Structural Characterization of Nickel-Base Alloy C-276 Irradiated with Ar Ions

The irradiation damage in nickel-base alloy C-276 irradiated with 115 keV Ar ions from low to very high doses was investigated. Structural characterization was performed using transmission electron microscopy (TEM), grazing incident X-ray diffraction (GIXRD) and atomic force microscopy (AFM). High density of interstitial type dislocation loops could be observed at a dose level of around 2.75 displacements per atom (dpa). With the irradiation dose increased to 27.5 dpa, the average size of loops increased from 5 nm to 16 nm, while the density of the loops decreased from 1.4 × 1011/cm2 to 4.6 × 1010/cm2. When the irradiation dose reached 82.5 dpa, original grains were transformed into subgrains whose sizes observed from TEM were about 20-60 nm. The fragmentation of grains was confirmed by GIXRD. The mean subgrain size was 40 nm, which was obtained from the full width at half maximum (FWHM) of the X-ray diffraction lines using the Scherrer formula and Williamson formula. AFM micrographs showed that nanometer-sized hillocks formed at the dose of 82.5 dpa, which provided further evidence of grain fragmentation at a high irradiation dose.     

Corrosion characteristics of Hastelloy N alloy after He+ ion irradiation

With the goal of understanding the invalidation problem of irradiated Hastelloy N alloy under the condition of intense irradiation and severe corrosion, the corrosion behavior of the alloy after He⁺ ion irradiation was investigated in molten fluoride salt at 700 °C for 500 h. The virgin samples were irradiated by 4.5 MeV He⁺ ions at room temperature. First, the virgin and irradiated samples were studied using positron annihilation lifetime spectroscopy (PALS) to analyze the influence of irradiation dose on the vacancies. The PALS results showed that He⁺ ion irradiation changed the size and concentration of the vacancies which seriously affected the corrosion resistance of the alloy. Second, the corroded samples were analyzed using synchrotron radiation micro-focused X-ray fluorescence, which indicated that the corrosion was mainly due to the dealloying of alloying element Cr in the matrix. Results from weight-loss measurement showed that the corrosion generally correlated with the irradiation dose of the alloy.     

Effect of high temperature annealing on ferromagnetism induced by energetic ion irradiation in FeRh alloy

Effects of thermal annealing on ion-irradiation induced ferromagnetism of Fe-50at.%Rh bulk alloy and the related structural change were investigated by means of superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS), respectively. Depending on the annealing temperature from 100 to 500 °C, the magnetization induced by 10 MeV iodine ion irradiation and the lattice structure of the alloy were remarkably changed. After 500 °C annealing, the magnetization and the lattice ordering of the alloy become similar to the states before the irradiation. The experimental result indicates that the thermal relaxation of irradiation-induced atomic disordering dominates the magnetic state of ion-irradiated Fe-50at.% Rh alloy.