Journal
METALS
Volume 12, Issue 11, Pages -Publisher
MDPI
DOI: 10.3390/met12111882
Keywords
cemented carbides; two-dimensional microstructural characterization; carbide grain size; phase fraction; carbide contiguity; binder mean free path; optical microscopy; SEM; EBSD
Funding
- Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation
- Deutsche Forschungsgemeinschaft [DFG-425923019, PID2019-106631GB-C41]
- Spanish Ministerio de Ciencia e Innovacion MICINN-FEDER (Spain) [INST 256/510-1 FUGG]
- Open Access Publication Funding program of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
- Saarland University
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This study focused on the microstructural characterization of cemented carbides, evaluating different methods and techniques for accurate analysis. The combination of optical microscopy and line analysis was found to be suitable for direct inspection and rapid estimation of larger carbide grain sizes, while the most precise results were achieved using line analysis of backscattered electron images obtained by scanning electron microscopy.
Cemented carbides, or hard metals, are ceramic-metal composites usually consisting of tungsten carbide particles bound by a cobalt-based alloy. They are the backbone materials for the tooling industry, as a direct consequence of the outstanding range of property combinations, depending on their effective microstructural assemblage, i.e., the physical dimensions and relative content of their constitutive phases. Hence, reliable microstructural characterization becomes key for hard metal grade selection and quality control. This work aimed to assess the practical two-dimensional characterization methods for the most important one- and two-phase properties of cemented carbides, i.e., the carbide grain size, phase fraction, carbide contiguity, and binder mean free path. Three different methods-point, line, and area analysis-were implemented to characterize four microstructurally distinct grades. The images were acquired by optical and scanning electron microscopy, with the latter through both secondary and backscattered electrons. Results were critically discussed by comparing the obtained values of properties and the different characterization methodology. Inspection technique combinations were finally ranked based on accuracy, accessibility, and operability considerations. The line method was used to analyze all the properties, the area method, for the one-phase properties, and the point method, for only the phase fraction. It was found that the combination of optical microscopy and the line analysis method was suitable for a direct inspection and rapid estimation for carbides above fine grain size. The most precise results were achieved using line analysis of the images obtained by the backscattered electrons of the scanning electron microscope.
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