Deformation of Polysynthetically Twinned (PST) TiAl Crystals at High Strain Rate and High Temperature

1996 ◽  
Vol 460 ◽  
Author(s):  
Zhe Jin ◽  
George T. Gray ◽  
Masaharu Yamaguchi
Keyword(s):  
High Temperature ◽  
High Strain ◽  
Deformation Mode ◽  
Dislocation Slip ◽  
Ordinary Dislocation ◽  
Mode 2 ◽  
Lamellar Interface ◽  
Deformation Modes ◽  
Loading Axis ◽  
Lamellar Interfaces

ABSTRACTDeformation microstructures in a 45°<321> oriented (the lamellar interface was tilted 45° from the loading axis about the <321> direction in the lamellar interface) poly synthetically twinned (PST) TiAl crystal deformed in compression at 3000 s-1 and 800 °C was studied. Deformation of this PST crystal is characterized as follows: 1) Deformation of domains [III] and [IV] is dominated by 1/6 [112] parallel twinning (twinning parallel to lamellar interfaces). Ordinary dislocations observed in these domains are found to be a complementary deformation mode. 2) Deformation of domains [II], [V] and [VI] is controlled by a 1/2<110] ordinary dislocation slip. Complementary deformation modes in these domains are ordinary dislocation slip, superdislocation slip and cross-twinning. 3) Domain [I] is not deformed after the specimen deforms up to ∼7% strain.

Microstructure Evolution of Near Gamma TiAl Intermetallic under Tensile Impact Loadings at High Temperatures

2010 ◽  
Vol 146-147 ◽  
pp. 1553-1556
Author(s):  
Yu Wang ◽  
Xiang Zan ◽  
Yue Hui He ◽  
Yang Wang
Keyword(s):  
Strain Rate ◽  
Microstructure Evolution ◽  
Deformation Mode ◽  
Deformation Twinning ◽  
Stacking Fault ◽  
Effect Of Temperature ◽  
Dislocation Slip ◽  
Tem Analysis ◽  
Dynamic Loadings ◽  
Deformation Modes

The effect of temperature and strain rate on the mechanical behavior and microstructure evolution of Near Gamma Ti-46.5Al-2Nb-2Cr (NG TiAl) was investigated at temperatures ranging from room temperatures to 840 under strain rates of 0.001, 320, 800 and 1350s-1. The TEM analysis indicated that deformation twinning and stacking fault are the main deformation modes under dynamic loadings and dislocation slip is another important deformation mode under quasi-static loadings. The density of deformation twinning and/or stacking fault increases with the increased temperature and strain rate.

scholarly journals Rationalization of the plastic flow behavior of Polysynthetically-twinned (PST) TiAl crystals based on slip mode observation using AFM and Schmid's law

2004 ◽  
Vol 842 ◽  
Author(s):  
Yali Chen ◽  
David P. Pope
Keyword(s):  
Flow Behavior ◽  
Plane Shear ◽  
Complex Deformation ◽  
Compression Direction ◽  
Out Of Plane ◽  
Slip Planes ◽  
Shape Curve ◽  
Deformation Modes ◽  
Loading Axis ◽  
Lamellar Interfaces

ABSTRACTPST TiAl samples of different orientations were prepared and deformed by compression at room temperature. The deformation structures on the free surfaces were scanned using an AFM. It was found that when the angle between the lamellar interfaces and the loading axis is between 20 degree and 80 degree, PST samples deform primarily by shear in slip planes parallel to the lamellar interfaces. When the angle is below 20 degree, both the gamma phase and the alpha 2 phase deform by shear in slip planes inclined with the lamellar interfaces, but the shear vectors lie in the interface. When the angle is close to 90 degree, complex deformation behavior occurs. Shear in planes parallel to the lamellar interfaces contributes more to the overall strain in the directions perpendicular to the loading axis and the out-of-plane shear contributes to the strain in the compression direction. The characteristic U-shape curve of the yield stress versus the angle between the loading axis and the lamellar interfaces can be explained quite well using different C.R.S.S. for the three different deformation modes.

