The Effect of Alternative Tungsten Carbide Grain Size Distribution on Microstructure and Mechanical Properties in Cemented Carbides

Sammanfattning: In the constant pursuit of better-performing cemented carbides, recent studies suggest that a combination of better hardness and toughness can be obtained by changing its WC grain size distribution. As the area is still rather unexplored, this  thesis  aims  to  broaden  the  knowledge  and  answer  whether mechanical properties can be changed by changing the WC grain size distribution, in the context of mining drill bit inserts. This was performed by producing four dual grained material as well as four single grained reference materials, for which the carbon content and presence of alloying element were varied. The materials were characterised and compared with regard to magnetic saturation, magnetic coercivity,  hardness,  fracture  toughness,  wear resistance,  energy  needed  to cause  fracture,  as  well  as  detailed microstructural  analysis  obtained  through imaging and electron backscatter diffraction analysis The results showed that mining drill bit inserts with alternative WC grain size distribution  could  successfully  be  produced,  but  that  a  traditional  bimodal distribution  with  two  peaks  could  not  be  obtained.  The  distribution instead became significantly wider as well as skewed towards larger grains for the dual grained materials compared with their references. It was further also confirmed that the alternative dual grain size distribution could be used to improve the mechanical properties of fracture toughness and wear resistance, but only for material that was not alloyed, and the magnitude of the improvement may be considered  to  be  small.  For  the  alloyed  materials,  it  turned  out  to  be more difficult to influence the mechanical properties, as the improving effect of analloying element outweighed the effect of grain size distribution.