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Development of Self-lubricating Nanocomposite Coatings impregnated with in-situ formed MoS2 for Tribological Applications

Final Report Summary - NANOCOAT (Development of Self-lubricating Nanocomposite Coatings impregnated with in-situ formed MoS2 for Tribological Applications)

In this project, the following scientific and technological objectives are aimed at during the period under report:
1) Formation of a nanocomposite by incorporation of WC and inorganic fullerene (IF) WS2 nanoparticles into CoW matrix by DC/pulse electrolysis and their detail characterization. WC particles are well known for its hardness and WS2 particles for its good lubrication property. Basic idea was to strengthen the CoW matrix by dispersing hard WC nanoparticles and to achieve simultaneously better self-lubrication property of the coating by incorporation of IF-WS2 was planned from a single solution electrolyte containing these two particles.
The main aim was to demonstrate the potentiality of these nanocomposites to become a suitable alternative to hard chrome, and that their use will contribute to a protection of the environment by suppressing liquid lubricants thanks to their intrinsic self-lubrication properties.
It is pertinent to mention here that instead of IF-MoS2 we have used IF-WS2 (average size ~100 nm) nanoparticles as another second phase particle because of better lubrication property and oxidation resistance.

Description of the Work and Results Achieved So far:
Electrodeposition of CoW-WC-IF-WS2 nanocomposite coatings was done via simultaneous incorporation of WC (average size ~ 500 nm) and IF-WS2 particles (average size ~ 100 nm) from a sulfate based electrolyte containing suspended nanoparticles. For comparison, we have also synthesized CoW-WC nanocomposite coating. Process optimization for deposition of these nanocomposites was carried out by varying current density, particle loading and ultrasonic agitation duration. We have found that intermittent ultrasonic agitation with 2 minute on-time (20 kHz) and 5 minute off-time helps in de-agglomeration of particles and better incorporation of the particles and followed the same agitation strategy for carrying out all the experiments. These coatings were prepared at current density (c.d.) of 30 and 50 Post deposition removal of loose particles from the top surface, XRD was taken and confirmed about the presence of dispersed particles into CoW matrix. EDS analyses also show presence of sulfur definitely a source from IF-WS2. FE-SEM investigation of as-deposited coatings show particle covered surface and growth of CoW through these particles. At identical deposition current density of 30 the nanohardness of CoW-WC and CoW-WC-IF-WS2 was 8228.43±450.03 and 9377.67±589.17 MPa respectively. An enhancement of matrix strengthening through dispersion of two different second phase particles into CoW matrix was confirmed. The measured corrosion potential (Ecorr) and corrosion current density (icorr) of CoW-WC and CoW-WC-IF-WS2 nancomposites were -703 and 663 mV vs. SCE; and 3.84 and 1.49 µ respectively. It established better corrosion resistance of CoW-WC-IF-WS2 nanocomposite compared to CoW-WC nanocomposite. The coefficient of friction obtained from dry sliding experiments was 0.32 for CoW-WC and 0.22 for CoW-WC-IF-WS2, a reduction in coefficient was evident upon incorporation of IF-WS2.

Publishable Summary
International Peer-Reviewed Journals
1. Ghosh, S. K. and Celis, J. P. (2012): Tribological and Tribocorrosion Behaviour of Electrodeposited CoW Alloys and CoW-WC Nanocomposites, Accepted for publication in Tribology International.
2. Ghosh, S. K. and Celis, J. P. (2012): Comparison of Structure and Properties of Electrodeposited CoW alloys and CoW-WC Nanocomposites, Communicated to Surface and Coatings Technology.
3. Ghosh, S. K. C. Srivastava, P. U. Sastry, Celis, J. P. and A.K. Suri (2013): Synthesis and Characterization of CoW-WC-IF-WS2 Nanocomposite Coatings by Electrodeposition, (In Preparation).

Papers Presented/to be presented in Conferences
1. Ghosh, S. K., Srivastava, C., Bidaye, A.C. Hubli, R.C. Suri, A. K., and Celis, J.P. (2011): Electrosynthesis of Inorganic Fullerene MoS2 (IF-MoS2) Based Thin Films Proc. of ISEAC-WS-2011, held at Cida de de Goa, Goa, 7-10 December, p212-216.
2. Ghosh, S.K. and Celis, J. P., (2012): Studies on Corrosion and Tribocorrosion Behaviour of Electrodeposited CoW-WC Nanocomposites; Paper presented (Oral Presentation) in 39th International Conference on Metallurgical Coatings and Thin Films ( 39th ICMCTF) held in Town & Country Resort Hotel and Convention Center during 23-27 April, San Diego, California, USA.
3. Ghosh, S. K., Suri, A.K. and Celis, J. P., (2012): Tribological Behaviour of Electrodeposited CoW-WC Nanocomposites Coatings, Paper presented in 39th International Conference on Metallurgical Coatings and Thin Films ( 39th ICMCTF) held in Town & Country Resort Hotel and Convention Center during 23-27 April, San Diego, California, USA.
4. Ghosh, S.K. and Celis, J. P., (2012):, A Comparison of Tribological and Tribocorrosion Properties of Electrodeposited CoW Alloys and CoW-WC Nanocomposites, Paper presented (Oral Presentation) in 3rd International Symposium on Tribo-Corrosion held in Georgia Institute of Technology during 19-20 April, Atlanta, Georgia, USA.
5. Ghosh, S. K., (2012): Nanostructured Surface Preparations by Electrochemical Techniques, Invited Seminar presented in ECTNSE-2012 held at HBNI, BARC during 5-6 January, Mumbai, India.

6. Ghosh, S. K., (2012): Behavior of Electrodeposited CoW Alloys and CoW-WC Nanocomposites under Dry and Wet Sliding, Accepted for presentation in 8th International Conference on Industrial Tribology (ICIT-2012) to be held during 7-9 December, Pune, India.

Expected Final Result and Potential Impact:
The present improvement in tribological properties of CoW-WC and CoW-WC-IF-WS2 nanocomposites ensures the initial idea of strengthening the CoW matrix via embedment of hard (WC-particle) as well as lubricating particles (IF-WS2). Not only wear resistance property, improvement in corrosion property was also noticed. Thus, the idea of achieving the self-lubricated nanocomposite coatings by electrodeposition has been realised at the end of the project. So far, CVD and PVD techniques were employed to obtain such types of self-lubricated coatings by simultaneously codepositing self-lubricated particles inside a metal matrix. However, electroplating, being a simple and economical, will definitely get much importance with respect to its commercialization. Academically, incorporation of two different types of particles with having entirely different properties inside a common matrix will also open up a new area of research for future materials scientists/technologists to develop advanced materials.