Influence of niobium alloying on the low cycle fatigue of cast TiAl alloys at room and high temperatures

摘要

The low-cycle fatigue properties of TiAl alloys with 2 at.% and 7 at.% of Nb with nearly lamellar microstructure were studied at room temperature and 750°C. Cyclic hardening/softening curves, cyclic stress-strain curves (CSSC) and fatigue life curves were obtained at both temperatures as well as monotonic tensile properties. Both materials show stable cyclic response at 750°C. At room temperature, significant cyclic hardening characteristic for 2 at.%Nb alloy is not observed for 7 at.% Nb alloy. This difference is attributed to higher Nb content which increases the stacking fault energy and thus prevents intensive twinning. Parameters of the CSSC, the Manson-Coffm law and the Basquin law were determined. The cyclic strength of the alloy with 7 at.% Nb is substantially higher in comparison with 2 at.% Nb, probably due to lower thickness of the lamellas.