Intermittent plasticity in individual grains: A study using high energy x-ray diffraction

Area of Science:

• Materials Science
• Solid Mechanics
• Crystallography

Background:

• Plasticity in metals is known to exhibit intermittent behavior.
• Connecting microscopic dislocation dynamics to macroscopic stress relaxation in bulk polycrystals remains challenging.
• Understanding these connections is crucial for predicting material failure and designing advanced alloys.

Purpose of the Study:

• To investigate the link between dislocation motion and stress relaxation during plastic deformation.
• To characterize intermittent plastic deformation events within individual grains of metallic alloys.
• To compare the intermittent plasticity behavior of a titanium alloy (Ti-7Al) and a magnesium alloy (AZ31).

Main Methods:

• Utilized high-energy X-ray diffraction (XRD) measurements.
• Employed far-field high-energy diffraction microscopy to determine complete grain stress states.
• Combined macroscopic stress relaxation data with rapid XRD spot measurements using a Mixed-Mode Pixel Array Detector.
• Monitored dislocation content by analyzing the 3D evolution of XRD spot intensity distributions.

Main Results:

• Observed significant stress fluctuations indicative of intermittent plastic flow in the Ti-7Al alloy.
• Found that the AZ31 magnesium alloy exhibited a lesser degree of intermittent plastic flow compared to Ti-7Al.
• Successfully linked changes in dislocation content within deforming grains to macroscopic stress relaxation events.

Conclusions:

• High-energy X-ray diffraction is effective in characterizing intermittent plastic deformation at the grain level.
• The Ti-7Al alloy demonstrates more pronounced intermittent plasticity than the AZ31 alloy.
• This work provides direct evidence connecting microscopic dislocation behavior to macroscopic stress relaxation phenomena in metallic alloys.