Micro- and macroscopic plastic flow responses in high Nb-containing TiAl alloy by nanoindentation

Abstract

High Nb-containing TiAl alloys have been widely developed and researched due to low density, high specific strength and stiffness, oxidation, and creep resistance. Nevertheless, high Nb-containing TiAl alloys demonstrate poor machinability owing to low plasticity and ductility. Accordingly, on basis of Kalidindi and Pathak's model, this paper systematically establishes a high-throughput and convenient method on extracting the macro- and microscopic plastic flow response of high Nb-containing TiAl alloy via nanoindentation experiment. And the mechanical properties of each individual microstructure were investigated by a series of indentation tests with Berkovich indenter. The results demonstrate that, i) the plastic flow behaviors of recrystallized γ grains are similar to that of fine lamellar colonies, whereas β/B2 grains are highly brittle; ii) according to the ratio of hardness to reduced modulus, the materials can present a better anti-wear capability with appropriate increase the content of β/B2 phase; iii) the Oliver-Pharr method combined with the energy method, the plastic recovery values of the recrystallized γ grains are larger than that of other microstructures, which indicate that the duplex microstructure γ-based TiAl alloy exhibits high ductile feature. Furthermore, the macroscopic plastic flow was extrapolated through the microscopic plastic flow curve combined with the volume fraction of each microstructure.