Effect of CO addition on the microstructure and properties of TiN coatings grown by chemical vapor deposition

TiN coatings with 0-8 vol.% CO addition were prepared by chemical vapor deposition at 1000 degrees C. Pure TiOCN phase was formed with different CO additions, and no apparent local elemental segregation was found. With increasing CO content up to 6 vol.%, the dissolution of O and C increased, accompanied by a decrease in N content and a reduction in grain size. Further increasing the CO content to 8 vol.% did not result in any apparent changes in the amount of O/C dissolution and coating grain size. The intensity of [111] orientation was the highest with 2 vol.% CO addition. The adhesion strength decreased as the CO addition increased, while the hardness first significantly increased with 2 vol.% CO addition, and then remained nearly constant with further increasing CO addition up to 8 vol.%. As the CO content increased to 8 vol.%, the insert continuous cutting life of machining QT500 spheroidal graphite cast iron exhibited a trend similar to that of the hardness.