Investigation of Localized Deformation in NiAl Single Crystals

1998 ◽  
Vol 120 (3) ◽  
pp. 206-211 ◽  
Author(s):  
Ashok V. Kumar ◽  
Chulho Yang ◽  
Vijay B. R. Seelam
Keyword(s):  
Single Crystals ◽  
Shear Bands ◽  
Slip Systems ◽  
Localized Deformation ◽  
Localized Modes ◽  
Element Analysis ◽  
Kink Bands ◽  
Simulation Results ◽  
Constitutive Parameters ◽  
Active Slip

Deformation of NiAl single crystals was studied using finite element analysis to investigate the modes of localized deformation. Constitutive parameters and hardening characteristics of the active slip systems were estimated by comparing numerical simulation results with experimental results. Deformation of tensile specimens of NiAl single crystal was simulated when loaded along different crystal orientations to understand the deformation mechanism that results in various localized modes of deformation. In particular, the formation of shear bands and kink bands was studied and the material and geometric characteristics that influence the formation of such localization were investigated.

Temperature Dependence of the Yield Stress in α-Titanium Investigated with Crystal Plasticity Analysis

2018 ◽  
Vol 941 ◽  
pp. 1474-1478
Author(s):  
Yelm Okuyama ◽  
Masaki Tanaka ◽  
Tetsuya Ohashi ◽  
Tatsuya Morikawa
Keyword(s):  
Finite Element ◽  
Temperature Dependence ◽  
Yield Stress ◽  
Crystal Plasticity ◽  
Slip Systems ◽  
Temperature Dependent ◽  
Element Analysis ◽  
Pyramidal Slip ◽  
Active Slip ◽  
Lattice Friction

The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.

Tensile Deformation of Magnesium and Magnesium Alloy Single Crystals

2014 ◽  
Vol 783-786 ◽  
pp. 341-345 ◽  
Author(s):  
Shinji Ando ◽  
Atsushi Kodera ◽  
Kazuki Fukushima ◽  
Masayuki Tsushida ◽  
Hiromoto Kitahara
Keyword(s):  
Single Crystals ◽  
Basal Slip ◽  
Tensile Deformation ◽  
Pure Magnesium ◽  
Slip Systems ◽  
Pyramidal Slip ◽  
Higher Temperature ◽  
Von Mises ◽  
Zn Alloy ◽  
Active Slip

According to von-Mises criterion, five kinds of independent slip systems are required for uniform deformation, so it is necessary to activate non-basal slip systems to show good ductility. However, it has not become clear the effect of Zn or Al for non-basal slip systems yet. To investigate deformation behavior of magnesium crystal by non-basal slip and alloying effect for the non-basal slip, pure magnesium and Mg-Al-Zn single crystals were stretched in the [110] direction. While {112}<23> second order pyramidal slip was activated at room temperature in pure magnesium, {101}<23> first order pyramidal slip became active slip at higher temperature. In Mg-Al-Zn alloy single crystal, {101} twin also activated by adding aluminum. These results indicate that active non-basal slip systems and twin in magnesium strongly depend on deformation temperature and alloying elements.

scholarly journals The Development of Dislocation Structure and Texture in Rolled Copper (001)[110] Single Crystals

1988 ◽  
Vol 10 (1) ◽  
pp. 67-75 ◽  
Author(s):  
M. Wróbel ◽  
S. Dymek ◽  
M. Blicharski ◽  
S. Gorczyca
Keyword(s):  
Electron Microscopy ◽  
Single Crystals ◽  
Dislocation Structure ◽  
Transverse Direction ◽  
Shear Bands ◽  
Taylor Factor ◽  
Initial Orientation ◽  
Slip Systems ◽  
Deformation Bands ◽  
Pole Figures

The initial orientation has split into two equally strong symmetric orientations: (112)[111¯] and (112)[1¯1¯1]. Areas of identical orientation were band shaped and were called deformation bands. Up to 60% reduction, deformation occurs by slip on one plane (one from two possible) in two directions. This leads to the appearance of deformation bands with transition bands between them. Due to such deformation the initial orientation rotates around transverse direction towards the end-orientation {112}〈111〉. Due to rotation of the crystallographic lattice with deformation, the Taylor factor M changes as well, and it causes the activation of two not coplanar slip systems which stabilize the end-orientations {112}〈111〉. Such a sequence of the slip systems activation was concluded from the agreement of the calculated and experimental pole figures. The electron microscopy investigations showed that first shear bands formed due to the activation of these new slip systems.

Effects of Deviation from Stoichiometry on Deformation Behavior of Hard-Oriented NiAl Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
R. Srinivasan ◽  
M. F. Savage ◽  
R. D. Noebe ◽  
M. J. Mills
Keyword(s):  
Transition Temperature ◽  
Single Crystals ◽  
Deformation Behavior ◽  
Mechanical Response ◽  
Slip Systems ◽  
Alloying Additions ◽  
Strain And Strain Rate ◽  
Deviation From Stoichiometry ◽  
Slip Transition ◽  
Active Slip

ABSTRACTNi-44A1, Ni-50Al and NiAl-0.3 at.% Hf single crystals have been studied in compression to understand the effects that alloying additions and deviation from stoichiometry can have on the mechanical response of NiAl-based single crystals. While all three single crystals deform through a<111> slip at lower temperatures, the active slip systems differ at higher temperatures. Climb of a<010> dislocations contributes to deformation in Ni-50AI single crystals beyond the slip transition temperature, while Ni-44Al and NiAl-0.3Hf crystals deform through a<101> glide. But several microstructural differences have been observed in the mode of deformation between Ni-44Al and NiAl-0.3Hf crystals. In addition, significant strengthening is exhibited in the Hf-doped crystals at higher temperatures. The post-deformation microstructure is also observed to be sensitive to both strain and strain rate. A possible explanation is offered for some of the observed differences in deformation behavior between the three alloys.

