Interface Structure and Slip Transmission in TI-49AL-3NB

1991 ◽  
Vol 229 ◽  
Author(s):  
Daniel S. Schwartz ◽  
S. M. L. Sastry
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Interphase Boundary ◽  
Elevated Temperatures ◽  
Interface Structure ◽  
Nucleation And Growth ◽  
Slip Bands ◽  
Α Phase ◽  
Slip Transmission

AbstractTwo types of special grain boundaries were examined in Ti-49Al-3Nb deformed at elevated temperatures. The first can be described as a Σ=2 order-changing boundary. This boundary is faceted and results from the nucleation and growth of variants of the γ phase from the parent α phase. The second type of grain boundary is a γ/α2 interphase boundary, and transmission of slip through this type of boundary was examined. Slip transmission from γ into α2 did not produce distinct slip bands in α2,. Slip transmission from γ through α2, and into the next γ lamella was possible even when the next γ lamella was in an orientation rotated relative to the first γ lamella.

Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation Effects

2000 ◽  
Vol 650 ◽  
Author(s):  
S. L. Dudarev
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Nucleation And Growth ◽  
Homogeneous Distribution ◽  
Rate Theory ◽  
Diffusional Growth ◽  
Standard Rate ◽  
Saturation Effects ◽  
Kinetics Of ◽  
Cascade Damage

ABSTRACTThe effect of inhomogeneous nucleation and growth of cavities near grain boundaries illustrates the failure of the standard rate theory to describe the kinetics of phase transformations in irradiated materials under cascade damage conditions. The enhanced swelling observed near grain boundaries is believed to result from the competition between the diffusional growth of cavities and their shrinkage due to the interaction with mobile interstitial clusters. Swelling rates associated with the two processes behave in a radically different way as a function of the size of growing cavities. For a spatially homogeneous distribution of cavities this gives rise to the saturation of swelling in the limit of large irradiation doses.We investigate the evolution of the population of cavities nucleating and growing near a planar grain boundary. We show that a cavity growing near the boundary is able to reach a size that is substantially larger than the size of a cavity growing in the interior region of the grain. For a planar grain boundary the magnitude of swelling at maximum is found to be up to eight times higher than the magnitude of swelling in the grain interior.

Effect of Grain Boundary Energy Anisotropy on Faceting and Migration of Low Angle Grain Boundaries

2014 ◽  
Vol 783-786 ◽  
pp. 1634-1639
Author(s):  
Dmitri A. Molodov ◽  
Jann Erik Brandenburg ◽  
Luis Antonio Barrales-Mora ◽  
Günter Gottstein
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Boundary Energy ◽  
Migration Behavior ◽  
Grain Boundary Energy ◽  
Contrast Imaging ◽  
Orientation Contrast ◽  
And Migration ◽  
Twist Boundaries

The faceting and migration behavior of low angle <100> grain boundaries in high purity aluminum bicrystals was investigated. In-situ technique based on orientation contrast imaging was applied. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry – the energy of pure tilt low angle <100> boundaries is anisotropic, whereas that of mixed tilt-twist boundaries isotropic with respect to boundary inclination.

Grain Boundary Cracking of Nickel-Based Alloy 625 Under Creep Loadings at Elevated Temperatures

2019 ◽  
Author(s):  
Yan Liang ◽  
Yifan Luo ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Power Plants ◽  
Elevated Temperatures ◽  
Thermal Power ◽  
Thermal Power Plants ◽  
Alloy 625 ◽  
Creep Fatigue ◽  
Creep Loading ◽  
Initial Cracks

