A Critical Study of Bead-on-Plate Laser Welding of Niobium Alloy PWC-11

Abstract

In the present work, laser welding of PWC-11 alloy has been tried in bead-on-plate (BOP) configuration. Experiments have been carried out to determine the range of input parameters for full penetration welding. Laser power (P) and scanning velocity (V) are selected as the input parameters for BOP experiments. Weld width, penetration depth and micro-hardness are the outputs for BOP experiments. The weld profile is analyzed using optical microscope to calculate the aspect ratio and relate its dependence on laser power and scanning velocity. The fusion zone is characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). Laser power and scanning velocity are to be maintained on the higher level to obtain full penetration weld and to avoid the formation of laser plume. The micro-hardness test has showed that the fusion zone has high hardness value in comparison to the base metal. The increment in the micro-hardness of the fusion zone is due to the formation of phases of oxides and nitride, which is confirmed by the XRD phase analysis. The SEM micrographs reveal the increase in grain size of the fusion zone and EDAX analysis of fusion zone indicates the presence of nitrogen and oxygen. From the present study, it is obvious that the key challenge is to re-establish the present methods of fabrication by laser to avoid the contamination of the future joint by oxygen, nitrogen, carbon dioxide at the time of welding along with weld geometry optimization with a focus on minimization of weld width.