Analysis of Solidification and Liquation Cracks in the Electron Beam Welding of IN738 Superalloy

IN738 super alloy is one of the most widely used materials in gas turbine blades. Welding is one of the most attractive methods of repairing and joining these blades. In this study, the behavior of solidification and liquation cracks of IN738 superalloy welded by electron beam welding (EBW) in the weld metal and heat-affected zone (HAZ) was evaluated. The results of this study showed that γ–γ′ eutectic, Cr-Mo boride, Ni-Zr intermetallic, MC carbide, and γ′ phase are the most effective secondary phases participating in liquation cracking. The most important reason for this was the segregation of elements with a segregation coefficient of less than one (K < 1). It was also observed in the weld metal that the start of crack nucleation is from the secondary phases in the inter-dendritic region. With increasing beam current in EBW welding, the tendency to form both liquidation and solidification cracks decreased. The reason for this was attributed to the backfilling of the melt in the cracks formed in the HAZ and the reduction of the shrinkage stresses and the cooling of the weld in the weld metal.