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Metals 2017, 7(4), 143; doi:10.3390/met7040143

Vickers Indentation Fracture Toughness of Near-Nano and Nanostructured WC-Co Cemented Carbides

Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia
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Academic Editor: Kevin Plucknett
Received: 13 January 2017 / Revised: 1 April 2017 / Accepted: 12 April 2017 / Published: 19 April 2017
(This article belongs to the Special Issue Cermets and Hardmetals)
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Abstract

In this paper, the fracture toughness KIc of near-nano and nanostructured WC-Co cemented carbides by Vickers indentation fracture toughness (VIF) was investigated. The aim was to research the type of cracking occurring in near-nano and nano-grained WC-Co cemented carbides with respect to the Co content and, consequently, to evaluate the appropriateness of different models for the fracture toughness calculation. The mixtures with different binder content—4, 6, and 9 wt. % Co—were consolidated by sintering in a hydrogen atmosphere. Vickers indentation using a test force of 294 N was used for the determination of fracture toughness. The type of crack that occurred as a consequence of the applied load on the corners of the Vickers indentations was analysed with optical microscopy before and after repolishing the samples. Different crack models, Palmqvist and radial-median, were applied for the calculation of KIc. Instrumented indentation testing was used to determine the modulus of elasticity of the consolidated samples. From the research it was found that near-nano and nanostructured cemented carbides with 9 and 6 wt. % Co do not exhibit median cracking and the indenter cracks remain radial in nature, while near-nano and nanostructured cemented carbides with 4 wt. % Co exhibit both radial and median cracking. Accordingly, it was concluded that the critical amount of the binder phase in near-nano and nanostructured WC-Co at which the crack changes its geometry from Palmqvist to radial-median is around 4 wt. % Co. Comparing different models it was found that KIc values are not consistent and differ for each method used. Models from Exner crack resistance for the Palmqvist crack showed good agreement. Radial-median crack models showed significant KIc deviations for the same testing conditions for all samples. View Full-Text
Keywords: fracture toughness; near-nano and nanostructured cemented carbides; Vickers indentation fracture toughness; Palmqvist crack; radial-median crack fracture toughness; near-nano and nanostructured cemented carbides; Vickers indentation fracture toughness; Palmqvist crack; radial-median crack
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Aleksandrov Fabijanić, T.; Ćorić, D.; Šnajdar Musa, M.; Sakoman, M. Vickers Indentation Fracture Toughness of Near-Nano and Nanostructured WC-Co Cemented Carbides. Metals 2017, 7, 143.

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