The key difference between dislocation creep and diffusion creep is that dislocation creep is the movement of dislocations through the crystal structure of a material, whereas diffusion creep is the diffusion of vacancies through crystal lattice occurs.
A deformation in physical chemistry refers to the continuum mechanics transformation of a body from a reference structure to a current structure.
CONTENTS
1. Overview and Key Difference
2. What is Dislocation Creep
3. What is Diffusion Creep
4. Side by Side Comparison – Dislocation Creep vs Diffusion Creep in Tabular Form
5. Summary
What is Dislocation Creep?
Dislocation creep is a type of deformation mechanism in crystalline materials that involves the movement of dislocations through the crystal lattice of the material. This is the mechanism opposite to that of diffusion creep. The dislocation creep causes the plastic deformation of individual crystals, thus, the material itself.
This type of deformation is very sensitive to the differential stress on the material. For example, at very low temperatures, dislocation creep is the dominant deformation mechanism in most crystalline materials.
Figure 01: An Edge Dislocation Creep in a Diagram
Dislocation creep in crystals takes place due to the movement of dislocations throughout the crystal lattice. When a dislocation is moving through the crystal, a part of the crystal tends to shift by one lattice point along a plane (which occurs relative to the rest of the crystal). The plane by which the shifted and unshifted regions are separated is named the slip plane. In order to allow this movement, all the ionic chemical bonds along the slip plane must get broke at once. Further, this bond breaking requires so much energy, in theory, to make it possible to take place the dislocation creep. Assuming that the movement takes place stepwise, the bond breaking is immediately followed by a new bond creating at a low energy level.
Due to the movement of a dislocation stepwise through a crystal lattice, it is possible to create a linear lattice defect between the parts of the crystal lattice. There are two types of dislocation creeps named edge and screw dislocations. In an edge dislocation creep, the edge of an extra layer of atoms inside the crystal lattice forms. In screw dislocation creep, it forms a line along which the crystal lattice jumps one lattice point.
What is Diffusion Creep?
Diffusion creep is a type of deformation mechanism in crystalline materials where the diffusion of vacancies through the crystal lattice occurs. This deformation technique causes plastic deformation rather than the brittle failure of the material.
This deformation type is comparatively more sensitive to the temperature than other types of deformations that take place in crystal lattices. Diffusion creep typically takes place at high homologous temperatures. Further, diffusion creep causes the migration of crystalline defects through the crystal lattice in a way that when a crystal is undergoing a greater degree of compression in one direction compared to another direction. There, the migration of the defects occurs towards the crystal faces along the direction of the compression. This causes a net mass transfer that causes the shortening of the crystal in the direction where maximum compression takes place.
Typically, crystals are not perfect on microscale. This is because some sites of atoms in this crystal lattice get occupied by point defect, particles or vacancies. These vacancies can be considered as chemical species that can be treated using heterogeneous phase equilibria. In this phenomenon, the number of vacancies is influenced by the number of chemical impurities in the crystal. These vacancies can move through the crystal structure due to the “jump” of neighbouring particles.
What is the Difference Between Dislocation Creep and Diffusion Creep?
A deformation in physical chemistry refers to the continuum mechanics transformation of a body from a reference structure to a current structure. The key difference between dislocation creep and diffusion creep is that dislocation creep is the movement of dislocations through the crystal structure of a material whereas diffusion creep is the diffusion of vacancies through crystal lattice occurs.
The below infographic tabulates the differences between dislocation creep and diffusion creep for side by side comparison.
Summary – Dislocation Creep vs Diffusion Creep
Dislocation creep and diffusion creep are two types of deformation mechanisms in crystal lattices. The key difference between dislocation creep and diffusion creep is that dislocation creep is the movement of dislocations through the crystal structure of a material, whereas diffusion creep is the diffusion of vacancies through crystal lattice occurs.
Reference:
1.“Diffusion Creep.” ScienceDirect Topics, Available here.
Image Courtesy:
1. “Disloc coin”- The original uploader was Fredmom at French Wikipedia. – Transferred from fr.wikipedia to Commons by User:zbisasimone. via Commons Wikimedia