Effect Of Grain Boundary Migration Research Articles

Grain boundary migration behavior and microstructure evolution during multilayer additive hot-compression bonding

Multilayer additive hot-compression bonding (MAHCB) was a new technology to prepare large-size homogeneous materials, the strain hardening at the bonding interface was an urgent issue for its application. In this paper, the effect of grain boundary migration on strain hardening was studied by the MAHCB process of pure copper. The results show that prolonging the holding time can significantly promote both interfacial grain boundary migration (IGBM) and matrix grain boundary migration (MGBM). The bonding interface became tortuous due to the promotion of IGBM, accompanied by the reduction in dislocation density at the interface and the gradual elimination of interfacial defects. It occurred mainly by the evolution of the triple junction grain boundary from T-type to equal type, which was driven by the decrease in the interface energy. On the other hand, the growth of dynamic recrystallization (DRX) grains was improved with MGBM, and enlarged the low dislocation density region. With the combined effect of both, strain hardening was completely eliminated, when the strain was 0.15 and the holding time was 3 h. Then the optimal bonding properties were obtained, the average tensile-shear strength and elongation were 191.2 MPa and 212 %, and the recovery rates were 99.7 % and 98.9 %, respectively, compared to the as-cast pure Cu samples.

Microstructure evolution and creep-rupture behaviour of a low-cost Fe-Ni-based superalloy

ABSTRACT The pursuit of low-cost superalloys with excellent creep property is of great importance for practical engineering application. In this study, the creep performance, microstructure evolution and deformation mechanism of a low-cost Fe-Ni-based superalloy under the condition of 750°C/130 MPa and 700°C/200 MPa were investigated. The creep rupture life reached 14,715 h and 12,716 h, respectively, under the aforementioned conditions. After long-term creep, carbides and γ′ particles (Ni3(Al,Ti)) with spherical shape grew gradually due to the Ostwald ripening. Abnormal coarse needle-like γ′ phase presented at grain boundaries and grew along preferred orientation under the synergy effect of grain boundary migration, stress, and diffusion. Influence of precipitate-free zones, carbides, and coincidence site lattice (CSL) boundary on the creep properties were discussed. The creep deformation mechanism of the Fe-Ni-based superalloy were dominated by dislocations slip. Dislocations moved via by-passing the γ′ phase and formed dislocation bows around the precipitates.

Precipitation behavior of γ′ precipitates in 21Cr-32Fe-41Ni heat-resistant alloy at different aging temperatures

The precipitation behavior of γ′ precipitates and mechanical properties of 21Cr-32Fe-41Ni alloy at different aging temperatures were investigated by scanning electron microscopy, transmission electron microscopy, chemical phase analysis, mechanical property tests. The results showed that the precipitates in 21Cr-32Fe-41Ni alloy included γ′ precipitates, MC phases, σ phases after aging heat treatment. There were two precipitation modes of γ′ precipitates: intragranular dispersed precipitation and grain boundary discontinuous precipitation. The number and size of intragranular γ′ precipitates increased with the increase in aging temperature. During the coarsening process, the γ′ precipitates were kept spherical. When the aging temperature was above 740 ℃, the discontinuous precipitation reaction occurred under the combined effect of grain boundary migration and solute diffusion-controlled equilibrium phase growth. According to SEM images, there were four different kinds of morphologies of discontinuous precipitated cellular γ′ at the grain boundaries. They were lamellae precipitates, short rod precipitates, granular precipitates and bidirectional parallel precipitates. When the aging temperature was between 650 ℃ and 740 ℃, the strength of the alloy increased rapidly due to the precipitation of a large number of intragranular spherical γ′, and the precipitation of grain boundary cellular γ′ was one of the main reasons for the toughness of alloy decreased rapidly above 740 ℃.

Effect of grain boundary migration on intergranular fracture in the weld metal of steels

ABSTRACT The relationship between grain boundary segregation behaviour of sulphur and intergranular fracture in 10% nickel steel weld metal solidified with austenite single phase was investigated. In the weld metal with sulphur added, sulphur is segregated at the grain boundaries, causing intergranular fracture, and the toughness is significantly deteriorated. The austenite columnar grain boundaries formed during solidification cause grain boundary migration during cooling after solidification, and sulphur segregated at the columnar grain boundaries is diffusely migrated along with the grain boundary migration. Intergranular fracture of the weld metal is not a fracture that occurs at the columnar grain boundaries formed during solidification but is a fracture that occurs at prior austenite grain boundaries, where sulphur is segregated, formed by migration after solidification.

