Wear, corrosion and fatigue properties of ion implanted titanium alloy Ti6Al4V

Ion implantation has been shown to improve the wear properties of the titan ium alloy Ti6A14V which is used in joint prostheses. In this paper, the rea sons for this effect are studied. Various metallic (Y+, Hf2+, Rh+, Pd+, Ir, Pt+, Au+) and nonmetallic (B+ C+, N+, N-2(+), O+, CO+ CO2+) species were implanted into Ti6A14V using systematically varied energy-dose combinations . The composition and structure of the implanted layers, the tribological b ehaviour during sliding against polymers (UHMWPE and PMMA), the electrochem ical behaviour in Ringer solution, and the fatigue behaviour are characteri sed quantitatively. Implantation of carbon, nitrogen or oxygen leads to the formation of compou nds (TiC, TiN, TiO) and stabilises the alpha-Ti phase. At high doses, nitro gen causes blistering. Implantation of boron or yttrium leads to amorphisat ion at high doses. Implanted noble metals form solid solutions and stabiliz e the two phase (alpha + beta)-microstructure. The thickness of the implant ed lavers is approximately 150 and 500 nm for the metallic and nonmetallic ions, respectively. By implanting at two or three ion energies subsequently , a more homogeneous distribution of N and C was achieved in the surface la yer which proved advantageous for improving wear resistance. The wear reduc tion is attributed to the increased hardness of the surface laver in combin ation with the reduction of the thickness of the oxide film formed on Ti6A1 4V. These effects reduce the danger of breakaway of oxide particles. The positive effect of ion implantation on wear resistance may be impaired by a reduction of corrosion resistance or fatigue life. Implantation of hig h doses indeed lends to a decrease of the breakdown potential, and pitting corrosion occurs. However, the non implanted alloy shows a much larger decr ease of the breakdown potential in a combined wear and corrosion test while the corrosion properties of nitrogen implanted alloys do not deteriorate d uring wear due to their significantly improved wear resistance. Fatigue lif e is only insignificantly affected by nitrogen implantation. In conclusion, ion implantation of nitrogen or carbon at optimized energies and doses is a suitable means for reducing the life-time limiting weal in hip and knee j oint prostheses.