Phase formation during air annealing of Ti-Ni-Ti laminate

The gradient coating synthesized on a nickelide titanium sample by sputtering a three-layer Ti-Ni-Ti laminate and annealing in air at 950–1000 °С was studied by XRD, SEM, TEM, and AFM methods. The thickness of the sputtered laminate layers was chosen equal to 0.5–1.0 μm to study the composition, structure and sequence of formation of the crystalline phases of the gradient coating. This thickness was sufficient for SEM and TEM studies and admissible large for XRD studies of phase composition. SEM and TEM techniques were used to determine the depth and patterns of grains occurrence of titanium carbonitrides. TEM and XRD techniques revealed that reactive synthesis of the coating is followed by transformation of the external amorphous layer of deposited titanium into heterogeneous crystalline titanium oxides. Crystallization of the oxide phase causes an increase in the volume of the external layer and intergranular cracking of the surface. AFM method showed an island microrelief of the external titanium layer formed during synthesis. The reaction synthesis of a multilayer laminate allows obtaining multifunctional nano-structured multilayer coatings with high chemical, mechanical and tribological characteristics, which ensures bioinertness of the surface of titanium nickelide implants.