Abstract
Locally increased amplitudes of Barkhausen Noise are usually due to changes of residual stresses versus tension and/or reduction of mechanical hardness. This rule was found not to be valid for a 5 to 10 μm thick surface layer with microstructural changes similar to friction martensite which was detected in a roller bearing of a helicopter intermediate gear, after running without lubrication for about 20 minutes. Besides of Barkhausen Noise Measurements and conventional Non Destructive Testing, X-Ray Diffraction Analysis and Stress Measurements, Scanning Electron Microscopy, ESCA and metallographic investigations were carried out. It is assumed that rearrangements of dislocations and interstitial atoms in connection with transformation of retained austenite have lead to an increase of the mobility of Bloch Walls and so caused the observed high noise amplitudes.
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