Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 20 of 36 for “"Grain Boundary Sliding"”.
-
Atomistic Study of Grain Boundary Sliding
… In both the creep deformation and damage, grain boundary sliding (GBS) plays a critical role. For example, in ceramics, GBS is the predominant mechanism since dislocation activity is quite suppressed. Although decades of work have gone in understanding GBS, there are several open questions …
-
A finite element model of grain boundary sliding for nanostructured metals
… metals, i.e., polycrystalline metals with grain sizes in the nanometer range, have elicited significant interest recently due to their potential for achieving higher material strength in combination with increased formability at lower temperatures and higher strain rates, among other …
-
Multiscale modeling of rate dependence and size effects on nanocrystalline metallic thin films
… large fraction of atoms that lie on the grain boundaries. The grain-boundary structure differs from the crystal lattice by presenting a less ordered arrangement, which promotes diffusion-based deformation mechanisms. The small grain size also affects dislocation-based mechanisms that …
-
High temperature creep behavior of Inconel 617 and Haynes 230
… mechanisms, including dislocation creep and grain boundary sliding, were found for the stress range of 10 to 55 MPa at 850oC, 900oC and 950oC for Alloy 617. In the contrast, only dislocation creep was found for Alloy 230 at 850oC, different from the creep mechanism with both grain boundary …
-
Atomistic simulations of deformation in Metallic Nanolayered Composites
… the roles of the interlayer spacing (grain size, d) and the intralayer biphase spacing (layer thickness, h) on mechanical response of Cu/Nb MNCs are examined by Molecular Dynamics (MD) simulations. The study of the strength of MNCs show that small changes in both d and h play a …
-
Atomistic Molecular Dynamics Studies of Grain Boundary Structure and Deformation Response in Metallic Nanostructures
… in this dissertation focuses on the response of grain boundaries in polycrystalline metallic nanostructures to applied strain using molecular dynamics simulations and empirical interatomic force laws. The specific goals of the work include establishing how local grain boundary structure affects …
-
Tensile Stress and Thermal Growth Effects on Grain Boundary Motion in Nanocrystalline Nickel
… involve molecular dynamics (MD) simulations of grain boundary motion in nanocrystalline (nc) nickel. The first study is conducted to examine the effects of an applied tensile stress on the grain boundary motion in 5 nm3 nc-Ni specimens, half of which contain free surfaces, while the other half …
-
Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods
… mechanical properties to their nanoscale grain size and high density of crystalline interfaces called grain boundaries. Recently, nanotwinned structures, containing special grain boundaries called twin boundaries, have become quite attractive as optimal motifs for strength, ductility, and …
-
Study of Nanowires Using Molecular Dynamics Simulations
… System X located at Virginia Tech. Thermal grain growth simulations were performed on 4 nm grain size nc-Ni by observing grain sizes over time for temperatures from 800K to 1450K and we discovered grain growth to be linearly time-dependant, contrary to coarse grained materials with square …
-
Densification and Mechanical Properties of Nanocrystalline FeAl
… is attributed to a deformation mechanism of grain boundary sliding. The discrepancy between the stress exponent in sinterforging and impression creep tests is attributed to the lower stresses employed in the impression creep experiments, suggesting different mechanisms are presumably in …
-
Continuum models of deformation mechanisms in nanocrystalline metals
… metals are polycrystalline metals with grain sizes in the nanometer range. They have attracted significant interest in recent years due to their unique mechanical and electrical properties. The main objective of this thesis is to develop continuum-scale descriptions of nanoscale …
-
Effects of Carbon on Fracture Mechanisms in Nanocrystalline BCC Iron - Atomistic Simulations
… investigated. It was found that as the average grain size changes the dominant energy release mechanism also changes. Because of this the role of the intergranular carbon changes and these mechanisms compete affecting the fracture toughness differently with changing grain size. Grain boundary …
-
Weakening of ice by magnesium perchlorate hydrate
… as an interconnected film between ice grains. These results suggest that grain boundary sliding (GBS) may be enhanced with respect to pure ice. As the enhancement of GBS is expected in polycrystalline aggregates containing a few percent melt or otherwise weak material distributed along …
-
The development of titanium nitride strengthened creep resistant ferritic steels
… play an important role in the development of the grain structure. The initial evaluation of the creep rupture properties found them to be very poor, below that of the base material. This was due to two factors; relatively coarse titanium nitride particles and very fine grain size (due to the …
-
Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust
… thermometry, stress is estimated from grain size, and deformation mechanisms are analyzed by microstructure and the presence or absence of a lattice preferred orientation (LPO). Our analyses indicate that mylonite layers deformed at a strain rate in the range of 10-12 to 10- 11 s-1, …
-
Control of Microstructure and Texture in Nanocrystalline Transition -Metal Nitride Coatings by Ion Beam Assisted Deposition Method
… density and the reactivity of Cr and N. The grain sizes, determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), were in nano-scale (∼15nm) when ion to atom ratio (J I/JM) = 2. Results of XRD pole figures showed that the films were highly textured. By the control …
-
Plagioclase preferred orientation in the layered mylonites : evaluation of flow laws for the lower crust
… thermometry, stress is estimated from grain size, and deformation mechanisms are analyzed by microstructure and the presence or absence of a lattice preferred orientation (LPO). Our analyses indicate that mylonite layers deformed at a strain rate in the range of 1012 to 101 s-1, while …
-
Multiscale In-Situ Characterization of Crystal Orientation, Temperature, and Microstructure Effects on Creep Defromation of Pure Magnesium and Mg-Al-RE Alloys
… resistance by obstructing dislocation glide and grain boundary sliding. A Hall-Petch-like relationship between β-phase spacing and creep displacement highlights microstructural refinement as a pathway to improved high-temperature performance. This work establishes advanced testing methodologies …
-
High temperature deformation mechanisms and strain heterogeneities in calcite rocks
… variations in reorientation of individual grains and heterogeneous deformation within the polycrystalline material. In Chapter 3, a new technique including a series of sample preparation and image analysis algorithms is developed to provide quantitative measurements of the scale of …
-
Creep crack initiation and growth in 2.25% chromium - 1% molybdenum alloy steel
… Evolution of M<sub>23</sub>C<sub>6</sub> grain boundary carbides to the equilibrium carbide, M<sub>6</sub>C, and the affect of the grain boundary sliding on the shape of the M<sub>6</sub>C, were proposed to be the most important microstructural phenomena contributing to the crack …
Page 1 of 2