A novel attempt to deform electron beam welded C-103 refractory alloy sheets using multi-stage single point incremental forming for space applications

Abstract

Tailor welded blank (TWB) technology can be economical to produce large blanks by suitably welding smaller size sheets of C-103 (Nb-10Hf-1Ti (wt.%)) alloy, and subsequently deforming these blanks through single point incremental forming (SPIF) process to fabricate critical space components. The present work aims to weld highly oxidation-prone C-103 sheets by electron beam welding and to deform the successfully welded blanks at room temperature into conical and pyramidal frustums with constant wall angle employing a multi-stage SPIF process. In this SPIF process, a tool path strategy was designed to obtain a higher wall angle, overcoming challenges such as surface galling and tool failures. Moreover, a reduction in axial force on the tool was observed after implementing this strategy due to a gradual decrease in wall angle increments in subsequent stages safeguarding the tool. The welded blanks fractured at a wall angle of 52.85° and 43.83° during the fabrication of the conical and pyramidal frustums, respectively. These angles were found to be lesser than the corresponding wall angle of monolithic sheets (57.34° and 50.19°). This decrease in wall angle was attributed to early fracture in weld zone (WZ) due to its higher hardness and reduced ductility resulting from the presence of nano-sized HfO₂ precipitates. The above findings suggested that the proposed multi-stage SPIF strategy can be implemented to deform TWBs of C-103 material for the fabrication of complex space components. In order to get further insight into the deformation behavior, texture analyses were carried out near the fracture region of the frustums. It was found that random orientation in the WZ tended to orient towards Rotated Cube {001}〈110〉 in the deformed WZ specimens. However, the intensity of Rotated Cube, Cube {001}〈100〉, and $\gamma$-fiber weakened in the base region of the deformed C-103 specimens as compared to the undeformed specimen.