Interface Microstructure and Numerical Simulation Investigations of Ni/TC18 Composite Tube Fabricated by Explosive Welding

The larger diameter Ni/TC18 bimetallic composite tube was successfully manufactured by explosive welding. The bonding interface waveform structure and the distribution of interfacial elements were characterized using scanning electron microscopy and energy dispersive spectroscopy. To examine the layered phase structure of the transition interface, transmission electron microscopy and high-angle annular dark-field-scanning transmission electron microscopy were conducted. The characterization results showed different levels of grain refinement and metal phase layering structures within the bonding interface. Within the transition interface, there is a significant amount of spherical nano-Ni3Ti phase and a small amount of nano-twinned Ni4Ti phase on the left side. On the right side, there is NiTi phase and a small amount of willow Ti phase. The interface strength and plastic deformation ability were improved due to the mixed nano-grains and twins, as well as the sputtered willow Ti grains. These key findings can reveal the microstructure characteristics at the interface of the composite tube which is made of rare metal with a large diameter. The process of creating the composite tube through explosive welding was simulated using three-dimensional numerical methods, and the pressure changes and velocity evolution in different directions during the welding process were obtained.