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

Abstract

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 (<i>β</i>) against the collision point velocity (<i>v<sub>c</sub></i>), was successfully established for the dissimilar Ta and steel plates. The upper limit prediction with <i>N</i>=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.