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Using Noise and Fluctuations for In Situ Measurements of Nitrogen Diffusion Depth

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Department of Materials Science, Transylvania University of Brasov, Brasov 500036, Romania
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Department of Electronics and Computer Science, Transylvania University of Brasov, Brasov 500036, Romania
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Heat Treatment Department, SKF, Schweinfurt 97421, Germany
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Department of Electronics and Computer Science, Transylvania University of Brasov, Brasov 500036, Romania
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Department of Material Science, Transylvania University of Brasov, Brasov 500036, Romania
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Author to whom correspondence should be addressed.
Materials 2016, 9(10), 819; https://doi.org/10.3390/ma9100819
Received: 30 May 2016 / Accepted: 15 September 2016 / Published: 5 October 2016
In manufacturing processes involving diffusion (of C, N, S, etc.), the evolution of the layer depth is of the utmost importance: the success of the entire process depends on this parameter. Currently, nitriding is typically either calibrated using a “post process” method or controlled via indirect measurements (H2, O2, H2O + CO2). In the absence of “in situ” monitoring, any variation in the process parameters (gas concentration, temperature, steel composition, distance between sensors and furnace chamber) can cause expensive process inefficiency or failure. Indirect measurements can prevent process failure, but uncertainties and complications may arise in the relationship between the measured parameters and the actual diffusion process. In this paper, a method based on noise and fluctuation measurements is proposed that offers direct control of the layer depth evolution because the parameters of interest are measured in direct contact with the nitrided steel (represented by the active electrode). The paper addresses two related sets of experiments. The first set of experiments consisted of laboratory tests on nitrided samples using Barkhausen noise and yieded a linear relationship between the frequency exponent in the Hooge equation and the nitriding time. For the second set, a specific sensor based on conductivity noise (at the nitriding temperature) was built for shop‐floor experiments. Although two different types of noise were measured in these two sets of experiments, the use of the frequency exponent to monitor the process evolution remained valid. View Full-Text
Keywords: diffusion; furnace; magnetic; manufacturing; nitriding; sensors; temperature; thermochemistry diffusion; furnace; magnetic; manufacturing; nitriding; sensors; temperature; thermochemistry
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Samoila, C.; Ursutiu, D.; Schleer, W.; Jinga, V.; Nascov, V. Using Noise and Fluctuations for In Situ Measurements of Nitrogen Diffusion Depth. Materials 2016, 9, 819.

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