Abstract
The relation between bending stress (σ) and rupture time (tr) in WC-10%Co alloy was investigated in the temperature range of 400∼900°C under the condition that tr was less than 2 h, and the ratio of σ to transverse-rupture strength was 0.4∼0.95. The tests were carried out in argon. The WC-10%Co high carbon two-phase alloy with a carbide grain size of 1.2 μm was vacuum-sintered at 1400°C for 1 h and used as specimens.
The results obtained were as follows: (1) The values of tr showed large scatter at low temperatures below 600°C; no such scatter was observed at high temperatures above 700°C. As a whole, a linear relation held between σ and logtr at each temperature, i.e., logtr decreased linearly with increasing σ and the slope decreased with rising temperature. (2) The creep rupture occurred through the following processes: (i) after a certain time of loading, microcracks formed mainly along the WC/WC or WC/binder interface; (ii) these microcracks connected with each other and the interconnected crack grew stably, absorbing microcracks formed ahead of the interconnected crack; and (iii) the stable crack led to rupturing of the specimen, when its length reached a critical value which is a function of temperature and σ. (3) The scattering of tr at lower temperatures was considered to be due to the fact that the stable crack often formed around microstructural defects and the time needed for the crack extension towards the critical one varied with the defect dimensions.
