Mohsin Rafique

Electrochemical behavior of hydrogen precipitated Zircaloy-4

This work investigates the hydrogen precipitation effects on the electrochemical behavior of Zircaloy-4 in acidic saline media. The specimens of Zircaloy-4 were hydrogen charged at 200, 400 and 600 ppm concentrations for 30 min at 400∘C. X-ray diffraction (XRD) studies confirmed the formation of delta hydrides in the material. Scanning electron microscopy (SEM) results also indicated the presence of elongated hydrides whose density and thickness increased with the increase of hydrogen concentration in the alloy. The corrosion kinetics of the specimens were explored before and after hydrogen precipitation using potentiodynamic anodic polarization (PAP) and electrochemical impedance spectroscopy (EIS) techniques. The results showed that hydrogen precipitation shifts the corrosion potential towards more positive and thus improves the corrosion resistance of the alloy. The charge transfer resistance (Rct) of the alloy was found to increase with increasing hydrogen concentration. This indicates an increased polarization tendency of the Zircaloy-4 surface with a limited dissolution tendency in the presence of delta hydrides.

Improvement in the pitting resistance of Inconel-600 by nitrogen ions implantation

The surface of Ni-Cr-Fe (Inconel-600) alloy was modified by implanting 500 keV nitrogen ions at room temperature using pelletron accelerator to dose of 1.87 × 1014 ions/cm2. X-ray diffraction analysis of the ions implanted samples indicated the formation of Cr2N phase. Electrochemical testing of Inconel-600 alloy before and after the ions implantation was conducted using potentiodynamic tafel scan, potentiodynamic anodic polarization and electrochemical impedance spectroscopy techniques in an acidic saline solution. The higher anodic polarization slope (βa), low cathodic polarization slope (βc) and decrease in corrosion current density after ions implantation were attributed to the modification of passive film by the nitrogen ions. The scanning electron microscopy and electrochemical analyses of the ions implanted samples revealed an improvement in the pitting resistance of the alloy.

Microstructural features and mechanical properties of 18 MeV He+ ions irradiated pure Zr

Samples of pure zirconium (Zr) were irradiated by 18 MeV helium (He+) ions in the dose range 0.00162–0.0324 dpa at 373 K by using Cyclotron accelerator. The atomic force microscopy (AFM) results indicated an increase in average surface roughness of Zr by increasing the irradiation dose. The AFM images revealed nucleation and growth of nano- and micro-size hillocks at lower doses (0.00162–0.00324 dpa), whereas formation of a volcano-like cavities and craters was observed within these hillocks by increasing the radiation dose from 0.00324 to 0.0324 dpa. The high-resolution X-ray diffraction (XRD) results showed a variation in the intensities and positions of the diffraction peaks after the irradiation. The transmission electron microscopy (TEM) results reported a significant decrease in the grain size after the He+ irradiation. The values of grain size, calculated using the TEM, were found to be in good agreement with the crystallite size calculated using the XRD analysis. The yield stress (YS) was increased by increasing the irradiation dose up to 0.0162 dpa, however, the YS exhibited a decreasing trend with a further increase of the dose. The changes in YS were elucidated by grain size reduction and localized heating at higher doses.

Effects of 3.5 MeV proton irradiation on pure zirconium

The effects of high energy proton irradiation on pure zirconium were investigated in this study. The annealed Zr specimens (50 mm × 3 mm × 0.8 mm) were irradiated by 3.5 MeV hydrogen ions with dose ranges from 1×1013 to 1 × 1015 ions/cm2 at 335 K. The range of the proton beam penetration was measured to be 68-70 μm, depending on the surface, which is in good agreement with the SRIM simulation results. X-ray diffractometer analysis revealed that the peak intensity of the basal plane increased and the position of the peak shifted due to the proton irradiation. Field emission scanning electron microscopy results showed that with increasing irradiation dose hydrogen micro-bubbles formed, concentrated, interconnected, and eventually burst due to the excessive hydrogen pressure inside, causing surface-crack development. Measured yield and ultimate tensile strength seemed to be insignificantly affected by the proton irradiation.