Mechanical behavior of powder metallurgy AlFeNi alloys

The tensile and creep response of three P/M processed AlFeNi dispersion-strengthened alloys has been evaluated at temperatures up to 400°C; dispersoid (FeNiAl 9) volume fractions were 0.19, 0.25 and 0.32. Ambient temperature strength increases with increasing volume fraction of dispersoid and decreases with dispersoid size for a given volume fraction. Strengthening at room temperature in these alloys is primarily due to the fine grains stabilized by the dispersoids. The observed yield strength is explained by the Hall-Petch relationship with a grain size exponent larger than 0.5 and a significantly higher friction stress than that of pure Al. The yield strength of the alloys decreases with increasing temperature. Below about 250 °C it is still determined by the grain size, but above 250 °C, the deformation mechanism changes and dispersoid volume fraction and size do not have a significant effect on yield strength. Fracture mode also exhibits a change at about 250 °C; below this temperature tensile failure occurs by void initiation around the grain boundary dispersoids and subsequent coalescence leading to fracture while above 250 °C the fracture surface exhibits coarse features. Creep data are independent of dispersoid volume fraction in the temperature range 250–400 °C. Sherby's structure-invariant dislocation model and Arzt's interface reaction-controlled diffusional creep model have been found to be consistent with the experimental creep data.