Liquation cracking in the heat-affected zone of IN939 superalloy tungsten inert gas weldments

The main aim of this study was to investigate liquation cracking in the heat-affected zone (HAZ) of the IN939 superalloy upon tungsten inert gas welding. A solid solution and age-hardenable filler metals were further studied. On the pre-weld heat-treated samples, upon solving the secondary gamma ' particles in the matrix, primary gamma ' particles in the base metal grew to ogdoadically diced cubes of about 2 mu m in side lengths. The pre-weld heat treatment reduced the hardness of the base metal to about HV 310. Microstructural studies using optical and field-emission scanning electron microscopy revealed that the IN939 alloy was susceptible to liquation cracking in the HAZ. The constitutional melting of the secondary, eutectic, and Zr-rich phases promoted the liquation cracking in the HAZ. The microstructure of the weld fusion zones showed the presence of fine spheroidal gamma ' particles with sizes of about 0.2 mu m after the post-weld heat treatment, which increased the hardness of the weld pools to about HV 350 and 380 for the Hastelloy X and IN718 filler metals, respectively. Application of a suitable solid solution filler metal could partially reduce the liquation cracking in the HAZ of IN939 alloy.