Experimental Investigation of the Effect of Injected Interstitials on Void Formation

Abstract

Pure nickel, a “pure” Type 316 stainless steel (P7), and two high-strength copper alloys have been irradiated with either 14-Me V nickel or copper ions to a peak damage level of 50 displacements per atom (dpa) (K = 0.8) at homologous temperatures ranging from 0.4 to 0.6 Tm. The irradiated foils have been examined in cross section in an electron microscope. The injected interstitial effect on the suppression of the measured void densities in nickel and P7 was found to increase with decreasing temperature. The comparison of these results with nucleation theory shows good qualitative agreement. Quantitative discrepancies are attributed to diffusional spreading of point defects and to the presence of impurity atoms in the matrix. A copper alloy irradiated at 300°C showed a small heterogeneous void density characteristic of the high temperature end of the void swelling regime, while no voids formed in the alloys irradiated ≧400°C. This result is in excellent agreement with nucleation theory that indicates the void swelling regime in ion-irradiated, low impurity copper should be less than 300°C (0.42 Tm.

Radiation-Induced Effects on Microstructure

“…The injected ions act as a source of additional interstitial atoms and can significantly suppress void nucleation and growth. 149,154,201,202 The peak concentration of the injected ions occurs near the displacement damage peak for ion irradiation, and therefore considerable care must be exercised when evaluating the void swelling data obtained near the peak damage region in ion-irradiated materials. 154,201,202 Figure 22 shows an example of the dramatic changes in microstructure that can occur in the injected ion region.…”

“…149,154,201,202 The peak concentration of the injected ions occurs near the displacement damage peak for ion irradiation, and therefore considerable care must be exercised when evaluating the void swelling data obtained near the peak damage region in ion-irradiated materials. 154,201,202 Figure 22 shows an example of the dramatic changes in microstructure that can occur in the injected ion region. 203 In this example, void formation in ion-irradiated nickel at 400 C is completely suppressed in the regions with the injected interstitials and the void microstructure is replaced with an aligned array of small interstitialtype dislocation loops.…”

Simulated spatial and temporal dependence of chromium concentration in pure Fe and Fe 14%Cr under high dpa ion irradiation

“…The diffusivities are used in Arrhenius form as in [17] and prefactors and activation energy terms for the d-values are given in Table 1. Pre-exponential factor for Fe SIA diffusivity ݀ ,ி 6.59 x 10 -7 m 2 s -1 [22] Pre-exponential factor for Cr SIA diffusivity ݀ , 6.85 x 10 -7 m 2 s -1 [22] Pre-exponential factor for Fe vacancy diffusivity ݀ ,ி ௩ 5.92 x 10 -6 m 2 s -1 [22] Pre-exponential factor for Cr vacancy diffusivity ݀ , ௩ 5.46 x 10 -6 m 2 s -1 [22] Activation energy for Fe SIA diffusivity ‫ܧ‬ ி,…”

“…The injected ion induces a compositional change when it comes to rest, and while the compositional modification is often relatively small, the injected interstitial acting as a physical rather than chemical entity has been recognized as influencing the radiation damage, e.g., exerting a powerful suppressive effect on void nucleation and the posttransient swelling rate [2][3][4][5][6]. However, compositional effects of implanted ion can be important for high irradiation cases.…”