Low-temperature instability of Ti₂SnC: A combined transmission electron microscopy, differential scanning calorimetry, and x-ray diffraction investigations

Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) investigations were conducted on the hot-pressed Ti₂SnC bulk ceramic. Microstructure features of bulk Ti₂SnC ceramic were characterized by using TEM, and a needle-shaped β-Sn precipitation was observed inside Ti₂SnC grains with the orientation relationship: (0001) Ti₂SnC // (200) Sn and Ti₂SnC // [001] Sn. With the combination of DSC and XRD analyses, the precipitation of metallic Sn was demonstrated to be a thermal stress-induced process during the cooling procedure. The reheating temperature, even as low as 400 °C, could trigger the precipitation of Sn from Ti₂SnC, which indicated the low-temperature instability of Ti₂SnC. A substoichiometry Ti₂Sn_xC formed after depletion of Sn from ternary Ti₂SnC phase. Under electron beam irradiation, metallic Sn was observed diffusing back into Ti₂Sn_xC. Furthermore, a new Ti₇SnC₆ phase with the lattice constants of a = 0.32 and c = 4.1 nm was identified and added in the Ti-Sn-C ternary system.