Evidence of Short-Range Order (SRO) by Dislocation Analysis in Single-Crystal Ni-Based Matrix Alloys with Varying Re Content After Creep

摘要

TEM characterization of the deformation micromecha-nisms after interrupted creep test at 980°C is proposed in the case of two single-crystal Ni-based matrix alloys without rhenium (Re) and with 9 wt% Re. This paper is aimed to propose an identification of the physical parameter at the origin of the strengthening effect of Re. The TEM observations carried out in the alloy with 9 wt % Re indicate that the deformation proceeds through the propagation of long dislocation pile-ups. A leading pair is observed within these pile-ups. As this dislocation configuration is a signature of short-range order (SRO), a quantitative approach is used to evaluate the SRO degree and thus the resistance due to SRO. The experimental positions of the dislocations are used to evaluate the total elastic force experienced by the dislocations. The strength associated with the SRO is evaluated to: γ_0 = 50 - 60 mJ/m~2. The observation of the matrix alloy without Re indicates the presence of both individual dislocations and some short dislocation pile-ups. It is also associated with a lower SRO degree. It can be concluded that the Re effect leads to an increase of the SRO degree. SRO is still present at high temperature (930°C), whereas it has been shown to disappear in similar matrix alloy with a lower amount of Re. Rhenium appears then to promote SRO. It can be at the origin of its well-known strengthening effect.