Algorithm Upgrade for Nano-Indentation Software -- a Way to Characterize Thin-Coated Materials (23044)
The invention is a set of methods that a supplier of nano-indentation systems can incorporate into its proprietary software. A new version of software could then provide existing and prospective customers with the unique capability to report elastic modulus and Poisson’s ratio for coatings and their substrates.
Current nano-indentation methods can report “reduced” elastic moduli, but only for uncoated materials or for coated materials where indentation depth is much less than coating thickness. Current methods require that Poisson’s ratio be known in advance in order to calculate the actual elastic modulus, and so current methods do not measure Poisson’s ratio. In addition, current methods require careful control of indentation depth in order to minimize substrate effects upon coating measurements. Current methods using spherical indenters assume a Hertzian pressure distribution; but this assumption is not accurate for coated materials. Most current methods are destructive, as they leave dents in samples after examination – cracking, creep and material pileup can result.
The invention makes no assumptions about pressure distribution, and it doesn’t require Poisson’s ratio to be known in advance. In fact, it calculates elastic modulus and Poisson’s ratio for coatings and their substrates from partial load/unload curves operating in the elastic range. Substrate effects are completely eliminated by so-called “extended Hertzian elastic theory.”
Results: Commercially available silicon wafers were coated with Titanium Nitride as samples. Thickness values were on the order of two or three microns in order to demonstrate this method, but this method is expected to work well for much thinner coatings. Load and displacement curves were obtained by using a commercially available nano-indentation system and a sapphire sphere (the invention is not restricted to spherical shape). Indentation data was reported and averaged over several tests. Elastic modulus data agreed among samples and with known data reported in the prior art based upon measurements using ultrasonic surface waves. The average Poisson’s ratio reported for TiN coatings was 0.29, and the average Elastic moduli of Titanium Nitride coatings for two samples were 383 and 376 GPa, respectively.
Comparison of the invention with numerical analysis indicates accuracy to within one-and-one-half percent (1.5%).
Having demonstrated success of the invention, Northwestern University is prepared to work with a licensing partner to develop and deliver a system to the market place. Northwestern therefore seeks a licensing partner or partners to commercialize this invention. U.S. Patent No. 7,165,463.
Jordan Liu and Jane Wang
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