Combined Effects of Grain Boundary Convection and Migration in Dynamic Phase Transformations

2016 ◽  
Vol 879 ◽  
pp. 72-77
Author(s):  
Frank Montheillet ◽  
David Piot
Keyword(s):  
Grain Boundary ◽  
Phase Transformations ◽  
Large Strain ◽  
Second Phase ◽  
Grain Boundary Mobility ◽  
Dynamic Phase ◽  
Second Phase Particles ◽  
Interphase Boundaries ◽  
And Migration ◽  
Analytical Approaches

During large strain deformation of polycrystals, grain or interphase boundaries are driven by the material flow, which is a convection movement. By contrast, upon static recrystallization or grain growth, their motion takes place with respect to matter, which is referred to as grain boundary or interphase migration. During hot working, where dynamic phase transformations commonly occur, convection and migration operate simultaneously. According to local geometrical (e.g., prescribed velocity field, grain boundary curvature) and physical (e.g., grain boundary mobility, dislocation densities) conditions, they can reinforce or oppose each other, but generally combine in more complex ways. The aim of this work is to analyze such effects on the basis of simple analytical approaches. The results suggest that second phase particles or grains dynamically generated (i.e., during straining) exhibit approximately equiaxed shapes.

Modeling Grain Boundary Mobility during Dynamic Recrystallization of Metallic Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 2303-2308 ◽  
Author(s):  
Frank Montheillet ◽  
Gilles Damamme ◽  
David Piot ◽  
S. Lee Semiatin
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Mesoscale Model ◽  
Solute Drag ◽  
Solute Concentration ◽  
Metallic Alloys ◽  
Second Phase ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Second Phase Particles

A simple analytical model is proposed for estimating grain boundary mobility during dynamic recrystallization in metallic alloys. The combined effects of solutes (solute drag) and second phase particles (Zener pinning) on mobility are considered. The approach is based on (and is consistent with) a recently published mesoscale model of discontinuous dynamic recrystallization. The dependence of grain boundary mobility on solute concentration and particle size is summarized in the form of two-dimensional maps.

In-Situ Quantification of Solute Effects on Grain Boundary Mobility and Character in Aluminum Alloys during Recrystallization

2004 ◽  
Vol 467-470 ◽  
pp. 997-1002 ◽  
Author(s):  
Mitra L. Taheri ◽  
Anthony D. Rollett ◽  
Hasso Weiland
Keyword(s):  
Aluminum Alloys ◽  
Grain Boundary ◽  
Solute Drag ◽  
Second Phase ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Second Phase Particles ◽  
Grain Boundary Motion ◽  
New Evidence

Aluminum alloys exhibit recrystallization kinetics that vary strongly with composition. The conventional understanding is that certain alloying elements, e.g. chromium, retard grain boundary motion due to the formation of fine dispersions of second phase particles, giving rise to particle drag of boundaries. There is countervailing evidence, however, that suggests that solute drag provides a stronger influence on grain boundary mobility. This paper presents new evidence for a pronounced effect of solute based on experiments in which individual boundaries migrate under the driving pressure of stored energy from prior plastic strain. As supported by the literature, boundaries exhibit a maximum mobility for a 38-39 degree <111> misorientation in initial annealing experiments. Specifically, this mobility maximum is asymmetric with a sharp cutoff below 38-39 degrees but a more gradual decrease at misorientations beyond 40 degrees. The occurrence of other, smaller mobility peaks is discussed within the context of the sharpening of evolving maxima with discussed within the context of the sharpening of evolving maxima with increased recrystallization. The presence of a minimum at 38-39 degrees is found at both higher temperatures and higher solute concentrations. This transition from a local mobility maximum to a minimum is discussed within the context of recent theories solute drag activity.

Structural Changes in a 9%Cr Creep Resistant Steel during Creep Test

2012 ◽  
Vol 715-716 ◽  
pp. 895-900
Author(s):  
Valeriy Dudko ◽  
Andrey Belyakov ◽  
Vladimir Skorobogatykh ◽  
Izabella Schenkova ◽  
Rustam Kaibyshev
Keyword(s):  
Structural Changes ◽  
Subgrain Size ◽  
Large Strain ◽  
Particle Growth ◽  
Second Phase ◽  
Second Phase Particles ◽  
Creep Rupture Test ◽  
Lath Structure ◽  
Creep Regime ◽  
Effective Stabilization

Structural changes in a 9%Cr martensitic steel after 1%, 4% creep and creep rupture test at 650°C and stress of 118 MPa were examined. Heat treatment provided the formation of tempered martensite lath structure (TMLS) in the steel. The precipitations of second phase particles along block and lath boundaries provide effective stabilization of the TMSL under annealing/aging condition. This structure hardly changed under creep conditions in grip portion of crept sample. Significant coarsening of both the second phase particles and the martensite laths takes place in neck portion. In addition, the latter ones lose their original morphology and are replaced by large strain-induced subgrains. It should be noted that the increase of subgrain size is in almost direct proportion to the particle growth during the creep to 4% strain. The rapid growth of martesite laths followed by their evolution to deformation subgrains takes place within the tertiary creep regime.

