XAFS and SRGI-XRD studies of the local structure of tellurium corrosion of Ni–18%Cr alloy

Abstract

The speciation and atomic structures of corrosion products in Ni-based alloys could provide basic information for understanding the Te corrosion mechanism. In this paper, two-dimensional synchrotron-radiation-induced grazing incidence X-ray diffraction was used to characterize the corrosion products of a Ni–18%Cr binary alloy at temperatures from 600 to 1000 °C. The results showed that a film of CrTe is preferentially formed when Te reacts with the Ni-based alloy at low temperatures (below 900 °C), while CrTe and Ni3Te2 are formed at 900 °C. Moreover, at a temperature of 1000 °C, a solid solution is formed without any changes in the Ni–Cr substrate lattice parameters. Furthermore, X-ray absorption fine structure and wavelet transform analyses were used to investigate the atomic local structure of Te. The investigation indicated that Te atoms diffuse into the Ni–Cr substrate to form a substitutional Ni–Cr–Te solid solution at 1000 °C. Notably, based on a discussion of the thermodynamics of the chemical reaction process, CrTe is considered to be the most stable and prevalent corrosion product due to its comparatively lower Gibbs free energy of formation. These results demonstrate that the Ni–18%Cr alloy is capable of resisting the diffusion of Te atoms.