Abstract Since the operating condition of thermal power plants has become harsher for minimizing the emission of CO2, Ni-based superalloys, such as Alloy 617 and 625, have been used in the plants to replace the conventional ferritic materials. Unfortunately, the increase of coefficient of thermal expansion compared with conventional steels is a concern. In addition, Ni-based superalloys have to suffer creep-fatigue random loading because thermal power plants have to compensate the random output of various renewable energies. It was found that the lifetime of Ni-based superalloys under creep-fatigue loading was much shorter than that under simple fatigue or creep loading. Thus, it has become very important to clarify the crack mechanism and establish the quantitative theory for estimating their lifetime under various loading conditions at elevated temperatures. Thus, the elucidation of the initial damage mechanism of Alloy 625 under various loading is indispensable. Hence, the initial cracking mechanism of Alloy 625 at grain boundaries under creep loading was investigated experimentally. The creep test was applied to small specimens in Argon atmosphere. The change of the micro texture during the creep test was observed by using SEM. It was confirmed that all the initial cracks appeared at certain grain boundaries. The change of the crystallinity was observed by EBSD (Electron Back-Scatter Diffraction) analysis quantitatively. It was found that the local accumulation of dislocations at the cracked grain boundaries caused the initial cracks at those grain boundaries. The initiation of cracks appeared clearly between two grains which had difference of KAM (Kernel Average Misorientation) values larger than 0.2. Therefore, dislocations were accumulated at one side of the grain boundary. By measuring the KAM values near grain boundaries, the appearance of initial cracks can be predicted approximately.

A Physically Based Constitutive Equation for Creep-Damaging Solids

1985 ◽  
Vol 52 (3) ◽  
pp. 615-620 ◽  
Author(s):  
A. J. Levy
Keyword(s):  
Constitutive Equation ◽  
Grain Boundary ◽  
Elevated Temperatures ◽  
Cavity Growth ◽  
Internal Variable ◽  
Nucleation And Growth ◽  
Creep Model ◽  
Steady Creep ◽  
Physically Based ◽  
Power Law Creep

Uniaxial and multiaxial forms of a constitutive equation, characterizing the creep-damaging behavior of metals at elevated temperatures, are developed based on Dyson’s constrained cavity growth mechanism. The model employs a single scalar internal variable which can be identified with the area fraction of cavitated boundaries. This variable, together with the power law creep model is capable of describing steady creep, tertiary creep, and dilatation arising from the nucleation and growth of grain boundary cavities.

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.

Motion of Grain Boundaries: Experiments on Bicrystals

2015 ◽  
Vol 5 ◽  
pp. 247-271
Author(s):  
Dmitri A. Molodov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Misorientation Angle ◽  
Elevated Temperatures ◽  
Activation Enthalpy ◽  
Boundary Migration ◽  
Boundary Energy ◽  
Boundary Plane ◽  
Migration Behavior ◽  
Twist Boundaries

Recent research on grain boundary migration is reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and the experimental results obtained on specially grown bicrystals are presented. Particularly, the investigated faceting and migration behavior of low angle grain boundaries under the curvature force in aluminum bicrystals was addressed. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The migration of planar grain boundaries induced by a magnetic field was measured in bismuth and zinc bicrystals. Various structurally different boundaries were investigated. The results revealed that grain boundary mobility essentially depends on the misorientation angle and the inclination of the boundary plane. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonously with misorientation angle, whereas for low angle boundaries the migration activation enthalpy was virtually the same. The motion of the mixed tilt-twist boundaries under stress was observed to be accompanied by both the translation of adjacent grains parallel to the boundary plane and their rotation around the boundary plane normal.

Atomic Scale Characterization of Oxygen Vacancy Segregation at SrTiO3 Grain Boundaries

2000 ◽  
Vol 654 ◽  
Author(s):  
R.F. Klie ◽  
N. D. Browning
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Oxygen Vacancies ◽  
Elevated Temperatures ◽  
Theoretical Models ◽  
Atomic Scale ◽  
Close Proximity ◽  
Scale Characterization

