Gamma ' Precipitation in Alloy 800 Investigation by Small Angle Neutron Scattering

摘要

Alloy 800 has become a steel of primary technological importance in Nuclear Power Plants, particularly for heat exchangers. The most important metallurgical problem concerns the creep behaviour, related to microstructural instability against time. Therefore much work has been devoted to correlate the evolution of microstructural properties (creep damage, carbides and gamma ' hardening phase) with aging conditions. The investigation of gamma '-phase evolution is much more difficult than in Nickel alloy because it precipitates as a dilute system of very small particles (10 to 200 A in diameter) and it is very difficult to get quantitative data about size distribution and volume fraction by conventional Transmission Electron Microscopy. Small Angle Neutron Scattering (SANS) has been used to determine both particle size distribution and volume fraction of gamma ' precipitates in Alloy 800. Effects of aging time, of aging temperature and of chemical composition are investigated. (Atomindex citation 12:612894)