On fracture mechanisms of iron and its alloys in various temperature and stress ranges

Investigated is the time-temperature dependence of stress-rupture characteristic for iron and its alloys containing nickel (10 and 25%) and manganese (5 and 20%). Fractographic, optical and electron microscopic methods have been used. It is shown that in the temperature (T/Tsub(m)=0.6-0.65) and stress [σ/G=(1-5)x104] ranges a fracture mode changes from a thermal fluctuation mechanism to a diffusion one. Thermal fluctuation fracture develops through wedge crack growth owing to a break of bonds in a crack tip, an activation energy being equal to a sublimation one. Diffusion fracture develops by pore growth and coalescence along the grain boundaries and has the energy which is equal to a self-diffusion one