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

In this article, we report on the fabrication and characterization of Ti2Al C, Ti2AlN, and Ti2AlC0.5N0.5 Reactive hot isostatic pressing (hipping) at a pproximate 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 predomina ntly single-phase samples of Ti2AlC. Despite our best efforts, samples of T i2AlN (hot isostatic pressed (hipped) at 1400 degrees C for 48 hours) conta in anywhere between 10 and 15 vol pet of ancillary phases. At approximate t o 25 mu m, the average grain sizes of Ti2AlC0.5N0.5 and Ti2AlC are comparab le and are significantly smaller than those of Ti2AlN, at approximate to 10 0 mu m. All samples are fully dense and readily machinable. The room-temper ature deformation under compression of the end-members is noncatastrophic o r 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 so lid-solution softening effect is occurring. The thermal-expansion coefficie nts (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 agr eement with the CTEs determined from high-temperature X-ray diffraction (XR D). 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.