Polarization of plastic deformation modes in polysynthetically twinned TiAl crystals

2003 ◽  
Vol 18 (3) ◽  
pp. 702-708 ◽  
Author(s):  
V. Paidar ◽  
K. Kishida ◽  
M. Yamaguchi
Keyword(s):  
Plastic Deformation ◽  
Deformation Mode ◽  
Deformation Twinning ◽  
Additional Stress ◽  
Burgers Vector ◽  
Stress Increase ◽  
Loading Direction ◽  
Deformation Modes ◽  
Lamellar Interfaces

Polarization of deformation twinning (its propagation in a certain sense but not in the opposite one) is taken for granted. However, the same phenomenon can occur for a superdislocation glide as well, as is demonstrated in this paper. The consequences for plastic deformation of polysynthetically twinned TiAl crystals with the lamellar interfaces parallel to the loading direction are discussed. It is not the interface itself that is an obstacle for propagating deformation but also the fact that a deformation mode with the parallel Burgers vector cannot be activated in the neighboring lamella due to the directionality of superdislocation motion leading to additional stress increase.

Microstructure Evolution of Ti-46.5Al-2Nb-2Cr at Different Strain Rates and Temperatures

2013 ◽  
Vol 535-536 ◽  
pp. 509-513
Author(s):  
Xiang Zan ◽  
Yu Wang ◽  
Yue Hui He ◽  
Yong Liu ◽  
Wei Dong Song
Keyword(s):  
High Strain Rate ◽  
Microstructure Evolution ◽  
Elevated Temperatures ◽  
Large Range ◽  
High Strain ◽  
Deformation Mode ◽  
Strain Rates ◽  
Deformation Twins ◽  
Ordinary Dislocation ◽  
Main Deformation

The microstructure evolution of Ti-46.5Al-2Nb-2Cr with different microstructure types loaded under a large range of strain rates and elevated temperatures is investigated by TEM. The results show that deformation twins are the main deformation mode under high strain rate loadings and both ordinary dislocation and super-dislocation are the additional modes under quasi-static loadings. The proportion of twinned grains increases with the increased strain rates.

scholarly journals Abnormal deformation behavior in Polysynthetically-twinned TiAl crystals with A and N orientations——an AFM study

2004 ◽  
Vol 842 ◽  
Author(s):  
Yali Chen ◽  
David P. Pope
Keyword(s):  
Plane Shear ◽  
Free Surfaces ◽  
Deformation Structures ◽  
Lamellar Interface ◽  
Axis Parallel ◽  
Slip Planes ◽  
Deformation Behaviors ◽  
Abnormal Phenomenon ◽  
Loading Axis ◽  
Lamellar Interfaces

ABSTRACTPolysynthetically-twinned TiAl crystals were deformed by compression with loading axis parallel and perpendicular to the lamellar interfaces. The deformation structures on the free surfaces were scanned using a dimension AFM with scan directions parallel and perpendicular to the lamellar interfaces. Abnormal deformation behaviors were observed to occur in both orientations. When the compression axis is parallel to the lamellar interfaces, the gamma and alpha lamellae deform primarily by shear in planes inclined with the lamellar interface, while the shear vectors lie in the interface. However, in-plane shear, shear in slip planes parallel to the lamellar interfaces, also occurs along the lamellar interfaces. When the loading axis is perpendicular to the lamellar interface, in-plane shear was found to be dominant at the beginning stage of plastic deformation and contributes more to the macroscopic strain. These behaviors are controversial to the Schmid's Law since the applied resolved shear stress for these deformation systems is zero. The abnormal phenomenon was explained by the large coherency stresses along the lamellar interfaces.

