22.08.2015   Comprehensive nuclear materials

Stacking Fault Tetrahedra

Irradiation of fcc metals under energetic displace­ment cascade conditions induces the formation of stacking fault tetrahedra. Figure 34 shows an exam­ple of the formation of small dislocation loops and SFTs (triangle-shaped projected images) in copper due to irradiation with 750 MeV protons (2.5 MeV average PKA energy) at -90 °C to -0.7 dpa.302

image314

Figure 33 Dislocation microstructure of pure copper following irradiation with 750 MeV protons at ~200 °C to ~2 dpa. Reproduced from Zinkle, S. J.; Horsewell, A.;

Singh, B. N.; Sommer, W. F. J. Nucl. Mater. 1994, 212-215, 132-138.

image315

Figure 34 Weak beam dark field (g, 4g), g = 002 microstructure of pure copper following irradiation with 750 MeV protons at ~90°C to ~0.7 dpa. The TEM figure is based on irradiated specimens described in Zinkle et al.302 The SFTs are visible as small triangle-shaped defects since the electron beam direction was near [110]

(data from S. J. Zinkle, unpublished research).

The SFTs are thermally stable up to recovery Stage V. SFTs have been observed in numerous irradiated fcc metals, including aluminum,305

copper,12’53’146’302’306’307 nickel,304’307-309 silver,306’307 gold,307’310’311 palladium,310,312 and austenitic stain­less steels.53’96’307’312’313 Evidence from thin film and low-dose irradiation studies using ion beams or other energetic displacement cascade conditions suggests that SFTs can be formed directly in displacement cascades when the PKA energy exceeds a threshold value of ~5—10 keV, in agreement with molecular dynamics simulations.26,29 There are also several observations of SFT formation in some fcc metals due to point defect nucleation and growth during electron irradiation.299,305 The results from irradiations performed under energetic displacement cascade con­ditions at temperatures near recovery Stage I suggest that SFTs are not visible, perhaps due to insufficient rearrangement of the vacancy-rich core within the rapidly quenched displacement cascade.74,305

Похожие посты: