Anomalous slip in body-centred cubic metals.

Area of Science:

• Materials Science
• Solid Mechanics
• Crystallography

Background:

• Crystal plasticity and strength depend on dislocation motion and interactions.
• Body-centered cubic (BCC) metals exhibit complex plasticity, with slip occurring on systems not having maximum resolved shear stress, especially at low temperatures.
• This phenomenon, known as anomalous slip, deviates from typical crystallographic deformation patterns.

Purpose of the Study:

• To investigate the underlying mechanisms responsible for anomalous slip in BCC metals.
• To elucidate the role of dislocation interactions and junction formation in controlling plastic deformation.
• To reconcile experimental observations with theoretical predictions regarding dislocation behavior.

Main Methods:

• In situ tensile testing within a transmission electron microscope (TEM) to observe dislocation dynamics.
• Atomistic simulations to model dislocation interactions and junction stability.
• Analysis of dislocation glide velocities and junction formation under stress.

Main Results:

• Anomalous slip in BCC metals is attributed to the high mobility of multi-junctions (junctions of >2 dislocations).
• These multi-junctions glide at velocities significantly exceeding those of single dislocations.
• Dynamic conditions allow the formation of binary junctions, predicted to be unstable in elastically anisotropic BCC metals like tungsten.

Conclusions:

• The high mobility of dynamically formed multi-junctions is the primary cause of anomalous slip in BCC metals.
• Experimental and simulation results confirm the existence and significance of these mobile junctions.
• This finding explains the widespread occurrence of anomalous slip across various BCC metals, including tungsten.