No abstract

Tensile creep tests of WC-10%Co and WC-10%TaC-10%Co alloys were carried out at terncreep rate decreases, the ruptured time increases and the fracture strain decreases with increase in carbide particle-size. The steady state creep rate is approximately proportional to inverse square of carbide particle-size. With TaC addition, the steady state creep rate remarkably decreases and the ruptured time increases. The creep deformation may be controlled by the two processes, i.e. (a) diffusional flow of vacancies in the binder phase, and (b) dislocation climb over the carbide particles.

To elucidate the nature of elevated temperature deformation and fracture of WC-(6-20)%Co alloys, the influence of the various factors such as the size and volume fraction of WC, defects (pores), and strain rate on the mechanical properties was investigated in bend testing over a temperature indicate that in each alloy, there exist three transition temperatures, TI, TII', and TII(TITII), T.R.S. of the coarse-particled alloy becomes larger than that of the fine particled alloy. Moreover, numerous microvoids originate from either WC/WC/Co or WC/Co boundaries. The microvoids which are located in the direction perpendicular to the tensile axis merge into parallel, interconnected cracks which propagate through the Co phase. The temperature range II'(TII'-TII) was found to be the transition range with reference to the fracture mode from the type specific for the range I to that for the range II. In regard to the effect of strain rate on deformation and fracture, it was found that the increase of strain rate gives an equivalent effect to the lowering of temperature. The mechanisms of the deformation and fracture in the respective temperature ranges were discussed.

No abstract

No abstract