Microstructure Evolution and Mechanical Properties of Ta-Cladded Ni-Cr-Mo Low Alloyed Steel via Explosive Welding

The effects of welding variables (stand-off distance and explosive thickness) on the interfacial microstructure evolution and mechanical properties of explosively welded Ta alloy to Ni-Cr-Mo low alloyed steel have been investigated. Regardless of welding conditions (a stand-off distance of 3-5 mm and explosive thickness of 40-80 mm), the Ta/steel interface consistently exhibited a wavy configuration. This wavy interface facilitated the formation of vortex, resulting in strong interlocking. The height of the vortex increased with a larger stand-off distance at a fixed explosive thickness of 60 mm. Similarly, increasing the explosive thickness at a stand-off distance of 3 mm also resulted in a greater vortex height. The explosive weldability window, plotting the collision angle (β) against the collision point velocity (vc), was successfully established for the dissimilar Ta and steel plates. The upper limit prediction with N=0.11, as proposed by Wittman, best matched the experimental results. This guided the determination of the optimal condition, which was a standoff distance of 3 mm and an explosive thickness of 40 mm. A vortex melted zone (VMZ) was identified, which resulted from the dynamic intermixing of Ta and steel, combined with localized melting caused by high-energy collisions and heat accumulation. The VMZ surrounded by a highly deformed Ta alloy, showed the highest hardness. Near the interface on the steel side, a fine recrystallized grain structure was observed. No significant inter-diffusion was detected at the wavy Ta/steel interface. The tension-shear properties of the wavy interface, which was subjected to loading parallel to interface, showed a good balance of strength and ductility, confirming the soundness of Ta/steel interface.