Tracking Grain Refinement After Severe Plastic Deformation

How Fine Is Fine Enough?

Severe plastic deformation techniques like ECAP are designed to push metals beyond their conventional grain size limits. But once grains shrink into the hundreds-of-nanometers range, conventional metallographic approaches start to fall short.

Without clear visibility into orientation and grain boundary behavior, it becomes difficult to assess whether a process sequence is producing the intended results, or whether it’s time to adjust parameters.

High-resolution SEM and EBSD mapping are used to assess microstructure after multi-pass deformation

The material under investigation was a commercially pure aluminum alloy processed through eight ECAP passes, introducing a high level of cumulative strain.

The following imaging sequence was conducted using a Tescan CLARA UHR SEM:

1. SE and BSE imaging with wide-angle signal capture to obtain both channeling contrast and topographic information

EBSD mapping performed on two regions:

1. 150 × 100 µm for texture overview

2. 40 × 25 µm for high-detail inspection

BrightBeam™ electron optics delivered field free UHR characterization, while In-Flight Beam Tracing™ ensured seamless and fast application of optimal beam imaging and analytical conditions. Spot Optimization was used to enable detailed mapping of large areas, even at high beam currents. 

Evidence of Microstructural Progress

The SEM images capturing channeling contrast revealed different crystal orientations for individual grains after ECAP processing. This helped with identifying regions of interest for subsequent EBSD analysis.

The EBSD maps confirmed significant grain refinement, with features reduced to the submicron scale. Orientation data revealed preferential alignment of grains in specific directions, consistent with ECAP-induced shear patterns. The results were suitable for pole figure analysis, giving further insight into the deformation texture.

Altogether, these methods provide both visual and quantitative confirmation that ECAP processing achieved its structural goal: creating a fine-grained, texture-controlled aluminum alloy.