CLADDING TECHNOLOGY SHANXI CO., LTDExperimental and Numerical Studies of Titanium Foil Steel Explosively Welded Clad Plate
Literature Overview and Research Context
This paper presents comprehensive experimental and numerical investigations into titanium foil-steel explosively welded clad plates. Titanium clad plates find extensive application in marine heat exchangers, chemical processing equipment, and desalination systems where corrosion resistance combined with structural strength is essential. The study combines high-speed photography, metallographic analysis, numerical simulation, and mechanical testing to characterize the bonding mechanism and interface quality of titanium-steel explosive cladding.
Core Technical Content
The explosive welding process involves accelerating a titanium flyer plate toward a steel backing plate at supersonic velocities, typically in the range of 500–2000 m/s, creating a jetting mechanism at the interface that forms a metallurgical bond. The paper examines multiple process parameters including flyer velocity, collision angle, stand-off distance, and material thickness ratios.
| Parameter | Range Studied | Optimal Value | Effect on Bonding |
|---|---|---|---|
| Flyer velocity | 800–1800 m/s | 1200–1500 m/s | Higher velocity improves bonding but risks overheating |
| Collision angle | 5°–15° | 8°–12° | Optimal angle produces stable Kelvin-Helmholtz instability |
| Stand-off distance | 3–10 mm | 5–7 mm | Affects collision geometry and jet formation |
| Ti/Steel thickness ratio | 1:2 to 1:5 | 1:3 | Ensures adequate backing plate support |
| Ti grade | Grade 1 / Grade 2 | Grade 2 | Better ductility for bonding |
Interpretation of Technical Points
The numerical simulation employs a smoothed particle hydrodynamics (SPH) approach coupled with Johnson-Cook constitutive model to capture the high-strain-rate deformation behavior during explosive welding. The simulation reveals that the bonding mechanism proceeds through three stages: initial contact and shock wave generation, plastic instability formation at the interface, and metallurgical bonding through jetting and interdiffusion. The titanium-steel interface exhibits a characteristic wavy morphology with amplitude of 50–200 μm and wavelength of 0.5–2.0 mm.
A critical finding is the formation of intermetallic compounds at the interface, primarily TiFe and Ti2Fe phases. These phases are brittle and can reduce the bond strength if excessive. The study demonstrates that controlling the collision parameters to limit intermetallic layer thickness below 5 μm is essential for achieving acceptable mechanical properties. The bond strength test results show shear strength values ranging from 280 to 380 MPa, meeting ASTM A263 requirements for titanium-steel clad plate.
Microstructural Analysis and Defect Assessment
Metallographic examination reveals that the titanium surface undergoes severe plastic deformation with grain refinement in the deformed layer (typically 50–150 μm thick), while the steel backing plate shows a tempered martensite structure in the affected zone. Non-destructive testing using ultrasonic testing (UT) and eddy current testing (ECT) is employed to detect bonding defects including unbonded areas, voids, and cracks. The defect detection sensitivity is characterized with reference to artificial defects of known size.
Integration with Engineering Practice
For pressure vessel fabrication, titanium-steel clad plates are commonly used for heat exchanger tubesheets and shell sections in seawater cooling systems. The key engineering concern is ensuring uniform bonding across large-format plates while maintaining dimensional accuracy. The study's numerical model can be used to optimize explosive welding parameters for specific plate dimensions and thickness combinations, reducing the need for trial-and-error qualification testing. Engineers should pay particular attention to the minimum bond ratio requirement of 95% as specified in ASTM A263 and NB/T 47014, and ensure that the intermetallic layer thickness remains within acceptable limits for the intended service environment.
Key Questions and Reflections
The study raises important questions about the scalability of titanium-steel explosive welding for large-diameter pressure vessel shells. While flat plate bonding is well-established, cylindrical cladding introduces additional complexity due to curvature effects on collision geometry. Furthermore, the long-term stability of the titanium-steel bond under cyclic thermal loading in heat exchanger applications warrants further investigation, as differential thermal expansion between titanium and steel can induce interface stresses over time.
Study Insights and Implications
The combined experimental and numerical approach provides a robust framework for predicting and optimizing titanium-steel explosive welding parameters. For engineers involved in bimetal product manufacturing, the ability to simulate the welding process prior to physical trials significantly reduces development time and cost. The insight that intermetallic phase formation is the primary mechanism limiting bond quality suggests that controlling collision energy input is more critical than maximizing flyer velocity. This principle can be extended to other dissimilar metal cladding systems where brittle intermetallic formation is a concern.