Chiang Mai Journal of Science

This research has an aim to search for the optimal heat treatment condition after TIG welding to refurbish fractured turbine blade (cast nickel-based superalloy grade Inconel 738) of  land-based gas turbine engines with the most proper final microstructural characteristics. The Inconel 738 (IN-738) specimens were welded by TIG welding process together then various heat treatment conditions were applied in order to reach the proper microstructure with uniform distribution of  proper size of  intermetallic phase, namely, gamma prime (γ ) in the metal matrix, for high performance in mechanical properties at elevated temperatures. The heat treatments consist of solutioning, primary aging and secondary aging at different heating temperatures. From the results, it was found that the postweld heat treatment provided both beneficial and detrimental effects depending on initial reheat treatment condition. The lowest solutioning temperature (1398 K) after weld process provided the most coarsening size of γ particles in uniform dispersion in base metal zone as well as uniform dispersion of  very fine γ particles in heat affected zone (HAZ) with very high area fraction. Furthermore, the higher solutioning temperatures after weld process resulted in smaller size of γ particles precipitating in both HAZ and base metal zone. The highest solutioning temperature of 1478 K resulted in hot cracking in base metal zone near weld band.