Deposition of Ti/N compositionally gradient film onto Ti-6Al-4V
alloy substrates was carried out by reactive DC sputtering, not only to
improve the blood compatibility of the alloy but also to relax the stress
concentrated at the interface between the film and the alloy substrate.
The compositional gradient was realized by varying continuously the
nitrogen content in Ar-N2 sputter gas during deposition. In
Auger electron spectroscopy (AES) analysis, Auger spectra were acquired in
the N(E) mode using the beam brightness modulation (BBM) method to
overcome the problem of the peak overlap of the principal Auger nitrogen
transition peak (N-KLL) with one of titanium peaks (Ti-LMM). The deposited
film appeared to be uniform and adhesive. TiN formation at the surface of
the film was assumed, because of its yellow gold color and the X-ray
diffraction (XRD) pattern for it. Under scanning electron microscopy, it
was found that the surface had fine particles dispersed on a smooth
accumulated deposit and that this depositing method improved the
structural property of the film at the surface. According to AES in-depth
profiles, the nitrogen (N) concentration in the film gradually decreased
in the depth direction from the surface toward the alloy, confirming that
a Ti/N compositionally gradient film had formed on the alloy
substrate.