The Effect of Prestrain on Deformation of Ni3Al Single Crystals

1988 ◽  
Vol 133 ◽  
Author(s):  
W. E. Dowling ◽  
R. Gibala
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Yield Strength ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Negative Temperature ◽  
Dislocation Dynamics ◽  
Positive Temperature ◽  
Initial Flow ◽  
Bcc Metals

ABSTRACTPrestrain of bcc metals at temperatures T>0.2Tm decreases the flow stress at lower temperatures (T<O.15Tm) where the yield strength has a large negative temperature dependence. This investigation has examined the influence of prestrain on the flow stress of Ni3A1, for which the yield strength has a large positive temperature dependence above 25°C. Nickel-rich Ni3Al single crystals with axial orientations near <001> or <123> were prestrained in compression up to 20% shear strain at -196°C and subsequently compression tested at 550°C. Specimens near the <123> axial orientation were also prestrained at 550°C and then tested at -196°C. The initial flow stress of samples prestrained at - 196°C and tested 550°C was reduced up to 50% compared to samples solely compression tested at 550°C. The magnitude of the reduced flow stress and its extent as a function of plastic strain were dependent upon the amount of prestrain and orientation. Prestraining at 550°C and subsequent testing at -196°C increased the flow stress by as much as 60% over samples solely tested at -196°C. Dislocation substructures obtained from selected samples coupled with arguments based on dislocation dynamics and obstacle strengthening are used to explain the results.

Strain Rate Dependence of the Flow Stress and Work-Hardening of Single Crystals of NI3(Al,Hf)B

1994 ◽  
Vol 364 ◽  
Author(s):  
S. S. Ezz ◽  
Y. Q. Sun ◽  
P. B. Hirsch
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Yield Stress ◽  
Strain Rate Sensitivity ◽  
Work Hardening ◽  
Room Temperature ◽  
Rate Sensitivity ◽  
Controlling Mechanism

AbstractThe strain rate sensitivity ß of the flow stress τ is associated with workhardening and β=(δτ/δln ε) is proportional to the workhardening increment τh = τ - τy, where τy is the strain rate independent yield stress. The temperature dependence of β/τh reflects changes in the rate controlling mechanism. At intermediate and high temperatures, the hardening correlates with the density of [101] dislocations on (010). The nature of the local obstacles at room temperature is not established.

Temperature Dependence of Impact Ionization Coefficients in 4H-SiC

2014 ◽  
Vol 778-780 ◽  
pp. 461-466 ◽  
Author(s):  
Hiroki Niwa ◽  
Jun Suda ◽  
Tsunenobu Kimoto
Keyword(s):  
Temperature Dependence ◽  
Temperature Coefficient ◽  
Breakdown Voltage ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Impact Ionization ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Ionization Coefficients

Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (Mp) and electrons (Mn), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

Plastic Deformations in L10-Ordered Single Crystals with their c/a Ratios Less than Unity

2007 ◽  
Vol 561-565 ◽  
pp. 459-462
Author(s):  
Katsushi Tanaka ◽  
Hiromitsu Ide ◽  
Yoshinori Sumi ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Room Temperature ◽  
The Other ◽  
Compressive Deformation ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
Temperature Range ◽  
Critical Resolved Shear Stress

Compressive deformation of L10-ordered single crystals of FePd whose c/a ratio less than unity have been investigated from room temperature to 823 K. The results show that the critical resolved shear stress (CRSS) for octahedral glide of ordinary dislocations is smaller than that of super-lattice dislocations in all the temperature range investigated, that is the opposite sense to the case of Ti-56 mol% Al. The CRSS for ordinary dislocations virtually independent to the temperature. On the other hand, the CRSS for super dislocations exhibits a weak positive temperature dependence from room temperature up to 573 K and decreases in higher temperatures.

