Heat-affected zone crack healing in IN939 repaired joints using hot isostatic pressing

Abstract

Simulation defects in IN 939 superalloy were repaired by gas tungsten arc welding (GTAW) using Nimonic C263 as filler metal. The microstructures and chemical compositions of fusion zone under the condition of as-welded and post-weld heat treatment (PWHT) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe X-ray microanalysis (EPMA). Moreover, the liquation cracking and strain age cracking in heat-affected zone (HAZ) were characterized as well. Post-weld hot isostatic pressing (HIP) was also applied to heal the HAZ cracks. The results show that elements segregation at as-welded joints could be significantly reduced by PWHT. HAZ cracks consisted of liquation cracking and strain age cracking. The liquation cracking was shorter than the strain age cracking. HIP is an effective way to heal the cracks in the repaired joints especially for liquation cracking. Though the strain age cracking can be healed by HIP, the healed trace concentrated with Al, Ti, B, and Zr elements can still be detected. Post-weld HIP is a necessary process to obtain crack-free joints.