Dislocation Structures and Anomalous Yielding in Ordered Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
P. M. Hazzledine ◽  
Y. Q. Sun
Keyword(s):  
Mechanical Properties ◽  
Electron Microscope ◽  
Strain Rate ◽  
Yield Stress ◽  
Work Hardening ◽  
Screw Dislocations ◽  
Ordered Alloys ◽  
Work Hardening Rate ◽  
Initial Work ◽  
Edge Dislocations

ABSTRACTThe strain, strain rate and temperature dependencies of the yield stresses of the model L12 materials Ni3Al, Ni3Ga and Co3Ti are described, as well as two associated properties, the initial work-hardening rate and the inverted creep. These mechanical properties, the electron microscope observations of <110> {111} APB coupled slip and the violations of Schmid's laws point to glissile-sessile-glissile transitions by cross slip of screw dislocations as the explanation for the yield stress anomaly. Similar explanations are probable for h.c.p. Be, B2 CoTi and tetragonal TiAl and MoSi2. A different kind of model, based on the behavior of edge dislocations is required for h.c.p. Mg, B2 CuZn and DO19 Ti3Al.

Antiphase Domain Boundary Tubes in Ordered Alloys

1986 ◽  
Vol 81 ◽  
Author(s):  
P.M. Hazzledine ◽  
Peter Hirsch
Keyword(s):  
Electron Microscopy ◽  
Work Hardening ◽  
Domain Boundary ◽  
Antiphase Domain ◽  
Orientation Dependence ◽  
Cross Slip ◽  
Proof Stress ◽  
Screw Dislocations ◽  
Ordered Alloys ◽  
Edge Dislocations

AbstractAPB tubes have been observed in both a B2 and an L12 ordered alloy by means of weak beamtransmission electron microscopy. The tubes are attached to near—edge dislocations, either to single superdislocations or to superdipoles. The majority appearto have been formed by cross slip of screw dislocations. A computer model of the cross slip process in B2 alloys is described. The tubes formed by cross slip drag on edge dislocations and are capable in principle of explaining the extra work hardening shown by ordered over disordered crystals. The temperature and orientation dependence of the work hardening are similar to those of the proof stress which is also thought to be controlled by cross slip. This new mechanism of work hardening is shown to give order of magnitudeagreement with experiment.

Dislocation microstructures in boron-doped Ni3Al

1990 ◽  
Vol 48 (4) ◽  
pp. 470-471
Author(s):  
Yu H.F. ◽  
I.P. Jones ◽  
R.E. Smallman
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Yield Stress ◽  
Work Hardening ◽  
Scientific Research ◽  
Tube Formation ◽  
Rate Dependence ◽  
Strain Rate Dependence ◽  
Boron Doped ◽  
Secondary Defect

Despite its relative engineering eclipse (at least in aeronautical terms), Ni3Al is still a rewarding area for scientific research, primarily because so much is already known about it. Many of its mechanical properties, however, are still not understood in terms of secondary defect populations and behaviour. For example, the fundamental Kear-Wilsdorf mechanism, wherein cross slip from {111} to {100} planes provides an increase in strength with temperature, has received intensive microscopic scrutiny recently, and it now appears that the movement of the superpartials on {100} is far more than the atom spacing or so envisaged in Paidar et al. Whether delocking occurs, however, and if so how often, is still not clear. Examples of other problems which remain are:a) What are the relative contributions to work hardening of the Kear-Wilsdorf mechanism, APB tube formation and SISF formation?b) Although the yield stress increases with temperature it also increases slightly with strain rate, whereas a negative strain rate dependence might have been expected.

