Nanoindentation mechanical properties of U-5.5 wt%Nb treated by continuous electron beam surface remelting

Understanding the microstructure evolution and mechanical property of the electron beam based process for remelting is important for manufacturing, repair, and surface modification. In this work, based on the nanoindentation theory, the sub-microscale mechanical properties of U-5.5 wt%Nb alloy (U-5.5 Nb) remelted by continuous electron beam scanning process (CEBSP) were systematically studied for the first time by the means of nanoindentation. Additionally, optical microscopy (OM) and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM/EDS) were used to evaluate the evolution of the microstructure and the element redistribution. The results revealed that the microstructure and/or the microsegregation of both niobium and carbon had a significant influence on the local mechanical properties of the CEBSP treated U-5.5 Nb. A surface strengthened layer with the average elastic modulus and hardness of 68.4 ± 15.1 GPa and 4.8 ± 1.2 GPa was obtained by CEBSP, which were much higher than the corresponding values of the untreated alloy (i.e. 47.2 ± 2.8 GPa and 2.6 ± 0.3 GPa for the substrate), suggesting a 15.6–44.5% increase in the anti-wear performance. Additionally, except for plasticity, the mechanical properties including yield strength, creep resistance, and fracture toughness increased by CEBSP. Finally, based on the experimental analysis results, the relationship between microstructure and mechanical property (especially the hardness) is discussed in detail, and a model is proposed to explain the plastic deformation mechanism during nanoindentation tests.