Abstract
Ti2AlC is a typical MAX (M: early transition metal, A: main group element, and X: carbon and/or nitrogen) phase with ceramic and metallic properties due to its unique nano-layered structure. In order to investigate the interaction behavior between Ag and Ti2AlC, a sessile drop experiment was conducted at 1080 °C for 5 min. The atomic rearrangement occurred at the Ag–Ti2AlC interface was revealed using high-angle annular dark-field scanning transmission electron microscopy coupled with high-resolution transmission electron microscopy analysis. The results show that Ag nanoclusters generally appeared in most of the Ag–Ti2AlC interaction regions thermally processed at 1080 °C. In addition, Ag can also substitute for Al and Ti atoms in the Ti2AlC, promoting local structural decomposition of the Ti2AlC and producing 4H–Ag with a hexagonal close-packed (hcp) structure. Additionally, Al atoms released from the Ti2AlC lattices can dissolve locally into the liquid Ag, particularly at the grain boundaries. When the loss concentration of Al exceeded the critical level, the Ti2AlC started to decompose and the residual Ti6C octahedrons and Al atoms recombined, giving rise to the production of anti-perovskite Ti3AlC with a cubic structure. Lastly, the discrepancy in substitution behavior of Ag in the Ti2AlC was compared when thermally processed at different temperatures (1030 °C and 1080 °C). This work contributes to the understanding of the intrinsic stability of Ti2AlC MAX ceramics under high-temperature treatment.
Highlights
Ti2 AlC ceramics, as a representative 211-type MAX phase, have attracted increased attention recently [1,2,3]
The ceramic has a coefficient of thermal expansion of 8.8 × 106 ◦ C−1, which means that it exhibits outstanding high-temperature oxidation resistance [10,11]
The Ti2 AlC ceramics synthesized by self-propagating high-temperature synthesis were purchased from Wuhan University of Technology
Summary
Ti2 AlC ceramics, as a representative 211-type MAX phase, have attracted increased attention recently [1,2,3]. The unique nano-layered structure and diverse bonding characteristics enable them to possess both ceramic and metallic properties [4,5,6]. Studies on Ti2 AlC ceramics are relatively few, which limits the understanding toward their intrinsic properties and structural characteristics. Among the MAX-phase materials, Ti2 AlC has a low density (4.11 g·cm−3 ) [7], high thermal conductivity (46 W/m·K) [8], and excellent electrical conductivity (4.42 × 106 S·m−1 ) [9]. It is difficult to prepare pure Ti2 AlC with a large size and complex shape because its compositional range is rather narrow [17]
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