Local-probe based electrical characterization of a multiphase intermetallic γ-TiAl based alloy

The requirements for high performance and low energy consumption call for novel light-weight high-temperature structural materials. A possible answer can be intermetallic γ-TiAl-based alloys, which—in terms of weight—clearly outperform the classical Ni based alloys. However, not only their mechanical properties, such as high specific strength and high creep resistance, are important for device design and use, but also their electrical behavior is of significant importance. In order to correctly interpret the results of electrical material testing techniques, such as eddy current testing, a profound knowledge on the electrical properties is essential. In this study, local-probe techniques, such as conductive atomic force microscopy (CAFM) and micro four-point probe (μ4PP) measurements, were used to determine the specific resistivity of the constituent phases of a Ti-43.5Al-4Nb-1Mo-0.1B (at. %) TNM γ-TiAl based alloy. It turned out that the different phases exhibit noticeably different resistivity values, which vary over two orders of magnitude, whereas the β_o phase has the smallest resistivity and the α₂ phase the highest. CAFM and μ4PP results were in rather good agreement for the α₂ and γ phases with resistivity values of ρ_α2,CAFM = (1.0 ± 0.7) × 10⁻⁵ Ω m and ρ_α2,4PP = (1.5 ± 1.5) × 10⁻⁵ Ω m for the α₂-phase, and ρ_γ,CAFM = (6.5 ± 2.1) × 10⁻⁶ Ω m, and ρ_γ,4PP = (1.4 ± 1.2) × 10⁻⁶ Ω m for the γ-phase. For the β_o phase, μ4PP measurements resulted in ρ_βo,4PP = (9.0 ± 5.0) × 10⁻⁷ Ω m. In this case, CAFM values are not reliable due to the formation of a contact barrier that deteriorates the measurements.