Improved Tribological Behavior of Boron Implanted Ti-6A1-4V

ABSTRACTPrevious research has compared the mechanical properties of Ti6A14V implanted with nitrogen using the plasma source ion immersion process and Ti6A14V implanted with boron using the beamline process [1]. Although the nitrogen implanted Ti6A14V had superior wear resistance it was concluded that the wear resistance of boron implanted Ti6AI4V might be improved to comparable levels if boron were implanted at lower energies to increase the concentration of boron at the surface. Boron implantation of Ti6A14V has been conducted at combinations of 32 and 40 keV to supplement that done previously at 75 keV. Shallower boron depth profiles with higher B-concentrations in the Ti64 surface have been obtained by tailoring the combinations of ion energy and dose. This work used three different ion energy and dose combinations of 4×1017 B-at/cm2 at 40 keV plus 2×1017 B-at/ cm2 at 32 keV, 4×1017 B-at/cm2 at 40 keV, and 4×1017 B-at/cm2 at 32 keV plus 2×1017 B-at/ cm2 at 40 keV. Comparisons are made between Ti6A14V with a shallow implanted boron depth profile, Ti6AI4V with a deeper boron depth profile and nitrogen implanted using a plasma source ion implantation process. It has been previously shown that while boron implanted Ti64 has a ~30% higher surface hardness than nitrogen implanted Ti64, the N-implantation reduced the wear coefficient of Ti64 by 25–120x, while B-implantation reduced the wear coefficient by 6.5x or less. The results show that no significant improvement is made in the wear resistance of boron implanted Ti6A14V by increasing the concentration of boron at the surface from approximately 10%to 43%. Transmission electron microscopy (TEM) and selected area diffraction (SAD) indicated the formation of crystalline TiB in the implanted surface layer. Shallower depth profiles result in reductions of the Ti6AI4V wear coefficient by 6.5x or less which is the same result obtained earlier with the deeper boron depth profile. Surface hardness of Ti6A14V with shallower boron depth profiles was improved approximately 10%compared to the results previously acquired with deeper boron depth profiles.