Comparative study on indentation fracture toughness measurements of cemented carbides

Abstract

Majority of the fracture toughness studies of metallic materials typically use the Chevron notch technique, compact specimens and round notched tensile specimens. These methods require considerable time for sample preparation and for the notch geometry control. Only a few of them can be applied for cemented carbides due to the very high brittleness of the hard phase. This is why various indentation fracture toughness (IFT) techniques have been developed [(superscript 1, 2)], which are more rapid and simple. Indentation toughness measurements results depend critically on the assumption about the crack type (Palmqvist or median/radial cracks), on the equations used for the calculation of fracture toughness and on the material-dependent and material-independent constants [(superscript 3)]. In the present work a comparative study of IFT calculation methods was carried out to find a reliable technique for studied materials (WC-Co, TiC-Fe/Ni). Several IFT equations for ceramic materials, recommended by standards and publications, were used for the evaluation of the fracture toughness and compared with published conventional fracture toughness data [(superscript 4, 5)]. Only few of the equations give reliable estimation of the fracture toughness of cemented carbides.