Study On Microstructure And Properties Of Reactive HVOF Spraying TiC-TiB₂-Ni Coatings

TiC-TiB₂-Ni coatings were successfully sprayed on the steel substrate with Reactive High Velocity Oxygen Fuel spraying and Ti-B4C-C-Ni reactive system.The reactive principle, microstructure and properties of TiC-TiB₂-Ni coatings'were researched. The analysis of ther- -modynamics of TiC-TiB₂-Ni utilizing the self-propagating high-temperature synthesis reaction of Ti-B4C-C-Ni system shows that adiabatic temperature decreases with the increase of nickel content, and increases with the increase of preheating temperature. Reactive High Velocity Oxygen Fuel spraying TiC-TiB₂-Ni coatings are composed of the major phases of TiC, TiB, Ni, some of Ti(C,N), Ti2O3, TiO2 and NiO. Laminate structure coating was formed after spraying particles experiencing stages of pregnant, flight reaction and colliding.On the condition that TiC/TiB₂ molar ratio is 1/2, TiC-TiB₂-Ni matrix coatings'porosity, lard and micro-hardness decrease gradually with the increase of nickel content. However, their binding strength and wear resistance rise at first and then fall with the increase of nickel content. The reaction of Ti-B4C system is more likely to occur than that of Ti-C system. As nickel content is 40%, coatings'micro-hardness, binding strength and wear resistance decrease with the increase of TiC/TiB₂ ratio. Therefore, the introduction of TiB₂ ceramic phase can significantly improve coatings'mechanical properties. The interaction of nickel content and TiC/TiB₂ molar ratio has a little effect on TiC-TiB₂-Ni coatings'mechanical properties. On the condition that nickel content is 40% and TiC/TiB₂ molar ratio is 1/2, coating's drying sliding wear weight and erosive loss are the lest of all, which are 16.5㎎ and 76.9㎎ separately. In addition, the drying sliding wear mechanism of coatings'is characterized by ploughing and spalling.TiC-TiB₂ ceramics improves NiCrBSi coating's wear resistance effectively.There is partial phenomenon between metal and ceramics phases in TiC-TiB₂ reinforced NiCrBSi coating, which decreases coating's uniformity. Impinging angle has great effect on coatings'erosive wear resistence.At 75°jet angle, erosive wear resistence of TiC-TiB₂ reinforced NiCrBSi coating is worse than those NiCrBSi coating's and NiCr-Cr₃C₂ coating's. However, at 30°jet angle, its erosive wear resistence is better than that of NiCrBSi coating's significantly.