A Novel Fabrication Strategy of Single-phase and Dense CrN Ceramics and its Tribological Behavior

Chromium nitride (CrN) is a promising structural and protective material with excellent mechanical properties and good wear and corrosion resistance. However, CrN tends to decompose into Cr2N at high temperatures, which makes the fabrication of single-phase and dense bulk CrN ceramics extremely challenging. In this work, a novel routine, ammonolysis followed by plasma activated sintering (PAS), has been proposed to fabricate single-phase and dense CrN ceramics. Single-phase CrN ceramics with a relative density of 98.2%, higher than those in previous work, were successfully fabricated at the sintering temperature of 1200 oC. Its hardness and fracture toughness reach 11.9 GPa and 3.98 MPa·m1/2, respectively, better than other CrN ceramics in literature. It exhibits friction coefficients of 0.75 to 0.45 and wear rates of 2.31×10-6 to 3.06×10-5 mm3·N-1·m-1 at the friction loads of 5-20 N. The successful fabrication of single-phase CrN ceramics can be attributed to the combined effect of the sintering atmosphere of extra N2 and rapid densification. During densification, N2 injected into the furnace will be encapsulated rapidly, creating a localized high nitrogen pressure that suppresses CrN decomposition and ultimately results in single-phase and dense CrN ceramic bulk.