Electron microscopic characterization of surface zones thermo-chemically modified by electrical discharge machining

Machining processes with main thermal impact like electro discharge machining (EDM) result in a change of temperature in the workpiece with temporal and spatial temperature gradients which have a large influence on the thermo-chemically modified surface microstructure and therefore a high impact on...

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Bibliographic Details
Published in:Journal of materials processing technology 2020-06, Vol.280, p.116596, Article 116596
Main Authors: Ehle, L.C., Schneider, S., Schwedt, A., Richter, S., Klink, A., Mayer, J.
Format: Article
Language:English
Subjects:
42CrMo4 steel
Cooling rate
Dendritic structure
Electric discharge machining
Electron backscatter diffraction
Electron imaging
Electron probe microanalysis
Electron probes
Microstructure
Perlite
Phase transformation
Process parameters
Process signatures
SDAS
Solidification
State variable
Surface integrity
Temperature gradients
Temperature profiles
Workpieces
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Summary:Machining processes with main thermal impact like electro discharge machining (EDM) result in a change of temperature in the workpiece with temporal and spatial temperature gradients which have a large influence on the thermo-chemically modified surface microstructure and therefore a high impact on the functional properties of the workpiece. However, as most state variables (like the temperature) cannot be measured directly during processing, further insight can be gained only by simulations. This problem can be addressed by using microstructural features like the secondary dendrite arm spacing for calculating the cooling rate and by validating the simulated temperature profiles with these values. This study analyzes the subsurface microstructure of EDM machined 42CrMo4 steel with a ferrite-perlite and a quenched-tempered matrix by a range of microstructure analysis techniques. Results of electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA) and analysis of secondary dendrite arm spacing of secondary electron images are presented and their dependence on the main processing parameters is discussed qualitatively and quantitatively.
ISSN:0924-0136
1873-4774
DOI:10.1016/j.jmatprotec.2020.116596