A Numerical Analysis of Deformation Processes in Oxide Dispersion-Strengthened Materials - Influence of Dislocation-Particle Interactions

2016 ◽  
Vol 258 ◽  
pp. 106-109
Author(s):  
Tomáš Záležák ◽  
Filip Šiška ◽  
Luděk Stratil ◽  
Natália Luptáková ◽  
Miroslav Šmíd ◽  
...  
Keyword(s):  
High Temperature ◽  
Applied Stress ◽  
Boundary Migration ◽  
Particle Interaction ◽  
Dislocation Dynamics ◽  
Critical Threshold ◽  
Particle Interactions ◽  
Scale Level ◽  
Creep Tests ◽  
Individual Dislocation

A recently developed 3D discrete dislocation dynamics (DDD) model is employed to study kinetics of dislocation ensembles subjected to high temperature creep in microstructures of metal matrix composites. We particularly focus on a migration of low angle tilt boundaries in a field of rigid impenetrable particles. This type of dislocation boundaries represents a typical microstructural feature mediating plastic deformation during the high temperature loadings. The article compares results of numerical studies that considered distinct dislocation-particle in-teractions in order to describe the response of dislocation structure to the applied stress. The resultssuggest that, regardless the details related to the dislocation-particle interactions, a critical applied stress always exists, below which the boundary migration process ceases [1,2]. The existence of crit-ical threshold is confirmed by creep tests of ODS materials. This critical threshold, contrary to theclassical Orowan stress, is proportional to the dislocation density. The displacements of individual dislocation segments on the micro-scale level reflect the changes in the dislocation-particle interactions quite sensitively. Atthemacro-scale level, the overall strain rate, which averages out velocities of all the individual dislocation segments, is also significantly influenced by the changes in dislocation-particle interaction

Creep Property of Boron Added 9Cr Heat Resistant Steels after Welding

2018 ◽  
Vol 941 ◽  
pp. 340-345
Author(s):  
Tetsuya Matsunaga ◽  
Maaouia Souissi ◽  
Ryoji Sahara ◽  
Hiromichi Hongo ◽  
Masaaki Tabuchi ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Rapid Heating ◽  
Boundary Migration ◽  
Creep Property ◽  
Creep Tests ◽  
Precipitate Morphology ◽  
Premature Failure ◽  
Heat Resistant ◽  
Type Iv

Although welding results in premature failure by type IV fracture under high temperature creep conditions, the alloy design of light elements such as boron addition and nitrogen reduction enhances the creep lifetime of 9Cr heat resistant steel. In particular, the simulated heat affected zone (SHAZ) sample of new 9Cr steel (called TA steel) shows about 10 times longer creep lifetime than that of the standard Gr. 91 steel. The welded TA steel is thus expected to exhibit good creep properties because its SHAZ sample has coarser grains and suppresses type IV fracture. The preservation of base metal’s microstructure after welding results from the precipitate morphology, such as high grain boundary coverage by precipitates and low amount of MX being nucleation sites of ferrite grains during the a-g phase transformation. In addition, the increase of stability of M23C6 affects high pinning pressure toward grain boundary migration upon rapid heating during welding. First-principles calculations confirm the increased stability when boron is absorbed by M23C6. Moreover, the calculations reveals that boron decreases the coherency between matrix and M23C6, suppressing grain coarsening during creep tests in TA steel. It is concluded that the increased microstructural stability during welding and long high temperature exposure generates the elongated creep lifetime in welded TA steel including about 0.01 wt% boron and less than 0.01 wt% nitrogen.

scholarly journals Dislocation Densities and Velocities within the γ Channels of an SX Superalloy during In Situ High-Temperature Creep Tests

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1527 ◽  
Author(s):  
Thomas Schenk ◽  
Roxane Trehorel ◽  
Laura Dirand ◽  
Alain Jacques
Keyword(s):  
High Temperature ◽  
Plastic Strain ◽  
Applied Stress ◽  
Load Transfer ◽  
Von Mises Stress ◽  
High Temperature Creep ◽  
Creep Tests ◽  
Temperature Creep ◽  
Von Mises

