Investigation of IN625,IN939 and IN738 superalloy filler powders utilization in the direct metal deposition repair practice of IN738 gas turbine blade

Abstract

In the present work, three different superalloy filler powders IN625, IN939 and IN738 subjected to direct metal deposition on IN738 substrate. The repair process was done on lower part of a blade airfoil. Then, the cross-section of repaired zones was characterised using optical microscopy, scanning electron microscopy and phase analysis. Also, the hardness of repaired zone, substrate and heat-affected zone were investigated. The results showed, in a certain processing parameter, the crack-free precipitates of IN625 and IN738 was obtained. For IN939, a macro-crack along the build direction was observed. Due to the difference in the growth direction of the dendrites on both sides of the macro-crack, a high-angle grain boundary (HAGB) with a large misorientation angle >15° was formed, resulting in increased cracking susceptibility and development of a macro-crack. No γ’ phase was observed for as-deposited IN738 and IN939 due to cooling rate faster than 10⁵(K.s⁻¹).