Hot Cracking of GTD-111 Nickel-Based Superalloy Welded by Pulsed Nd:YAG Laser

Abstract

The hot cracking behavior of GTD-111 nickel-based superalloy joint has been investigated. Welding was performed by pulsed Nd:YAG laser with average power of 250 W. The observation of some microsegregation patterns in the fusion zone revealed that W and Mo elements were distributed in dendrite core zones when the element distribution coefficient (K) was > 1, when Ti, Al, and Ta elements were displaced to interdendritic zones by the melt during weld solidification. Due to their strong reaction with carbon, Ti and Ta formed MC carbides in interdendritic zones, therefore representing the most important factor in the formation of solidification cracks. Ti was identified as the most important factor in the formation of liquation cracks in the heat-affected zone (HAZ) by reducing the start temperature of the γ–γ′ eutectic reaction and increasing the γ′ dissolution temperature. Chemical analysis at crack edges in the HAZ revealed the presence of large amounts of Ti and Al elements, which can be attributed to γ′ partial melting. Gleeble physical simulations revealed that, in the cast sample, liquation started at temperatures significantly lower than the value of 1200 °C for solution heat-treated samples; This is attributed to the dissolution of boride and intermetallic particles during the 1200 °C heat treatment. Finally, the mechanical behavior of a welded joint was studied using tensile testing and microhardness measurements.