Processing of top creep and oxidation resistant Fe-Al based ODS alloys

Abstract

The Fe-Al based oxide dispersion strengthened (ODS) alloys are investigated since the 1960’s. The alloys are produced by mechanical alloying of metal and Y2O3 powders followed by hot consolidation such as extrusion, rolling or rotary swaging. The oxides are dissolved during mechanical alloying in the matrix and they subsequently precipitate during the hot consolidation and thermal treatment. The processing involves several parameters which need to be carefully optimized and controlled to produce a successful alloy with excellent creep properties. The presented systematic testing and microstructure studies are necessary to identify the values of the most important parameters. The coarse-grained ferritic Fe-10Al-4Cr-4Y2O3 oxide dispersion strengthened alloy exhibits top creep and oxidation resistance. Compared to commercial INCOLOY MA956 it involves twice more Al, ten times more Y2O3 precipitates and exhibits twice higher creep strength at 1100-1300°C. Moreover, the creep rate is practically immeasurable and the time to fracture reaches several thousands of hours at applied stresses of 60-70 % of the ultimate strength under the strain rate 10−6 s−1 in the order of 120 MPa at 1100°C and 60 MPa at 1300°C. The paper describes decisive processing steps and characterizes the most important microstructural and mechanical properties.