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 oil the hot-pressed Ti2SnC bulk ceramic. Microstructure features of bulk Ti2SnC ceramic were characterized by using TEM, and a needle-shaped beta-Sn precipitation was observed inside Ti2SnC grains with the orientation relationship: (0001) Ti2SnC // (200) Sn and [1 (2) over bar 10] Ti2SnC // [001] Sn. With the combination of DSC and XRD analyses, the precipitation of metallic Sri was demonstrated to be a thermal stress-induced process during the cooling procedure. The reheating temperature, even as low as 400 degrees C, Could trigger the precipitation of Sn from Ti2SnC, which indicated the low-temperature instability of Ti2SnC. A substoichiometry Ti2SnxC formed after depiction of Sn from ternary Ti2SnC phase. Under electron beam irradiation, metallic Sri was observed diffusing back into Ti2SnxC. 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.