Micro-Magnetic and Microstructural Characterization of Wear Progress on Case-Hardened 16MnCr5 Gear Wheels.

Marina Knyazeva,Dirk Biermann,Leonard Gondecki,Monika Kipp,Werner Theisen,Frank Walther,Julian Rozo Vasquez,Peter Tenberge,Max Weibring,Fabian Pöhl

doi:10.3390/ma11112290

Marina Knyazeva, Dirk Biermann + Show 8 more

Open Access

https://doi.org/10.3390/ma11112290

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Journal: Materials	Publication Date: Nov 15, 2018
Citations: 18	License type: CC BY 4.0

Affiliation: TU Dortmund University, Ruhr University Bochum

Abstract

The evaluation of wear progress of gear tooth flanks made of 16MnCr5 was performed using non-destructive micro-magnetic testing, specifically Barkhausen noise (BN) and incremental permeability (IP). Based on the physical interaction of the microstructure with the magnetic field, the micro-magnetic characterization allowed the analysis of changes of microstructure caused by wear, including phase transformation and development of residual stresses. Due to wide parameter variation and application of bandpass filter frequencies of micro-magnetic signals, it was possible to indicate and separate the main damage mechanisms considering the wear development. It could be shown that the maximum amplitude of BN correlates directly with the profile form deviation and increases with the progress of wear. Surface investigations via optical and scanning electron microscopy indicated strong surface fatigue wear with micro-pitting and micro-cracks, evident in cross-section after 3 × 105 cycles. The result of fatigue on the surface layer was the decrease of residual compression stresses, which was indicated by means of coercivity by BN-analysis. The different topographies of the surfaces, characterized via confocal white light microscopy, were also reflected in maximum BN-amplitude. Using complementary microscopic characterization in the cross-section, a strong correlation between micro-magnetic parameters and microstructure was confirmed and wear progress was characterized in dependence of depth under the wear surface. The phase transformation of retained austenite into martensite according to wear development, measured by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) was also detected by micro-magnetic testing by IP-analysis.

Highlights

The lifetime of gears is limited by different damage mechanisms such as tooth root break, pitting or scuffing
In the wear state 2, a first local material removal starting at the tooth root with a depth of 4 μm appears
The combination of different techniques for surface analysis like profilometry, topography analysis, X-ray diffraction, microscopy and micro-magnetic testing allows for the acquiring of comprehensive information of the superficial state of the gear wheels tooth flanks

Summary

Introduction

The lifetime of gears is limited by different damage mechanisms such as tooth root break, pitting or scuffing. Micro-pitting describes a wear and fatigue phenomenon, which mainly occurs on highly loaded and case-hardened tooth flanks in slow running gear stages of industrial gears. The fatigue phenomenon is decisively influenced by the geometry of the gear, the loading and the chemical reactions between the tooth material and the additives of the oil within the atmosphere [1]. The term micro-pitting describes the matt grey areas on tooth flanks, which are primarily formed on areas with negative sliding speeds and high sliding paths. The phenomenon starts first with short cracks on the tooth’s flank surface whereas the crack density increases with the number of load changes. With an increasing number of microscopic outbreaks, a profile form deviation emerges, which starts at the tooth root

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