Investigation of the phase boundary and site occupation of atoms in pure and doped TiAl/Ti3Al intermetallic by means of the tomographic atom probe (TAP)

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Dual-phase Ti-Al alloys with lamellar structure, comprising g-phase plus a small amount of a2-phase, have a great potential application as high temperature materials. Alloying addition of Nb is very effective in improving strength and oxidation resistance of these alloys, however, the impact of Nb-addition on the microstructure development and consequently, on the mechanism of these improvements has not been clarified yet. 3D-tomographic atom probe (TAP) is a powerful tool to gain detailed characterization of the microstructures on the atomic scale. In this proposal, dual-phase TiAl/T3Al alloys with addition of 0-5at%Nb will be investigated by means of TAP and supporting TEM, HRTEM and TEM in-situ tensile testing. The impacts of Nb-alloying addition on the variation of different microstructural parameters, such as lamellar size, composition of the two phases, boundary structures, will be reported. The Nb-atomic site occupancies in TiAl- and Ti3 Al-phases, as well as any clustering and/or ordering of Nb atoms will be revealed. The possible segregation or depletion of Nb-atoms at grain boundaries, interphase boundaries and twist boundaries will be elucidated. On the bases of these experiments the mechanism of improvement in both strength and oxidation resistance by Nb alloying addition in these alloys will be modeled.