The Deformation Microstructure in NI3Si Polycrystals Strained Over the Range of Temperature of Flow Stress Anomaly

1988 ◽  
Vol 133 ◽  
Author(s):  
B. Tounsia ◽  
P. Beauchamp ◽  
Y. Mishima ◽  
T. Suzuki ◽  
P. Veysslière
Keyword(s):  
Flow Stress ◽  
Slip System ◽  
Room Temperature ◽  
Peak Temperature ◽  
Effect Of Temperature ◽  
Screw Dislocations ◽  
Thermally Activated ◽  
Cube Plane ◽  
Octahedral Slip ◽  
Increasing Temperature

ABSTRACTIn order to correlate the flow stress anomaly of Ni3Si with dislocation properties, a weakbeam study ofpolycrystalline samples deformed between ambient and the peak temperature was carried out. Samples with two extreme Ni/Si ratios were tested.The most frequently activated slip system changes progressively from octahedral to cubic with increasing temperature. The transformation of superdislocations into Kear-Wilsdorf configurations gives rise to screw dislocations that are rectilinear only after deformation at room temperature. The effect of temperature is to gradually promote bending of Kear-Wisdorf configurations in the cube plane, from a few nanometers at 230°C to several tenths of micrometers at intermediate temperature. Cube slip begins to be massively activated a little below the peak temperature. It is suggested that the flow stress anomaly is controlled by progressive exhaustion of octahedral slip by thermally-activated expansion of superdislocations on the cube cross-slip plane.

Slip trace characterisation of Ni3Al by atomic force microscopy.

2000 ◽  
Vol 646 ◽  
Author(s):  
Christophe Coupeau ◽  
Tomas Kruml ◽  
Joël Bonneville
Keyword(s):  
Atomic Force Microscopy ◽  
Flow Stress ◽  
Plastic Strain ◽  
Slip System ◽  
Mean Free Path ◽  
Force Microscopy ◽  
Atomic Force ◽  
Slip Traces ◽  
Octahedral Slip ◽  
Increasing Temperature

ABSTRACTWe examined by atomic force microscope the slip traces produced on Ni3Al single crystals pre-deformed up to nearly 1% plastic strain at three temperatures in the anomaly domain: 293K, 500K and 720K. It is observed that, whatever the deformation temperature, the slip traces essentially belong to the primary octahedral slip system. The lengths of the slip lines become shorter and shorter with increasing temperature, while the number of dislocations that constitutes the lines is approximately constant. These results are interpreted in terms of a decreasing mean free path of the mobile dislocations when the temperature is raised. The implications of these results in the understanding of the flow stress anomaly are underscored.

Effect of Temperature on Crater Formation and Ejecta Composition in Aluminum Alloy Targets

2012 ◽  
Vol 706-709 ◽  
pp. 768-773
Author(s):  
Masahiro Nishida ◽  
Koichi Hayashi ◽  
Junichi Nakagawa ◽  
Yoshitaka Ito
Keyword(s):  
Aluminum Alloy ◽  
High Temperature ◽  
Low Temperature ◽  
Room Temperature ◽  
Effect Of Temperature ◽  
Crater Formation ◽  
Influence Of Temperature ◽  
Gas Gun ◽  
Influence Of Temperature On ◽  
Increasing Temperature

The influence of temperature on crater formation and ejecta composition in thick aluminum alloy targets were investigated for impact velocities ranging from approximately 1.5 to 3.5 km/s using a two-stage light-gas gun. The diameter and depth of the crater increased with increasing temperature. The ejecta size at low temperature was slightly smaller than that at high temperature and room temperature. Temperature did not affect the size ratio of ejecta. The scatter diameter of the ejecta at high temperature was slightly smaller than those at low and room temperatures.

Dislocation Core Structure and the Normal Yield Behavior of L12 Ordered Alloys

1984 ◽  
Vol 39 ◽  
Author(s):  
G. Tichy ◽  
V. Vitek ◽  
D. P. Pope
Keyword(s):  
Yield Stress ◽  
High Temperatures ◽  
Flow Behavior ◽  
Dislocation Core ◽  
Screw Dislocations ◽  
Thermally Activated ◽  
Normal Behavior ◽  
Ordered Alloys ◽  
Increasing Temperature ◽  
Good Agreement

ABSTRACTA rapid increase of the yield stress with increasing temperature, often observed in L12 ordered alloys, is commonly called the “anomalous flow behavior”. This phenomenon is believed to result from the thermally activated transformation of the core of 1/2<110> screw dislocations from a glissile form to a sessile form at high temperatures. It is shown here that another class of L12 alloys exists in which these two forms of the screw dislocation core are not available. These are the alloys in which the APB on {111} planes is not stable and the atomistic studies of screw dislocations in such alloys show that their cores are always sessile. The yield stress of these alloys then increases with decreasing temperature and no increase at high temperatures occurs. Such behavior has been observed, for example, in Pt3Al. This “normal” behavior is analogous to that of b.c.c. metals and a theory of the temperature dependence of the yield stress has been developed along the same lines as in the case of b.c.c. metals. Comparison of this theory with measurements on Pt3Al single crystals shows a good agreement.

