Functionally gradient PECVD Ti(C,N) coatings
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ABSTRACT Ti(C,N) hard coating is well known as a suitable material for protecting substrate, and functionally gradient design is a method to improve the performance of it. In this study, functionally gradient Ti(C,N) coatings were performed by the technique of capacitive RF PECVD based on the investigation of Ti(C,N) monolayers with different C and N ratios. The results show that the composition and growth rate of Ti(C,N) monolayers are influenced by the nitrogen/methane ratio as other deposition parameters are fixed. A model is also proposed from the results obtained and is employed to calculate the reaction gas ratio and duration time needed for deposition in the gradient coating. The elements of Ti and N in the gradient coatings were analyzed by Auger electron spectroscopy (AES) and revealed that the composition changed linearly as designed. The residual stress of the gradient coatings was also measured to show that the gradient design provides the possibility for adjusting the stress distribution of PECVD hard coatings.
INTRODUCTION Functional design is a method to tailor a material for the specific performance requirement of an intended application, from which dissimilar materials are combined in ways that take advantage of each one. Multilayer, multicomponent and gradient coatings are widely used to upgrade thin film performance, and these ideas can be applied to the hard coatings in which TiC and TiN are extensively interesting materials for tribology application via their strength and wear resistance [1,2]; besides, an interest in the functional design of TiC and TiN has emerged in light of their similar structure. Several studies have been done on regarding the Ti(C,N) functional design. Multilayer Ti(C,N) coatings are realized successfully for wear reduction and strength improvement [3,4]. Eroglu et al. [5] investigated Ti(C,N) graded CVD coating as a function of the source gas composition, and showed that the experimental profile was in good agreement with the designed one. Godse et al. [6] demonstrated that composite CVD+PVD coatings could provide better machining applications than CVD or PVD coatings. Besides CVD and PVD, PECVD has been known as a technique with the advantage of homogeneity and low deposition temperature[7-9]; however, few studies have been done on the design of gradient profile in PECVD process. In this paper, a method of gradient Ti(C,N) design with PECVD is presented to afford a possibility of controlling the performance. The influence of gradient profile on internal stress is also presented for the established model.
EXPERIMENT The schematic diagram of the 13.56 MHz capacitive RF PECVD apparatus is shown in Fig. 1 in which the internal parallel electrodes were capacitively coupled with a matching network. The substrate of silicon wafer and Coming 7059 glass heated by a graphite heater were placed on the RF electrode with self-biasing. The ground electrode was a stainless steel gas shower above the 407 Mat. Res. Soc. Symp. Proc. Vol. 555 ©1999 Materials Research Society
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