Investigation of Strain Hardening in NiAl Single Crystals Using Three-Dimensional FEA Models

1999 ◽  
Vol 123 (1) ◽  
pp. 20-27 ◽  
Author(s):  
Chulho Yang ◽  
Ashok V. Kumar
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Strain Hardening ◽  
Single Crystals ◽  
Three Dimensional ◽  
High Rate ◽  
Large Strains ◽  
Slip Systems ◽  
Element Analysis ◽  
Hardening Model

Single crystals of NiAl are very ductile at intermediate temperatures (400–700 K) and were observed to exhibit high strain hardening rates at large strains when loaded in the [110] orientation. The experimentally observed strain hardening in NiAl single crystals could not be predicted using simple hardening models and two-dimensional finite element analysis. The primary slip systems that activate during the deformation are (010)[100] and (100)[100], however, it has been hypothesized that activation of secondary slip on {011} slip planes may be responsible for the high rate of hardening observed. The hardening of intermetallic single crystals when multiple slip systems are activated is not well understood. To study this further, a three-dimensional hardening model and constitutive equations were implemented into a finite element analysis program. Since the parameters required to describe the hardening model such as latent hardening ratios are difficult to obtain experimentally, a parametric study was conducted to estimate values for these parameters that enable the prediction of the experimentally observed load versus elongation curves.

Anisotropy in the hardness of single crystals

1971 ◽  
Vol 322 (1548) ◽  
pp. 73-88 ◽  
Keyword(s):  
Crystal Structure ◽  
Shear Stress ◽  
Single Crystals ◽  
Dislocation Motion ◽  
Slip Systems ◽  
Maximum Hardness ◽  
Indentation Process ◽  
Wide Range ◽  
Knoop Indentation ◽  
Active Slip

The results of this work, and those published by other researchers who have used Knoop indentation measurements, confirm that the nature of anisotropy in hardness is essentially determined by the crystal structure and the primary slip systems which accommodate dislocation motion during indentation. Materials belonging to the same class of crystal structure and having common slip systems possess similar anisotropic properties. The varying extent of work-hardening or fracture, associated with indentations, does not appear to influence the anisotropy— although twinning on the basal planes of hexagonal closepacked metals may have a significant effect. An analysis of the indentation process is presented which establishes a clear relationship between the ‘effective resolved shear stress’ (t 0 '), in the bulk of the crystal beneath the indenter, and the observed hardness. Directions which correspond to the minimum values of t' e , on specific crystallographic surfaces, are those of maximum hardness and conversely. The analysis is shown to be equally applicable to a wide range of crystalline solids including nonmetallic materials, of various crystal structure, and typical f.c.c., b.c.c. and c.p.h. metals. Finally, anisotropy in hardness can be used to identify active slip systems in those crystals where it is possible for dislocations to move on more than one system.

Dislocation Boundaries and Slip Systems in Uniaxially Deformed Crystals

2001 ◽  
Vol 683 ◽  
Author(s):  
Grethe Winther ◽  
Xiaoxu Huang ◽  
Søren Fæster Nielsen ◽  
John Wert
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Crystal Orientation ◽  
Boundary Plane ◽  
Slip Systems ◽  
Crystal Boundary ◽  
Secondary Slip ◽  
Slip Planes ◽  
Planar Dislocation ◽  
Active Slip

ABSTRACTThe dislocations in the extended planar dislocation boundaries formed during deformation are generated by the active slip systems. Investigation of the boundaries is therefore a tool to obtain information on the active slip systems. Here, the orientation of the dislocation boundaries in uniaxially deformed aluminum poly- and single crystals are compared. It is found that the single crystal boundary planes are consistent with those found in polycrystals, indicating that the active slip systems in single and polycrystals are the same. However, boundaries are closer to the slip planes in the single crystals. This is taken as an indication that the secondary slip systems are more active in the polycrystal. The orientation of the boundary plane varies with the crystal orientation in a way that is consistent with activation of the five most stressed slip systems.

A Viscoplastic Model for Single Crystals

1992 ◽  
Vol 114 (1) ◽  
pp. 19-26 ◽  
Author(s):  
E. H. Jordan ◽  
K. P. Walker
Keyword(s):  
Elevated Temperature ◽  
Constitutive Model ◽  
Single Crystals ◽  
Deformation Behavior ◽  
Slip Systems ◽  
Thermomechanical Loading ◽  
Straightforward Manner ◽  
Viscoplastic Model ◽  
Active Slip ◽  
Anisotropic Deformation

A viscoplastic constitutive model is described in which deformation behavior is postulated on representative slip systems and the behavior of the entire crystal is determined by summing the slip on the active slip systems. By building in the slip geometry known from the metallurgical literature, it is possible to predict the anisotropic deformation behavior and to model in a straightforward manner other phenomena which have been described by metallurgists in crystallographic terms. Elevated temperature tension-torsion tests were run and used to verify the model’s predictive abilities. Ratchetting behavior under thermomechanical loading conditions is specifically addressed.

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