*2.3. Experimental Methods*

After laser processing, the cross-sections of each unit were cut parallel to the laser direction, and their width and depth were observed under an optical microscope (OLYMPUS, PMG3, Tokyo, Japan). The microstructure was characterized on a scanning electron microscope (SEM, Zeiss, Evo18, Oberkochen, Germany), when the unit cross-sections were smoothed with sandpaper, polished with woolen polished cloth and then corroded for 40 s with a 4% nitric acid alcohol solution. The microhardness of the units was measured using a digital micro hardness meter (Hua Yin, HVS-1000A, Beijing, China) with a 200 g applied load. In addition, phase structures were determined by X-ray diffraction (D/Max, 2500PC, Tokyo, Japan) equipped with Cu Ka radiation at an operating voltage of 40 kV, and a current of 40 mA and a scanning speed of 4◦/min.
