It has been previously reported by the present authors that the transverse-rupture strength of WC-Co cemented carbide could clearly be explained based on the analysis of the structural defects retained in the alloy, because the strength is usually controlled by the defects. The present work is related to the same subject as above for titanium carbide base cermets. The TiC-(10-30)%Mo-(20-40)%Ni and p(5-70%WC)-(15-20)%Ni alloys with mean grain size of about (1.2-2.6)μ and 2.5μ, respectively, were vacuum-sintered and used as specimens.
The results obtained were as follows: 1) It was confirmed that the strength of these alloys was also directly controlled by the dimension and location of the defects (residual micropore and coarse carbide grain). 2) In each alloy, the calculated external stress (σd) which operated at the defects when the fracture was initiated" correlated so strongly to the dimension of defects (2a), that the linear relation was found between σd-1 and √a. However, the strength (σO) of the matrix (free from defects) obtained in each alloy from the extrapolated value of the straight line to the vertical axis, was found in the range from about 230 to 290 kg/mm2 (according to JIS), which was very much lower than the value of about 800 kg/mm2 in conventional WC-10%Co alloy. 3) Thus, it was made clear that the transverse-rupture strength of the present titanium carbide base cermets would not exceed the value of about 250 kg/mm2 at room temperature, even though the strength increases as the defect size decreases. Discussion as to the lower value of σO in the cermet has been given.