"Smart coatings" denotes a class of high-temperature-resistant, multilayer, thin (total thickness < 10 µm) films that contain predominantly planar layers of sensor circuitry sandwiched between tough, protective, electrically insulating layers. These films are being developed to enable in situ monitoring of aircraft engines during flight or inspection. "Smart coatings" could be deposited on turbine and compressor blades, turbine-blade hubs, and other critical engine parts to detect incipient failures and other adverse phenomena.

'Smart Coatings' containing redundant arrays of eddy-current sensors, crackwires, and capacitive sensors were deposited on nickel-alloy coupons with dimensions of 4 by 1 by 1/8 in. (102 by 25.4 by 3.2 mm).

The concept of "smart coatings" incorporates and extends the concept of wireless resonant crackwires, described in "Resonant Crackwires for In Situ Monitoring of Jet Engines" (LEW-16758), NASA Tech Briefs, Vol. 24, No. 6 (June 2000), page 8a. Experimental "smart coatings" that have been developed thus far include not only crackwires (for detecting cracks and plastic deformation at instrumented surfaces) but also eddy-current sensors for detecting plastic deformations below the instrumented surfaces, and capacitive sensors for detecting surface contamination (e.g., fuel, ice, or liquid water).

The figure shows some nickel-alloy coupons with experimental "smart coatings." In preparation for fabricating the thin-film sensors, each coupon was ground flat and polished. Each coupon was then coated with an insulating layer of either SiO2 or Al2O3. Next, thin-film aluminum conductors of sensor circuits were fabricated on the insulating layers by use of photolithographic and deposition techniques and equipment like those used to manufacture integrated circuits.

Tests of coupons containing eddy-current and crackwire sensors have demonstrated that these sensors can detect cracking and plastic deformation. Tests of a capacitance sensor showed that the sensor could detect such surface contaminants as fuel, water, and ice. Tests also revealed that of the two types of sensors for detecting cracks and plastic deformations, crackwires are more practical for use as wireless crack detectors (wireless in the sense that they would be interrogated by radio).

This work was done by Bruce W. McKee, Scott R. Dahl, and Ekaterina Y. Shkarlet of Innovative Dynamics, Inc., for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center,
Commercial Technology Office,
Attn: Steve Fedor,
Mail Stop 4—8,
21000 Brookpark Road,
Cleveland, Ohio 44135.

Refer to LEW-16919.