Single-phased hard coatings of the metastable Cr3(C0.8N0.2)2 ternary phase grown by low pressure MOCVD

Single-phased coatings of Cr3(C0.8N0.2)2 have been deposited by combining a metal–organic chemical vapor deposition (MOCVD) process and an annealing post-treatment. The films were grown in the temperature range 683–793 K by low pressure MOCVD using Cr(NEt2)4 as the single-source precursor. As-deposited films are very smooth and X-ray amorphous. A relatively low amount of nitrogen is uniformly incorporated into the film. The nitrogen content is nearly independent of the growth conditions and it amounts to exactly the value required to form the title ternary phase (∼7 at.%). The as-deposited films crystallize upon annealing at 873 K under vacuum to form the orthorhombic Cr3(C0.8N0.2)2 phase. No evidence for additional phases has been found. Both as-deposited and annealed coatings exhibit a high hardness and a good adhesion on stainless steel substrates. The hardness increases slightly upon crystallization to typically reach 17 GPa. Preliminary properties of this metastable carbonitride phase are reported and its potential as a hard metallurgical coating is discussed.