Application of ASTM C1421 to WC-Co fracture toughness measurement

Abstract The accurate measurement of fracture toughness of cemented carbides is essential for material development, characterization, and application; however, varying methodologies are used to characterize this critical material property. In this study, the surface crack in flexure and single-edge precracked beam methods in ASTM C1421, along with the Palmqvist indentation/crack length method outlined in ISO 28079, were used to determine the fracture toughness of tungsten carbide (WC) materials containing between 10 and 25 wt.% cobalt (Co). The surface crack in flexure method was not successful because an appropriate precrack did not form underneath the Knoop indentation in any of these compositions. Cracks also did not form at the tips of the Vickers indentations in WC with 15% and higher Co content, rendering the Palmqvist method useless for these materials. The single-edge precracked beam method was the only method that yielded consistent and repeatable toughness values for all compositions.