Title

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

Abstract

In this article, we report on the fabrication and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5. Reactive hot isostatic pressing (hipping) at ≈40 MPa of the appropriate mixtures of Ti, Al4C3 graphite, and/or AlN powders for 15 hours at 1300°C yields predominantly single-phase samples of Ti2AlC0.5N0.5; 30 hours at 1300°C yields predominantly single-phase samples of Ti2AlC. Despite our best efforts, samples of Ti2AlN (hot isostatic pressed (hipped) at 1400°C for 48 hours) contain anywhere between 10 and 15 vol pct of ancillary phases. At ≈25 μm, the average grain sizes of Ti2AlC0.5N0.5 and Ti2AlC are comparable and are significantly smaller than those of Ti2AlN, at ≈100 μm. 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°C, a solid-solution softening effect is occurring. The thermal-expansion coefficients (CTEs) of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5 are, respectively, 8.2 × 10-6, 8.8 × 10-6, and 10.5 × 10-6 °C-1, in the temperature range from 25°C to 1300°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 × 106 (Ω m)-1) is in between those of Ti2AlC and Ti2AlN, which are 2.7 × 106 and 4.0 × 106 Ω-1 m-1, respectively.

Publication Title

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

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