Wear 270 (2011) 325–331 Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear Short communication Development of ultrananocrystalline diamond (UNCD) coatings for multipurpose mechanical pump seals A.M. Kovalchenko a,∗ , J.W. Elam b , A. Erdemir b , J.A. Carlisle b , O. Auciello b , J.A. Libera b , M.J. Pellin b , D.M. Gruen b , J.N. Hryn b a Georgia Institute of Technology, Atlanta, GA 30332, USA b Argonne National Laboratory, Argonne, IL 60439, USA article info Article history: Received 27 February 2010 Received in revised form 8 September 2010 Accepted 25 October 2010 Available online 18 November 2010 Keywords: CVD coatings Ultrananocrystalline diamond Seals Wear testing Electron microscopy Profilometry abstract The reliability and performance of silicon carbide (SiC) shaft seals on multipurpose mechanical pumps are improved by applying a protective coating of ultrananocrystalline diamond (UNCD). UNCD exhibits extreme hardness (97 GPa), low friction (0.1 in air) and outstanding chemical resistance. Consequently, the application of UNCD coatings to multipurpose mechanical pump seals can reduce frictional energy losses and eliminate the downtime and hazardous emissions from seal failure and leakage. In this study, UNCD films were prepared by microwave plasma chemical vapor deposition utilizing an argon/methane gas mixture. Prior to coating, the SiC seals were subjected to mechanical polishing using different grades of micron-sized diamond powder to produce different starting surfaces with well-controlled surface roughnesses. Following this roughening process, the seals were seeded by mechanical abrasion with diamond nanopowder, and subsequently coated with UNCD. The coated seals were subjected to dynamic wear testing performed at 3600 RPM and 100 psi for up to 10 days during which the seals were periodically removed and inspected. The UNCD-coated seals were examined using Raman microanalysis, scanning electron microscopy, optical profilometry, and adhesion testing before and after the wear testing. These analyses revealed that delamination of the UNCD films was prevented when the initial SiC seal surface had an initial roughness >0.1 m. In addition, the UNCD surfaces showed no measurable wear as compared to approximately 0.2 m of wear for the untreated SiC surfaces. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Over the years, great strides have been made in improving the performance and durability of mechanical seals by controlling their structure and mechanical properties. In fact, the failure modes of today’s seals are seldom related to the microstructure or mechan- ical properties of the base seal materials. However, failures due to dry or near-dry running conditions (especially at the start up), severe and un-even loading or load fluctuations during operations, as well as blistering and other near-surface defects and/or deficien- cies can still occur and limit the useful lifetimes of seal components used by the sealing industry. Surface defects, such as uneven sur- face finish, local variations in surface texture and/or mechanical properties, un-removed grinding or polishing furrows, nicks, and dents introduced during manufacturing and/or machining opera- ∗ Corresponding author at: Georgia Institute of Technology, Manufacturing Research Center, 813 Ferst Drive, N.W., Atlanta, GA 30332, USA. Tel.: +1 404 894 3594; fax: +1 404 894 3913. E-mail addresses: andrii.kovalchenko@gatech.edu, and.kovalch@juno.com (A.M. Kovalchenko). tions, may cause chipping (especially in SiC-based seals) and hence trigger micro-fracture and eventually seal failure. In addition, large variations in contact stresses during operation, as well as very high normal and tangential pressures developing at asperity levels dur- ing rotating contacts can give rise to severe temperature spikes and surface distress that can ultimately cause seal failures. To improve the surface-sensitive properties of mechanical seals, researchers have tried two general approaches in recent years. First, they developed advanced laser machining methods to achieve spe- cific geometric profiles and/or textures on seal faces and second, they have tried a variety of surface engineering or hard coating technologies to improve the surface tribological and mechanical characteristics of seals to prevent wear-related failures. Recent advances in surface metrology, polishing, and handling methods have also reduced the number of surface irregularities and thus reduced the causes of failures resulting from such irregularities. Among the many types of hard physical- and chemical-vapor deposition (PVD and CVD) coatings, diamond and diamond-like carbon coatings have attracted the most attention for sliding or rotating tribological surfaces in recent years, especially in micro- electromechanical systems (MEMS), biomedical, and nano-scale application [1–5]. In particular, diamond coatings were thought to 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.10.059