A study on the mechanical behaviour of WC/Co hardmetals

Abstract

The hardmetal cutting tools used in machining are submitted to extreme conditions in terms of temperature and mechanical loading. A better understanding of the failure of cutting tools and capability to predict tool life are key factors in the development of new tool materials with improved mechanical behaviour. Main failure mechanisms are wear, thermal-mechanical fatigue and brittle fracture. The aim of present work is to study the mechanical behaviour of two hardmetals. The properties studied were Young's modulus, bending strength, fracture toughness and fatigue endurance. The resonant technique was used to determine elastic properties and a good agreement was found with three-point bending results.

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

“…Measured Palmqvist toughness values correspond to already-published research [19]. Fang reported KIc values in the range from 8.8 to 9.5 MPa·m 1/2 for the hardness range from 1887 to 2084 HV [1].…”

“…Measured Palmqvist toughness values correspond to already-published research [19] [10]. The values are lower compared to the measured Palmqvist toughness values, which can be explained by significantly higher values of the applied load, meaning that the affected area of the indent consists of the WC grains and Co binder.…”

“…The differences between the two types of cracks occur after polishing the surface layers away. The radial-median crack system exhibits radial and median cracks and remains connected to the inverted pyramid of the indentation after polishing, while the Palmqvist cracks remain radial in nature and the cracks become detached from the tips of the Vickers indentation [17,19]. The calculation of the fracture toughness depended on the nature of the cracks; therefore, it is necessary to identify the crack profile and to select an appropriate equation (model) for obtaining the accurate fracture toughness values.…”

“…Several static methods have been used to determine the elastic modulus E of cemented carbides; tensile testing, bending testing, and instrumented indentation testing [19,20]. The tension test is very Metals 2017, 7, 143 6 of 16 difficult to perform due to the high rigidity and the brittle nature of the material.…”

“…The tension test is very Metals 2017, 7, 143 6 of 16 difficult to perform due to the high rigidity and the brittle nature of the material. The instrumented indentation test, also known as depth sensing indentation or nanoindentation, is adequate to obtain local values of rigidity and is widely used for thin film and homogenous materials, like mono crystals [19]. It has been widely used for the determination of the mechanical properties of the individual phases in cemented carbides and single WC crystals since their properties are orientation-dependent [12].…”