SURFACE SPECTROSCOPIC CHARACTERIZATION OF TINI NEARLY EQUIATOMIC SHAPE-MEMORY ALLOYS FOR IMPLANTS

In spite of the generally good biocompatibility of TiNi revealed in nu merous in vivo studies, medical applications of these shape memory all oys as implants are hindered due to the lack of knowledge on the natur e of their biocompatibility. Better material characterization is neces sary for understanding the chemical and physical properties which dete rmine biocompatibility. The purpose of the present investigation is to use angle-resolved x-ray photoelectron spectroscopy to identify the d ifferences in surface chemical state and composition between the layer s formed on the surface of TiNi alloys after mechanical polishing, che mical etching, autoclaving in water and steam, and exposure to H2O2 or air. The surface chemistry drastically depends on the preparation met hod; the Ni surface concentration can be varied in the range 0-30 at. %. In natural conditions (air, water, and steam) TiNi surfaces reveale d a tendency to be covered by TixNiyO2x oxides (where x varies in the range of 7-20 and y varies in the range of 0-5 depending on preparatio n procedure) with a small amount of Ni in metallic state (similar to 0 .5 at. %). This finding is considered to be the reason for the good bi ocompatibility of TiNi. (C) 1995 American Vacuum Society.