Interfacial investigation of explosion-welded titanium/steel bimetallic plates

Commercial pure titanium and low carbon steel were explosive welded. The interfacial structures were examined using a combined microstructural analysis and nanoindentation tests. The interface has a wavy morphology with an isolated mixing zone where a mixing of elemental titanium (Ti) and iron (Fe) occurs. Constituents in the mixing zone vary even under the same explosive welding conditions; for example, some are dominated by Fe2Ti intermetallics, whereas some consists of Fe2Ti and FeTi intermetallics. The nanoindentation tests and fracture observation confirm the brittle nature of the Fe-Ti intermetallics that formed in the mixing zone. The FeTi phase (~ 20.3 GPa) showed higher hardness than the Fe2Ti phase (~ 14.2 GPa). Simple approaches to estimate the cooling rate at the Ti/steel interface are proposed, and the calculated rate is 2.1 × 107 K/s. Such a high cooling rate combined with the chemical compositions results in the formation of the nanoscaled Fe2Ti structure in the mixing zone.