This study investigates high-current pulsed electron beam (HCPEB)-induced molybdenum (Mo) surface alloying of Zircaloy-4. Mo films with nominal thicknesses of 50, 100, and 200 nm were pre-deposited on the Zircaloy-4 surface to regulate the amount of Mo introduced into the near-surface region. Microstructural characterization revealed that all Mo-alloyed samples exhibited martensitic features in the near-surface region after HCPEB irradiation. The Mo-50 sample was mainly characterized by relatively coarse α'-Zr martensite, whereas the Mo-100 sample exhibited a higher density of finer α'-Zr martensite. When the Mo film thickness was further increased to 200 nm, excessive Mo promoted substantial β-Zr retention and the localized formation of metastable ω-Zr, thereby weakening the α'-Zr martensitic characteristics. Corrosion tests showed that the near-surface microstructural optimization induced by an appropriate amount of Mo in solid solution improved corrosion resistance, with the Mo-100 sample exhibiting the best corrosion performance. In contrast, excessive Mo in solid solution deteriorated corrosion resistance by introducing near-surface microstructural heterogeneity and instability, causing the corrosion resistance of the Mo-200 sample to be even lower than that of the untreated sample. These results provide an experimental basis for the surface alloying design and corrosion-resistance optimization of zirconium alloys.
Tungsten–copper (WCu) composites combine high-temperature strength with superior thermal and electrical conductivity, making them essential for fusion reactor components and aerospace applications. Assessing these materials using miniature specimens is crucial when the amount of material is limited. This study investigated the mechanical and fracture behaviour of WCu composites (50–90 wt% W) using mm-sized mesoscale and cm-sized macroscale tensile specimens and the small punch test (SPT), complemented by neutron diffraction and fractography. Both tensile geometries were suitable for composites up to 80 wt% W, yielding consistent values for yield and ultimate tensile strengths, although only macroscale specimens produced valid measurements for brittle W10Cu. Elastic modulus, yield strength, and ultimate tensile strength (UTS) increased with W content, with yield strength increasing from ∼200 to ∼640 MPa and UTS from ∼390 to ∼720 MPa. Elongation decreased with increasing W content from ∼14% to ∼2% and was most sensitive to specimen size. SPT curves showed reduced ductility and earlier fracture with increasing W content. SPT fractography showed a progressive shift from semi-ductile to brittle behaviour. Empirical relationships between SPT parameters and tensile properties enabled practical estimation of mechanical properties. Neutron diffraction showed plastic deformation was mainly in the Cu, whilst the W exhibited minimal detectable plasticity and remained largely elastic, consistent with an apparent progressive increase in its load-bearing role with increasing W content. As Cu volume fraction and connectivity decreased, plastic deformation became increasingly localised, consistent with enhanced load transfer to the W skeleton. W30Cu marked a critical composition at which reduced apparent Cu continuity was associated with a shift to cleavage-dominated fracture behaviour. These results established a direct link between phase connectivity, strain localisation, and fracture mode in WCu composites.
