Synchrotron Radiation Study on Alloy 617 and Alloy 230 for VHTR Application

Abstract

High-energy synchrotron radiation has proven to be a powerful technique for investigating fundamental deformation processes for various materials, particularly metals and alloys. In this study, high-energy synchrotron X-ray diffraction (XRD) was used to evaluate Alloy 617 and Alloy 230, both of which are top candidate structural materials for the Very-High-Temperature Reactor (VHTR). Uniaxial tensile experiments using in-situ high-energy X-ray exposure showed the substantial advantages of this synchrotron technique. First, the small volume fractions of carbides, e.g. ∼6% of M6C in Alloy 230, which are difficult to observe using lab-based X-ray machines or neutron scattering facilities, were successfully examined using high-energy X-ray diffraction. Second, the loading processes of the austenitic matrix and carbides were separately studied by analyzing their respective lattice strain evolutions. In the present study, the focus was placed on Alloy 230. Although the Bragg reflections from the γ matrix behave differently, the lattice strain measured from these reflections responds linearly to external applied stress. In contrast, the lattice strain evolution for carbides is more complicated. During the transition from the elastic to the plastic regime, carbide particles experience a dramatic loading process, and their internal stress rapidly reaches the maximum value that can be withstood. The internal stress for the particles then decreases slowly with increasing applied stress. This indicates a continued particle fracture process during plastic deformations of the γ matrix. The study showed that high-energy synchrotron X-ray radiation, as a non-destructive technique for in-situ measurement, can be applied to ongoing material research for nuclear applications.

Synchrotron study on load partitioning between ferrite/martensite and nanoparticles of a 9Cr ODS steel

“…8) The Y 2 Ti 2 O 7 nanoparticles exhibit a superior capacity for taking load. The final achieved internal stress of ~3.5 GPa is much higher than many strengthening phases in metallic materials, including carbides [17,19] and cementite [11] in iron-based steels, and carbides in Ni-based alloys [33]. Compared to these particles, the loading capacity of Y 2 Ti 2 O 7 nanoparticles is considerably higher, despite a much lower volume fraction of nanoparticles within the ODS steel.…”

Development of Austenitic ODS Strengthened Alloys for Very High Temperature Applications

“…dislocation structure evolution) during the deformations. Previous studies confirm that the (311) reflection is a suitable representation for characterization of macroscopic stresses and strains for face-centered cubic (FCC) metals [18,123]. From a recent study in a ferritic/martensitic ODS steel, the loading behavior of different reflections show little difference during the entire tensile test [15].…”

“…A great number of other types of precipitates had been used to enhance the mechanical properties of alloys before the invention of ODS steels [15,[18][19][20][21][22][23]. However, precipitates within conventional alloys still have significant size, which limits they contributions to the enhancement of the mechanical strength.…”

“…Therefore, with the in-situ tensile stage, synchrotron Xray source is a powerful mean to monitor the dynamic properties of the load-partitioning phenomenon in precipitate-strengthened alloys. In fact, in-situ synchrotron tensile investigation has already been employed to explore the load-partitioning phenomenon in a couple of conventional precipitate-strengthened steels [15,[18][19][20]45]. For example, Pan et al, found that the M23C6 carbides take more load than the matrix does during the entire plastic deformation, as shown in Figure 2.4.…”

“…Load-Partitioning Phenomenon within a Fe-9Cr-0.1C Model Alloy[Load-Partitioning Phenomenon within Alloy 617 and Alloy 230[18] …”