Metastable carbides and their impact on recrystallisation in IN738LC processed by selective laser melting

Selective laser melting of nickel based superalloys opens up new possibilities for gas turbine engine manufacturers; namely, efficient production of low component volumes, decreased component cost through reduced post-machining procedures and access to new component geometries that cannot be fabricated by conventional processing methods. However, processing high performance nickel-based superalloys components via additive manufacturing, without the occurrence of defects, is challenging and requires a better understanding of the resulting microstructure, especially as different compositions can lead to significant changes in the microstructure obtained. In addition, carefully selected post-processing heat-treatments are required to alter the microstructure and attain the required mechanical properties. In this study, the microstructure of the nickel base superalloy IN738LC has been characterised in the as-deposited and stress relieved heat-treated states, as well as following high temperature heat treatments. The data acquired highlights the influence of the stress relief step on the recrystallisation temperature and its relation with the distribution of carbide particles present in the alloy's microstructure.