Mechanical and Tribological Properties and High-Speed Drilling Performance of NbTiN Coatings Prepared by High-Power Impu
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JMEPEG https://doi.org/10.1007/s11665-020-05305-8
Mechanical and Tribological Properties and High-Speed Drilling Performance of NbTiN Coatings Prepared by High-Power Impulse Magnetron Sputtering with Varying Nitrogen and Acetylene Flux Rates Y.L. Su, W.H. Kao, and Y.C. Chang Submitted: 19 July 2020 / Revised: 27 September 2020 / Accepted: 24 October 2020 NbTiNx and NbTiN25-CHx coatings (where x indicates the nitrogen or acetylene flux rate) were deposited on SKH51 substrates by high-power impulse magnetron sputtering. The study comprised three stages. In the first stage, NbTiNx coatings with nitrogen flux rates varying from 0 to 50 sccm were deposited to determine the nitrogen flux rate which yielded the best mechanical and tribological properties. In the second stage, NbTiN25-CHx coatings with acetylene flux rates varying in the range of 5-25 sccm were prepared using the optimal nitrogen flux rate determined in the first stage in an attempt to further improve the tribological performance. In the final stage, the NbTiN25-CHx coating with the best tribological properties was deposited on micro-drills and used to perform a series of high-speed through-hole drilling tests under dry conditions using printed circuit board specimens. Among the various NbTiNx coatings, the NbTiN25 coating showed an excellent adhesive strength (Lc > 100 N) and superior tribological properties. The NbTiN25 coating was thus selected for further experimentation using various acetylene additions. The NbTiN25-CH25 coating was found to possess a sufficient carbon content (34.9 at.%) to produce a transition from a metal nitride crystalline (NbTiN25) structure to a diamond-like carbon structure with a high sp2 concentration. The coating exhibited a high hardness/elastic modulus ratio of 0.063 and an adhesive strength of Lc > 100 N. Consequently, a carbon-rich solid lubricant layer was formed at the contact interface under ball-on-disk sliding, which resulted in an excellent tribological performance. The NbTiN25CH25 coating was thus chosen for deposition on micro-drills. The coating increased the lifetime of the microdrill by around three times compared to that of an uncoated drill. Even after drilling 6000 holes, the holes showed an excellent quality with a low nail head ratio and surface roughness and a diameter error of less than 1.5%. Keywords
HiPIMS, micro-drill, NbTiN, niobium, titanium, tribology
1. Introduction Magnetron sputtering is the method of choice for most physical vapor deposition (PVD) industrial applications nowadays (Ref 1). High-power impulse magnetron sputtering (HiPIMS) utilizes a high-voltage pulsed power source to produce a short duration burst of energy focused on the target coating material. The resulting high-density plasma induces an ionization of the coating material in the plasma, and the positive ions then bombard the substrate surface under the effects of a negative bias voltage (Ref 2). Compared to conventional thinfilm deposition methods, such as radio frequency (RF) magnetron sputtering, HiPIMS has many advantages, incl
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