Enhanced surface radiation damage resistance in SETE-modified RAFM steel

Abstract

The enhancement of radiation surface damage resistance of RAFM steel has been crucial to the failure protection and engineering application of nuclear fusion reactors. Here, a novel spatial extrusion–twist–extrusion (SETE) process was proposed to improve the radiation surface damage resistance through microstructures modification. The transmission electron microscope (TEM) and scanning electron microscope (SEM) were performed to investigate and reveal the behavior and mechanism enhancement of surface radiation damage. Crack and ablation were investigated in the initial sample, while only smaller bubbles and shallow depth channels were observed in the SETE-deformed samples. Additionally, the increase of dislocations and grain refinement caused by the SETE deformation, can effectively promote the recombination of irradiation defects, and weaken stress concentration by inhibiting the aggregation and growth of helium bubbles, hence inhibiting crack initiation.

Appendix

The relevant parameters of diffraction peaks corresponding to different RAFM samples before and after irradiation obtained by XRD are shown in Table 1.

Table 1 Relative parameters of diffraction peaks of different RAFM samples before and after He²⁺ irradiation

The dislocation density is calculated by crystallite size and micro-strain, which is expressed as

$$\rho = \frac{{2\sqrt 3 \left\langle {\varepsilon^{2} } \right\rangle^{{{\raise0.5ex\hbox{$\scriptstyle 1$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 2$}}}} }}{{\left| {\overline{b}} \right|L}}$$

(1)

where ρ is the dislocation density in the RAFM samples. is the Burgers vector of RAFM steel, which is 1/2 < 110 > . L and < ε² > ^1/2 are the crystallite size and micro-strain obtained by XRD diffraction, respectively. Their calculation form is,

$$\left\{ {\begin{array}{*{20}c} {L = \frac{\lambda }{b}} \\ { < \varepsilon^{2} >^{{{\raise0.5ex\hbox{$\scriptstyle 1$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 2$}}}} = \frac{\sqrt a }{5}} \\ \end{array} } \right.$$

(2)

where λ is the wavelength of the X-ray, λ is 0.154184 nm, b is the intercept after fitting the diffraction peak integral width by Cauchy–Gaussian equation (CG fitting), and a is the slope after fitting the diffraction peak integral width by CG fitting. The curve fitted by the CG equation is shown in Fig. 4

Fig. 4

The fitting CG curves of different RAFM samples, a before He²⁺ ions irradiation, b after He.²⁺ ions irradiation

The intercept and slope obtained by fitting in Fig. 4 are substituted into Eqs. (1) and (2), and the dislocation density of different RAFM samples before and after He²⁺ ions irradiation were obtained. The calculated dislocation densities of different RAFM samples after He²⁺ ions irradiation are illustrated in Fig. 5.

Fig. 5

The dislocation densities of different RAFM samples, a before He²⁺ ions irradiation, b after He²⁺ ions irradiation