Flow stress anomaly and order-disorder transitions in Fe_3Al-based Fe-Al-Ti-X alloys with X = V, Cr, Nb, or Mo

摘要

The stress-strain behaviour as a function of temperature as well as the critical temperatures of the D0_3 reversible B2 and B2 reversible A2 structural transitions were studied on quaternary Fe_3Al-based Fe-26 at. percent Al-4 at. percent Ti-X alloys containing 2 or 4 at. percent of X = V, Cr, Nb, or Mo. The microstructures of the alloys were characterized by light optical microscopy, transmission electron microscopy (TEM), and electron-probe microanalysis (EPMA). The alloys containing V, Cr, or Mo form solid solutions, whereas additions of 2 and 4 at. percent Nb result in the formation of Laves phase precipitates. A comparison of the temperatures of the maximum of the flow stress anomaly and the D0_3 reversible B2 transitions determined in compression tests and by differential thermal analysis (DTA), respectively, clearly reveals that there is no correlation between the stress anomaly and the degree of ordering. The effect of the different alloying elements on the order-disorder transition temperatures of the quaternary alloys is discussed and compared with that of respective ternary Fe_3Al-X alloys without Ti.