Effect of Graphite Addition on Structure and Properties of Ti(CN) Coatings Deposited by Reactive Plasma Spraying

Ti(CN) coatings with graphite addition ranging from 0 to 50 wt.% were prepared using reactive plasma spraying technology and their microstructure, mechanical, and tribological properties were investigated using scanning and transmission electron microscopy, x-ray diffraction analysis, x-ray photoelectron spectroscopy, Vickers microhardness testing, and block-on-ring wear testing. The results showed that graphite addition resulted in crystallite size refinement and an increase in the amount of amorphous phase. The Ti(CN) coatings consisted of a mixture of Ti(CN), graphite, CN x , and amorphous phases. The hardness first increased then decreased as the graphite content was increased, with a maximum of 1450 HV 0.2 for 30 wt.% graphite addition. The fracture toughness decreased from 4.38 MPa m 1/2 to 2.76 MPa m 1/2 with increasing graphite content. The friction coefficient decreased due to unreacted graphite embedded in the matrix. Also, the wear rate first decreased then increased, with a minimum value of 2.65 × 10 −6 mm 3 N −1 m −1 for 30 wt.% graphite addition. The wear mechanisms of the Ti(CN) coatings included abrasive, adhesive, and oxidation wear.