モリブデンに対するビーム振動を用いた電子ビーム溶接法の適用

Abstract

The purpose of this study is to investigate the effects of macrostructure change of the weld joint on the ductility of electron-beam-welded molybdenum sheet. The material used was electron-beam-melted molybdenum. Beam oscillation was applied in order to change the unfavourable structure of the joint, particularly even flat and straight interfaces at the center of the weld metal or at the bond of weld. The ductility of the weldment was determined by tensile tests at -70°C and 20°C. Fracture mode and location of crack initiation and propagation were examined by a scanning electron microscopy.The results were summarized as follows:1) Fracture strength at -70°C of the weldment was increased by using beam oscillation.2) Strength and elongation at 20°C of the weldment were also increased by using beam oscillation. 3) Origin of fracture was located to be mainly at the grain boundaries on the bead surface at -70°C, whilst crack was initiated mainly from the grain boundaries in bulk at 20°C.4) Crack was propagated only along the center of the weld metal or the bond of weld without beam oscillation. On the other hand, the crack was propagated not only along these weak interfaces but also through other areas with beam oscillation.