Effect of grain boundary migration on intergranular fracture in the weld metal of steels

Effect of grain boundary migration on intergranular fracture in the weld metal of steels

Effect of grain boundary migration in Cu–Cr–Zr–Ti manufactured using different casting processes

ABSTRACTGrain boundary migration in different casting processes directly affects the grain size of the ingot, which affects the mechanical properties of the alloy. In this study, Cu–Cr–Zr–Ti rods are manufactured using upward continuous casting and casting-extrusion processes followed by drawing. It is found that the strength of the upward continuous casting rods is 621 MPa, greater than that of the casting-extrusion rods 571 MPa, which is a result of different microstructure evolution during solution treatment. Calculations of the driving force and resistance of grain boundary migration were performed to explain the observations.

Effect of grain boundary migration on impact toughness of 316L diffusion bonding joints

316L stainless steel was vacuum diffusion bonded under the stress of 10 MPa, the temperature ranged as 900 °C ∼ 1100 °C and the holding time varied as 45 ∼ 90 min. The joint microstructures were examined. Tensile test and Charpy impact test were performed. The bonding interface showed ‘Y’ intersection or boundary migration (i.e., bulging migration) effected by boundary energy balance and strain inhomogeneity. The impact toughness increased linearly with the grain boundary migration ratio. Increasing grain size by increasing bonding temperature further distorted the bonding interface that increased crack propagation resistance. The highest impact toughness of the joint was 173.1 J cm−2 with the grain boundary migration ratio of 96%, obtained by the joint bonded at 1050 °C for 60 min.

Irreversible thermodynamics of creep in crystalline solids

We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a non-hydrostatically stressed multi-component solid medium with non-conserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general expression for the entropy production rate and use it to identify of the relevant fluxes and driving forces and to formulate phenomenological relations among them taking into account symmetry properties of the material. As a simple application, we analyze a one-dimensional model of a bicrystal in which the grain boundary acts as a sink and source of vacancies. The kinetic equations of the model describe a creep deformation process accompanied by grain boundary migration and relative rigid translations of the grains. They also demonstrate the effect of grain boundary migration induced by a vacancy concentration gradient across the boundary.

Effect of Grain Boundary Migration on Texture Formation in Al-3mass%Mg Solid Solution during High Temperature Deformation

Uniaxial compression deformation is conducted on solid solution Al-3mass%Mg and Al-3mass%Mg-0.2mass%Sc with Al3Sc precipitates in the strain rates ranging from 1.0×10-4s-1 to 5.0×10-3s-1 at 723K. High temperature yielding is observed. Fiber texture is constructed in all the deformation conditions. While the main component of the fiber texture changes from {011} to {001} in Al-3mass%Mg alloy with an increase in strain rate, no big change in texture main component is seen for Al-3mass%Mg-0.2mass%Sc alloy with Al3Sc precipitates. It is experimentally shown that the development of {001} fiber texture can be attributed to the grain boundary migration.

Effects of dynamic grain boundary migration during the hot compression of high stacking fault energy metals

A simple one-dimensional model is proposed for predicting the effects of grain boundary migration (GBM) occurring during hot compression testing of polycrystalline specimens. Strain hardening, dynamic recovery, and GBM induced softening are accounted for using a modified Laasraoui–Jonas equation. The movement of grain boundaries has two origins, viz. convection driven by material flow, and migration induced by the local dislocation density differences. The disappearance of grains during straining leads to changes in the local topology. Using parameters pertaining to aluminium, it is shown that the average grain thickness tends to a steady state value, while significant flow stress softening occurs, both predictions in agreement with experimental data. Moreover, the model allows the true average migration rate to be simply estimated from grain thickness evolution.

Texture competition during thin film deposition – effects of grain boundary migration

In this paper, we describe an implementation of grain boundary migration in the atomistic simulator of thin film deposition (ADEPT), and apply the simulator to study effects of the grain boundary migration on texture evolution. In the implementation, atoms are classified into two categories: those belong to a single grain and those at grain boundaries. An atom is defined as one at a grain boundary if it has more than half of its neighbors occupied and not all of the neighboring atoms are in the same grain. The grain boundary atom is attempted to re-align with neighboring grains to represent the grain boundary migration; the attempt probability is defined by the grain boundary migration coefficient. Our studies show that grain boundary migration does not always assist formation of texture with a top surface of the lowest energy. At the nucleation stage of thin film deposition, high migration coefficient of grain boundaries may enhance the formation of grain nuclei with top surfaces of higher energy, and therefore effectively may suppress formation of textures with a top surface of the lowest energy. This effect may provide an extra dimension to engineer textures of thin films.

