A brittle fracture mechanism in thermally aged duplex stainless steels revealed by in situ high-energy X-ray diffraction

A direct relationship between the microstructural evolution and macroscopic fracture behaviors of a thermally aged (at 475 degrees C for 400 h) duplex stainless steel (DSS) has been established with experimental results from atom probe tomography (APT), nanoindentation and in situ synchrotron-based high-energy X-ray diffraction (HE-XRD). The APT experiments demonstrate that ferrite in DSS spinodally decomposes into Cr-enriched and Cr-depleted domains during thermal aging, which leads to a severe hardening effect in ferrite. The lattice strain development during deformation acquired with the in situ HE-XRD measurements confirms the cleavage fracture of alpha{110} and alpha{200} ferrite grains aligned perpendicular to loading direction. The thermally aged DSS can be readily fractured by connecting the cleavage cracks in ferrite. The spinodal-decomposition-induced hardening in ferrite and the premature failure of ferrite control the final brittle fracture in the aged DSS.