Influence of Porosity on Strength of WC–10%Co Cemented Carbide

Abstract

A model has been developed which describes the influence of size distributions of defects such as pores on the distribution of transverse rupture strength (TRS) in three point bend testing of hard materials. The model is based on knowledge of three things: the stress distribution in the test specimen during loading; the three dimensional size distribution of the defects in the material; and the relationship between fracture toughness K _IC, applied stress, and critical defect size for brittle fracture according to linear fracture mechanics. By using the fracture toughness of the material and the defect size distribution as input data the distribution of strengths of the material can be calculated. The model was tested on two WC–10%Co cemented carbides with relatively high porosity contents. The size distributions of defects such as pores and inclusions were evaluated with automatic image analysis on sections through the materials. Pores which had initiated the fracture were identified on fracture surfaces. K _IC values and distributions of TRS values were measured. There was good agreement between the theoretically predicted distributions of transverse rupture strengths and the experimentally measured values. The difference in stress was only 6–8%. PM/0471