The Activation Parameters And The Mechanisms Of Plastic Deformation Of Al-Pd-Mn Single Quasicrystals

1998 ◽  
Vol 553 ◽  
Author(s):  
U. MessersChmidt ◽  
B. Geyer ◽  
M. Bartsch ◽  
M. Feuerbacher ◽  
K. Urban
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Activation Parameters ◽  
Friction Mechanism ◽  
Dislocation Generation ◽  
Voltage Electron ◽  
Video Recordings ◽  
Lower Strain ◽  
First Time

AbstractIn situ straining experiments on Al-Pd-Mn single quasicrystals in a high-voltage electron microscope between 675 °C and 750°C showed viscously moving dislocations with segments oriented in preferred directions. First measurements from video recordings indicate that dislocations on parallel traces move at two different velocities. For the first time, macroscopic samples were deformed in compression below 680 °C. Above a transition temperature of about 635°C for specimens of a fivefold compression axis and a strain rate of 10−5 s−1, the specimens show a yield point followed by a range of steady state deformation. Below that temperature, they are brittle. However, plastic deformation was achieved down to 555°C by using a lower strain rate and performing stress relaxation tests before the fracture stress was reached. The samples then show very strong work-hardening. The rapid decrease of the activation volume with decreasing temperature, which is characteristic of the high-temperature range, does not continue at low temperatures.The results are interpreted by dislocation generation and recovery and by the cluster friction mechanism controlling the dislocation mobility.

scholarly journals Hot Workability of 300M Steel Investigated by In Situ and Ex Situ Compression Tests

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 880 ◽  
Author(s):  
Rongchuang Chen ◽  
Haifeng Xiao ◽  
Min Wang ◽  
Jianjun Li
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Hot Working ◽  
Ex Situ ◽  
Lower Strain Rate ◽  
Hot Workability ◽  
Compression Tests ◽  
300M Steel ◽  
Lower Strain

In this work, hot compression experiments of 300M steel were performed at 900–1150 °C and 0.01–10 s−1. The relation of flow stress and microstructure evolution was analyzed. The intriguing finding was that at a lower strain rate (0.01 s−1), the flow stress curves were single-peaked, while at a higher strain rate (10 s−1), no peak occurred. Metallographic observation results revealed the phenomenon was because dynamic recrystallization was more complete at a lower strain rate. In situ compression tests were carried out to compare with the results by ex situ compression tests. Hot working maps representing the influences of strains, strain rates, and temperatures were established. It was found that the power dissipation coefficient was not only related to the recrystallized grain size but was also related to the volume fraction of recrystallized grains. The optimal hot working parameters were suggested. This work provides comprehensive understanding of the hot workability of 300M steel in thermal compression.

Temperature and Strain Rate Dependence of Deformation-Induced Point Defect Cluster Formation in Metal Thin Foils

2001 ◽  
Vol 673 ◽  
Author(s):  
K. Yasunaga ◽  
Y. Matsukawa ◽  
M. Komatsu ◽  
M. Kiritani
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Cluster Formation ◽  
Vacancy Cluster ◽  
Long Tail ◽  
Vacancy Clusters ◽  
Thin Foils ◽  
Lower Strain ◽  
Wide Range ◽  
Deformation Speed

ABSTRACTThe mechanism of plastic deformation in thin metal foils without involving dislocations was examined by investigating the variations in vacancy cluster formation during deformation for a range of deformation speeds and temperatures. The deformation morphology was not seen to change appreciably over a very wide range of strain rate, 10-4/s – 106/s, whereas the number density of vacancy clusters was observed to increase with increasing strain rate up to saturation value that is dependent on materials and temperature. The density of vacancy clusters decreased to zero with decreasing deformation speed. The strain rate at which the density of vacancy clusters begins to decrease was found to be proportional to the vacancy mobility, suggesting that the vacancies are generated as dispersed vacancies and escape to the specimen surfaces during slow deformation without forming clusters. A very long tail in the distribution of the density of vacancy clusters towards lower strain rates was reasonably attributed to the generation of small vacancy complexes due to deformation. These results give valuable information that can be used to establish new models for plastic deformation of crystalline metals without involving dislocations.

High-Resolution Dynamic Analysis of the Phase Transformation in Ge2Sb2Te5 Alloy

2007 ◽  
Vol 26-28 ◽  
pp. 1199-1202
Author(s):  
Se Ahn Song ◽  
Wei Zhang ◽  
Hong Sik Jeong ◽  
Jin Gyu Kim ◽  
Youn Joong Kim
Keyword(s):  
Phase Transformation ◽  
Crystal Growth ◽  
High Resolution ◽  
Large Scale ◽  
Voltage Electron ◽  
Transmission Electron ◽  
In Situ Heating ◽  
First Time ◽  
Crystal Growth Behavior

Phase transformation and crystal growth behavior of Ge2Sb2Te5 were investigated systematically by means of in situ heating (from room temperature to 500 oC) of amorphous Ge2Sb2Te5 alloy in a high voltage electron microscope with real-time monitoring. Large-scale crystallization occurred to amorphous Ge2Sb2Te5 around 200 oC. Large crystal growth developed on heating from 200 oC to 400 oC, and single crystalline grains grew up to 150 nm. Eventually the onset of partial melting of thin Ge2Sb2Te5 foil was at 500 oC and liquid Ge2Sb2Te5 was observed for the first time by high-resolution transmission electron microscopy. Hexagonal Ge2Sb2Te5 phase remains after a subsequent cooling.

