scholarly journals A correlation between grain boundary character and deformation twin nucleation mechanism in coarse-grained high-Mn austenitic steel

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chang-Yu Hung ◽  
Yu Bai ◽  
Tomotsugu Shimokawa ◽  
Nobuhiro Tsuji ◽  
Mitsuhiro Murayama
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Austenitic Steel ◽  
Deformation Twin ◽  
Local Stress ◽  
Nucleation Mechanism ◽  
Stacking Fault ◽  
Dislocation Dynamics ◽  
Coarse Grained ◽  
Twin Nucleation

AbstractIn polycrystalline materials, grain boundaries are known to be a critical microstructural component controlling material’s mechanical properties, and their characters such as misorientation and crystallographic boundary planes would also influence the dislocation dynamics. Nevertheless, many of generally used mechanistic models for deformation twin nucleation in fcc metal do not take considerable care of the role of grain boundary characters. Here, we experimentally reveal that deformation twin nucleation occurs at an annealing twin (Σ3{111}) boundary in a high-Mn austenitic steel when dislocation pile-up at Σ3{111} boundary produced a local stress exceeding the twining stress, while no obvious local stress concentration was required at relatively high-energy grain boundaries such as Σ21 or Σ31. A periodic contrast reversal associated with a sequential stacking faults emission from Σ3{111} boundary was observed by in-situ transmission electron microscopy (TEM) deformation experiments, proving the successive layer-by-layer stacking fault emission was the deformation twin nucleation mechanism, different from the previously reported observations in the high-Mn steels. Since this is also true for the observed high Σ-value boundaries in this study, our observation demonstrates the practical importance of taking grain boundary characters into account to understand the deformation twin nucleation mechanism besides well-known factors such as stacking fault energy and grain size.

scholarly journals Investigating the dislocation reactions on Σ3{111} twin boundary during deformation twin nucleation process in an ultrafine-grained high-manganese steel

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chang-Yu Hung ◽  
Tomotsugu Shimokawa ◽  
Yu Bai ◽  
Nobuhiro Tsuji ◽  
Mitsuhiro Murayama
Keyword(s):  
Grain Boundary ◽  
Twin Boundary ◽  
Deformation Twin ◽  
Coarse Grained ◽  
Manganese Steel ◽  
High Manganese ◽  
Twin Boundaries ◽  
Dominant Type ◽  
Twin Nucleation ◽  
Ultrafine Grained

AbstractSome of ultrafine-grained (UFG) metals including UFG twinning induced plasticity (TWIP) steels have been found to overcome the paradox of strength and ductility in metals benefiting from their unique deformation modes. Here, this study provides insights into the atomistic process of deformation twin nucleation at Σ3{111} twin boundaries, the dominant type of grain boundary in this UFG high manganese TWIP steel. In response to the applied tensile stresses, grain boundary sliding takes place which changes the structure of coherent Σ3{111} twin boundary from atomistically smooth to partly defective. High resolution transmission electron microscopy demonstrates that the formation of disconnection on Σ3{111} twin boundaries is associated with the motion of Shockley partial dislocations on the boundaries. The twin boundary disconnections act as preferential nucleation sites for deformation twin that is a characteristic difference from the coarse-grained counterpart, and is likely correlated with the lethargy of grain interior dislocation activities, frequently seen in UFG metals. The deformation twin nucleation behavior will be discussed based on in-situ TEM deformation experiments and nanoscale strain distribution analyses results.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

scholarly journals On the Role of Local Grain Interactions on Twin Nucleation and Texture Evolution in Hexagonal Materials

2011 ◽  
Vol 702-703 ◽  
pp. 265-268 ◽  
Author(s):  
Anand K. Kanjarla ◽  
Irene J. Beyerlein ◽  
Ricardo A. Lebensohn ◽  
Carlos Tomé
Keyword(s):  
Grain Boundaries ◽  
Texture Evolution ◽  
Probability Model ◽  
Local Stress ◽  
Stress Fields ◽  
Full Field ◽  
Twin Nucleation ◽  
Deformation Twins ◽  
Hexagonal Materials

Texture evolution in plastically deformed HCP metals is strongly influenced by the nucleation and growth of deformation twins and twin variant selection. Statistically based EBSD analyses of deformed microstructures in HCP metals indicate that the nucleation of deformation twins depends on, among other factors, the local stress fields arising from neighboring grain interactions at grain boundaries [1]. Inspired by these findings a probability model for twin nucleation was developed [2,3], based on the activation of defect sources statistically occurring in grain boundaries. This nucleation model was implemented in a Visco-Plastic Self-Consistent (VPSC) code. Because the latter is based on an Effective Medium assumption and the inclusion formalism, it only provides average stress values in the grains, and the nature of local stress fields at grain boundaries had to be considered in a heuristic manner. In order to have better insight on the effect of local textures on twin nucleation, in this work we employ a viscoplastic full field Fast Fourier Transform (FFT) method as a numerical tool for conducting virtual experiments to study the role of crystal orientation and local neighbor grain interactions on stress localization close to the interfaces and, consequently, on twin nucleation in hexagonal materials, such as Zr and Mg.

