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.

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.

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.

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.

Microstructural Evolution of Nuclear Power Steel A508-III in the Creep Process at 800°C

2016 ◽  
Vol 853 ◽  
pp. 153-157
Author(s):  
Zhi Gang Xie ◽  
Yan Ming He ◽  
Jian Guo Yang ◽  
Zeng Liang Gao
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Grain Size ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
Microstructural Evolution ◽  
Creep Process ◽  
Second Phase ◽  
Creep Stage ◽  
Second Phase Particles

The A508-III steel is widely used to manufacture the lower heads of commercial reactor pressure vessels (RPV). In severe accident, the reactor core in the RPV begins to melt and meanwhile the technology of in-vessel retention (IVR) exerts its role. In this case the inner surface of RPV will expose to temperatures over a phase transition temperature. However, the significant nonlinear feature of creep curve of A508-III steel suffered heterogeneous damage was not studied. In this work, the creep tests were performed for the steel at the phase transition temperature of 800°C. The microstructural evolution at different creep stages was characterized by scanning electron microscopy and transmission electron microscopy. The results show that, at the second creep stage, more coarsening second phase particles occur in the steel. With the creep processing, the grain size and diameter of second phase particles increase. At the tertiary creep stage, the grain size increases significantly, and the second phase particles coarsen during the process of atom migration. In addition, Micro-cracks and voids also come into being in the situation and they can become larger by combing each other during the creep process. At this stage, the growth of cavities and second phase particles coarsening become the main mechanism of creep damage. The trend of microstructural evolution is consistent with the creep constitutive equation obtained for the A508-III steel at the phase transition temperature of 800°C. The results obtained provide indispensable foundation to establish the relationship between the macroscopic creep and microscopic damage.

scholarly journals Evaluation of the Temperature Dependent Flow Stress Model for Thermoplastic Fiber Metal Laminates

2015 ◽  
Vol 24 (1) ◽  
pp. 52-61 ◽  
Author(s):  
E.T. Park ◽  
B.E. Lee ◽  
D.S. Kang ◽  
J. Kim ◽  
B.S. Kang ◽  
...  
Keyword(s):  
Flow Stress ◽  
Stress Model ◽  
Temperature Dependent ◽  
Fiber Metal Laminates ◽  
Fiber Metal ◽  
Dependent Flow ◽  
Flow Stress Model

Phase Field Study of Second Phase Particles-Pinning on Strain Induced Grain Boundary Migration

2020 ◽  
Vol 993 ◽  
pp. 967-975
Author(s):  
Kai Li ◽  
Yao Shen ◽  
Da Yong Li ◽  
Ying Hong Peng
Keyword(s):  
Grain Boundary ◽  
Phase Field ◽  
Boundary Migration ◽  
Phase Field Model ◽  
Energy Difference ◽  
Second Phase ◽  
Grain Boundary Migration ◽  
Stored Energy ◽  
Second Phase Particles ◽  
Theoretical Predictions

A phase field model was presented to investigate the effect of particles-pinning on grain boundary migration in materials containing stored energy differences across the grain boundaries. The accuracy of the phase field framework was examined by comparing the simulated results with theoretical predictions. The pinning effects of coherent and non-coherent second phase particles on the boundary migration were studied in triple-grain models. 2D simulations with second phase particles of different sizes or different area fractions were performed. The effect of stored energy difference across the boundary on the particles-pinning was also investigated. The results showed that the pinning effect could be enhanced by the decrement of the particle size and the increment of particle area fraction. Increasing the stored energy difference across the grain boundary induced higher grain boundary migration velocity and weaker particles-pinning.

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