The high-temperature creep behavior of a rafted [001] oriented AM1 Ni-based single crystal superalloy was investigated during in situ creep tests on synchrotrons. Experiments were performed at constant temperatures under variable applied stress in order to study the response (plastic strain, load transfer) to stress jumps. Using two different diffraction techniques in transmission (Laue) geometry, it was possible to measure the average lattice parameters of both the γ matrix and the γ ′ rafts in the [100] direction at intervals shorter than 300 s. The absolute precision with both diffraction techniques of the constrained transverse mismatch (in the rafts’ plane) is about 10−5. After stress jumps, special attention is given to the evolution of plastic strain within the γ channels. The relaxation of the Von Mises stress at leveled applied stress shows evidence of dislocation multiplication within the γ channels. From the analysis, we showed an interaction between plastic stress and dislocation density of the γ phase.

Increased Thermal Stability of Co-silicide Using Co-Ta Alloy Films

2001 ◽  
Vol 670 ◽  
Author(s):  
Min-Joo Kim ◽  
Hyo-Jick Choi ◽  
Dae-Hong Ko ◽  
Ja-Hum Ku ◽  
Siyoung Choi ◽  
...  
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Grain Boundary ◽  
Reaction Rate ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Alloy Films ◽  
Post Annealing ◽  
Alloy Process ◽  
Thermal Stability Of

ABSTRACTThe silicidation reactions and thermal stability of Co silicide formed from Co-Ta/Si systems have been investigated. In case of Co-Ta alloy process, the formation of low resistive CoSi2phase is delayed to about 660°C, as compared to conventional Co/Si system. Moreover, the presence of Ta in Co-Ta alloy films reduces the silicidation reaction rate, resulting in the strong preferential orientation in CoSi2 films. Upon high temperature post annealing in the furnace, the sheet resistance of Co-silicide formed from Co/Si systems increases significantly, while that of Co-Ta/Si systems maintains low. This is due to the formation of TaSi2 at the grain boundaries and surface of Co-silicide films, which prevents the grain boundary migration thereby slowing the agglomeration. Therefore, from our research, increased thermal stability of Co-silicide films was successfully obtained from Co-Ta alloy process.

Creep Properties and Interfacial Microstructure of SiC Whisker Reinforced Si3N4

1989 ◽  
Vol 170 ◽  
Author(s):  
Håkan A. Swan ◽  
Colette O'meara
Keyword(s):  
High Temperature ◽  
Creep Resistance ◽  
Interfacial Microstructure ◽  
Deformation Mechanisms ◽  
Amorphous Films ◽  
Creep Tests ◽  
Creep Properties ◽  
High Temperature Exposure ◽  
Temperature Exposure

AbstractPreliminary creep tests were performed on SiC whisker reinforced and matrix Si3N4 material fabricated by the NPS technique. The material was extensively crystallised in the as received material, leaving only thin amorphous films surrounding the grains. No improvement in the creep resistance could be detected for the whisker reinforced material. The deformation mechanisms were found to be that of cavitation in the form of microcracks, predominantly at the whisker/matrix interfaces, and the formation of larger cracks. Extensive oxidation of the samples, as a result of high temperature exposure to air, was observed for the materials tested at 1375°C.

Cementite Precipitation of a H21 Tool Steel after Hot Compression and Double Temper

2014 ◽  
Vol 1043 ◽  
pp. 154-158
Author(s):  
Meilinda Nurbanasari ◽  
Panos Tsakiropoulos ◽  
Eric J. Palmiere
Keyword(s):  
High Temperature ◽  
Applied Stress ◽  
Tool Steel ◽  
Hot Deformation ◽  
Lower Bainite ◽  
Precipitation Behavior ◽  
Transformation Mechanism ◽  
Tempered Martensite ◽  
Bainite Transformation ◽  
Precipitation Behaviour

The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 oC and 1000 oC and the double temper process was carried out at 650 oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe3C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbides in tempered martensite and decreasing number of single variant carbides occurred in tempered lower bainite.