Mechanical Properties of E21 (Mn, Fe)3AIC-Base Alloys

1998 ◽  
Vol 552 ◽  
Author(s):  
Kensyo Suzuki ◽  
Hideki Hosoda ◽  
Shuji Hanada
Keyword(s):  
Mechanical Properties ◽  
Flow Stress ◽  
Temperature Dependence ◽  
Volume Fraction ◽  
Primary Phase ◽  
Positive Temperature ◽  
Compression Tests ◽  
Positive Temperature Dependence ◽  
Fe Content ◽  
Work Hardening Coefficient

ABSTRACTMechanical properties of E21 (Mn, Fe)3AlC-base alloys were investigated. The E21 crystal structure is closely related to L12, and thereby E21 compounds are expected to exhibit superior properties similar to those of the L12 Ni3AL. Nominal compositions are fixed to be 60mol%(Mn, Fe)-20mol%A1–20mol%C. Alloys were prepared by mechanical alloying and hot pressing. ICP chemical analysis, X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis were carried out for alloy characterization. Mechanical properties were evaluated by Vickers hardness tests at room temperature (RT) and compression tests from RT to 1273K. Strain rate dip tests were also carried out. It is found that most alloys are composed of two phases of E21 as the primary phase and graphite as the precipitates, and that the volume fraction of graphite increases with increasing Fe content. Hardness and 0.2% flow stress at RT are raised with increasing Fe content. At RT, 0.2% flow stress and fracture strength of Fe3A1C alloy used are 2.9GPa and 3.4GPa, respectively. An alloy containing 40%Mn-20%Fe shows weak positive temperature dependence of strength at 700–800K, similar to the observation in some Co3AIC alloys. Moreover, work-hardening coefficient of all alloys shows strong positive temperature dependence below 700K. These results suggest the occurrence of K-W related mechanism for plastic deformation in these alloys.

scholarly journals Equivalent plastic strain gradient plasticity with grain boundary hardening and comparison to discrete dislocation dynamics

2015 ◽  
Vol 471 (2184) ◽  
pp. 20150388 ◽  
Author(s):  
E. Bayerschen ◽  
M. Stricker ◽  
S. Wulfinghoff ◽  
D. Weygand ◽  
T. Böhlke
Keyword(s):  
Plastic Strain ◽  
Yield Strength ◽  
Grain Boundary ◽  
Continuum Model ◽  
Equivalent Plastic Strain ◽  
Elastic Interaction ◽  
Dislocation Dynamics ◽  
Discrete Dislocation Dynamics ◽  
Discrete Dislocation ◽  
The Continuum

The gradient crystal plasticity framework of Wulfinghoff et al. (Wulfinghoff et al. 2013 Int. J. Plasticity 51, 33–46. ( doi:10.1016/j.ijplas.2013.07.001 )), incorporating an equivalent plastic strain γ eq and grain boundary (GB) yielding, is extended with GB hardening. By comparison to averaged results from many discrete dislocation dynamics (DDD) simulations of an aluminium-type tricrystal under tensile loading, the new hardening parameter of the continuum model is calibrated. Although the GBs in the discrete simulations are impenetrable, an infinite GB yield strength, corresponding to microhard GB conditions, is not applicable in the continuum model. A combination of a finite GB yield strength with an isotropic bulk Voce hardening relation alone also fails to model the plastic strain profiles obtained by DDD. Instead, a finite GB yield strength in combination with GB hardening depending on the equivalent plastic strain at the GBs is shown to give a better agreement to DDD results. The differences in the plastic strain profiles obtained in DDD simulations by using different orientations of the central grain could not be captured. This indicates that the misorientation-dependent elastic interaction of dislocations reaching over the GBs should also be included in the continuum model.