Molecular Dynamics Simulations of Orientation Effects During Tension, Compression, and Bending Deformations of Magnesium Nanocrystals

2015 ◽  
Vol 82 (10) ◽  
Author(s):  
Haidong Fan ◽  
Jaafar A. El-Awady
Keyword(s):  
Molecular Dynamics ◽  
Uniaxial Tension ◽  
Uniaxial Compression ◽  
Deformation Mode ◽  
Dislocation Slip ◽  
Pure Bending ◽  
Axis Orientation ◽  
Orientation Effects ◽  
Loading Direction ◽  
Deformation Modes

The deformation modes in magnesium nanocrystals during uniaxial tension, uniaxial compression, and pure bending are investigated using molecular dynamics (MD) simulations at room temperature. For each loading condition, the crystal orientation effects are studied by increasing the crystal c-axis orientation angle θ relative to the loading direction from 0 deg to 90 deg by a 15 deg increment. The simulation results reveal a number of different deformation modes and an obvious tension–compression asymmetry in magnesium nanocrystals. As the c-axis is rotated away from the tension loading direction, the deformation mode at yielding changes from tension twinning (θ ≤ 45 deg) to compression twinning (θ > 45 deg). For compression loading, yielding is dominated by only dislocation slip on the pyramidal (θ < 15 deg), basal (15 deg < θ < 60 deg) and prismatic (θ > 60 deg) planes. The nucleation stress in general decreases with increasing θ for both uniaxial tension and uniaxial compression loadings. For pure bending simulations, the yielding is mostly controlled by the weaker deformation mode between the compressive and tensile sides. The bending nucleation stress also decreases as the c-axis deviates away from the loading direction.

Microstructure Evolution of TiAl under Tensile Impact Loadings

2013 ◽  
Vol 747-748 ◽  
pp. 14-18
Author(s):  
Xiang Zan ◽  
Li Ouyang ◽  
Yu Wang ◽  
Yue Hui He ◽  
Yong Liu ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Microstructure Evolution ◽  
Deformation Process ◽  
High Strain ◽  
Deformation Mode ◽  
Dislocation Slip ◽  
Strain Rates ◽  
Tensile Impact ◽  
Tial Intermetallics

The microstructure evolution of TiAl intermetallics with different microstructures loaded under different strain rates and temperatures was investigated. The results showed that the deformation twinning dominated the deformation process under high strain rate, while dislocation slip was another dominating deformation mode under quasi-static loadings. The proportion of twinned grain increased with the increased strain rate. In Duplex TiAl, the plastic deformation was mainly found in equaxied grains and seldom found in lamellar grains.

scholarly journals Fingerprinting shock-induced deformations via diffraction

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Avanish Mishra ◽  
Cody Kunka ◽  
Marco J. Echeverria ◽  
Rémi Dingreville ◽  
Avinash M. Dongare
Keyword(s):  
High Speed ◽  
Shock Loading ◽  
Dislocation Slip ◽  
Line Profiles ◽  
X Ray Diffraction ◽  
Final State ◽  
X Ray ◽  
Shock Testing ◽  
Local Pressures ◽  
Deformation Modes

AbstractDuring the various stages of shock loading, many transient modes of deformation can activate and deactivate to affect the final state of a material. In order to fundamentally understand and optimize a shock response, researchers seek the ability to probe these modes in real-time and measure the microstructural evolutions with nanoscale resolution. Neither post-mortem analysis on recovered samples nor continuum-based methods during shock testing meet both requirements. High-speed diffraction offers a solution, but the interpretation of diffractograms suffers numerous debates and uncertainties. By atomistically simulating the shock, X-ray diffraction, and electron diffraction of three representative BCC and FCC metallic systems, we systematically isolated the characteristic fingerprints of salient deformation modes, such as dislocation slip (stacking faults), deformation twinning, and phase transformation as observed in experimental diffractograms. This study demonstrates how to use simulated diffractograms to connect the contributions from concurrent deformation modes to the evolutions of both 1D line profiles and 2D patterns for diffractograms from single crystals. Harnessing these fingerprints alongside information on local pressures and plasticity contributions facilitate the interpretation of shock experiments with cutting-edge resolution in both space and time.

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