In order to understand alloying effects on the corrosion resistance of titanium, polarization curves were measured at 343 K in 10 mass% HCl solution with various Ti-M binary alloys (M= Al, Nb, Ta, Zr, Hf, Fe, V, Cr, Mo, Co and Ni). The results were interpreted using an alloying parameter obtained by a molecular orbital calculation. The parameter is the bond order (Bo) which is a measure of the strength of the covalent bonds between titanium and alloying elements. It was found that alloys containing the elements with higher Bo values showed a lower critical anodic current density in the polarization curve and hence higher corrosion resistance. It is likely that the Bo is a convenient parameter for describing the corrosion rate of titanium alloys in a acid environment such as a hydrochloric acid.
