Hardness response to the stability of a Ti(+N) solid solution in an annealed TiN/Ti(+N)/Ti mixture layer formed by nitrogen ion implantation into titanium

The presence of a Ti(+N) solid solution in nitrogen implanted commercially pure titanium grade II was investigated using XRD, TEM and nanoindentation. A TiN/Ti(+N)/Ti mixed layer was observed. Post-implantation annealing in the temperature stability range of TiN (300-600 °C) showed a falling amount of Ti(+N) and microstrain relaxation. A gradual decrease in hardness was observed, from 27 GPa for an implanted sample without annealing to 21 GPa for an annealed sample at 600 °C. The redistribution of interstitially located nitrogen was found to be responsible for the decrease in hardness. There was an improvement in hardness by a factor of 9-7 in comparison with the non-implanted sample.