Microstructures Of Nickel-Base Single-Crystal Superalloy Prepared By Laser Solid Forming

Single-crystal superalloys have been commonly used in modern advanced aero engines to produce high-pressure high-temperature turbine blades. In order to extend the lifetime of single-crystal turbine blades, repair of cracked and worn ones is of great interest. Laser Solid Forming (LSF) is a prospective technology that can be used to repair single-crystal blades. In this study, the microstructure of the as-deposited and heat-treated LSF single-crystal superalloy has been characterized through optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-deposited LSF sample shows a directionally solidified columnar dendrites growing almost parallel to the building direction. Between the dendrites, nearly round microporosity and blocky MC carbide particles are dispersed uniformly. TEM results indicate that many nano gamma' particles precipitate in gamma matrix. In addition, during LSF deposition process, stress is formed, which generates plenty of dislocations. During heat treatment, the LSF sample experiences full recrystallization. The recrystallization grains are in different sizes, and twins are found in some recrystallized grains. Because the residual stress is fully released during heat treatment, the size and shape of gamma' precipitates in the recrystallized and un-recrystallized regions are similar to those in conventionally cast samples.