Effect of Temperature and Strain Rate on the Mechanical Properties of 99.5 Aluminium Rods Extruded by KOBO

2016 ◽  
Vol 879 ◽  
pp. 230-235
Author(s):  
Sonia Boczkal ◽  
Marzena Lech-Grega ◽  
Wojciech Szymanski ◽  
Paweł Ostachowski ◽  
Marek Lagoda
Keyword(s):  
Strain Rate ◽  
Room Temperature ◽  
High Strain ◽  
Effect Of Temperature ◽  
Recrystallization Process ◽  
Extrusion Force ◽  
Strain Rates ◽  
High Strain Rates ◽  
Constant Frequency ◽  
Increasing Temperature

In this study, aluminium rods were cold extruded in a direct process by KOBO method in two variants: variant I with varying (decreasing) frequency of die oscillations necessary to maintain a constant extrusion force, and variant II with constant frequency of die oscillations, leading to a decrease in the extrusion force. The tensile test of rods was carried out in a temperature range of 20 - 200°C and at a strain rate from 8xE10-5 to 8xE10-1 s-1. Significant differences in the elongation of the tested rods were observed. It was found that rods extruded at variable die oscillations and stretched at room temperature had similar elongation, independent of the strain rate. With the increase of temperature, the elongation of samples stretched at a low speed was growing from a value of about 8% at room temperature up to 40% at 200°C. At high strain rates, despite the increasing temperature, the elongation remained at the same level, i.e. 5-6%. In rods extruded at constant die oscillations, the elongation at a low strain rate was growing with the temperature from 10% at room temperature up to 29% at 200°C. At high strain rates, the elongation decreased from 28% at room temperature to 11% at 200°C. The results were interrelated with examinations of the structure of rods and fractures of tensile specimens. In the material extruded by KOBO method with constant die oscillations, the beginnings of the recrystallization process were observed, absent in the material extruded at variable die oscillations.

The Effect of Temperature on the Material Damping of Graphite/Epoxy Composites in a Simulated Space Environment

1990 ◽  
Vol 112 (3) ◽  
pp. 277-279 ◽  
Author(s):  
G. T. Spirnak ◽  
J. R. Vinson
Keyword(s):  
Room Temperature ◽  
Damping Ratio ◽  
Theoretical Models ◽  
Space Environment ◽  
Effect Of Temperature ◽  
Time Cost ◽  
Material Damping ◽  
Temperature Dependent ◽  
Increasing Temperature ◽  
Free Beam

An experimental method for measuring material damping is described, which employs a free-free beam lightly supported at the nodes. A thermal space environment is simulated by measuring the material damping in air at temperatures ranging from −65°F to 225°F, and then subtracting out the effects of atmospheric damping. This method saves considerable time, cost and experimental difficulties associated with performing the experiments in a vacuum. Graphite/epoxy AS4/3501-6 composite beam specimens were tested. At room temperature, the [0°]12 composites were found to have an average damping ratio of 0.0556 percent. The [90°]12 composites were found to have an average material damping ratio of 0.55 percent. These data agree well with the theoretical models and experimental measurements performed in a vacuum. The material damping ratio is temperature dependent over the range −65°F to 225°F, increasing with increasing temperature. For the [0°]12 composite, the material damping ratio varies from 0.0397 percent at −65°F to 0.083 percent at 225°F. For the [90°]12 composite, the material damping ratio varies from 0.408 percent at −65°F to 0.860 percent at 225°F.

Infrared spectra of the ammonium ion in crystals. Part VII. Existence of symmetrically trifurcated hydrogen bond in ammonium halides

1980 ◽  
Vol 58 (3) ◽  
pp. 270-282 ◽  
Author(s):  
Osvald Knop ◽  
Wolfgang J. Westerhaus ◽  
Michael Falk
Keyword(s):  
Room Temperature ◽  
Ammonium Ion ◽  
Effect Of Temperature ◽  
Hydrogen Bonding Interaction ◽  
Maximum Probability ◽  
Threefold Axis ◽  
Ammonium Halides ◽  
Bonding Interaction ◽  
Increasing Temperature

This investigation deals with the effect of temperature, between 10 and 293 K, on the ir spectrum of the NH3D+ probe ion in polycrystalline NH4SnF3, NH4CuSO3, cubic (NH4)2SiF6, and (NH4)2SnCl6. The results lead to the following conclusions. At 10 K these crystals contain symmetrically trifurcated [Formula: see text] bonds, i.e. bonds in which the N—H orientation of maximum probability is on the threefold axis. With increasing temperature these bonds lose progressively their symmetrically-trifurcated character to become highly bent, highly dynamic [Formula: see text]•bonds, and the strength of the hydrogen-bonding interaction increases. This is reflected in the decrease of the ND stretching frequency of the probe ion with increasing temperature, which is the opposite of the behaviour observed with normal (i.e. essentially straight) [Formula: see text] bonds.Re-determination of the room-temperature crystal structure of NH4CuSO3 has confirmed the correctness of the structure reported previously by Nyberg and Kierkegaard.

