Abstract
The transverse-rupture strength of WC-Co cemented carbide was studied at room temperature in relation to carbide grain-size and binder content, and analyses of the strength were carried out on the basis of our previous work which demonstrated that the strength is directly controlled by the existence of microstructural defects. The rupture strength was analyzed as a function of dimensions and location of the defect observed on the fracture surface. The following equation was assumed for the strength analysis: σd(1+2\sqrta⁄ρ)=σ0, where σd is the external stress which acted on the defect at the moment of fracture, a is one half of the defect size, ρ is the effective radius of curvature at the end of the longitudinal axis of the defect, σ0 is the strength of the sound matrix free from defects.
Results obtained were as follows. (1) The transverse-rupture strength reached a maximum at certain mean grain size (binder content) when the binder content (mean grain size) was kept constant. However, both values of the structural parameters giving a maximum strength were smaller than those reported by previous reseachers. This was thought to be due to the fact that the strength is governed by the defect characteristic of the specimen. (2) Thus, it was noted that both values of the structural parameters as well as the strength of the alloy have to be discussed in terms of σ0, ρ, a, etc. The σ0 vs. λ (mean free path of binder phase) and the ρ vs. λ plots were shown by a single curve, respectively, regardless of the grain size and the binder content. The peak of the σ0 vs. λ plot, about 850 kg/mm2 in height, was located at λ\simeq0.15 μ. (3) Further study about the nature of σ0 and ρ obtained seems to be needed, since the influence of carbide contiguity or plastic deformation should be taken into account in the evaluation of the above values.
