Boriding of titanium and its alloys into different crystalline structures and investigating the effect of boriding on their microstructure, mechanical behaviour and biocompatibility

In this study, solid state boriding technique was applied to the samples produced from α-type Grade-2 Ti, (α+β)-type Ti-6Al-4V and β-type Ti-45Nb alloys, into a mixture of amorphous boron, anhydrous borax and active carbon. Dual boride layers comprised of TiB2(.NbB2) and TiB phases with various thicknesses were formed on the surfaces of the titanium samples due to their different growth kinetics. Structural, mechanical and tribological properties as well as biocompatibility of borided layers developed on the surfaces of titanium samples at specific temperatures were investigated. The maximum hardness at upper most layer of the samples of Grade-2 Ti and Ti-6Al-4V alloy after boriding reached up to 4000 HV while that of Ti-45Nb alloy sample reached up to 3500 HV. Adhesions of borided layers to the titanium substrates were sufficient. While thick and adhered borided layer on Grade-2 Ti sample resulted in higher upper critical load, the borided layer of Ti-45Nb alloy sample showed lower critical load than those on others. The borided samples of all types of titanium materials exhibited excellent wear resistance compared to as-received ones. Borided Grade-2 Ti and Ti-6Al-4V alloy samples has superior wear resistance than borided Ti-45Nb alloy sample due to their different structural and mechanical properties. Boriding applied to all types of titanium samples slightly decreased cell proliferation compared to as-received ones.