Abstract
In the present work, we reviewed and studied the fabrication process of hard erosion resistant TiN protective coatings on the inner surfaces of narrow tubes using a Non-Line-Of-Sight (NLOS) approach. Initially, while evaluating the growth of DLC and TiN by the CW RF PECVD process, we found that the use of a hydrocarbon precursor to obtain DLC provides uniform film thickness along the tube axis, while the use of the TiCl4 precursor for TiN leads to a significant thickness nonuniformity of 80% and large differences between the film properties in the middle of the tube compared to the edges. Following detailed plasma analysis, we demonstrate that the uniformity can be substantially enhanced by applying pulsed-DC PECVD, while uniform (better than 20%) hard TiN films were prepared by low-frequency (5 kHz) pulsed-DC PECVD. The TiN films (about 12 μm thick), systematically studied by SEM, XRD, and nanoindentation, when prepared under optimized conditions, exhibit high hardness and reduced Young's modulus (25 and 225 GPa, respectively) corresponding to the (111) preferred crystallographic orientation, and a very low Cl contamination (<3%). The film uniformity has been correlated to that of the discharge light emission intensity along the tube axis, and the microstructural evolution is interpreted in terms of surface densification due to substrate temperature and ion bombardment of the inner surface. The pulsed DC PECVD NLOS process providing TiN coatings with a hardness markedly higher than the hardness of the erodent particles and with a solid particle erosion resistance increased by a factor of >15 compared to the bare substrate is well suited for the protection of aerospace, manufacturing, and other critical components with a complex shape of inner surfaces.
Published Version
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