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

Abstract

Abstract:In this paper, the fracture toughness K Ic 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 K Ic . 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 K Ic 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 K Ic deviations for the same testing conditions for all samples.

Tribological Properties of Coatings Applied on Near-Nano and Nanostructured WC-Co Hardmetals by Using Plasma-Assisted Chemical Vapour Deposition Technique

“…The TiCN surface layer exhibits the hardness of almost 3500 HV0.005, which is a significant surface hardness improvement compared to the substrate. The TiN and TiCN coating hardnesses are as expected [52]. The average critical normal loads are scattered when different substrate materials and coating systems are compared, Figure 3.…”

Hot Sliding Wear of 88 wt.% TiB–Ti Composite from SHS Produced Powders

“…The indentation fracture toughness (IFT) was calculated from the length of radial cracks emanating from the corners of the indents following the Palmqvist approach [20]. The load of 50 kg•f on the indenter resulted in the quite well-developed crack systems, which mitigate any surface effects of the indentation.…”

Analysis of Different Complex Multilayer PACVD Coatings on Nanostructured WC-Co Cemented Carbide

“…Instrumented nanoindentation was used to determine the value of the reduced (effective) modulus of elasticity (E r ), which includes the elastic displacements of the sample, but also of the indenter in accordance with constants E i and ν i , as shown in the following Equation (2) [41,42]:…”