Gradient crystalline coating on a biomedical TiNi alloy prepared by magnetron sputtering and annealing

A gradient crystalline coating was created on a TiNi substrate by magnetron sputtering of a three-layer (Ti-Ni-Ti) nanolaminate with a layer thickness of 60-100 nm and subsequent argon annealing of the sample at 900 degrees C. The coating was synthesized to study the features of its structure formation and phase composition, created by reaction synthesis to improve the corrosion resistance of TiNi implants. TEM, EDS, XRD, and EBSD methods showed that annealing initiated solid-state reaction processes between the nanolaminate layers and the substrate, as a result of which a three-layer amorphous nanolaminate transformed into a gradient two-layer coating bonded with the modified substrate through the diffusion zone. The diffusion growth of the nanolaminate layers during formation of the gradient coating was found to increase 10-20-fold. A comparative assessment of the substrate and coating has shown that oxide and oxycarbonitride layers in the coating effectively improve its biocompatibility.