Mechanism of macroscopic geometric configuration regulating atomic supply and reaction pathways at titanium/steel composite interfaces

Abstract

The mechanical performance of laminated metal composites is dictated by intermetallic compounds formed at composite interfaces. However, their control has long been restricted to traditional process parameters (temperature, time, and deformation), failing to recognize the fundamental limits imposed by geometric constraints on atomic supply. Through comparative experiments on acute-angle and obtuse-angle inverse geometric configurations in a titanium/steel composite system, this study reveals that altering solely the macroscopic geometric configuration—under identical temperature, time, and deformation conditions—yields an order-of-magnitude difference in interfacial bending life. Mechanistic investigations demonstrate that in the acute-angle configuration, the insufficient localized steel thickness at the tip causes rapid carbon depletion within a confined space, interrupting the growth of the TiC diffusion barrier layer and triggering the formation of β-Ti and brittle FeTi/Fe₂Ti phases, which leads to interfacial cracking after only 4 repetitive bending cycles. Conversely, the obtuse-angle configuration guarantees a continuous carbon supply owing to its sufficient steel thickness, forming a continuous submicron TiC layer that remains intact even after 40 repetitive bending cycles. A quantitative geometry–diffusion–reaction model based on atomic mass conservation was established, deriving the critical geometric condition for forming a continuous TiC diffusion barrier layer as $D_{\text{critical}}=K\frac{x}{C_0-S_C}d$. This work highlights the governing role of macroscopic geometric configurations as a key parameter controlling atomic supply to dictate interfacial reaction pathways, extends the theoretical analysis from semi-infinite planar conditions to finite geometric constraints, and offers a new physical framework and quantitative design criterion for tailoring interfacial reaction pathways in dissimilar material joining.