In this paper, we report the characterization of springback degradation of an Invar sheet with a combination of gamma-ray irradiation and repeated hot-then-cold stresses. The springback factor value of fresh Invar without radiation shows a linear increase with the number of hot-then-cold stress cycles. Continuous springback degradations are observed as the number of hot-then-cold stress cycles reaches 100. When the Invar sheet is subjected to gamma-ray irradiation, the springback factor is greater than that of the repeated hot-then-cold stressed samples. After applying the repeated hot-then-cold stresses to the post-irradiated Invar sheets, the springback factors are first restored to the value of fresh Invar, and then revert to an increasing trend. Our previous X-ray diffraction (XRD) analysis excluded the crystalline structural changes in the post-irradiated Invar. It is believed that the radiation-induced defects, which are closely related to the springback degradation, are possibly annealed during the first 20 hot-then-cold stress cycles. These cycles ultimately dominate the springback behavior of the stressed Invar sheets.

In this paper, we report a new phenomenon observed in the gamma-ray radiation-induced hydrophobic effects on an Invar surface: When the Invar alloy is subjected to different doses of gamma-ray irradiation, the contact angle increases with the radiation dose. Invar samples with exposed to a higher dose appear more hydrophobic, but this tendency disappears following post-irradiation etching. The contact angles of the irradiated and etched Invar samples can be restored back to a stable value with small deviation after 30 min of annealing at 150°C. X-ray diffraction (XRD) analysis found no crystalline structural changes. High resolution field emission scanning microscope (FE-SEM) analyses showed that irradiation might induce crack-like surfaces which could be removed at higher radiation dose in the following acid etchings. It is believed that the chemical bonds of Invar oxide on the surface were broken by the gamma-ray irradiation, thus raising the likelihood of binding with free ions in the air and resulting in the exclusion of the hydrophilic OH bonds, leaving a hydrophobic post-irradiation Invar surface.