*3.4. Sub-Surface Features of the Weld*

Similar to the transition region HAZ/TMAZ, the surface region of the weld also experiences plastic deformation. The saw-tooth feature at the weld crown (region 1, Figure 2a) corresponds to the plastic deformation and the dynamic slip-stick engagement between the material and the shoulder. Figure 10 illustrates a gradient of the size of grains laterally (Regions A-B-C).
