Elevated temperature intergranular cracking of heat-resistant alloy under tensile stress

In a 2.25Cr1.5W heat-resistant alloy, it is shown that the time to intergranular failure under tensile stress t can be expressed by $t_0 \sigma ^{ - n} \exp \left({Q/RT} \right)$, where t0 is the constant of proportionality, n is the stress exponent, and Q is the activation enthalpy. It is shown that the dimples observed at elevated-temperature intergranular fracture surfaces are not the micro-ductile fracture areas but the interfaces between the grain boundary carbides and the neighboring grains. It is also shown that the segregation concentration of solute atoms is much higher at the grain boundary carbide interfaces than at the carbide-free grain boundaries. Under tensile stress, the elevated-temperature intergranular cracking occurs through the decohesion of grain boundary carbide interfaces, which is followed by the eventual carbide-free grain boundary cracking.