Toughness

The Palmqvist method uses the corner crack of a Vickers hardness indentation to derive the fracture toughness. The critical stress intensity factor is defined as:
K_1C=6.2(HV50/∑L)^1/2 in MN/m^3/2

When components in tools like cemented carbide rolls are exposed to external loads, static or dynamic, mechanical stresses occur within the material. The mechanical strength and deformability of the material are therefore important. In many cases, particularly in carbide rolls, when dealing with shock loading, both these properties must be considered simultaneously. This forms the background to the term “toughness”, which can be defined as “the ability to resist fracture” (i.e., a complete separation into at least two parts).

A method commonly used for determining the toughness of cemented carbides is the Palmqvist method. In this case, the fracture toughness of the material is represented by its critical stress intensity factor K_1C.

The results of toughness tests show that this property increases with increasing binder content and with increased WC grain size.