Improvement of structures and properties of hafnium nitride coatings by yttrium introduction

In recent years, rare earth element doping has become an important emerging way to improve material properties. In this study, the effects of rare earth Y doping on the morphology, microstructure and properties of Hf-Y-N composite coatings were analyzed by combining equipment characterization methods and simulation methods. The results showed that when the content of Y was 9.8 at.%–18.5 at.%, (Hf, Y) N substituted solid solution was formed by Y atoms replacing Hf atoms. And as the Y content increased, the lattice distortion of coatings increased and the grain size decreased. The maximum hardness of the coating was 34.6 GPa when the doping amount of Y was 18.5 at.% and the hardness values of the Hf-Y-N composite coatings were greater than those of the binary HfN coatings. The fracture toughness of the composite coatings increased with the increase of Y doping content. The maximum fracture toughness was 4.8 MPa. m1/2, which was nearly five times higher than the fracture toughness of binary HfN coatings. The solid solution strengthening and fine grain strengthening effects caused by the doping of Y were responsible for that. At the same time, the adhesion between the coatings and the substrate was significantly improved. In addition, the doping of Y improved the thermal stability and corrosion resistance of the coating, and the corrosion current density of Hf-Y-N coating increased by two orders of magnitude compared to substrate, with a minimum of 4.21 × 10−8 A ∙ cm−2.