Ion Irradiation Effects Of Metallic Glasses And Composites

Metallic glasses?MGs?exhibit extremely high strength and superior resistance to corrosion.They are also supposed to be resistant against displacive irradiation due to their inherent disordered structure,and thereby are potential candidates for applications in irradiation environments.Because of their homogenous and isotropic structure and lack of linear and planar defects,MGs are also regarded as the ideal models to study the interaction between energetic ions and materials.In this thesis,the different systems of bulk metallic glasses?BMGs?,MG ribbons and metallic glass matrix composites?MGMCs?were selected.The responses of structure,surface damage and mechanical properties in materials after low energy and high energy ion irradiation are studied in detail.Low energy ion irradiation experiments of BMGs,MG ribbons and MGMCs specimens were conducted using 100 keV He⁺ions at the fluence range from 2×10¹77 ions/cm² to 1.0×10¹⁸ions/cm².The Fe₇₈Si₈B₁₄4 and Fe₇₈P₈B₁₄4 ribbons were prepared by melt-spinning at different wheel speeds.At the fluence of 5×10¹77 ions/cm²,both the ribbons prepared at low and high wheel speeds behave the similar irradiation responses:peeling,flaking and multi-layer damages occur.The crystal contents of Fe₇₈Si₈B₁₄4 and Fe₇₈P₈B₁₄4 ribbons prepared at wheel speed of 35 m/s are 6.5%and 4.2%,which possess the largest un-exfoliated area and exhibit the best irradiation resistance ability compared with the fully amorphous ones.The partial amorphous ribbons prepared at a low wheel speed possess lots of unstable crystalline grain boundaries owing to the precipitation of Si-or P-rich phase,which may act as the source for the irradiation-induced defects annihilation.The results show the size and a fraction of precipitate phases in amorphous matrix may play a dominated role in resisting the ion irradiation.Recently,pronounced work hardening and considerable tensile ductility have been achieved in CuZr-based BMGCs through the precipitation of B2-CuZr phase.The Cu₄₈Zr₄₈Al₄BMGCs possess the B2-CuZr particles with a volume fraction of 28±3vol%.The phenomenon of surface relief can be observed on the polished surface after He⁺ion irradiation.XRD results show that the B2-CuZr phase can undergo a martensitic transformation from a cubic primitive phase?Pm-3m?to two monoclinic?P21/m and Cm?phases.Meanwhile,the changes of the mechanical properties were characterized by nanoindentation.It is noted that the hardness and Young's modulus in the amorphous regions decrease with the increase of fluence,owing to the increase of the free-volume concentration and the formation of extra atomic-scale defects.In contrast,the crystalline regions present a distinct hardening effect due to the appearance of martensitic phases.However,the macroscopic hardness of BMGCs obtained by Vickers indentation instrument is basically unchanged before and after irradiation,which suggests that these materials could maintain a stable performance because of the combined effects of hardening and softening.Vit₁(Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5)metallic glass and DH₃(Zr_39.6Ti_33.9Nb_7.6Cu_6.4Be_12.5),Cu₄₈Zr₄₈Al₄ metallic glass composites were irradiated with 20 MeV Cl⁴⁺ion at a fluence of5×10¹55 and 1×10¹66 ions/cm²,Vit₁ remained amorphous structure after irradiation.However,DH₃ and Cu₄₈Zr₄₈Al₄,which possess a certain degree of crystallization,showed noncrystallzation after irradiation.The phenomenon of pop-in events was studied by nanoindentation before and after irradiation.After irradiation,the hardness of Vit₁ did not change and the serrated flow was not obvious.However,DH₃ and Cu₄₈Zr₄₈Al₄ samples showed different degrees of softening,and the characteristics of serrated flow became more irregular than that of the unirradiated sample.Besides,there is a significant increase in the free volume inside the matrix,which can improve the plastic-deformation ability and lead to the serrated flow appears in advanced.These results show that ion irradiation changes the structure of material and leads to the change of concentration and distribution of defects,which affects the deformation characteristics of BMGs.