*2.4. Characterization of the Coatings*

The surfaces of coated specimens were analyzed using XRD (model Rint-2500; Rigaku Corp., Tokyo, Japan) via a parallel-beam method using Cu–K*α* radiation (40 kV; tube current: 100 mA). Representative specimens were analyzed over the 2θ range from 10 to 60◦ using a step size of 0.02◦ and a scan speed of 0.25◦/min. The XRD patterns were obtained at 25 ◦C and analyzed qualitatively using PDXL2 software (Rigaku) based on the International Center for Diffraction Data (ICDD) database for phase identification and quantification.

To observe the coated layers and analyze their compositions on the cross-sectioned surface, specimens were encapsulated in an epoxy resin (Epofix; Struers, Copenhagen, Denmark) and cross-sectioned with a slow-speed, water-cooled diamond saw (Isomet; Buehler, Lake Bluff, IL, USA), then ground and polished using a series of silicon carbide abrasive papers and a final slurry of 0.05-μm alumina particles. All specimens were sputter-coated with pure gold for scanning electron microscopy (SEM) evaluation (model SSX-550; Shimadzu); the SEM was operated at 15 kV. The composition of a coated specimen was determined by energy-dispersive X-ray spectroscopy (EDS) at a working distance of 15 mm and a data acquisition time of 300 s.
