Microstructure, chemical and phase composition of the hard layer formed on the Ti-6Al-4V alloy after duplex surface treatment were investigated by light microscopy (LM), X-ray diffraction (XRD) and analytical scanning, transmission and scanning transmission electron microscopy (SEM, TEM, STEM), electron diffraction and focused ion beam (FIB). Advanced electron microscopy techniques used for unambiguous identification of phases present in the surface multilayer are critically discussed. The relationship between multilayer micro/nanostructure containing several phases from the Ni-Ti-P-Al system and improved mechanical and tribological properties is established.