Investigation of macrostructure, microstructure, and hot cracking susceptibility of laser-welded Inconel-718 superalloy under various post-cold treatment environments

Abstract

In the present study, the effect of various cooling environments on macrostructural, microstructural, and hot cracking sensitivity of Nd: YAG pulsed laser welded Inconel-718 superalloy was investigated. Laser welding was performed under air, water, brine and oil cooling environments with heights of 1–4 mm of the environment from surface of the samples. By measuring the macrostructural aspects in the presence of cooling environments, the depth of penetration of welds under water, brine and oil cooling conditions increased, respectively. By measuring the values of dendrite arm spacing in the weld microstructure, it was found that the brine environment with the highest ability of cooling intensity produces the finest and minimal dendrite arm spacing. Subsequently, the water and oil environments, due to the lower cooling intensities, cause relatively coarser microstructures in comparison to brine environment. It was determined that the samples welded under water and brine showed the lower quantities of maximum solidification crack length and maximum liquation crack length leading to improved weldability in comparison to the reference specimen. Also, the height of 3 mm of water and brine environments from the surface shows no solidification and liquation cracks. By using the oil environment with the height of 4 mm, the presence of cracks decreased as compared to the reference specimen. The hardness of welded zone under brine shows the maximum value due to the highest cooling rate causing the finest microstructure and stronger solid solution. The results obtained in the current research can be utilized to design a new and practical cooling procedure during welding as a post weld spraying or quenching in order to control the cooling rates of the welds for improving the properties, weldability and microstructure of austenitic nickel-based superalloys.