High-Temperature Severe Plastic Deformation of Ferritic Steel by Torsion

2010 ◽  
Vol 667-669 ◽  
pp. 403-408
Author(s):  
Aries Setiawan ◽  
Daisuke Terada ◽  
Nobuhiro Tsuji
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Strain Rate ◽  
Equivalent Strain ◽  
Phase Region ◽  
Low Carbon ◽  
Ultrafine Grained ◽  
Lower Strain ◽  
Higher Temperature ◽  
Torsion Deformation

An ultra-low carbon IF steel was heavily deformed up to an equivalent strain of 36 at various high temperatures of ferrite single-phase region and various strain rates. Effects of temperature and strain rate on the microstructures evolved in torsion deformation were clarified. On the other hand, it was found that homogeneous ultrafine grained structures were not obtained by the present torsion deformation though very high strain was applied. The coarser grain sizes than those obtained by conventional severe plastic deformation (like ARB) were due to the deformation at higher temperature and lower strain rate, but lower fraction of high-angle grain boundaries in the torsion specimen was suggested to be attributed to the characteristics of monotonic torsion (or simple shear) deformation including the way of strain evaluation.

Dislocation Dynamics During the Deformation of Intermetallic Alloys and the Flow Stress Anomaly

1998 ◽  
Vol 552 ◽  
Author(s):  
U. Messerschmidt ◽  
M. Bartsch ◽  
S. Guder ◽  
D. Häussler
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Dislocation Dynamics ◽  
Intermetallic Alloys ◽  
Intrinsic Nature ◽  
Voltage Electron ◽  
Macroscopic Deformation

ABSTRACTIn situ straining experiments on NiAl, NiAl-0.2at% Ta, γ-TiAl, and MoSi2 in a high-voltage electron microscope showed a transition from the obstacle controlled dislocation motion or the Peierls mechanism at low temperatures to either an unstable or viscous motion at high temperatures. It is suggested that the viscous motion is due to the formation of point defect atmospheres around the dislocations, which cause additional drag and may be responsible for the flow stress anomaly in some of these materials. The atmospheres may be of an extrinsic or an intrinsic nature. A new model is proposed for the origin of intrinsic atmospheres assuming that the energy of a dislocation in an intermetallic alloy may be lowest if the dislocations contain a number of point defects in their core. The dragging of atmospheres may lead to an “inverse” dependence of the strain rate sensitivity on the strain rate, as observed experimentally. The macroscopic deformation data of the studied materials are discussed in terms of the model.

In situ experimentation: Seeing is believing

1989 ◽  
Vol 47 ◽  
pp. 610-611
Author(s):  
E. Paul Butler
Keyword(s):  
Environmental Control ◽  
High Surface ◽  
Volume Ratio ◽  
List Type ◽  
Voltage Electron ◽  
Specimen Holder ◽  
High Voltage Electron Microscope ◽  
Two Factors ◽  
First Time

The advent of the high voltage electron microscope (HVEM) in the early 1970's initiated a period of intense interest and growth in dynamic in situ experimentation. The two factors responsible for this change were:– increased volume in the pole-piece gap– increased penetration of thicker samplesIncreased volume freed up space for the stage designer to construct complex yet robust and reliable stages capable of heating/cooling, deformation and environmental control. His task was made easier in side entry stage configurations, which simplified the job of supplying services to and from the specimen holder and provided one ready made axis of tilt along the rod itself. Increased penetration made it possible to observe the true course of many reactions for the first time, overcoming the effects of high surface/volume ratio which so often resulted in a distortion of reaction events in very thin specimens.

Effect of Ion Irradiation on Dislocation Processes in Stainless Steel

2011 ◽  
Vol 1363 ◽  
Author(s):  
Josh Kacher ◽  
Grace S. Liu ◽  
May Martin ◽  
I.M. Robertson
Keyword(s):  
Stainless Steels ◽  
Ion Irradiation ◽  
Electron Tomography ◽  
Austenitic Stainless Steels ◽  
Dislocation Motion ◽  
Irradiation Damage ◽  
Dislocation Generation ◽  
Transmission Electron ◽  
First Time

ABSTRACTThe effects of ion irradiation damage on dislocation generation and propagation in austenitic stainless steels were studied by means of in situ transmission electron microscopy and electron tomography. Tensile samples were irradiated in situ to a dose on the order of 1017 ions/m2 with 1MeV Kr+ and strained at 300 K as well as 673 K. Dislocation motion through the irradiation-obstacle field was jerky and discontinuous, dislocation pile-ups formed in grain interiors and at boundaries, long straight dislocations were generated decorating the channel-matrix walls, and dislocation cross-slip within the channel created debris along the channel leading to channel widening. Electron tomography was applied for the first time to reveal new detail about the dislocation reactions in the channel wall.

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