AbstractWe have examined the structure, composition and bonding at an un-doped 58° [001] tilt grain-boundary in SrTiO3 in order to investigate the control that the grain boundary exerts over the bulk properties. Room temperature and in-situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements indicate that the widely observed electronic properties of grain boundaries may be due to an excess of mobile oxygen vacancies that cause a highly doped n-type region in the close proximity ( ≍ 1 unit cell) to the boundary. These results are shown to be consistent with both theoretical models and lower resolution chemical analysis.

scholarly journals The effect of particles on creep rate and microstructures of granular ice

2008 ◽  
Vol 54 (186) ◽  
pp. 533-537 ◽  
Author(s):  
Min Song ◽  
Ian Baker ◽  
David M. Cole
Keyword(s):  
Creep Rate ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Initial Stress ◽  
Nucleation Rate ◽  
Boundary Migration ◽  
Nucleation And Growth ◽  
Grain Boundary Migration ◽  
Before And After

AbstractThe microstructures of particle-free granular freshwater ice and ice containing 1 wt.% of 50 ± 10 mm uniformly distributed particles were investigated before and after compressive creep to ∼10% strain with stresses of 1.45 MPa at −10°C and 0.4 MPa at −5°C. Creep rates of particle-containing ice were always higher than those of particle-free ice. For an initial stress of 1.45 MPa at −10°C, dynamic recrystallization occurred with new grains nucleating and growing along grain boundaries for both sets of specimens, and the ice with particles showed a higher nucleation rate. Under creep with an initial stress of 0.4 MPa at −5°C, dynamic recrystallization also occurred by the nucleation and growth of new grains along the grain boundaries for ice containing particles, but recrystallization in the particle-free ice occurred through grain boundary migration.

Microstructural Analysis of Spall Damage Nucleation and Growth in Multicrystalline Titanium

2016 ◽  
Author(s):  
Elizabeth V. Fortin ◽  
Andrew D. Brown ◽  
Leda Wayne ◽  
Pedro D. Peralta
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Shock Loading ◽  
Microstructural Analysis ◽  
Nucleation And Growth ◽  
Boundary Effects ◽  
Material Failure ◽  
Face Centered Cubic ◽  
Spall Damage ◽  
Grain Boundary Effects

Shock loading is a dynamic condition that can lead to material failure and deformation modes at the microstructural level such as cracking, void nucleation and growth, and spallation. Knowledge of shock loading and spall failure is of great benefit to understanding ballistic impact in military vehicles and armor, crash impacts in automobiles, space vehicles, and satellite loadings, and geological events such as earthquakes. Furthermore, studying material failure at the microstructural level is important to understand macroscale behavior. Spallation, the nucleation, growth, and coalescence of voids, is a phenomenon where variability at the microscale can affect overall response. By analyzing incipient and intermediate damage patterns at and around interfaces and boundaries on the microstructural level, can help further our understanding of the process leading to damage and provide insight on how to develop stronger structures that can withstand impacts and rapid crack propagation. Most of the existing work has looked into the effect of grain boundaries in spall damage for body and face centered cubic (BCC, FCC) materials, but research is still lacking on grain boundary effects in spall damage in hexagonal close packed materials, such as titanium. Samples of high purity Ti were heat treated to obtain large grains, averaging 250 microns in size (multicrystals), in order to isolate grain boundary effects. These multicrystals were shocked using laser-launched flyer plates at the Trident laser at Los Alamos National Laboratory (LANL) and monitored using a velocity interferometry system for any reflector (VISAR). Pressures used were 5–8 GPa. Samples were soft recovered and cross-sectioned to perform quantitative characterization of damage. Spallation damage observed in the titanium targets was characterized using electron backscattering diffraction (EBSD), optical microscopy, and scanning electron microscopy (SEM) to gather information on the crystallographic characteristics of damage nucleation sites, with emphasis on grain boundaries and grain orientations that lead to damage localization. Initial results show that damage localized along grain boundaries, and the damage mode switched from intergranular to transgranular where grains were larger than average.

Sign in / Sign up

Export Citation Format

Share Document