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Streszczenie:
In order to utilise NiTi shape memory alloys in environments with extreme radiation, it is essential to understand how irradiation affects their superelastic properties on a nanoscale level. We use a spherical nanoindentation technique in two perpendicular directions, combined with indentation work analysis to evaluate the nanoscale superelastic behavior and functional degradation of Fe+ ion irradiated NiTi. Cross-sectional nanoindentation reveals that the maximum hardening and the lowest superelastic response occur near the depth of peak Fe⁺ concentration (2.6–2.8 μm). Importantly, the superelastic behavior exhibits a non-monotonic dependence on damage level: complete loss of superelastic recovery is observed at 1.7 d.p.a., whereas partial recovery reappears at 8.5 d.p.a., indicating a competition between lattice amorphization and irradiation-mediated. Using cross-sectional nanoindentation, we can capture variations in stiffness and recoverable work at the nanoscale, as a function of depth, that cannot be resolved using conventional surface indentation methods. We conclude that ion irradiation leads to significant hardening and suppression of superelasticity phenomena due to inhibition of the stress-induced B2→B19′ martensitic transformation. These findings demonstrate that two-directional spherical nanoindentation is an effective approach for probing irradiation-induced functional gradients.

Słowa kluczowe:
NiTi SMA, Ion irradiation, Superelasticity, Indentation, Indentation work, Surface modification