The Creep Behavior of Cr Modified Ni3 Al Single Crystals

1988 ◽  
Vol 133 ◽  
Author(s):  
S. E. Hsu ◽  
C. H. Tong ◽  
T. S. Lee ◽  
T. S. Liu
Keyword(s):  
Activation Energy ◽  
Steady State ◽  
Single Crystals ◽  
Creep Behavior ◽  
Aluminum Content ◽  
Dislocation Core ◽  
Transient Creep ◽  
Cr Addition ◽  
Dislocation Core Structure ◽  
Different Levels

ABSTRACTNi-Al-Cr single crystals with 4 at% Cr and different levels of aluminum content are grown in a directional solidification facility. The crystals are creep tested at temperatures from 760°C to 860°C. Steady state, as well as transient, creep rates are measured. The results show that Cr modified Ni3 A1, when tested along the <100> direction, exhibit remarkably high values of activation energy for creep. Along with evidence from dislocation structures, it is likely that there is a change in the dislocation core structure upon Cr addition.

The Compression Creep Behavior of Ni3Al-X Single Crystals

1990 ◽  
Vol 213 ◽  
Author(s):  
Seiji Miura ◽  
Tohru Hayashi ◽  
Mitsuhiro Takekawa ◽  
Yoshinao Mishima ◽  
Tomoo Suzuki
Keyword(s):  
Activation Energy ◽  
Single Crystals ◽  
Power Law ◽  
Creep Behavior ◽  
Creep Resistance ◽  
Constant Strain Rate ◽  
State Equation ◽  
Ternary Alloys ◽  
Plastic Behavior ◽  
Compression Tests

ABSTRACTCompressive creep behavior is investigated in ternary Ni3Al single crystals containing Ti, Si, Hf and Cr with stress axes parallel to the crystallographic orientation near [001]. Then a comparison is made with the results of high temperature compression tests under a constant strain rate for the same orientation where plastic behavior is characterized by a distinct yield drop followed by steadystate deformation. It is found that the deformation mechanism for the two cases is identical, namely octahedral viscous flow being expressed by the state equation of the power-law type with a stress exponent of about 3 to 4. The effect of offstoichiometry on the creep resistance is then examined in Ni3(Al,5 at%Ti) alloys with different Ni concentrations. The results support the observation in the polycrystalline compound where the creep resistance increases with Ni concentration on both sides of stoichiometry exhibiting a discontinuity at stoichiometry. Finally, the apparent activation energy in the power-law type state equation for the steady state creep deformation is estimated for all the ternary alloys examined. They are in general in good agreement with that for diffusion of ternary elements in Ni3Al. However, the relative magnitude of the value can not simply be compared since the activation energy depends on deviations from stoichiometry.

Effect of Off-Stoichiometry on the Creep Behavior of Binary and Ternary Ni3Al

1990 ◽  
Vol 213 ◽  
Author(s):  
Tohru Hayashi ◽  
Tetsumori Shinoda ◽  
Yoshinao Mishima ◽  
Tomoo Suzuki
Keyword(s):  
Activation Energy ◽  
Steady State ◽  
Power Law ◽  
Creep Behavior ◽  
Creep Resistance ◽  
Steady State Creep ◽  
Steady State Creep Rate ◽  
Creep Equation ◽  
Ternary Element ◽  
Ternary Additions

ABSTRACTCompressive creep behavior is investigated In polycrystalline Ni3Al intermetallic compounds in which the focus is put on the effect of offstoichiometry and ternary additions of Ti, Ta, V and Co on the creep resistance of the compounds. In all cases, the steady-state creep rate has the power-law type dependence on the applied stress. The stress exponent thereby obtained leads us to regard the creep behavior of the compound to be of the Class I type. It is shown that the creep resistance Increases with increasing Ni concentration on both sides of the stoichiometric Ni3Al composition and a discontinuity exists in the variation at stoichiometry. The gap at the discontinuity becomes clearer by the addition of ternary element in most cases as compared to the binary Ni3Al. Although the exact reason for the phenomenon is not clearly understood at present, it is shown that it could be interpreted by the concentration dependence of activation energy in the power-law type creep equation.

