Thermal stability of nano-structured ferritic alloy

The excellent tensile and creep strength and the potential for managing radiation damage make nano-structured ferritic alloys (NFAs) promising candidates for high-temperature applications in spallation proton, advanced fission and fusion neutron environments. The thermal stability of NFAs is critical for such applications, hence, this has been investigated in a series of aging experiments on MA957 at 900 °C, 950 °C and 1000 °C for times up to 3000 h. Optical and transmission electron microscopy (TEM) studies showed the fine scale grain and dislocation structures are stable up to 1000 °C. TEM and small angle neutron scattering (SANS) showed that the nm-scale solute cluster-oxide features (NFs), that are a primary source of the high strength of NFAs, were stable at 900 °C and coarsened only slightly at 950 °C and 1000 °C. Porosity that developed during high-temperature aging was minimal at 900 °C and modest at 950 °C, but was much larger after 1000 °C. Microhardness was basically unchanged after the 900 °C aging, and decreased only slightly (⩽3%) after aging at 950 °C and 1000 °C.