Dislocation climbing dominated decomposition and fracture of carbides in a Ni-based superalloy

Metal carbides (MC) are typical strengthening phases in steels and superalloys. However, the decomposition of carbides can occur during high-temperature creep, which is generally considered to be detrimental to the hightemperature performance of superalloys. Here, through transmission electron microscopy and atomistic simulation, we report the atomistic to micro-scale mechanisms of MC decomposition. We identify that MC can deform plastically during high-temperature creep, which is supported by the observation of high-density dislocations within MC and steps at matrix/MC interfaces. This could release the stress concentration at the matrix/MC interfaces, thus improving the creep resistance. With Cr segregation along the dislocation line and continuous dislocation climb, decomposition of MC into M23C6 occurs in grain interiors, which could lead to crack inside the MC carbides, i.e., fracture at the partially coherent M23C6/MC interfaces. This is new to the existing knowledge that MC decomposition and fracture occur at matrix/MC interfaces.

Automated summary

Through transmission electron microscopy and atomistic simulation, we investigated the mechanisms of MC decomposition at the atomistic to micro-scale. We found that MC can deform plastically during high-temperature creep and observed high-density dislocations and steps at matrix/MC interfaces. This release of stress concentration improves the creep resistance. Moreover, we discovered that MC decomposition into M23C6 occurs in grain interiors, leading to cracks at the partially coherent M23C6/MC interfaces, which is different from the existing understanding.