Processing and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5

In this article, we report on the fabrication and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5 Reactive hot isostatic pressing (hipping) at approximate to 40 MPa of the appropriate mixtures of Til Al4C3 graphite, and/or AlN powders for 15 hours at 1300 degrees C yields predominantly single-phase samples of Ti2AlC0.5N0.5; 30 hours at 1300 degrees C yields predominantly single-phase samples of Ti2AlC. Despite our best efforts, samples of Ti2AlN (hot isostatic pressed (hipped) at 1400 degrees C for 48 hours) contain anywhere between 10 and 15 vol pet of ancillary phases. At approximate to 25 mu m, the average grain sizes of Ti2AlC0.5N0.5 and Ti2AlC are comparable and are significantly smaller than those of Ti2AlN, at approximate to 100 mu m. All samples are fully dense and readily machinable. The room-temperature deformation under compression of the end-members is noncatastrophic or graceful. At room temperature, solid-solution strengthening is observed; Ti2AlC0.5N0.5 is stronger in compression, harder, and more brittle than the end-members. Conversely, at temperatures greater than 1200 degrees C, a solid-solution softening effect is occurring. The thermal-expansion coefficients (CTEs) of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5 are, respectively, 8.2 x 10(-6), 8.8 x 10(-6), and 10.5 x 10(-6) degrees C-1, in the temperature range from 25 degrees C to 1300 degrees C. The former two values are in good agreement with the CTEs determined from high-temperature X-ray diffraction (XRD). The electrical conductivity of the solid solution (3.1 x 10(6) (Omega m)(-1)) is in between those of Ti2AlC and Ti2AlN, which are 2.7 x 10(6) and 4.0 x 10(6) Omega(-1) m(-1), respectively.