A Constitutive Description of Aluminum-1% Magnesium Alloy Deformed Under Hot-Working Conditions

2001 ◽  
Vol 123 (3) ◽  
pp. 301-308 ◽  
Author(s):  
E. S. Puchi Cabrera
Keyword(s):  
Flow Stress ◽  
Magnesium Alloy ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Working Conditions ◽  
Work Hardening ◽  
Hot Working ◽  
Initial Flow ◽  
Work Hardening Rate ◽  
Initial Work

A constitutive description of the deformation of commercial aluminum-1% magnesium alloy (AA5005) under hot working conditions has been formulated on a rational basis. The strain dependence of the flow stress is described by means of the evolution law earlier advanced by Sah et al. The optimization procedure of the experimental stress-strain data allowed the determination the extrapolated values of the initial flow stress and saturation stress which were subsequently correlated with temperature and strain rate by means of the kinetic model proposed by Kocks. It is shown that the initial work-hardening rate of this alloy is strongly dependent both on temperature and strain rate and that the temperature dependence is much more significant than that explained by the temperature dependence of the shear modulus of aluminum. The best description of the experimental flow stress data is obtained by expressing the initial work-hardening rate as a function of the effective strain rate, in terms of a simple parametric relationship, rather than considering a constant value for this parameter, independent of temperature and strain rate. The accuracy of the constitutive description proposed, regarding the reproduction of both the experimental flow stress and work-hardening rate, makes it reliable for its use in the analysis of hot-working processes involving this material.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

scholarly journals Investigation of the Mechanical Properties of St. Lawrence River Ice

1971 ◽  
Vol 8 (2) ◽  
pp. 163-169 ◽  
Author(s):  
L. W. Gold ◽  
A. S. Krausz
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Yield Stress ◽  
Power Law ◽  
River Ice ◽  
Stress Strain ◽  
Strain Behavior ◽  
Brittle Transition ◽  
Ductile To Brittle Transition ◽  
St Lawrence River

Observations are reported on the stress–strain behavior at −9.5 ± 0.5 °C of four types of ice obtained from the St. Lawrence River. The ice was subject to nominal rates of strain covering the range 2.1 × 10−5 min−1 to 5.8 × 10−2 min−1. A ductile-to-brittle transition was observed for strain rate of about 10−2 min−1. In the ductile range the four types had an upper yield stress that increased with strain rate according to a power law.

The Effects of Interstitial Content and Annealing on the Flow and Fracture behavior of Polycrystalline ÿ-NiAl

1994 ◽  
Vol 364 ◽  
Author(s):  
M. L. Weaver ◽  
V. Levit ◽  
M. J. Kaufman ◽  
R. D. Noebe
Keyword(s):  
Strain Rate ◽  
Yield Stress ◽  
Work Hardening ◽  
Strain Aging ◽  
Fracture Behavior ◽  
Rate Sensitivity ◽  
Dynamic Strain ◽  
Aging Behavior ◽  
Aging Theories ◽  
Tenfold Increase

AbstractThe strain aging behavior of three polycrystalline NiAl alloys has been investigated at temperatures between 300 and 1200 K. Yield stress plateaus, yield stress transients upon a tenfold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed between 700 and 800 K. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories.

Effect of Hot Extrusion on the Flow Behaviour of a Nickel-Based P/M Superalloy

2019 ◽  
Vol 298 ◽  
pp. 43-51
Author(s):  
Jia Yong Si ◽  
Song Hao Liu ◽  
Long Chen
Keyword(s):  
Activation Energy ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Work Hardening ◽  
Rate Sensitivity ◽  
Hot Extrusion ◽  
Turbine Disk ◽  
Flow Behaviour ◽  
Strain Rates ◽  
Work Hardening Rate

This research investigated the effect of hot extrusion on the flow behaviour of nickel-based superalloy FGH4096 by hot compression experiments in the temperature range from 1020 to 1110 °C and strain rates ranging from 0.1 to 0.001 s-1. The influence of the hot extrusion on the initial microstructures, work hardening rate, strain rate sensitivity, and activation energy of deformation were discussed. The results show that the extruded microstructure is constituted by the fine dynamic recrystallisation of grains. The true strain-true stress curves show that the as-HIPed and as-HEXed FGH4096 superalloy present double flow stress peaks and discontinuous flow softening. The as-HEXed FGH4096 is easily dynamically softened at high temperatures and high strain rates compared with as-HIPed microstructures. As for the work hardening rate, the as-HEXed FGH4096 exhibits higher θ values than that of as-HIPed. It is beneficial to the homogenous deformation and grain refinement during subsequent turbine disk forging. Comparing to as-HIPed FGH4096, the highest strain rate sensitivity value of as-HEXed is 0.306 at 1110 °C. The isothermal superplastic forging of a P/M turbine disk may be carried out at this temperature. The deformation activation energy value of the as-HIPed FGH4096 is lower which means that dislocation sliding and climbing can be easily initiated in the as-HIPed alloy.

