Investigation of the Microstructure of Plastically Deformed Cemented Carbide

Sammanfattning: During machining operation, cemented carbide tools are exposed to high loads and temperatures, which eventually leads to plastic deformation of the tool material. The aim of this work was to investigate if the microstructures of creep deformed micro grain cemented carbides can be linked to alloying elements and mechanical properties. Eleven different fine-grained Tungsten carbide (WC) and Cobalt (Co) based materials have been exposed to compressive creep tests at application relevant temperature. The WC grain size, Sigma 2 (∑2) boundary fraction, and crystallographic structure of the creep deformed materials were investigated with scanning electron microscopy equipped with an electron backscatter diffraction detector. Furthermore, the microstructure of some materials was analysed before and after creep deformation using scanning electron microscopy. A screening of alloying elements that have the potential to increase creep resistance was performed. Growth perpendicular to the load axis was observed in several creep deformed materials, and it could be linked to lower creep resistance. Transition metals from group 4 and 6 limited grain growth, and therefore, improved creep resistance. It was found that a high ∑2 boundary fraction is related to higher creep resistance. The ∑2 boundary fraction was observed to be affected by grain size and alloyingelements.