*3.1. Grain Number across Wall Thicknesses of Staring Materials*

Figure 4 shows the IPF maps of the starting materials. The average grain size *g* of the stainless-steel, copper, and aluminum alloy tubes were 9 µm, 17 µm, and 71 µm, respectively. Therefore, the grain numbers across the wall thicknesses of starting materials *t*0/*g* of the stainless-steel, copper, and aluminum alloy tubes were 23, 12, and 3, respectively.

**Figure 4.** Inverse pole figure (IPF) maps of the starting materials. The symbols DD, TD, and ND indicate drawing direction, transversal direction, and normal direction, respectively. The grain boundaries were drawn on as black lines on IPF maps, using the OIM AnalysisTM.
