Using Analytical Electron Microscopy to Design Radiation Resistant Steels for Fusion Applications
- PDF / 3,693,187 Bytes
- 9 Pages / 604.8 x 806.4 pts Page_size
- 65 Downloads / 186 Views
36
austenitic stainless steels are easily fabricated, nonmagnetic, reasonably strong and tough, commercially available, and familiar, they also remain as candidate materials for fusion. They have also been extensively studied for use in various fission reactor systems as well. The austenitic and stainless properties of FeCr-Ni alloys and steels were discovered during 1900-1915. 3A Commercial grades like AISI types 304 and 316 stainless steels were developed prior to World War II. The effects of irradiation on materials have been studied since 1942, when Eugene P. Wigner anticipated that fission fragments a n d energetic neutrons would damage crystalline materials by displacing atoms to create point defects (vacancies and interstitials). 5 The advent of fast fission reactor programs in the 1960s led to the exploration of new regimes of temperature and displacement damage. Irradiation experiments at these new conditions led to the discovery of a wide range of new radiation-induced materials phenomena in austenitic stainless steels, including void swelling, 6 - 7 i r r a d i a t i o n - c r e e p , 8 radiation-induced precipitation, 910 and solute segregation. 1 1 Observations of these p h e n o m e n a induced by fission
reactor irradiation have contributed a significant a m o u n t of k n o w l e d g e to materials science concerning (a) pointdefects and their effects on materials, (b) n o n e q u i l i b r i u m p h e n o m e n a a n d processes, and (c) microstructural and microcompositional evolution and their effects on properties. 12 ' 14 In addition to creating displacement damage, neutron irradiation results in helium generation from various (n,a) reactions. For steels irradiated in the core of a fast breeder reactor (FBR), the ratio of helium generated to the number of d i s p l a c e m e n t s p e r a t o m (He/dpa ratio) by fast fission neutrons with energies of 0.1-2 MeV is < 1 . In a fusion reactor first wall, however, the He/dpa ratio will be much higher. N e u t r o n s with energies u p to 14 MeV from the deuterium-tritium fusion reaction will induce (n,a) reactions with the atoms of all the elements that constitute any candidate structural material. In steels, fusion neutrons will produce He/dpa ratios of 10-12 appm/dpa. Experiments to explore the effects of high He/dpa ratios have shown that helium can have a powerful influence on the evolution of the microstructure and properties. 12 " 19 Because helium atoms are virtually insoluble in most materials, they precipitate rapidly as small b u b b l e s in which the high internal gas pressure is balanced by the internal surface tension. Bubble growth is driven by the gas atoms absorbed. Because displacement damage occurs as energetic neutrons create cascades of vacancies and interstitials in the crystalline matrix, excess point defect concentrations build up in the matrix during irradiation. A vacancy supersaturation arises from the biased absorption of radiation-produced interstitial point defects at dislocations, which then leaves a net excess of va
Data Loading...
