Abstract
The aim of the present work is to verify the microstructural behavior of a B 521 tantalum alloy UNS Grade R05200 after welding, in relation to the welding thermal cycle. The joint design was a 1.5 mm thickness circumferential butt welding, on a 32 mm outside diameter pipe, welded in 1 G position (horizontal, flat, and rotating). The chosen welding process was gas tungsten arc welding (GTAW). The microstructural analysis showed the presence of coarse, dendritic-columnar structures, as well as a hexagonal cell, with no cracks noted. Hardness tests showed an increase in hardness, from 120 HV to 425 HV, in the heat-affected zone. Through finite element methods, the behavior of the temperature field was estimated and compared.
Highlights
Tantalum is inherently a gray, soft, fabricable, and weldable metal that possesses a high hardness and melting temperature, 3269 ◦C, as well as excellent ductility
A shear phenomenon can occur, and it is observed in the microstructures of the weld
In the B 521 tantalum alloy UNS Grade R05200, metallurgical variations are observed in the different areas of the joint consisting of coarse columnar, and dendritic structures, as well as a network of hexagonal recrystallized cells, none of them prone to cracking
Summary
Tantalum is inherently a gray, soft, fabricable, and weldable metal that possesses a high hardness and melting temperature, 3269 ◦C (surpassed only by tungsten and rhenium), as well as excellent ductility (at lower temperatures). Its high melting point provides excellent characteristics for structural use at temperatures higher than other common refractory materials Tantalum surpasses others, such as tungsten, with regard to fabricability, ductility, and weldability [1]. One of the potential applications is the manufacturing (through welding processes) of heat exchangers for special applications that require high resistance to temperature or corrosion (ultra-corrosive or oxidizing applications) Those are usually considered difficult to weld, due to their great affinity with oxygen and other gaseous elements during the high temperature welding processes. Despite the abundance of bibliography, in reference to tantalum high alloys, with other elements such as aluminum or titanium, the welding of the metal itself has hardly been explored
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