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 gamma-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 (mu 4PP) measurements, were used to determine the specific resistivity of the constituent phases of a Ti-43.5Al-4Nb-1Mo-0.1B (at. %) TNM gamma-TiAl based alloy. It turned out that the different phases exhibit noticeably different resistivity values, which vary over two orders of magnitude, whereas the beta(o) phase has the smallest resistivity and the alpha(2) phase the highest. CAFM and mu 4PP results were in rather good agreement for the alpha(2) and gamma phases with resistivity values of rho(alpha 2,CAFM) = (1.0 +/- 0.7) x 10(-5) omega m and rho(alpha 2,4PP) = (1.5 +/- 1.5) x 10(-5) omega m for the alpha(2)-phase, and rho(gamma,CAFM) = (6.5 +/- 2.1) x 10(-6) omega m, and rho(gamma,4PP) = (1.4 +/- 1.2) x 10(-6) omega m for the gamma-phase. For the beta(o) phase, mu 4PP measurements resulted in rho(beta o,4PP) = (9.0 +/- 5.0) x 10(-7) omega m. In this case, CAFM values are not reliable due to the formation of a contact barrier that deteriorates the measurements.

Automated summary

The study reveals that different phases of γ-TiAl-based alloys exhibit significantly different resistivity values. Results from CAFM and μ4PP measurements show good agreement for the α(2) and γ phases, while measurements of the β(o) phase using μ4PP are unreliable due to the formation of a contact barrier.