Mechanism of Carbon Diffusion and Phase-Transition-Induced FCC-TiC Formation via Hot Pressing

Titanium carbide (TiC), which typically forms at the solid-state diffusion interface in steel-titanium (Ti) composite structures, significantly influences steel-Ti interface bonding. However, the atomic-level formation mechanism of this carbide remains unclear. Herein, the TiC crystal structure and formation mechanism are investigated through experiments involving TA2 pure Ti and 45# carbon steel under solid-state diffusion conditions. Analysis of the solid-state diffusion behavior between the steel and Ti, based on selected area electron diffraction, reveals the formation of a continuous micro-nano TiC layer with a balanced (FCC) crystal structure on the substrate near the Ti side of the interface. Using the integrated differential phase contrast technique, occupation of the octahedral interstices in the FCC-TiC lattice by carbon (C) atoms is confirmed for the first time. Additionally, it is suggested that C diffusion and phase transformation jointly induce the FCC-TiC crystal phase transformation under hot-pressing conditions. Finally, the atomic-scale TiC formation mechanism is elucidated. The findings of this study may guide the design and development of high-performance materials with unique properties for aerospace equipment manufacturing.