Thermal Equilibrium Concentrations and Effects of Ga Vacancies in n-TYPE GaAs

1993 ◽  
Vol 300 ◽  
Author(s):  
Teh Y. Tan ◽  
Homg-Ming You ◽  
Ulrich M. Gösele
Keyword(s):  
Temperature Dependence ◽  
Point Defect ◽  
Thermal Equilibrium ◽  
Quantitative Data ◽  
Equilibrium Concentration ◽  
Negative Temperature ◽  
Positive Temperature ◽  
Self Diffusion ◽  
N Doping ◽  
Equilibrium Concentrations

ABSTRACTWe have calculated the thermal equilibrium concentrations of the various Ga vacancy species in GaAs. That of the triply-negatively-charged Ga vacancy, V3Ga has been emphasized, since it dominates Ga self-diffusion and Ga-Al interdiffusion under intrinsic and ndoping conditions, as well as the diffusion of Si donor atoms occupying Ga sites. Under strong n-doping conditions, the thermal equilibrium V3Ga concentration, CeqvGa.3−(n), has been found to exhibit a temperature independence or a negative temperature dependence, in the sense that the CeqvGa.3−(n) value is either unchanged or increases as the temperature is lowered. This is contrary to the normal positive temperature dependence of point defect theerqmal equilibrium concentrations, which decreases as the temperature is lowered. This CeqvGa.3−(n) property provides explanations to a number of outstanding experimental results, either requiring the interpretation thatV3−Ga has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect non-equilibrium phenomena. Furthermore, there exist also a few quantitative data which are in agreement with the presently calculated results.

Positive temperature dependence of strength observed in ordered cu3pt single crystals

1992 ◽  
Vol 65 (3) ◽  
pp. 737-747 ◽  
Author(s):  
S. Miura ◽  
K. Mitsui ◽  
Y. Tanaka ◽  
Y. Mishima ◽  
T. Suzuki
Keyword(s):  
Temperature Dependence ◽  
Single Crystals ◽  
Positive Temperature ◽  
Positive Temperature Dependence

The Effects of Alloy Addittons of Si and Transitton Metal Elements on the Mechanical Properties Of B-Doped Ds Ni3Al

1990 ◽  
Vol 213 ◽  
Author(s):  
Yun Zhang ◽  
Dongliang Lin(T.L.Lin)
Keyword(s):  
Solid Solution ◽  
Flow Stress ◽  
Mechanical Behavior ◽  
Temperature Dependence ◽  
Liquid Nitrogen Temperature ◽  
Tensile Tests ◽  
Positive Temperature ◽  
Metal Elements ◽  
Solid Solution Strengthening ◽  
Solution Strengthening

ABSTRACTThe temperature dependence of the flow stress in the B-doped DS Ni3Al containing Si as well as transition metal elements was systematically investigated by tensile tests. The effects of the alloy elements on the magnitude of the positive temperature dependence of the flow stress were evaluated. The calculated activation energy which results in the anomalous mechanical behavior the Ni3Al decreases for each element addition. The flow stress near liquid nitrogen temperature, taken as a measure of the degree of solid solution strengthening, increases linearly with the element concentration. The influences of the element additions on the solid solution strengthening were discussed. Also discussed were the mechanisms of the anomalous mechanical behavior in the Ni3 Al affected by the element additions.

Plastic Deformations in Single Crystals of FePd with the L10 Structure

2008 ◽  
Vol 1128 ◽  
Author(s):  
Katsushi Tanaka ◽  
Wang Chen ◽  
Kyosuke Kishida ◽  
Norihiko L. Okamoto ◽  
Haruyuki Inui
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Yield Stress ◽  
Room Temperature ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
L10 Structure ◽  
Critical Resolved Shear Stress

AbstractCompressive deformations of L10-ordered single crystals of FePd have been investigated from room temperature to 873 K. The critical resolved shear stress for superlattice dislocations is hard to determine resulting from buckling that occurs after a small amount of conventional plastic deformation. The CRSS for superlattice dislocations determined from yield stress is significantly larger than that of ordinary dislocations. The CRSS for octahedral glide of ordinary and superlattice dislocations are virtually independent of the temperature, and the positive temperature dependence of the yield stress is not observed for both, ordinary and superlattice dislocations, by the present experiments.

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