Effect of cathodic arc PVD parameters on roughness of TiN coating on steel substrate
Introduction
Titanium nitride (TiN) thin films deposited by PVD technology have a wide range of commercial application such as cutting tools and artificial jewelry. In all such applications the smoothness of the finished surface is of prime importance. In this context, the terms surface finish and surface roughness are used very widely in industry and are generally used to quantify the smoothness of a surface finish.
Surface finish could be specified through different parameters. According to Lou et al. [1], roughness average (Ra) and root-mean-square (rms) roughness (Rq) are the most widely used surface parameters in industry. More recently, however other parameters like surface roughness of the maximum profile height (Rp) and surface roughness of the maximum profile valley depth (Rv) etc., have also been used. In this study the first three parameters (Ra, Rp, Rq) have been used to characterize TiN based hard coatings.
Section snippets
Experimental procedure
The objective of the present work is to study the influence of processing parameters on the surface roughness of TiN coatings deposited on D2 tool steel by using cathodic arc physical vapor deposition (CAPVD) technique. In this work, Titanium nitride (TiN) single layer coatings have been deposited in a commercially available HTC 625/2 ARC coating system, detailed description of which is given elsewhere [2]. The deposition parameters studied are given in Table 1, Table 2. A partial pressure of N2
Results and discussion
The variation in the surface roughness for both uncoated and coated samples was studied. In all cases, the average surface roughness was measured at five different locations and results were averaged. The baseline roughness of the D2 steel substrate exists mainly because of the migration of tiny particles of SiC emery paper into the sample during metallography process. Again, these tiny particles of SiC increase the surface roughness of TiN-coated samples. Uniformity in surface roughness within
Conclusions
From the present work, it can be concluded that surface roughness mainly depends on nature of substrate and its surface, deposition time, coating thickness, substrate temperature and bias voltage, whether metal ion etching has been performed or not. The surface roughness increase, resulting from deposition of the TiN coatings should be attributed to the cathodic arc PVD process character and occurrence of the characteristic macro-droplets. Again, the variation in surface roughness is due to
Acknowledgements
One of the authors, Mubarak Ali, would like to thank the Government of Malaysia, for the award of a scholarship for PhD studies and AMREC, SIRIM Berhad for the access to the experimental facilities for this research.
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