Lecture

Thermally Activated Dislocation Motion

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In course

PHYS-307: Physics of materials

This course discusses materials physics associated with the mechanical and structural properties of solids, primarily focusing on the physics of dislocation defect dynamics and linking diffusion kinetics to the fundamental physics of phase transformations. ...

Description

This lecture covers the thermally activated motion of dislocations, starting with the Orowan equation and the concept of activation energy. It delves into the calculation of Gibbs free energy, activation volume, and the geometric aspects of dislocation climb. The instructor discusses experimental measurements of thermodynamic parameters, the concentration of jogs, and the climb velocity of dislocations. Special cases like jogs on a screw dislocation and steady-state creep are also explored, providing insights into the mechanisms governing dislocation motion.

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Instructor

Thomas La Grange

Expertise Electron Microscopy, Aberration Correct Scanning Transmission Electron Microscopy, Electron Diffraction, Ultrafast Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, Energy Dispersive Spectroscopy, Materials Science, High-speed deformation, Dislocation Dynamics, Skyrmionics, Martensitic Phase Transformation Theory, Solidification Expertise Electron Microscopy, Aberration Correct Scanning Transmission Electron Microscopy, Electron Diffraction, Ultrafast Transmission Electron Micro

Official source

Related concepts (28)

Dislocation

In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to slide over each other at low stress levels and is known as glide or slip. The crystalline order is restored on either side of a glide dislocation but the atoms on one side have moved by one position. The crystalline order is not fully restored with a partial dislocation.

Gibbs free energy

In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol ) is a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure-volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure. It also provides a necessary condition for processes such as chemical reactions that may occur under these conditions. The Gibbs free energy is expressed as where p is pressure, T is the temperature, U is the internal energy, V is volume, H is the enthalpy, and S is the entropy.

Laws of thermodynamics

The laws of thermodynamics are a set of scientific laws which define a group of physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems in thermodynamic equilibrium. The laws also use various parameters for thermodynamic processes, such as thermodynamic work and heat, and establish relationships between them. They state empirical facts that form a basis of precluding the possibility of certain phenomena, such as perpetual motion.

Thermodynamic free energy

In thermodynamics, the thermodynamic free energy is one of the state functions of a thermodynamic system (the others being internal energy, enthalpy, entropy, etc.). The change in the free energy is the maximum amount of work that the system can perform in a process at constant temperature, and its sign indicates whether the process is thermodynamically favorable or forbidden. Since free energy usually contains potential energy, it is not absolute but depends on the choice of a zero point.

Cross slip

In materials science, cross slip is the process by which a screw dislocation moves from one slip plane to another due to local stresses. It allows non-planar movement of screw dislocations. Non-planar movement of edge dislocations is achieved through climb. Since the Burgers vector of a perfect screw dislocation is parallel to the dislocation line, it has an infinite number of possible slip planes (planes containing the dislocation line and the Burgers vector), unlike an edge or mixed dislocation, which has a unique slip plane.

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