FLORIDA SOLAR ENERGY

CENTERA Research Institute of the University of Central Florida

Development of Tribological Coatings

for Cryocoolers Task III. 4 Hydrogen Storage for

Spaceport and Vehicle Applications

Neelkanth G. Dhere and Anil Pai

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

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

Deposition Nitrogen Argon Actual Average Average ResistivityTime Pressure Pressure Power Sheet Resistance Coating Thicknesshour mtorr mtorr watt Ω per sq.cm Angstrom Ω-cm

2 0.5 6 150 28.4 14356 0.0041

1.5 0.5 4 150 18.15 8071 0.0015

2 1 4 150 15.75 11575 0.0018

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

Sample ID N2 : Ar Element Atomic Percent

Ratio1 0.5 : 6 Nitrogen 50.3

Titanium 49.7

2 0.5 : 4 Nitrogen 53.05Titanium 46.95

3 1 : 4 Nitrogen 52Titanium 48

Titanium Nitride (TiN) Coatings

Results of microhardness measurement carried out with the assistance of Dr. Raj Vaidynathan at UCF

HV –Vicker’s Hardness

Sample ID N2 : Ar Average Hardness Avg. Elastic

Ratio Gpa HV (Kgf/mm2) Modulus (Gpa)1 0.5 : 6 9.3161 878.4697 144.2014

2 1 : 4 16.6180 1567.0152 200.2102

Inte

nsi

ty

(a.u

)

Diffraction Angle (Deg.)

TiN-1

TiN-3

TiN-2

TiN-4

Titanium Nitride (TiN) Coatings

XRD analysis to be done

Figure: Extra Slow XRD patterns

Titanium Nitride (TiN) Coatings

XRD Analysis would tell usOrientation 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 narrowThere 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

Wear and coefficient of friction to be tested at UCF with the assistance of Dr. Chen and his colleagues.

Titanium Nitride (TiN) Coatings

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.

TiN Sample

Si Sample with TiNfilm on bump

Bumps

SlidingForce

SlidingForce

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

Schedule: Thru May 31, 2003: Preparation and characterization of TiN,

CrN, TiC and MoS2 coatingsDec 1-Mar 31, 2003: Fabrication and installation of MWCVDApr 1 – Aug 31, 2003: Preparation and characterization of

DLC coatingJul 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.