Stress distribution in depth of NiCr + Cr2O3 systems using high-energy synchrotron X-rays in transmission mode

Abstract

NiCr alloys develop chromia layers in oxidizing high temperature environments. The stress in oxide layer was largely explored, whereas too few works were devoted to the stress distribution in the underlying metallic substrate. To determine the stress distribution in a duplex oxide-metallic substrate system, a variant of sin2ψ method in transmission mode using high-energy synchrotron X-rays has been developed. 103.4 keV synchrotron X-rays have been used to penetrate 6 × 6 × 0.4 mm and Ø6 × 0.9 mm samples with different oxidation conditions. In order to obtain the stress gradient from the top surface to the bottom surface, the patterns of diffraction were collected and then were analyzed by a complete data processing. The stress varies towards the surface in a non-linear manner, especially near the interface zone. In order to better understand the stress distribution of such a duplex oxide-metallic substrate system, the stress caused by chromium diffusion is investigated by proposing numerical values for coupling coefficient, which finally can partially explain the stress variation near the interface zone.