Characterization of Boride Layer Formed on Ti–6Al–4V Alloy by Electron Beam Evaporation Technique

Abstract

Ti–6Al–4V alloy was borided by using a two-stage boriding process. In the first stage, boron atoms accumulated on Ti–6Al–4V alloy samples via electron beam evaporation technique. The second stage included annealing of samples after boron deposition at various temperatures in order to achieve boride layer with high hardness and adherence. After the boriding treatment, phases formed on the surface of the Ti–6Al–4V alloy were identified by X-ray diffraction technique. The microstructure and thickness of boride layers were examined by scanning electron microscope. Microstructural analyses indicated that surface structure of borided samples comprised of TiB2 layer on the top and TiB whiskers towards the substrate. It was revealed that boriding by electron beam evaporation technique resulted in formation of a hard and adhered surface structure after annealing especially at 950°C for 24 h. Microhardness measurements showed that boride layer on Ti–6Al–4V has mean hardness value of about 1937 HV. Boriding at 950°C for 24 h brought about an improvement in wear resistance of Ti–6Al–4V alloy. The borided surface exhibited higher wear resistance along with higher coefficient of friction as compared to as-received one.