Effect of He-irradiation fluence on the size-dependent hardening and deformation of nanostructured Mo/Zr multilayers

• Published in: International journal of plasticity 2018-12, Vol.111, p.36-52
• Main Authors: Wu, S.H., Cheng, P.M., Wu, K., Hou, Z.Q., Wang, Y.Q., Liang, X.Q., Li, J., Kuang, J., Zhang, J.Y., Liu, G., Sun, J.
• Format: Article
• Language: English
• Subjects: Damage tolerance; Deformation effects; Deformation mechanisms; Dependence; Dislocations; Dynamic strain aging; Fluence; Grain boundaries; Ion irradiation; Irradiation; Mechanical properties; Mo/Zr multilayers; Multilayers; Nanostructure; Nanostructured materials; Plastic deformation; Precipitation hardening; Radiation damage; Size effects; Strain rate; Strain rate sensitivity; Thickness; Zirconium
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2018.07.008

Previous studies demonstrated that the He ion irradiation damage tolerance of nanostructured metallic multilayers (NMMs) was closely dependent on the layer thickness (h): smaller h led to lower irradiation hardening. Here in Mo/Zr NMMs, we uncovered that the h-dependent irradiation hardening and corresponding plastic deformation characteristics are also sensitive to the He+ irradiation fluences. At a low irradiation fluence of 1.0 × 1016 He+·cm−2, the irradiation hardening decreased monotonically with reducing h. While at a high irradiation fluence of 1.0 × 1017 He+·cm−2, a non-monotonic h-dependence was unexpectedly displayed with the minimum irradiation hardening at h of ∼25 nm. The irradiation fluence also affects the strain rate sensitivity (m) remarkably. Irradiation of 1.0 × 1016 He+·cm−2 induced a transition in SRS m from positive in the as-deposited Mo/Zr NMMs to negative SRS in their irradiated counterparts. This transition was rationalized in terms of dynamic strain aging that considered dislocation-bubble interactions. Irradiation of 1.0 × 1017 He+·cm−2, however, resulted in a non-monotonic h-dependence of m, with the bottom located at a turning point of h ∼50 nm. Coupling effect of the layer thickness and the applied fluence on irradiation hardening and plastic deformation characteristics was quantitatively elucidated by employing a strengthening model and a thermally activated model, respectively, where parameters of the characteristic microstructural features, i.e., the layer thickness and irradiation (He) defects, were both included. [Display omitted] •The Mo/Zr NMMs with smaller h display the greater radiation resistance with a lower bubble density.•Under the high-fluence irradiation, a critical thickness h (∼15 nm) exists below which the irradiation hardening becomes more significant.•The low-fluence irradiated Mo/Zr NMMs present the negative SRS m, while the high-fluence irradiated Mo/Zr NMMs present the non-monotonic size-dependent positive SRS m.