New iron–aluminium alloy with thermally stable coherent intermetallic nanoprecipitates for enhanced high-temperature creep strength

Abstract

Poor ductility and strength at high temperatures, especially under slow strain rate or creep conditions, have prevented the use of iron–aluminium alloys or aluminide intermetallics, despite decades of intensive research. The low strength at high temperature is due to the inability of hardening particles such as carbides to resist dissolution or coarsening at these temperatures. A new iron–aluminium alloy with zirconium and chromium additions has been discovered that forms fine coherent precipitates on annealing cast material that remain very fine even after extended annealing at temperatures as high as 900 °C. These precipitates have a complex Fe 3Zr structure and form in a cube-on-cube orientation relationship in the body-centred cubic matrix. The excellent stability of these intermetallic precipitates, due to low solute solubility and diffusivity in the iron–aluminium matrix, and the low energy, near-coherent interface, allows important improvements in high-temperature creep stresses.