The Effect of Grain Boundary Chemistry on the Slip Transmission Process Through Grain Boundaries in Ni3Al

1991 ◽  
Vol 238 ◽  
Author(s):  
I. M. Robertson ◽  
T. C. Lee ◽  
Raja Subramanian ◽  
H. K. Birnbaum
Keyword(s):  
Stress Concentration ◽  
Grain Boundary ◽  
Slip System ◽  
Grain Boundaries ◽  
Local Stress ◽  
Crack Advance ◽  
Boron Doped ◽  
Show Evidence ◽  
Fcc Alloy ◽  
Boundary Chemistry

ABSTRACTThe conditions established in disordered FCC systems for predicting the slip system that will be activated by a grain boundary to relieve a local stress concentration have been applied to the ordered FCC alloy Ni3Al. The slip transfer behavior in hypo-stoichiometric Ni3Al with (0.2 at. %B) and without boron was directly observed by performing the deformation experiments in situ in the transmission electron microscope. In the boron-free and boron-doped alloys, lattice dislocations were incorporated in the grain boundary, but did not show evidence of dissociation to grain boundary dislocations or of movement in the grain boundary plane. The stress concentration associated with the dislocation pileup at the grain boundary was relieved by the emission of dislocations from the grain boundary in the boron-doped alloy. The slip system initiated in the adjoining grain obeyed the conditions established for disordered FCC systems. In the boron-free alloy, the primary stress relief mechanism was grain-boundary cracking, although dislocation emission from the grain boundary also occurred and accompanied intergranular crack advance. Because of the importance of the grain boundary chemistry in the models for explaining the boron-induced ductility in hypo-stoichiometric Ni3Al, the chemistry of grain boundaries in well-annealed boron-doped and boron-free alloys was determined by using EDS. No Ni enrichment was found at the grain boundaries examined. These observations are discussed in terms of the different models proposed to explain the ductility improvement in the boron-doped, hypo-stoichiometric alloy.

Grain Boundary Diffusion of Hydrogen in Nano-Structured Pd/Ag Alloy Membranes

2008 ◽  
Author(s):  
Logan S. McLeod ◽  
Levent F. Degertekin ◽  
Andrei G. Fedorov
Keyword(s):  
Grain Boundary ◽  
Diffusion Process ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Appreciable Amount ◽  
Bottom Surface ◽  
Fast Diffusion ◽  
Average Grain Size

Palladium and its alloys have long been used as hydrogen separation membranes due to their extremely high permeability and selectivity to hydrogen over all other gases [1]. The hydrogen permeation process begins with selective chemisorption of the gas onto the metal surface. As the adsorption process is the point in the permeation sequence where the majority of gases become excluded, it follows that a cleverly designed device could be created to take advantage of the so-called ‘fast’ diffusion paths of surface and grain-boundary diffusion to further enhance permeability without sacrificing selectivity. The contribution of grain-boundary diffusion to the overall permeation rate is dependent on the relative volume in the membrane occupied by grain-boundaries versus bulk material. Typically, grain boundaries only make up a miniscule fraction of the overall volume and therefore only contribute an appreciable amount to the overall diffusion process at temperatures low enough to make the bulk diffusion process nearly stagnant. However, in the case of a nanostructured membrane this paradigm is no longer valid. The fabrication methods associated with extremely thin membrane deposition typically lead to highly non-equilibrium microstructure with an average grain size on the order of tens of nanometers [2]. In order to exploit the potential advantages of grain boundary diffusion the nano-scale grains must persist throughout operation. To avoid the tendency for the grain structure to relax to a more equiaxed, coarse-grained morphology the self-diffusion of metal atoms in the film must be minimized by operating the membranes at a temperature much lower than the membrane melting temperature. Figure 1 shows the microstructural changes in a thin, sputtered, Pd/Ag alloy film before and after annealing. The initial fine-grained structure on the bottom surface of the membrane is due to a combination of low substrate temperature during deposition and the Ti adhesion layer onto which the Pd/Ag layer was deposited. After annealing at 400 C the grains have coarsened and the top and bottom structure are identical.