scholarly journals The Effect of Temperature and Mo Content on the Lattice Misfit of Model Ni-Based Superalloys

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 700 ◽  
Author(s):  
Amy J. Goodfellow ◽  
Lewis R. Owen ◽  
Katerina A. Christofidou ◽  
Joe Kelleher ◽  
Mark C. Hardy ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Room Temperature ◽  
Lattice Misfit ◽  
Lattice Parameter ◽  
Lattice Parameters ◽  
Effect Of Temperature ◽  
General Decrease ◽  
Mo Content ◽  
Increasing Temperature ◽  
Mo Additions

The lattice parameters and misfit of the γ and γ′ phases in a series of model quaternary Ni-based superalloys with and without Mo additions have been determined using neutron diffraction between room temperature and 700 °C. Despite the fact that Mo is typically expected to partition almost exclusively to the γ phase and thereby increase the lattice parameter of that phase alone, the lattice parameters of both the γ and γ′ phases were observed to increase with Mo addition. Nevertheless, the effect on the γ lattice parameter was more pronounced, leading to an overall decrease in the lattice misfit with increasing Mo content. Alloys with the lowest Mo content were found to be positively misfitting, whilst additions of 5 at.% Mo produced a negative lattice misfit. A general decrease in the lattice misfit with increasing temperature was also observed.

Properties of the Deformation Microstructure in Al-Rich γ-TiAl Deformed by Ordinary Dislocations

1999 ◽  
Vol 578 ◽  
Author(s):  
Fabienne Grjégori ◽  
Patrick VeyssiÈRe
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Peak Temperature ◽  
Clear Correlation ◽  
Microstructural Investigation ◽  
Screw Dislocations ◽  
Burgers Vector ◽  
Dislocation Pinning ◽  
The Relationship ◽  
Line Direction

AbstractIn the near vicinity of the [021] load orientation, γ-TiAl deforms via ordinary dislocations (Burgers vector b = 1/2<110]). As for deformation by <110] dislocations, the flow stress shows a peak at about 600°C. Results of an extensive microstructural investigation aimed at identifying the origin of this mechanical anomaly are presented. The analysis was conducted on single crystals oriented for single slip. It confirmed that ordinary dislocations tend to align themselves along the screw direction. This preferential line direction becomes gradually accentuated as the deformation temperature is raised up to the peak temperature. This effect is accompanied by a strong tendency towards forming cusps, but there is indication that the immobilisation along the screw direction takes place prior to dislocation pinning. In the vicinity of the peak temperature, screw dislocations gather in the form of bundles. No clear correlation is found between the temperature dependence of the flow stress and that of the density of pinning points. The relationship between these microstructural findings and the occurrence of a flow stress anomaly is discussed.

Effect of Temperature and Loading Frequency on the Fatigue Behavior of Ti-17

2015 ◽  
Vol 664 ◽  
pp. 131-139 ◽  
Author(s):  
Jiu Kai Li ◽  
Yong Jie Liu ◽  
Qing Yuan Wang ◽  
Fang Hou
Keyword(s):  
Room Temperature ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Effect Of Temperature ◽  
Fatigue Properties ◽  
Frequency Effect ◽  
Loading Frequency ◽  
Ultrasonic Fatigue ◽  
Increasing Temperature

A high-temperature ultrasonic fatigue testing system was developed to evaluate the gigacycle fatigue properties of Ti-17. Ultrasonic (20 kHz) fatigue tests were performed at room temperature, 200°C and 350°C, respectively. The dynamic Young’s modulus and fatigue endurance limit decrease with increasing temperature linearly. Rotating bending (50 Hz) tests were performed to evaluate the influence of loading frequency at room temperature, 200°C and 350°C, respectively. There is an obviously loading frequency effect at elevated temperature, although no loading frequency effect at room temperature.

An Analysis of The Slip of Screw Dislocations in Ll2 Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
Patrick Veyssière ◽  
Lem
Keyword(s):  
Numerical Simulation ◽  
Applied Stress ◽  
External Load ◽  
Elastic Anisotropy ◽  
Cross Slip ◽  
Screw Dislocations ◽  
Thermally Activated ◽  
Cube Plane

ABSTRACTThe annihilation of dislocations by cross-slip is studied by numerical simulation of infinitely long dissociated screw dislocations, allowed to move in an elastically anisotropie crystal. The external load is along [123] and cross-slip is permitted both on the octahedral and on the cube plane. The latter, together with cube slip, is thermally activated. Anisotropie elasticity modifies the properties of cross-slip significantly. Under the conditions of the simulations, the processes of APB jumps (APBJs) and repeated APB jumps (RAPBJs) can be largely promoted by interactions with other dislocations, while it is much less likely to occur at an isolated dislocation submitted to the same applied stress. The encounter of dislocations of opposite signs produces dipoles which may or may not tend to annihilate by cross-slip. APB tubes may form upon annihilation under certain circumstances again largely controlled by elastic anisotropy.

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