Phase formation in aluminium implanted titanium and the correlated modification of mechanical and corrosive properties

Surface modification of titanium is of interest considering the necessary i mprovement of mechanical properties of this material for applications as, f or example, medical implants. This work is devoted to the formation of a la yer with a high content of the titanium aluminides Ti3Al and TiAl below the surface by high dose aluminium implantation. If the maximum aluminium conc entration exceeds 20 at.% precipitation of Ti3Al is detected by X-ray diffr action already in the as-implanted state. For maximum aluminium concentrati ons between 50 and 55 at.% the phase TiAl is found beside Ti3Al after annea ling at 70 degreesC. For a double implantation resulting in an aluminium co ncentration of approximately 60 at.% in the depth range between 100 and 200 nm a disordered fee TiAl phase is observed after implantation as precursor for the ordered tetragonal TiAl formed by subsequent annealing at 60 degre esC. The influence of a pre-implantation of 3 x 10(17) V cm(-2) on the phas e formation is also reported. The depth dependent maximum hardness in the n ear surface range increases with increasing Al dose up to a factor 4. Signi ficantly enhanced wear resistance is observed for Al doses greater than or equal to 10(18) cm(-2) after annealing. High dose implantation of Al into T i results in an enhanced corrosion in 5 M HCl. However, subsequent annealin g reduces the corrosion current compared to unimplanted Ti. (C) 2000 Elsevi er Science S.A. All rights reserved.