Effect of Pre- and Post-weld Heat Treatment on Microstructure and Mechanical Properties of GTD-111 Superalloy Welds

Abstract

In this paper, the liquation cracking and strain-age cracking behavior of nickel-based GTD-111 superalloy which is welded by Nd:YAG pulse laser through several heat treatment cycles, has been studied. The effort was to develop the most suitable microstructure concerning shape, morphology and γʹ phase volume fraction by several different heat treatment cycles in order to obtain a weld without any defects. The results revealed that γʹ, γ–γʹ eutectic, MC carbide, Boride enriched with Cr–Mo, and Ni–Zr intermetallic phase are the most important parameters in the formation of grain boundary melt and cracks in HAZ in casting conditions. Before welding, a full solution heat treatment resulted in the omission of liquation cracking, which attributed to full solution of boride and Ni–Zr intermetallic phases, and the solution treatment of a high percentage eutectic phases, and γʹ. Investigations on the hardness of the base metal showed that there was a direct relationship between hardness of the base metal and crack length. In such case, as the hardness of the base metal increases, it’s not only added to absorption of more welding stresses, but also stress release decreased, which resulted in the expansion of cracking in HAZ. Added to this, aging treatment of samples which were undergone aging treatment before welding, resulted in the formation of strain-age cracking due to γʹ phase precipitation.