The liquation cracking behavior of IN738LC superalloy during low power Nd:YAG pulsed laser welding

The liquation cracking behavior of low power pulsed Nd:YAG laser welded IN738LC was studied using several pre-weld heat treatment cycles. The results showed that liquation cracks in the alloy were associated with grain boundaries constituents such as γ–γ′ eutectic, MC carbide, Cr–Mo boride and Ni–Zr intermetallic. The liquation cracking in the weld heat affected zone (HAZ) was observed to be affected by the hardness of base-alloy. In addition, the results revealed that the presence of Cr–Mo rich borides in the pre-weld alloy constitutes a major factor enhancing susceptibility to liquation cracking. The boride particles reduce the temperature at which non-equilibrium intergranular liquation initiates in the HAZ, during the heating cycle of welding. Gleeble physical simulation revealed that in samples heat treated at 1050 °C for 2 h, the liquation started at significantly lower temperatures than in 1120 °C solution heat treated samples, this is attributed to the occurrence of the boride particles in the 1050 °C samples, which had dissolved by the 1120 °C heat treatment.

► liquation cracking behavior of IN738LC in pulsed laser welding was carefully studied.
► both mechanical and metallurgical aspects was considered.
► the effect of microstructure on constitutional liquation start point were clarified.
► some heat treatment cycles and Gleeble simulation tests were used for clarification.
► Cr–Mo borides and hardness were revealed as main causes of liquation cracking.