in a Niobium Microalloyed Steel

Austenite grain growth in microalloyed steels is governed by the coarsening of fine precipitates present at grain boundaries below the grain coarsening temperature. Zener model is widely used in metals to describe the pinning effect of second phase particles precipitated in the matrix. In this work it has been discussed whether grain boundary or volume diffusion is the rate controlling process for the coarsening of the niobium carbonitrides. Calculations on austenite grain growth kinetics, obtained coupling Zener theory and both rate controlling processes of precipitate coarsening, have been compared against experimental austenite grain size results under nonisothermal heating conditions. In this sense, it has been concluded that the coarsening of niobium carbonitrides is mainly controlled by volume diffusion of Nb in austenite.

Grain Boundary Character and Pinning Effect during Grain Growth of Two-Phase Alloys

Monte Carlo technique was extensively used to simulate various recrystallization stages. In this study, the effect of second phase particles is studied in presence of varied populations of low and high angle grain boundaries. Results show that a significant pinning effect can be responsible for an abnormal growth when varying the population of low angle grain boundaries.

Optimizing homogenization parameters for better stretch formability in an Al–Mn–Mg alloy sheet

The present study examines the effect of homogenization of roll-cast material on the formability and microstructure of Al–Mn–Mg alloy sheets under uniaxial and biaxial deformation modes. The effect of various process variables investigated and an optimized homogenization cycle for improving the stretch formability are presented. The stretch formability of sheets have been characterized in terms of limit strains in forming limit diagrams (FLDs). The phenomenon of recrystallization and the effect of second phase particles have been investigated in cold rolled sheets and the limiting grain sizes at different annealing temperature calculated on the basis of the Zener limit equation. It appears that surface roughening which is in turn a result of grain coarsening is an important formability parameter in the homogenized materials annealed at high temperatures.

Development of Creep Resistant Mg Alloys

A study has been made on the tensile and creep properties of squeeze and die cast Mg alloys, with emphasis on the effect of second phase particles. Two different microstructures were compared; the microstructure with thermally unstable particles along grain boundaries (AZ91 alloy) and the microstructure with thermally stable particles along grain boundaries as well as within matrix (MX alloy). The experimental MX alloy has equivalent room temperature tensile strength to AZ91 alloy with higher ductility. Moreover, elevated temperature tensile properties and creep resistance of MX alloy are higher than those of AZ91 alloy. Such improved properties of MX alloy over those of AZ91 alloy are due to the optimized microstructure of the former.

Formability of AA8011 aluminum alloy sheet in homogenized and unhomogenized conditions

The present study examines the microstructure and formability of homogenized and unhomogenized AA8011 aluminum alloy sheets under uniaxial and biaxial deformation modes. The stretch formability of sheets has been characterized in terms of limit strains in forming limit diagrams (FLDs). The formability of the material is associated with combinations of strain hardening, strain-rate hardening and surface roughening which is developed during the plastic deformation of the material. The phenomenon of recrystallization and the effect of second phase particles has been investigated in cold rolled sheets. It appears that surface roughening which is in turn a result of the grain coarsening is more important in the homogenized materials annealed at high temperatures.

The effect of coarse second-phase particles on the rate of grain refinement during severe deformation processing

The effect of second-phase particles on the rate of grain refinement during severe deformation processing has been investigated, by comparing the microstructure evolution in an AA8079 aluminium alloy, containing 2.5 vol.% of ~2 μm particles, with that in a high purity, single-phase, Al-0.13% Mg alloy, deformed identically by ECAE to an effective strain of ten. The materials were analysed by high-resolution EBSD orientation mapping, which revealed that grain refinement occurred at a dramatically higher rate in the particle-containing alloy. A submicron grain structure could be achieved by an effective strain of only five in the particle-containing alloy, compared to ten in the single-phase material. The mechanisms that contribute to this acceleration of the grain refinement process are discussed.

Ａｌ‐Ｍｇ‐Ｓｉ系合金の曲げ加工性に及ぼす第２相粒子の影響

The effect of second phase particles on the bendability of Al–Mg–Si alloy for outer panels in autobodies was investigated by changing solution heat treatment condition and quenching rate. Slow quenching rate made inferior bendability. Because the number of second phase particles on the grain boundaries increased. Crack by bending test was not observed with short solution heat treatment time. However, in the case of long solution heat treatment time, the crack was observed. Depth of the crack increased with solution heat treatment time to maximum value and then decreased. The number of second phase particles decreased and the formation of shear bands by deformation increased with solution heat treatment time. When the formation of shear bands is observed significantly and the number of second phase particles is many, the crack occurs easily along the shear bands and the second phase particles.

Mechanical behaviour of alloys containing stable or evolving heterogeneous arrangements of particles

The effect of second phase particles on the deformation behaviour of a particle strengthened (e.g. oxide dispersion strengthened) alloy was studied. Instead of dealing with average characteristics of dislocation glide (such as the average mean free path), a particular distribution of particles in the glide plane was considered. A homogenisation technique based on the Delaunay triangulation was used that is considered to be a better representation of local particle arrangement than the Voronoi tessellation proposed previously. A softening effect of particle clustering was found. The method was also applied to a population of particles whose density decreases during plastic deformation due to Ostwald ripening.