Neelkanth G. Dhere and Anil Pai Development of Tribological Coatings for Cryocoolers Task III. 4 Hydrogen Storage for Spaceport and Vehicle Applications Neelkanth G. Dhere and Anil Pai

Titanium Nitride (TiN) Coatings - By RF Magnetron Sputtering The 6” six-way cross vacuum chamber was tested for vacuum leaks. Leaks were eliminated so as to improve the vacuum from 8x10-5 Torr to 6.1x10-6 Torr. Initial depositions of TiN (hard coating) were done by reactive magnetron sputtering on glass substrate. RF cable from the RF tuner to the target was shortened to obtain an impedance matching at the RF frequency of 13.56 MHz and consequently to minimize the reflected power. As a result thickness of coatings improved.

Titanium Nitride (TiN) Coatings - By RF Magnetron Sputtering Depositions were carried out by varying the proportion of nitrogen to argon sputtering gas and using forward power in the range of 80-150 watt, reflected power of 1-2 watt. This resulted in >5000 Å TiN thin films. Visual inspection and sheet resistance measurements have shown the films to be deficient in nitrogen.

Titanium Nitride (TiN) Coatings - By DC Magnetron Sputtering DC Magnetron Sputtering was used to achieve film thicknesses of > 1 micron Number of Depositions have been carried out by DC Magnetron Sputtering under varying conditions. Achieved film thickness of > 1 micron. Analysis by Energy Dispersive Spectroscopy (EDS) has been carried out for three samples and the results are shown in the following slides.

Titanium Nitride (TiN) Coatings Data showing deposition parameters of samples used for EDS Analysis Resistivity of Ti - 5.54 * 10-5 Ω -cm Resistivity of TiN – 2.5 * 10-5 Ω -cm

Titanium Nitride (TiN) Coatings Energy Dispersive Spectroscopy (EDS Analysis) Films have shown good stoichiometric ratio of Ti & N

Titanium Nitride (TiN) Coatings Results of microhardness measurement carried out with the assistance of Dr. Raj Vaidynathan at UCF HV –Vicker’s Hardness

Titanium Nitride (TiN) Coatings XRD analysis to be done TiN-1 TiN-2 Intensity (a.u) TiN-3 TiN-4 Diffraction Angle (Deg.) Figure: Extra Slow XRD patterns

Titanium Nitride (TiN) Coatings XRD Analysis would tell us Orientation of the film – Require (111) Compound formation and crystallnity of the film – If TiN is fully reacted, peak intensity will be high as in TiN-1 If the grain size is large, peaks will be narrow There is an optimum grain size for achieving the highest microhardness XRD equipment at UCF is under repair and so we had to send it to NREL and are awaiting the results

Titanium Nitride (TiN) Coatings Wear and coefficient of friction to be tested at UCF with the assistance of Dr. Chen and his colleagues. Require deposition of films on a thin glass substrate (1 mm) for the test. Prepare a silicon sample (1 cm2) with small bumps on the sample by photolithography with the assistance of Dr. Sundaram TiN coating will be deposited on these bumps to carry out the friction and wear test. Bumps Si Sample with TiNfilm on bump Sliding Force Sliding Force TiN Sample

Hard Coatings at Cryogenic Temperatures Literature search of friction behavior and wear resistance of high hardness coatings under cryogenic temperatures Only diamond-like-carbon (DLC) and nitrides of high-melting metals (e.g. TiN, ZrN) studied These coatings have shown to have coefficient of friction less than 0.1 at room temperature.

Hard Coatings at Cryogenic Temperatures (continued) Cryogenic environment leads to increase in the coefficient of friction and DLC coatings have lower coefficient of friction and good wear resistance as compared to hard coatings of nitrides. DLC coatings can be deposited by Microwave assisted plasma chemical vapor deposition system (MWCVD). A special cryogenic tribometer required for the study.

Schedule and Progress Characterization of TiN coatings is being done. Thru May 31, 2003: Preparation and characterization of TiN, CrN, TiC and MoS2 coatings Dec 1-Mar 31, 2003: Fabrication and installation of MWCVD Apr 1 – Aug 31, 2003: Preparation and characterization of DLC coating Jul 1 – Aug 31, 2003: Improve coatings and prepare report Characterization of TiN coatings is being done. Deposition of bilayer coatings of TiN and MoS2 on a glass substrate to be started soon. Testing of the above film will be carried out for satisfying requirements of good wear resistance and low coefficient of friction coatings.