Study of the effect of grain boundary migration on hillock formation in Al thin films

We have studied the effect of grain boundary migration on hillock formation in unpassivated Al thin films during thermal cycling. Hillocking occurs more frequently in Al films that experience grain growth during thermal cycling than in films with stabilized grain structures. The hillocking frequency is at least four times greater in the films that experience grain growth, as judged by the number of hillocks observed per initial grain boundary triple junction. This latter measure takes account of the smaller initial grain size in the film that experiences grain growth and shows that grain boundary migration itself must enhance the hillocking frequency.

Effect of grain boundary migration on grain boundary grooving

Based on volume diffusion and small slope approximation, the effect of grain boundary migration on grain boundary grooving is studied. Using the Fourier transformation, a closed form solution for grain boundary groove profile is obtained. With a finite migration velocity, the groove profile develops asymmetrically with time (the atoms accumulate faster in the direction of the migration velocity and form a higher peak), and the asymmetry also increases with migration velocity.

Fe-3%Si合金の析出物(AlNとMnS)の存在下での粒成長後の結晶方位と粒径分布に及ぼす対応粒界の影響

Texture evolution by grain growth in the presence of precipitates of MnS and AlN in Fe-3%Si alloy has been investigated by SEM-ECP technique. The two texture groups A and B are evolved by grain growth from the primary texture (grain diameter of 6 μm) composed mainly of {111}〈112〉. The group A (gtain diameter of 2600 μm) is mainly composed of the Goss orientation and its rotated orientations of about 0.26 to 035 rad around the ND axis, while the group B (grain diameter of 700 μm) had the intensity level of about one-fifth of that of the group A and has near {112}〈110〉 orientations. The group A has a low intensity of Σ1 and has either the highest frequency of Σ9 or a higher value of the product of its intensity and the intensity of Σ9 in the primary texture. The group B has a higher intensity of Σ1 and a higher value of the product of its intensity and the intensity of Σ9 in the primary texture. The mechanism of the texture evolution mentioned above can be explained in terms of the preferential migration of Σ9 boundaries in the presence of the precipitates and under the inhibitor effect of grain boundary migration by Σ1 boundaries.

Effect of grain boundary migration on apparent boundary diffusion coefficients

The effect of grain boundary migration on the tracer concentration depth profiles that develop during a diffusion experiment is evaluated. An expression for the average tracer concentration within a plane at depth x and time t for a boundary migrating with velocity V is derived. This average concentration is compared to that expected for a stationary boundary. Results indicate that considerable errors in both the magnitude and temperature dependence of the apparent diffusion coefficient may arise if grain boundary migration is neglected.

Grain boundary migration and fabric development in experimentally deformed octachloropropane

In this study in-situ observations of a deforming aggregate of the hexagonal material octachloropropane have been analysed. Calculations of micro-strains and measurement of c-axis orientations have enabled the processes influencing fabric development to be distinguished, and the importance of dynamic recrystallization to be assessed. It was found that, in this material, inter-grain strain contrasts could be large, and the effect of grain boundary migration was to modify the fabric in a measurable way. A simple model for the driving force for grain boundary migration based on dislocation density contrasts, as controlled by intra-grain strains and grain orientations, is proposed and tested, with an 80% success rate for the mobile grain boundaries studied.

Effect of grain boundary migration in solution treatment on grain boundary precipitation of Al-Fe dilute alloys

Grain boundary internal friction in the Al-0.002 wt.% Fe alloy was measured to examine an interaction between moving boundaries and solute atoms. When both the alloys solution treated for a short time at 773K in which grains are growing and solution treated for a prolonged time in which grain growth has been ceased are subsequently aged at 593K, grain boundary precipitation occurs within a shorter time in the former. This fact is in consistent with the assumption that greater quantities of solute atoms segregate in moving boundaries than in stationary boundaries. If the alloy is solution treated at elevated temperatures above 823K, however, longer times are required for grain boundary precipitation when grains are growing in the solution treatment. This may be due to the breaking away of the moving boundary from the solute atmosphere.

Effect of Grain Boundary Migration and Recrystallization on the Creep Strength of Inconel 617

Effect of Grain Boundary Migration and Recrystallization on the Creep Strength of Inconel 617

Inconel 617合金のクリープ強度におよぼす粒界移動および再結晶の影響

Inconel 617合金のクリープ強度におよぼす粒界移動および再結晶の影響