scholarly journals Survey of Grain Boundary Energies in Tungsten and Beta-Titanium at High Temperature

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 156
Author(s):  
Hong He ◽  
Shangyi Ma ◽  
Shaoqing Wang
Keyword(s):  
Heat Treatment ◽  
Molecular Dynamics ◽  
High Temperature ◽  
Grain Boundary ◽  
Body Centered Cubic ◽  
Molecular Statics ◽  
Hexagonal Close Packed ◽  
Bcc Metals ◽  
Α Phase ◽  
Beta Titanium

Heat treatment is a necessary means to obtain desired properties for most of the materials. Thus, the grain boundary (GB) phenomena observed in experiments actually reflect the GB behaviors at relatively high temperature to some extent. In this work, 405 different GBs were systematically constructed for body-centered cubic (BCC) metals and the grain boundary energies (GBEs) of these GBs were calculated with molecular dynamics for W at 2400 K and β-Ti at 1300 K and by means of molecular statics for Mo and W at 0 K. It was found that high temperature may result in the GB complexion transitions for some GBs, such as the Σ11{332}{332} of W. Moreover, the relationships between GBEs and sin(θ) can be described by the functions of the same type for different GB sets having the same misorientation axis, where θ is the angle between the misorientation axis and the GB plane. Generally, the GBs tend to have lower GBE when sin(θ) is equal to 0. However, the GB sets with the <110> misorientation axis have the lowest GBE when sin(θ) is close to 1. Another discovery is that the local hexagonal-close packed α phase is more likely to form at the GBs with the lattice misorientations of 38.9°/<110>, 50.5°/<110>, 59.0°/<110> and 60.0°/<111> for β-Ti at 1300 K.

scholarly journals Molecular Dynamics Simulation on Creep Behavior of Nanocrystalline TiAl Alloy

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1693
Author(s):  
Fei Zhao ◽  
Jie Zhang ◽  
Chenwei He ◽  
Yong Zhang ◽  
Xiaolei Gao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Grain Size ◽  
Steady State ◽  
High Temperature ◽  
Grain Boundary ◽  
Tial Alloy ◽  
Boundary Diffusion ◽  
Dislocation Motion ◽  
High Temperature Creep ◽  
Creep Stage

TiAl alloy represents a new class of light and heat-resistant materials. In this study, the effect of temperature, pressure, and grain size on the high-temperature creep properties of nanocrystalline TiAl alloy have been studied through the molecular dynamics method. Based on this, the deformation mechanism of the different creep stages, including crystal structure, dislocation, and diffusion, has been explored. It is observed that the high-temperature creep performance of nanocrystalline TiAl alloy is significantly affected by temperature and stress. The higher is the temperature and stress, the greater the TiAl alloy’s steady-state creep rate and the faster the rapid creep stage. Smaller grain size accelerates the creep process due to the large volume fraction of the grain boundary. In the steady-state deformation stage, two kinds of creep mechanisms are manly noted, i.e., dislocation motion and grain boundary diffusion. At the same temperature, the creep mechanism is dominated by the dislocation motion in a high-stress field, and the creep mechanism is dominated by the diffusion creep in the low-stress field. However, it is observed to be mainly controlled by the grain boundary diffusion and lattice diffusion in the rapid creep stage.

scholarly journals Eliminating continuous grain boundary α phase in laser melting deposited near β titanium alloys by heat treatment

2019 ◽  
Vol 563 ◽  
pp. 022025
Author(s):  
Penglin Li ◽  
Changmeng Liu ◽  
Jie Wang ◽  
Jiping Lu ◽  
Shuyuan Ma ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Titanium Alloys ◽  
Laser Melting ◽  
Α Phase

A Molecular Dynamics Study on Pressure Dependence of Ag Diffusion in Ag3SI

2010 ◽  
Vol 72 ◽  
pp. 337-342
Author(s):  
Masakazu Yarimitsu ◽  
Masaru Aniya
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
High Temperature ◽  
Pressure Dependence ◽  
Distribution Functions ◽  
Intermediate Temperature ◽  
Β Phase ◽  
Α Phase ◽  
Method Of Molecular Dynamics ◽  
Pair Distribution Functions

The pressure dependence of the diffusion coefficient in the superionic α- and β-phases of Ag3SI has been studied by using the method of molecular dynamics. It is shown that in the high temperature α-phase, the Ag diffusion coefficient decreases with pressure. On the hand, in the intermediate temperature β-phase, the Ag diffusion coefficient exhibits a maximum at around 2.8 GPa. The structural origin of this behavior is discussed through the pressure dependence of the pair distribution functions.