Grain Boundary Radiotracer Diffusion of Ni in Ultra-Fine Grained Cu and Cu - 1wt.% Pb Alloy Produced by Equal Channel Angular Pressing

2008 ◽  
Vol 584-586 ◽  
pp. 380-386 ◽  
Author(s):  
Jens Ribbe ◽  
Guido Schmitz ◽  
Y. Amouyal ◽  
Yuri Estrin ◽  
Sergiy V. Divinski
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Equal Channel Angular Pressing ◽  
Boundary Diffusion ◽  
Ion Beam ◽  
Short Circuit ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Angular Pressing ◽  
Diffusion Paths

The radiotracer technique was applied for measuring grain boundary diffusion of Ni in ultrafine grained (UFG) copper materials with different nominal purities and in a Cu—1wt.%Pb alloy. The UFG specimens were prepared by equal channel angular pressing at room temperature. The stability of the microstructure was studied by focused ion beam imaging. Grain boundary diffusion of the 63Ni radioisotope was investigated in the temperature interval from 293 to 490K under the formal Harrison type C kinetic conditions. Two distinct short-circuit diffusion paths were observed. The first (relatively slow) path in the UFG materials corresponds unambiguously to relaxed high-angle grain boundaries with diffusivities which are quite similar to those in the respective coarse-grained reference materials. The second path is characterized by significantly higher diffusivities. The experimental data are discussed to elucidate the contribution of nonequilibrium grain boundaries in the deformed materials. Alternative contributions of other shortcircuit diffusion paths cannot be ruled out, particularly for the Cu-Pd alloy.

Effect of Ppm Level Dopant on Ductility of Ultrafine Grained Gold Wires

2009 ◽  
Vol 633-634 ◽  
pp. 449-457
Author(s):  
E. Chew ◽  
H.H. Kim ◽  
C. Ferraris ◽  
Yong Hao Zhao ◽  
Enrique J. Lavernia ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Selection Criteria ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Effective Strategy ◽  
Ultrafine Grained ◽  
Simulation Results ◽  
Gold Wires ◽  
Ppm Level

The addition of calcium (Ca) simultaneously improves the ductility and strength of UFG Au wires. Based on the observation on stacking faults, microstructures, simulation results and significant effect of Ca on grain boundary related properties, it is inferred that segregation of Ca to stacking faults and grain boundaries has occurred to induce effective stacking fault energy (SFE) reduction and properties improvement. Considering the known greater impact of SFE in UFG/ NC metals, segregating dopants are proposed to be an effective strategy for achieving dual improvement in this class of materials. Also, dopant selection criteria for this purpose is also suggested and verified.

Effect of stacking fault energy on formation of deformation twin in high Mn austenitic steel

2013 ◽  
Vol 17 (sup2) ◽  
pp. s73-s78 ◽  
Author(s):  
K. H. Oh ◽  
J. S. Jeong ◽  
Y. M. Koo ◽  
D. Nyung Lee
Keyword(s):  
Austenitic Steel ◽  
Deformation Twin ◽  
Stacking Fault ◽  
Stacking Fault Energy

Grain-Boundary Characteristics in Austenitic Steel

1996 ◽  
Vol 54 ◽  
pp. 344-345
Author(s):  
M.D. Caul ◽  
V. Randle
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Austenitic Steel ◽  
Material Properties ◽  
Degrees Of Freedom ◽  
Precipitate Formation ◽  
Grain Boundary Characteristics ◽  
Boundary Geometry ◽  
Individual Grains ◽  
Boundary Characteristics

Grain boundaries are an active area of research interest due to their effect on material property and structure relationships. In order to discuss material properties with regard to grain boundaries it is necessary to know the boundary type. The optimum technique for performing this task is Electron Backscatter Diflfraction (EBSD) in concert with the Scanning Electron Microscope (SEM). By collecting texture measurements in the form of individual orientations from grains it is possible to obtain misorientation measurements from grain boundaries. These measurements are three of the five degrees of freedom necessary to geometrically describe a grain boundary. The other two can be obtained by a serial sectioning technique.Grain boundaries in austenitic steel specimens, isothermally aged at either 700°C or 800°C, have been evaluated with the aim of relating boundary geometry to Cr2N precipitate formation. Samples were analysed using SEM and EBSD in order to obtain orientation measurements of individual grains to misorientations at grain boundaries and to Cr2N precipitates. These precipitates are detrimental to room temperature properties of high nitrogen stainless steels, so a reduction in their formation at grain boundaries would be advantageous. The steel is therefore an ideal candidate material for relating boundaries to material properties. The 700°C isothermally aged sample induces precipitate formation at grain boundaries whereas precipitation by cellular decomposition of austenite occurs in the 800 CC sample. The 700°C sample was used to categorise boundary types using the CSL model and relate this to Cr2N formation. The 800°C sample was used to examine the effect of aging temperature on boundary inclination. Therefore all five degrees of freedom in grain boundary geometry were obtained.

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