How do grain boundaries interact with dislocations?

Grain boundaries and interfaces between dissimilar metals can act as sinks, traps and sources of lattice dislocations. On interacting with a grain boundary, the leading lattice dislocations can become incorporated in it and the others will form a dislocation pile-up at the point of intersection.

Why do grain boundaries hinder dislocation motion?

Since the lattice structure of adjacent grains differs in orientation, it requires more energy for a dislocation to change directions and move into the adjacent grain. The grain boundary is also much more disordered than inside the grain, which also prevents the dislocations from moving in a continuous slip plane.

What is the effect of grain boundaries?

Grain boundaries are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep.

What is grain boundary dislocation?

Dislocations can move through the crystal grains and can interact with each other (1). Grain boundaries often hinder their transmission, creating a dislocation pile-up at the boundary and thereby making the material harder to deform.

How do you observe dislocations?

Dislocations can be observed in the transmission electron microscope (TEM). Due to the lattice distortion of around the core of the dislocation, some Bragg diffraction of the electron beam occurs in a localised region around the core.

What is Hall Petch effect?

The Hall–Petch relationship tells us that we could achieve strength in materials that is as high as their own theoretical strength by reducing grain size. Indeed, their strength continues to increase with decreasing grain size to approximately 20–30 nm where the strength peaks.

How do grain boundaries affect strength of a material?

Smaller grains have greater ratios of surface area to volume, which means a greater ratio of grain boundary to dislocations. The more grain boundaries that exist, the higher the strength becomes.

What type of defects are grain boundaries?

A grain boundary is a planar defect that occurs where two such crystallites meet—the same crystal structure and chemical composition exists on each side but the orientation differs.

What is grain boundary embrittlement?

Grain boundary embrittlement occurs when a solute enriches at a grain boundary and lowers its cohesive energy.

How is grain boundaries formed?

Grain boundaries are usually the result of uneven growth when the solid is crystallizing. Grain sizes vary from 1 µm to 1 mm. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid.