Investigation of the Effect of Preweld Heat Treatment on the Liquation Cracking of GTD-111 Superalloy

Abstract

GTD-111 is a γ′ strengthened Ni-based superalloys, which is used in critical applications such as turbine blades. Liquation cracking during welding is recognized as being one of the most important problems of this type of components. The present paper outlines a new preweld heat treatment to control the liquation cracking occurred in HAZ regions of GTD-111 turbine blades. Different preweld heat treatments were carried out on the samples extracted from the root of turbine blades and then they welded by gas tungsten arc welding (GTAW) process The microstructural analysis of the joints was carried out using optical microscopy, scanning electron microscopy, and image analysis technique. The results showed that the preweld heat treatment regimes can obviously affect the intensity of liquation cracking. While the optimum solutionizing temperature and time were found to be 1180°C and 2 hours, the samples with no heat treatment showed the lowest resistance to liquation cracking. It was also concluded that the liquation cracking is mainly affected by the relative intensity of the base metal hardness, the average length and volume fraction of γ′ precipitates, presence of carbides, and the existence of low melting phases.

Fig. 5 The HAZ zone microstructure, under C (1125°C/2 h) condition.