Plastic deformation and fracture characteristics of Hadfield steel subjected to high-velocity impact loading

2002 ◽  
Vol 216 (10) ◽  
pp. 971-982 ◽  
Author(s):  
W-S Lee ◽  
T-H Chen
Keyword(s):  
Strain Rate ◽  
Work Hardening ◽  
Shear Bands ◽  
Rate Sensitivity ◽  
Constitutive Law ◽  
Hadfield Steel ◽  
Flow Strength ◽  
Rate Dependent ◽  
Work Hardening Rate ◽  
The Impact

Investigation of the impact behaviour of Hadfield steel has been carried out in a broad range of strain rates from 10−3 to 9 × 103s−1 by means of a servo-hydraulic machine and a compressive split Hopkinson bar. The effects of strain rate on the impact properties, substructure evolution and fracture resistance have been evaluated. The observed stress-strain response is influenced greatly by strain rate, resulting in obvious changes of work hardening rate, strain rate sensitivity and activation volume. This rate-dependent behaviour is in good agreement with model predictions using the Zerilli-Armstrong constitutive law. Dislocation tangle and deformation twin substructures are also found to develop as a function of strain rate. Increasing dislocation and twin densities enhance the work hardening rate and flow strength. Catastrophic failure at high rates results from the formation of localized shear bands. With increasing strain rate, there is an increase in brittle cleavage microfracture, resulting in ductility loss. Microcracking initiates at grain boundaries due to the presence of carbide precipitates.

The mechanical properties of pure iron tested in compression over the temperature range 2 to 293 °K

1967 ◽  
Vol 261 (1121) ◽  
pp. 253-287 ◽  
Keyword(s):  
Mechanical Properties ◽  
Flow Stress ◽  
Strain Rate ◽  
Single Crystals ◽  
Yield Stress ◽  
Low Temperatures ◽  
Pure Iron ◽  
Constant Strain Rate ◽  
Frictional Stress ◽  
Strain And Strain Rate

The mechanical properties of pure iron single crystals and of polycrystalline specimens of a zone-refined iron have been measured in compression over the temperature and strain rate ranges 2.2 to 293 °K and 7 x 10 -7 to 7 x 10 -3 s -1 respectively. Various yield stress parameters were determined as functions of both temperature and strain rate, and the reversible changes in flow stress produced by isothermal changes of strain rate or by changes of temperature at constant strain rate were also measured as functions of temperature, strain and strain rate. Both the temperature variation of the flow stress and the strain rate sensitivity of the flow stress were generally identical for the single crystals ( ca. 0.005/M carbon) and the polycrystalline specimens ( ca. 9/M carbon). At low temperatures, the temperature dependence of the yield stress was smaller than that of the flow stress at high strains, probably because of the effects of mechanical twinning, but once again the behaviour of single and polycrystalline specimens was very similar. Below 10 °K, both the flow stress and the extrapolated yield stress were independent of temperature. The results show that macroscopic yielding and flow at low temperatures are both governed by the same deformation mechanism, which is not very impurity sensitive, even in the very low carbon range covered by the experiments. The flow stress near 0 °K is ca. 5.8 x 10 -3 u where [i is the shear modulus. On the basis of a model for thermally activated flow, the activation volume at low temperatures (high stresses) is found to be ca. 5 b 3 . The exponent in the empirical power law for the dislocation velocity against stress relation is ca. 3 near room temperature, but becomes quite large at low temperatures. The results indicate that macroscopic deformation at low temperatures is governed by some kind of lattice frictional stress (Peierls-Nabarro force) acting on dislocations.

Sign in / Sign up

Export Citation Format

Share Document