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

A solid‐state diffusion bonding steel‐titanium interface is designed, revealing the formation of continuous micro–nano‐sized FCC‐TiC grains at the interface. Carbon atoms occupying the octahedral interstice in the FCC‐TiC lattice are directly observed. The study shows that FCC‐TiC formation is driven by carbon diffusion and titanium phase transformation, providing new insights into atomic‐scale regulation of titanium carbide. Abstract 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. A solid-state diffusion bonding steel-titanium interface is designed, revealing the formation of continuous micro–nano-sized FCC-TiC grains at the interface. Carbon atoms occupying the octahedral interstice in the FCC-TiC lattice are directly observed. The study shows that FCC-TiC formation is driven by carbon diffusion and titanium phase transformation, providing new insights into atomic-scale regulation of titanium carbide. Abstract 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. Advanced Science, Volume 12, Issue 48, December 29, 2025.