Partnerzy

Streszczenie:
The objective of the present study is to investigate the hardening behavior, superelastic recovery, and structural properties of NiTi Shape Memory Alloy (SMA) after 10 MeV high-energy Fe+ ion irradiation to damage levels of 1.2 and 6.0 d.p.a (displacements per atom). According to Stopping and Range of Ions in Matter (SRIM) calculations, Secondary Ion Mass Spectroscopy (SIMS) analysis, and Transmission Electron Microscopy (TEM) imaging, a 3-micron irradiation layer was obtained with an amorphous structure; the maximum values of damage and Fe+ ion concentration occurred at 2.4 and 2.7 microns, respectively. The mechanical response was characterized in two-direction nanoindentation tests: parallel and perpendicular to the ion beam direction. Cross-sectional nanoindentation indicates that the maximum hardening corresponds to the maximum of the Fe+ ion concentration; the maximum hardness was found at 2.7 microns for both d.p.a. levels. The changes in superelastic properties were achieved in the amorphous layer that suppressed the B2-B19′ phase transformation at a sub-micron scale. We show that cross-sectional nanoindentation is an appropriate method for determining the subtle micromechanical property changes in near-surface regions. It also allows the material and structural properties at a selected point in the non-homogeneous irradiated layer to be correlated with the local level of irradiation damage or ion concentration. This is very important in the development of SMAs and their applications in nuclear technologies