scholarly journals Dislocation dynamics modelling of the creep behaviour of particle-strengthened materials

2021 ◽  
Vol 477 (2250) ◽  
pp. 20210083
Author(s):  
F. X. liu ◽  
A. C. F Cocks ◽  
E. Tarleton
Keyword(s):  
Elevated Temperatures ◽  
Creep Behaviour ◽  
Particle Interaction ◽  
Three Dimensional ◽  
Cross Slip ◽  
Dislocation Dynamics ◽  
Dislocation Slip ◽  
Fundamental Particle ◽  
Dislocation Glide ◽  
Time Scale Separation

Plastic deformation in crystalline materials occurs through dislocation slip and strengthening is achieved with obstacles that hinder the motion of dislocations. At relatively low temperatures, dislocations bypass the particles by Orowan looping, particle shearing, cross-slip or a combination of these mechanisms. At elevated temperatures, atomic diffusivity becomes appreciable, so that dislocations can bypass the particles by climb processes. Climb plays a crucial role in the long-term durability or creep resistance of many structural materials, particularly under extreme conditions of load, temperature and radiation. Here we systematically examine dislocation-particle interaction mechanisms. The analysis is based on three-dimensional discrete dislocation dynamics simulations incorporating impenetrable particles, elastic interactions, dislocation self-climb, cross-slip and glide. The core diffusion dominated dislocation self-climb process is modelled based on a variational principle for the evolution of microstructures, and is coupled with dislocation glide and cross-slip by an adaptive time-stepping scheme to bridge the time scale separation. The stress field caused by particles is implemented based on the particle–matrix mismatch. This model is helpful for understanding the fundamental particle bypass mechanisms and clarifying the effects of dislocation glide, climb and cross-slip on creep deformation.

scholarly journals Creep damage behavior of red sandstone after high temperature

2021 ◽  
Author(s):  
Xiaokang Pan ◽  
Filippo Berto ◽  
Xiaoping Zhou
Keyword(s):  
High Temperature ◽  
Uniaxial Compression ◽  
Deformation Modulus ◽  
Creep Damage ◽  
Viscosity Coefficient ◽  
Creep Tests ◽  
Red Sandstone ◽  
Instantaneous Strain ◽  
Treated Sample ◽  
Instantaneous Deformation

This work discusses the results from tests conducted to investigate the uniaxial compression and creep behavior of red sandstone. The original untreated sample and the 800 ℃ treated sample have been selected to carry out the experiments. It has been found that high temperature has obvious influence on the mechanical properties of red sandstone. The relationship between creep strain and instantaneous strain, as well as instantaneous deformation modulus and creep viscosity coefficient have been analyzed. It has been found that high temperature reduces the ability of red sandstone to resist instantaneous deformation and creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests, providing a powerful means for damage evolution analysis of red sandstone.

Analysis on Fracture Morphology and Microstructure of T92 Steel after High Temperature Multiaxial Creep

2013 ◽  
Vol 860-863 ◽  
pp. 967-971
Author(s):  
Xue Ping Mao ◽  
Xiao Wang ◽  
Sai Dong Huang ◽  
Chao Li ◽  
Hong Xu ◽  
...  
Keyword(s):  
High Temperature ◽  
Stress State ◽  
Standard Specimen ◽  
Uniaxial Stress ◽  
Fracture Morphology ◽  
Multiaxial Stress ◽  
Creep Life ◽  
Creep Tests ◽  
Multiaxial Stress State ◽  
Multiaxial Creep

The high temperature creep tests of standard specimen and double U-type notch specimen of T92 steel were carried out under different stresses at 650 °C. Then optical microscopy and scanning electron microscopy were used to observe the fracture morphology and microstructure. The results show that the multiaxial stress state leads to the creep fracture cracking initiation in notch. Under multiaxial stress state, the failure mode of T92 steel is transgranular and dimple plastic fracture, and is more obvious with the increase of creep life. Compared with under uniaxial stress state, the precipitates under multiaxial stress state are larger in size and quantity, and are much coarser.

Sign in / Sign up

Export Citation Format

Share Document