Study On Nanocrystalline TiN Coatings Materials Prepared By The Reactive Plasma Spraying

The nano-crystalline titanium nitride coating material was prepared by reactive plasma spraying (RPS) micron-Ti powders in this paper. The gas-tunnel type reaction chamber was designed, and parameters of spraying TiN coatings were majorized. The phases, microstructure of the TiN coating were analyzed by XRD, SEM, TEM and HRTEM, and formation mechanism of the TiN coating was discussed. The mechanical property, wear and friction property, and corrosion resistance were investigated. Microstructure and property of the coating after treatment were analyzed, too. The research conclusions as follow were obtained:Four generation reaction chambers was designed and fabricated, and nano-crystalline TiN coatings were fabricated via spraying Ti powders using the special spraying gun composing the self-designed gas-tunnel type reaction chamber with general plasma spray gun and XX-XX type spraying gun.The microstructure of TiN coating was characterized. Through observing using SEM, TEM, HRTEM and calculating using Scherrer formula, it was found that TiN coatings are composed of nano-scaled crystal grains of TiN,a little Ti3O and non-crystal. The substructure of crystal phase is that the bundles, which are made of nano-bars, random stack in space. The nano-bars, whose diameter range is from 70 to 100 nm, are parallel each other. Many growth twins were observed in the TiN coating. The phenomenon of movability dislocations sliping and interacting were found in TiN which deposit in reaction chamber.The mechanics properties of TiN coating were studied. It was found that the TiN coating present higher micro-hardness and fracture toughness. The average hardness and KIC of cross-section of the TiN coating is 1720HV100g and 7.065MPam1/2; respectively, and those of the longitudinal section of TiN coatings were 1260 HV100g and 4.915 MPam1/2. The TiN coating presents apparent indentation size effect. The phenomenon of work-hardening and deformation was found in TiN coating materials via observing indentation and friction surface and indentation size effect.The wear and corrosion resistance of TiN coatings were investigated. The wear resistance of the TiN coating is better than that of quenched M2 steel under dry friction and wear condition. The friction coefficient between TiN coating and GCr15 is 0.4, and the invalidation mode of the TiN coating is coatings scaling. TiN coatings present good corrosion resistance. The passivation current of steel coated with TiN coating is smaller than 18-8 stainless steel in 0.5mol/L HCl solution, but destroy potential is higher than stainless steel.The microstructure and property of TiN after annealing at 1000℃were discussed. It was found that the density of the TiN coating enhanced, toughness was improved and the friction coefficient decreased, which reflect the self-lubrication character of the TiN coating, through 1000℃annealing under nitrogen shield.The formation dynamics of nano-crystalline TiN coating was analyzed. It is found that, for reactive plasma spraying nano-TiN coatings, combustion synthesis between Ti and N is the necessary condition, and plasma spraying and shock cooling is the sufficient condition. Combustion synthesis reaction melts the reaction products, and refines TiN liquid drops. TiN liquid drops shock-cooling under the plasma spraying condition, solidify and form nano-crystal TiN coating on substrates.