Effect of pre-cold treatment on weldability of Inconel 718 superalloy using Nd:YAG pulsed laser

Inconel 718 is precipitation strengthened Ni-base superalloy that is strengthened by “γ″ precipitate with the Ni3Nb chemical composition, is widely used for medium and high temperature applications in many industries. The aim of this study is to evaluate the effects of pre-cold treatment on microstructure, geometry of weld, Weldability, and mechanism of HAZ liquation cracking in Inconel 718 superalloy by Nd:YAG pulsed laser welding. Microstructure was investigated, using optical microscope and scanning electron microscope and hardness test was used to investigate mechanical properties. The results of numerical calculations using Rosental relation showed that the length of different welding regions including Mushy Zone (MZ), Partially Melted Zone (PMZ), and Heat Affected Zone (HAZ) decreased by 46%, 46%, and 56%, respectively. The experimental calculations also indicated that the length of PMZ and HAZ, as well as the HAZ area decreased by 2.1, 2.5, and 2.5 times, respectively. Considering that grain boundary liquation was observed in all samples, the possible mechanism for HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourages the formation of liquid films in the grain boundaries and causes HAZ liquation cracking in this region. Also, the hardness profile indicates that the hardness of the weld metal increased by using pre-cold conditions.