抄録
Room and high temperature four point bend tests for Si3N4/SUS304 joints were carried out at constant loading.Fracture surfaces of the interlayer of joints were observed using SEM to discuss the fracture mechanism at high temperature. Furthermore, the fracture strength distribution was estimated on the basis of the unified estimation method considering the fracture mechanism.
(1) Failure of brazed Si3N4/metal joints in high stress level was occurred at a flaw in ceramics near bonding interface. On the other hand, failure of the interlayer in low stress level was occurred due to creep rupture. Creep rupture of joints was dominated on steady-state creep of the interlayer. Then, creep rupture life also could be predicted from minimum creep strain rate in interlayer by using both equation of Monkman-Grant and Norton's law.
(2) The fracture strength of the joints could be evaluated considering the temperature dependence of strength as follows:
σf·teff1/nj=σfexp[(-Qi/k)(1/T+273-1/Tθ+273)]mi√ln(1-Pf)-1
(3) Reliability structural design of joints had better determine the stress level and proof life considering failure of the interlayer with small scatter of rupture lives.