Phase-field Model for Diffusional Phase Transformations in Elastically Inhomogeneous Polycrystals

2011 ◽  
Vol 172-174 ◽  
pp. 1084-1089 ◽  
Author(s):  
Tae Wook Heo ◽  
Saswata Bhattacharyya ◽  
Long Qing Chen
Keyword(s):  
Grain Boundary ◽  
Phase Field ◽  
Field Model ◽  
Boundary Segregation ◽  
Phase Field Model ◽  
Transformation Process ◽  
Second Phase ◽  
Perturbation Scheme ◽  
Local Pressure ◽  
Second Phase Particles

A phase-field model is described for predicting the diffusional phase transformation process in elastically inhomogeneous polycrystals. The elastic interactions are incorporated by solving the mechanical equilibrium equation using the Fourier-spectral iterative-perturbation scheme taking into account elastic modulus inhomogeneity. A number of examples are presented, including grain boundary segregation, precipitation of second-phase particles in a polycrystal, and interaction between segregation at a grain boundary and coherent precipitates inside grains. It is shown that the local pressure distribution due to coherent precipitates leads to highly inhomogeneous solute distribution along grain boundaries.

The plasticity and cleavage of polycrystalline beryllium II. The cleavage strength and ductility transition temperature

1980 ◽  
Vol 370 (1740) ◽  
pp. 29-39 ◽  
Keyword(s):  
Transition Temperature ◽  
Flow Stress ◽  
Grain Boundary ◽  
Stress Axis ◽  
Second Phase ◽  
Temperature Dependent ◽  
Second Phase Particles ◽  
Cleavage Strength ◽  
Dependent Flow ◽  
Strength And Ductility

For a grain diameter d, the cleavage strength is proportional to d -1/2 , but intercepts the stress axis. Initiation of cleavage in second phase particles of a size that varies suitably with d could produce this relation. More likely, the cleavage strength is determined by the condition for propagation of a microcrack across a grain boundary. An explanation of the stress intercept is given in terms of the probability that the critical microcrack size is an increasing multiple of d as the grains become finer. Directly measured ductility transition temperatures agree with those deduced from the intersection of a temperature dependent flow stress with a temperature independent cleavage strength.

Annealing in a Natural Laboratory: an EBSD and Cl Study of Calcite and Quartz Growth from Volumes of Rock Heated by a Nearby Melt Intrusion

2007 ◽  
Vol 550 ◽  
pp. 333-338 ◽  
Author(s):  
Sandra Piazolo ◽  
David J. Prior ◽  
M.D. Holness ◽  
Andreas O. Harstad
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Crystallographic Orientation ◽  
Lattice Distortion ◽  
Temperature History ◽  
Second Phase ◽  
Gradual Change ◽  
Twin Boundaries ◽  
Second Phase Particles ◽  
Crystallographic Orientations

Annealing is an important mechanism of microstructural modification both in rocks and metals. In order to relate directly changes in crystallographic orientation to migrating boundaries the researcher has the option to investigate either samples where the grain boundary motion can be directly tracked or a series of samples exhibiting successively higher degrees of annealing. Here we present results from rock samples collected from two well characterised contact aureoles (a volume of rock heated by the intrusion of a melt in its vicinity): One quartz sample in which patterns revealed by Cathodoluminescence (CL) indicate the movement of grain boundaries and a series of calcite samples of known temperature history. Electron backscatter diffraction (EBSD) analysis is used to link the movement of grain, twin boundaries and substructures with the crystallographic orientation / misorientation of a respective boundary. Results from the quartz bearing rock show: (a) propagation of substructures and twin boundaries in swept areas both parallel and at an angle to the growth direction, (b) development of slightly different crystallographic orientations and new twin boundaries at both the growth interfaces and within the swept area, and (c) a gradual change in crystallographic orientation in the direction of growth. Observations are compatible with a growth mechanism where single atoms are attached and detached both at random and at preferential sites i.e. crystallographically controlled sites or kinks in boundary ledges. Strain fields caused by defects and/or trace element incorporation may facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces but also at continuously migrating boundaries. Calcite samples show with increasing duration and temperature of annealing: (a) systematic decrease of the relative frequency of low angle grain boundaries (gbs), (b) decrease in lattice distortion within grains, (c) development of distinct subgrains with little internal lattice distortion, (d) change in lobateness of gbs and frequency of facet parallel gbs and (e) change in position of second phase particles. These observations point to an increasing influence of grain boundary anisotropy with increasing annealing temperature, while at the same time the influence of second phase particles and subtle driving-force variations decrease. This study illustrates the usefulness of using samples from natural laboratories and combining different analysis techniques in microprocess analysis.

