Welding of thin molybdenum sheets by EBW and GTAW

Abstract

Two welding technologies (EBW, GTAW) were used to weld thin Mo sheets. Sheets thick 0.2 mm were welded by EBW and 0.4 mm thick samples were welded by GTAW welding methods. Welds were tested by means of metallography, optical microscopy, hardness measurement, chemical analysis etc. Mo welding is difficult because of inherently low ductility of Mo and high affinity to oxygen. Experiments proved that EBW is much better for welding thin Mo sheets, because it is done in vacuum and has much lower heat input. HAZ width of EBW was 1.4 mm compared to more than 35 mm for GTAW weld.

Electron Beam Welding of TZM Sheets

“…For each of these four parameters, two levels were determined and systematically varied according to DoE [10], as displayed in Table 1. This results in 2 4 = 16 trial welds. Pre-heating was conducted by the EBW machine itself, by constantly heating an area of 120x40 mm with the electron beam.…”

“…Refractory metals, amongst molybdenum, in general are difficult to weld, due to their high melting temperature and mainly due to grain coarsening since no lattice transformation takes place [2]. Trials with TIG, electron beam welding (EBW), and laser beam welding showed some success [3], [4], [5], but with considerable embrittlement of the weld and heat affected zone. Electron beam welding (EBW) facilitates a very high energy density which enables welding with less total energy input compared to other welding techniques, thus accomplishing a smaller weld and heat affected zone [6].…”

Technology of Welding and Joining

“…Furthermore, they also found that pore defects only appear around the arc starting and arc extinguishing positions in weld seam during TIG welding, whereas pore defects greatly increase in weld seam during EBW welding in the vacuum environment. Kolarikova et al (2012) [28] investigated EBW and TIG welding of pure Mo sheets. Widths of FZs in joints obtained through EBW and gas tungsten arc welding (GTAW) separately are 0.8 mm and 1.7 mm, whereas HAZs are significantly different in width (1.4 mm and 35 mm).…”