Comparison of TEM Observations with Dislocation Core Structure Calcuiations in B2 Ordered Compounds

1990 ◽  
Vol 213 ◽  
Author(s):  
D. Farkas ◽  
R. Pasianot ◽  
E. J. Savino ◽  
D.B. Miracle
Keyword(s):  
Single Crystals ◽  
Computer Simulations ◽  
Slip Plane ◽  
Structural Transition ◽  
Tensile Ductility ◽  
Dislocation Line ◽  
Dislocation Core ◽  
Core Structure ◽  
Dislocation Core Structure

ABSTRACTDislocation core structures have been calculated using atomistic computer simulations in NiAl and other B2 compounds. In the present work the calculated dislocation core structure are correlated with the known deforniatiorn behavior of B2 alloys. It is found that for the high ordering energy compounds <111> dislocations do not split in the simulations, in agreement with the experimental observations. It is also found that core structures for certain <111> and 1/2 <111> dislocations are spread in { 112} planes, which is consistent with the slip plane often reported for these dislocations. For the < 100> dislocations several orientations of the dislocation line produce sessile core configurations, whereas other orientations produce relatively more glissile cores. However, a structural transition of each of these dislocation cores may be required before < 100> dislocations become mobile, and this is consistent with the limited tensile ductility observed in NiAl “soft” single crystals below 200°C. Core structure simulations for < 110> dislocations are also reported and are discussed with respect to the importance of these dislocations in the deformation of NiAl.

scholarly journals MCMC inversion of the transient and steady-state creep flow law parameters of dunite under dry and wet conditions

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Sagar Masuti ◽  
Sylvain Barbot
Keyword(s):  
Activation Energy ◽  
Steady State ◽  
Upper Mantle ◽  
Physical Mechanism ◽  
Transient Creep ◽  
Steady State Creep ◽  
Postseismic Deformation ◽  
Nonlinear Stress ◽  
Dry And Wet Conditions ◽  
Flow Law

AbstractThe rheology of the upper mantle impacts a variety of geodynamic processes, including postseismic deformation following great earthquakes and post-glacial rebound. The deformation of upper mantle rocks is controlled by the rheology of olivine, the most abundant upper mantle mineral. The mechanical properties of olivine at steady state are well constrained. However, the physical mechanism underlying transient creep, an evolutionary, hardening phase converging to steady state asymptotically, is still poorly understood. Here, we constrain a constitutive framework that captures transient creep and steady state creep consistently using the mechanical data from laboratory experiments on natural dunites containing at least 94% olivine under both hydrous and anhydrous conditions. The constitutive framework represents a Burgers assembly with a thermally activated nonlinear stress-versus-strain-rate relationship for the dashpots. Work hardening is obtained by the evolution of a state variable that represents internal stress. We determine the flow law parameters for dunites using a Markov chain Monte Carlo method. We find the activation energy $$430\pm 20$$ 430 ± 20   and $$250\pm 10$$ 250 ± 10  kJ/mol for dry and wet conditions, respectively, and the stress exponent $$2.0\pm 0.1$$ 2.0 ± 0.1 for both the dry and wet cases for transient creep, consistently lower than those of steady-state creep, suggesting a separate physical mechanism. For wet dunites in the grain-boundary sliding regime, the grain-size dependence is similar for transient creep and steady-state creep. The lower activation energy of transient creep could be due to a higher jog density of the corresponding soft-slip system. More experimental data are required to estimate the activation volume and water content exponent of transient creep. The constitutive relation used and its associated flow law parameters provide useful constraints for geodynamics applications. Graphical Abstract

Direct structure images of 30° partial dislocation cores in silicon

1987 ◽  
Vol 45 ◽  
pp. 242-243
Author(s):  
J. C. Barry ◽  
H. Alexander
Keyword(s):  
Dislocation Core ◽  
Preparation Technique ◽  
Burgers Vector ◽  
Vector Type ◽  
Sample Preparation Technique ◽  
Lattice Images ◽  
Dislocation Core Structure ◽  
Type Lattice ◽  
Direct Inspection

Dislocations in silicon produced by plastic deformation are generally dissociated into partials. 60° dislocations (Burgers vector type 1/2[101]) are dissociated into 30°(Burgers vector type 1/6[211]) and 90°(Burgers vector type 1/6[112]) dislocations. The 30° partials may be either of “glide” or “shuffle” type. Lattice images of the 30° dislocation have been obtained with a JEM 100B, and with a JEM 200Cx. In the aforementioned experiments a reasonable but imperfect match was obtained with calculated images for the “glide” model. In the present experiment direct structure images of 30° dislocation cores have been obtained with a JEOL 4000EX. It is possible to deduce the 30° dislocation core structure by direct inspection of the images. Dislocations were produced by compression of single crystal Si (sample preparation technique described in Alexander et al.).

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