Surface crack propagation and morphology in cutting tools
Abstract
Purpose
The purpose of this paper is to investigate the driving mechanisms for crack propagation regarding the related microstructures. Cracks in white etching layers have been found at the surface of submerged steel blades subjected to frictional sliding conditions.
Design/methodology/approach
In-situ monitoring revealed a fluctuation between mixed lubrication and hydrodynamic lubrication conditions. One lamella including a crack tip was prepared for transmission electron microscopy (TEM) using focused ion beam milling. Transmission electron microscope analysis was performed with the aim to understand the characteristics of the crack propagation, especially considering the influence of the microstructural configuration (grain refinement, carbides, martensite and ferrite grains).
Findings
The investigations have shown a grain-refined plastically deformed layer (friction martensite with grain sizes of < 100 nm) which influences the propagation direction of cracks introduced at the frictionally stressed surface. Thereby, the crack propagation is dominantly parallel to the margin of the grain-refined martensitic layer at the surface and the base material. Cracks were split into side cracks what mostly appears at present carbides. In this case, the crack propagation might strike through the carbide or separate it from the matrix due to the mechanical misfit.
Originality/value
For obtaining the results of this paper, a very special preparation of tribologically stressed samples was performed. Accordingly, specific findings of the crack propagation behavior under such conditions were achieved and are documented in the presented work. Moreover, the described crack propagation process is a combination of several mechanisms which occur in very limited region underneath the surface and are investigated by high-resolution TEM.
Keywords
Acknowledgements
This work was funded by the Austrian COMET-Program (Project K2 XTribology, Grant No. 849109) and has been carried out within the Excellence Centre of Tribology and the University Service Centre for Transmission Electron Microscopy (Vienna University of Technology).
Citation
Linz, M., Walzhofer, F., Krenn, S., Steiger-Thirsfeld, A., Bernardi, J., Winkelmann, H. and Badisch, E. (2016), "Surface crack propagation and morphology in cutting tools", Industrial Lubrication and Tribology, Vol. 68 No. 1, pp. 141-148. https://doi.org/10.1108/ILT-10-2015-0144
Publisher
:Emerald Group Publishing Limited
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