Decoupling of defect and short-range order contributions to resistivity recovery measurements in binary alloys

Abstract

We report a new and improved approach that uses low-temperature resistivity recovery measurements to study the defect kinetics in metallic binary alloys. This method is able to decouple the effect related to the irradiation defect contribution to the resistivity from that of the short-range order, which is enhanced by the free migration of defects. This approach can provide reliable experimental data which are more suitable for comparisons with current computational models. Furthermore, the difference in this method with respect to the classical one is that our method gives information concerning the role of vacancies and interstitials on short-range order. The method is applied to a model alloy Fe-5%Cr, of interest for fusion applications, where short-range order effects have been previously found to play a role. In general, concentrated alloys have enough solute concentration to perturb the electronic structure and the phonon spectrum. Typically this composition range starts at 1%-2% of the solute concentration. These perturbations lead to an atomic configuration which is never fully random; there are certain atomic correlations that can be described as short-range order (SRO). The SRO parameters (α i ) are defined as the correlation between first-and next-nearest neighbors (NN) of an atom [1]. Every alloy has different SRO equilibrium configurations for every solute concentration and temperature [2], which also depend on the thermomechanical process experienced [3,4]. Quenching experiments have been widely used to study the kinetics of ordering [2][3][4][5][6][7][8] given the linear relation of the resistivity (ρ) with α i (cf. Refs. [1,8]). Concurrently, resistivity recovery (RR) experiments have been commonly used to investigate radiation effects in pure metals, based on the recovery of the residual resistivity up to its original value after low-temperature irradiation and subsequent isochronal annealing [9][10][11][12][13][14][15][16][17]. However, in the case of concentrated alloys, the presence of migrating defects allows solute rearrangements and changes in the SRO, which in turn affect the residual resistivity of the alloy. This effect might thus significantly alter the RR results and their interpretation, as it has been discussed in the case of Fe-Cr [18,19].In the field of energy advanced materials development there is specific interest in the study of Cr effects on nuclear alloys [20,21], given that Cr concentrations (C Cr ) close to 9% reduce swelling [22,23], reduce the radiation-induced ductile-brittle transition temperature (DBTT) [24], and increase protection against corrosion [25]. The physics of these effects is not yet well understood though it is believed that the minimum of the SRO parameters might play a role in affecting the kinetics of radiation defects in a concentrated Fe-Cr system. Indeed, it has been proven that α i change their sign at C Cr close to 10% [26][27][28]. At C Cr < 11% the SRO becomes negative, i.e., Cr tends to distribute as far * begona.gomez-ferrer@externos.ciemat.es...

Impact of chemical short-range order on radiation damage in Fe-Ni-Cr alloys

“…1ce, respectively. The apparent Cr clustering is consistent with previous experimental and computational studies [4,[23][24][25].…”

“…Thermodynamically, CSRO is enhanced by atom diffusion, which is a thermally slow process due to a low concentration of defects. By contrast, radiationenhanced diffusion can promote an efficient increase of CSRO [4,6,19] over the timescale of radiation experiments. However, how the CSRO correlates with radiation dose and the existence of steady-state CSRO remain to be elaborated.…”

“…CSRO has been commonly reported in multiple principal element concentrated alloys such as medium or high entropy alloys (MEA/HEA). Due to the perturbations of electronic structure and phonon spectrum of the constituent species, the atomic configuration exhibits some atomic correlations that can be described as CSRO [2,4,5]. CSRO has been used to explain the increased mechanical characteristics in various alloys [2,[5][6][7][8].…”

“…To reveal the impact of CSRO on the radiation damage in Fe-Ni-Cr alloys, we consider Fe 0.2 Ni 0.5 Cr 0.3 with an experimentally stable face-centered cubic (FCC) lattice [20], where a high concentration of Cr (>10-11%) is known to induce Cr clustering [4,21]. Hence, the Cowley short-range order parameter α [22] is used to indicate the degree of Cr clustering in a quasi-binary alloy:…”

RMATE: A device to test radiation-induced effects under controlled magnetic field and temperature

“…High-chromium ferritic/martensitic steels are good candidates as structural materials for fusion reactors because of their high resistance to irradiation [5,6]. However, it is well-known that micro-structural and mechanical properties of these materials are modified by radiation-induce propagating defects [7,8]. In addition, since they are based on Fe-Cr alloys, which are ferromagnetic materials, the presence of high magnetic fields could also play a role in the performance of these steels.…”