SYMPOSIA PAPER Published: 01 January 1996
STP37955S

Comparison of Spectral Analysis with Fast Fourier Transform and Maximum Entropy Method. Application to the Role of Molybdenum Implantation on Localized Corrosion of Type 304 Stainless Steel

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A comparison of a spectral analysis using the fast Fourier transform (FFT) and the maximum entropy method (MEM) was carried out in the case in which both methods can be performed, that is, when several time acquisitions can be recorded. A summary of the principles of the MEM is given. Then the main properties of this method are investigated, that is, influence of the MEM order on the spectrum accuracy, validity of the low-frequency plateau usually given by this technique, overlapping of spectra measured for different frequency bandwidths, and influence of a slow evolution of the amplitude of the signal fluctuations.

The susceptibility to pitting corrosion of type 304 stainless steel and type 304 modified by molybdenum (Mo) by means of ion implantation was studied. The power spectral densities (PSD) measured with the FFT and MEM techniques are in reasonable agreement, except for low electrochemical current noises (ECN) buried in the parasitic noise generated by the power supply. In that case, the FFT technique is more appropriate than the MEM, which gave qualitative results only. The type 304 stainless steel showed a large metastable pitting leading to only a few macroscopic pits, whereas the type 304 Mo-implanted specimen showed a very low metastable pitting leading to many hemispheric pits covered by the Mo-implanted layer, under which localized corrosion occurred.

Author Information

Beaunier, L
Université Pierre et Marie Curie, Paris Cedex 05, France
Frydman, J
Université Pierre et Marie Curie, Paris Cedex 05, France
Gabrielli, C
Université Pierre et Marie Curie, Paris Cedex 05, France
Huet, F
Université Pierre et Marie Curie, Paris Cedex 05, France
Keddam, M
Université Pierre et Marie Curie, Paris Cedex 05, France
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Details
Developed by Committee: G01
Pages: 114–128
DOI: 10.1520/STP37955S
ISBN-EB: 978-0-8031-5562-6
ISBN-13: 978-0-8031-2032-7