Microstructural Evolution and Precipitation Mechanism of α-Phase in Ti-55531 Alloy Aged at High Temperature

2013 ◽  
Vol 747-748 ◽  
pp. 912-918 ◽  
Author(s):  
Xue Zhang ◽  
Yi Chen ◽  
Feng Shou Zhang ◽  
Jun Ting Yang ◽  
Yun Jin Lai ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Boundary Energy ◽  
High Energy ◽  
Ageing Temperature ◽  
Α Phase ◽  
Temperature Ageing ◽  
Annealing Heat Treatment

After two-stage annealing heat treatment process, the near β-Titanium alloys reveal a mixed microstructure containing lath-like α phase and finer acicular α phase in β matrix, leading to the improvement of strength-ductility balance. In this paper, the microstructural evolution and the behaviour of α precipitate during high temperature ageing process were investigated by SEM in a near β-Titanium alloy called Ti-55531.The relationship between α precipitates and the β grain orientation in high temperature was investigated by EBSD. The results show that the α-phase precipitated only at some places of the β grain boundaries at higher ageing temperature (~780 °C); the amount of grain boundary α increased with the decreased of the ageing temperature; after ageing at 720 °C for 45 min, we found that the α-phase precipitated not only at grain boundaries but also within the grains. It seems that the precipitation of grain boundary α is strongly influenced by β grain boundary energy which means that grain boundary α tends to form preferentially at high energy grain boundaries (high-angle grain boundaries); The α-phase precipitates more easily at the grain boundaries where the {110} plane of adjacent β grains have the same orientation.

scholarly journals Effect of Heat treatment on Microstructure and Mechanical Properties of Ti-6Al-2Zr-1Mo-1V Bar

2020 ◽  
Vol 321 ◽  
pp. 11046
Author(s):  
Xu Enen ◽  
Tian Yanwen ◽  
Hao Fang ◽  
Cu Linin ◽  
Du Yuxuan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Tensile Strength ◽  
High Temperature ◽  
Microstructure Evolution ◽  
Second Stage ◽  
Β Phase ◽  
Α Phase ◽  
Duration Time ◽  
Stage Heat Treatment

In this paper, the microstructure evolution and mechanical properties fluctuation of Ti-6Al-2Zr-1Mo-1V forging state bar after the first stage heat treatment at 950℃~955℃ and the second stage heat treatment at 760℃~840℃ were studied. In the first stage of heat treatment, the content of primary α and the tensile strength decreases with the increase of temperature, and the high temperature duration time is obviously prolonged. During the second stage of heat treatment, the metastable β phase precipitates third α phase, and with the increase of temperature, the tensile strength increases and the high temperature duration time prolongs.

Heat Treatment Microstructures of a Directionally Solidified Nickel Base Superalloy under High Temperature Gradient

2014 ◽  
Vol 788 ◽  
pp. 519-524
Author(s):  
Wei Guo Zhang ◽  
Xue Mei Yi ◽  
Chu Ang Feng
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Temperature Gradient ◽  
Grain Boundary ◽  
Solution Treatment ◽  
Grain Boundary Sliding ◽  
Chinese Script ◽  
Nickel Base Superalloy ◽  
Directionally Solidified ◽  
High Temperature Gradient

The heat treatment of a directionally solidified superalloy under high temperature gradient with different dendritic size was studied. The evolution rules of each phase in DZ125 alloy after heat treatment were analyzed. The results show that γ' phase presents cube and uniform distribution after heat treatment. Its size is about 0.4μm and its area ratio is about 65%. MC carbide transforms into MC(2) carbide with high concentration of Hf. The morphology of MC carbide changes from Chinese-script to block and its size reduces gradually with increasing solidification rate under directional solidification. There is bulk γ' phase around carbide. MC(2) carbide and γ' phase in the grain boundary form chain along grain boundary, and effectively retard grain boundary sliding. γ+γ' eutectic is basically eliminated by solution treatment and only a little γ+γ' eutectic exists around carbide.

scholarly journals Molecular Dynamics Simulation of High-Temperature Creep Behavior of Nickel Polycrystalline Nanopillars

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2606
Author(s):  
Xiang Xu ◽  
Peter Binkele ◽  
Wolfgang Verestek ◽  
Siegfried Schmauder
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Grain Boundary ◽  
Creep Behavior ◽  
Activation Energies ◽  
Dynamics Simulation ◽  
Dislocation Creep ◽  
Creep Process ◽  
High Temperature Creep ◽  
Temperature Creep

As Nickel (Ni) is the base of important Ni-based superalloys for high-temperature applications, it is important to determine the creep behavior of its nano-polycrystals. The nano-tensile properties and creep behavior of nickel polycrystalline nanopillars are investigated employing molecular dynamics simulations under different temperatures, stresses, and grain sizes. The mechanisms behind the creep behavior are analyzed in detail by calculating the stress exponents, grain boundary exponents, and activation energies. The novel results in this work are summarized in a deformation mechanism map and are in good agreement with Ashby’s experimental results for pure Ni. Through the deformation diagram, dislocation creep dominates the creep process when applying a high stress, while grain boundary sliding prevails at lower stress levels. These two mechanisms could also be coupled together for a low-stress but a high-temperature creep simulation. In this work, the dislocation creep is clearly observed and discussed in detail. Through analyzing the activation energies, vacancy diffusion begins to play an important role in enhancing the grain boundary creep in the creep process when the temperature is above 1000 K.

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