Phase stability and thermal aging behavior in high-strength Fe-Ni-Cr-Al alloys

Abstract

High-strength Fe-Ni-Cr-Al alloys, developed as accident-tolerant fuel cladding materials, exhibited superior properties in anticipated accident conditions and good corrosion resistance in the water chemistry of light water reactors. The alloys showed a high tensile strength of approximately 1 GPa owing to the duplex structure with NiAl precipitates and were successfully manufactured. However, it is a limitation for practical application that the ferrite phase of Fe-base alloys is susceptible to being embrittled at the operating temperature of about 360 °C. In addition, literature on the phase stability of NiAl-rich precipitates at about 360 °C was hardly found. Thus, it is difficult to estimate the thermal aging behavior of the high-strength Fe-Ni-Cr-Al alloys during normal operation. In this thesis, the phase stability of NiAl-rich precipitates was studied at the temperature range of 375 °C to 475 °C. After then, the thermal aging behavior of the entire alloy system was investigated. At the end of this thesis, the improved aging behavior with different microstructures of the alloys was proposed.