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Metals 11(7), 1139 -1160 (2021). doi:10.3390/met11071139, Being one of the most high-demand structural materials, titanium has several disadvantages,including low resistance to high-temperature oxidation and wear. The properties of titaniumand its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thickTi-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beamcladding. The microstructure and phase compositions of the samples were different for variousalloying elements. The Cr-containing layer consisted of 2, , and B2 phases, while the Ta-containinglayer additionally consisted of !0 phase (P3m1). At the same atomic concentrations of aluminum andan alloying element in both layers, the volume fraction of the B2/! phase in the Ti-41Al-7Ta alloywas significantly lower than in the Ti-41Al-7Cr alloy, and the amount of phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximumoxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer., Published by MDPI, Basel

Titanium and titanium alloys are highly important structural materials for many industries where low density in combination with high mechanical strength and corrosion resistance are required. However, titanium is not applicable for tribological or high temperatures purposes due to its interaction with atmospheric gases and friction seizure during the contact with most metallic materials. To protect the surface of titanium and improve its wear resistance intermetallic coatings can be applied. In this study, the Ti-Al intermetallic layers were fabricated on Ti surface by electron beam melting of Al and Ti powders. By variation of Al/Ti ratio in the initial powders it was possible to control elemental and phase composition of the layers. The formation of TiAl, Al2Ti and Ti3Al phases was observed in the layers. Independently on Al content the layers had lamellar type of structure. Microhardness, wear resistance and oxidation resistance were measured to evaluate the quality of the layers. The microhardness and wear resistance were in good agreement with each other. The coating, consisted of pure Ti3Al phase, demonstrated the highest level of these properties. Oxidation resistance of the coatings increased proportionally to the aluminium content due to formation of alumina in oxide scale.

Ti-Al-Nb based intermetallic layers of sufficient quality and thickness were obtained by non-vacuum electron beam cladding on the surfaces of Ti workpieces. Optical microscopy and X-ray tomography did not reveal any dramatical defects in the structure of cladded layers. X-ray diffraction as well as scanning and transmission electron microscopy were applied to thoroughly investigate the structure and phase composition of coatings. It was found that non-equilibrium cooling conditions of coatings provided by fast removal of heat to untreated Ti substrate after the electron beam cladding was terminated induced the proceeding of metastable phase transformations. For example, γ-phase formation was suppressed in these coatings. In coatings with 8 and 20 at.% Nb (46 and 43% Al respectively) along with ordered with α2, formation of disordered solution of the alloying elements in α-Ti took place. In high-Nb alloys β(B2) phase has undergone the diffusionless transformation to ω’, which is the intermediate phase in β → ω and the coating with the maximum Nb content characterized by appearance of γ1 as a main phase. ω-phase had negative influence to hardness and wear resistance of coatings, however, generally this paremeter increased in 1.3–1.75 times compared to cp-Ti. The high temperature creep and oxidation properties decreased proportionally with increasing Nb and decreasing Al content in the cladded layers.