Diffusion of nitrogen in plasma nitrided iron and structural evolution during the nitriding process were evaluated by several characterization techniques including optical microscopy (OM), microhardness depth profiling (HDP), scanning electron microscopy (SEM), x-ray diffraction (XRD), glow discharge optical emission spectroscopy (GDOES), and secondary ion mass spectroscopy (SIMS). Plasma nitriding was carried out on high purity iron substrate at a temperature of 550°C in an atmosphere of 75%H2 25%N2. Case depth, thickness of the compound layer, micro-hardness profile, nitrogen depth profile, and characteristics of intermediate nitrides including epsilon, gamma prime, and Fe16N2 were studied. The results of characterization of plasma nitrided iron indicated a good agreement with experimental findings; thus, the techniques confirmed one another. For accurate measurement of nitrogen within the diffusion zone, where concentration was below 0.1 wt%, secondary ion mass spectroscopy technique was used. The extent of nitrogen diffusion detected by secondary ion mass spectroscopy in this work was greater than 1800mm; a value which is not reported in the literature.

Two-step anodizing approach is a simple way to produce an adhesive and continuous layer while improving the stability of titanium oxide in aggressive aqueous media. A comparative study of the electrochemical behavior of TiO2 anodic films formed by single-step (SSA) and two-step (TSA) anodizing processes has been investigated. The anodic films have been characterized by SEM, EDX, GDOES, XRD, and FTIR analysis. Potentiodynamic polarization and EIS were used to investigate corrosion behavior in corrosive environments. A completely different surface morphology of anodic films has been obtained. Surface oxide film thicknesses of specimens were estimated at 51.86 and 60.67 µm for the SSA and TSA processes, respectively. In both cases, X-ray diffraction revealed an amorphous nature. EIS results showed that corrosion performance is closely related to anodic film morphology including thick layers, compactness, uniformity, and stability, as proved by the TSA process. Analysis of dynamic potential polarization confirmed that the TSA approach enhanced corrosion resistance by increasing (Ecorr) and lowering (Icorr). The corrosion potential (Ecorr) increased from -0.309 V/ECS to -0.271 V/ECS for the SSA and TSA and the Icorr value decreased from 1.410 μA.cm-2 to 1.032 μA.cm-2 for SSA and TSA approaches respectively.