Structure and Corrosion Resistance of Ti-Ta-Nb Coatings Obtained by Electron Beam Cladding in the Air-Atmosphere

Abstract

The results of structural investigations, mechanical properties and corrosion resistance testing of materials produced by the electron beam cladding of tantalum and niobium powders on cp-titanium substrates are presented in this paper. The treatment resulted in the formation of remelted alloyed layers of ~2 mm thickness. Any voids or cracks were not observed in coatings. Dendritic segregation of alloyed elements during cladding process occurred, however the microstructure was represented by fine laminar-type crystals. X-ray diffraction analysis showed the presence of α’-, α”- and β-phases. Formation of such structure is explained by a high crystallization rate. Microhardness of cladded layers was equal to ~ 350 HV while the base material hardness level was 170 HV. The corrosion resistance was estimated based on the sample mass loss. A concentrated solution (68%) of HNO3 at the boiling temperature was used as a corrosion medium. It was found that alloying the titanium with 16 wt. % Ta and 5 wt. % Nb decreased the corrosion rate by factor of 24 against cp-titanium while adding 16 wt. % Ta and 16 % wt. Nb decreased the corrosion rate by factor of 96.