Surface Alloying of Ti–6Al–4V with Zirconium by Pulsed Electron-beam Melting of Zr/Ti Multilayers

Surface alloying of Ti–6Al–4V with Zr aiming at depletion of Al and V was realized by liquid-phase intermixing of multi-layer film [Zr(20 nm)/Ti(20 nm)]₁₂ of total thickness of 480 nm with substrate (Ti–6Al–4V) using a low energy (~20 keV), high-current electron beam (2.5 μs, 3.5 J/cm²). Scanning electron microscopy and energy dispersive X-ray spectroscopy, Auger electron spectroscopy, X-ray diffraction, and atomic force microscopy were used to study the surface morphology, microstructure, elemental and phase compositions of the alloyed layer. It was found that a homogeneous intermixing of all Zr/Ti nanolayers and diffusion of Zr into the substrate up to a depth of ≈1 μm take place after a singleshot pulsed melting. The surface layer of depth ≈ 0.5 μm is free of Al and V and contain ≈ 30 at % Zr. The near-surface layer, due to quenching from the melt, has a sub-microcrystalline grain structure with an average grain size of 112 nm. The post-irradiation vacuum annealing (500 °С, 2 h) leads to enrichment of alloyed layer with O and С impurities, and decrease of grain size up to 90 nm. As a result, the nanohardness of the alloyed layer was increased in comparison with the substrate.