The Effect of Grain-Boundary and Matrix Precipitates on High Temperature Strength in Fe3Al Based Alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
Ryo Makihara ◽  
Satoru Kobayashi ◽  
Takayuki Takasugi
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Tensile Tests ◽  
High Temperature Strength ◽  
Second Phase ◽  
Proof Stress ◽  
Second Phase Particles ◽  
The Matrix

ABSTRACTThe effect of grain boundary (GB) and matrix precipitates on high temperature strength was investigated in Fe3Al base alloys containing Cr, Mo and C. Tensile tests were conducted at 600°C for three types of microstructures consisting of: (I) film-like κ phase precipitates covering GBs and fine M2C particles in the matrix, (II) only fine M2C particles in the matrix and (III) no second-phase particles in the matrix. It was found that κ films on GBs are more than twice as effective as finely dispersed M2C particles for improving the proof stress.

The Role of Metallurgical Solid State Phase Transformations on the Formation of Residual Stress in Laser Cladding and Heating

2014 ◽  
Vol 777 ◽  
pp. 19-24 ◽  
Author(s):  
Ryan Cottam ◽  
Vladimir Luzin ◽  
Kevin Thorogood ◽  
Yat C. Wong ◽  
Milan Brandt
Keyword(s):  
Residual Stress ◽  
Solid State ◽  
Phase Transformations ◽  
Contour Method ◽  
Second Phase ◽  
Heating And Cooling ◽  
Second Phase Particles ◽  
The Matrix ◽  
Packing Arrangement

There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.

Atomic structures and migration mechanisms of interphase boundaries during body- to face-centered cubic phase transformations

2019 ◽  
Vol 52 (5) ◽  
pp. 1176-1188 ◽  
Author(s):  
Yunhao Huang ◽  
Jincheng Wang ◽  
Zhijun Wang ◽  
Junjie Li
Keyword(s):  
Phase Transformations ◽  
Interphase Boundary ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Orientation Relationships ◽  
Atomic Structures ◽  
Interphase Boundaries ◽  
Face Centered ◽  
And Migration ◽  
Kinetics Of

Atomic structures and migration mechanisms of interphase boundaries have been of scientific interest for many years owing to their significance in the field of phase transformations. Though the interphase boundary structures can be deduced from crystallographic investigations, the detailed atomic structures and migration mechanisms of interphase boundaries during phase transformations are still poorly understood. In this study, a systematic study on atomic structures and migration mechanisms of interphase boundaries in a body-centered cubic (b.c.c.) to face-centered cubic (f.c.c.) massive transformation was carried out using the phase-field crystal model. Simulation results show that the f.c.c./b.c.c. interphase boundaries can be classified into faceted interphase boundaries and side surfaces. The faceted interphase boundaries are semi-coherent with a group of dislocations, leading to a ledge migration mechanism, while the side surfaces are incoherent and thus migrate in a continuous way. After a careful analysis of the simulated migration process of interphase boundaries at atomic scales, a detailed description of the ledge mechanism based on the motion and nucleation of interphase boundary dislocations is presented. The ledge-forming process is accompanied by the nucleation of new heterogeneous dislocations and motions of original dislocations, and thus the barrier of ledge formation comes from the hindrance of these two dislocation behaviors. Once the ledge is formed, the original dislocations continue to advance until the ledge height reaches 1/|Δg|, where Δg represents the difference in reciprocal lattice vectors between two phases. The new heterogeneous dislocation moves along the radial direction of the interphase boundary, resulting in ledge extension. The interface dislocation behaviors greatly affect the migration of the interphase boundary, leading to different migration kinetics of faceted interphase boundaries under the Kurdjumov–Sachs and the Nishiyama–Wasserman orientation relationships. This study revealed the mechanisms and kinetics of complex structure transition during a b.c.c.–f.c.c. massive phase transformation and can shed some light on the process of solid phase transformations.

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