Laser powder bed fusion provides valuable prospects for nickel-based superalloys that are used in many applications e.g. aerospace, automotive, chemical, and nuclear industries. However, the microstructure and mechanical properties of these materials are especially sensitive to the manufacturing conditions and post-treatments that are applied to relieve the internal stresses, as they are susceptible to the formation of different types of precipitates, depending on the alloy chemistry, temperature and time. Generally, a two-step annealing is performed to obtain the desired microstructure, meanwhile resulting in stress relief in the as-built condition. Such treatments are however non-economic and change significantly the as-built microstructure, which is often deliberetly manipulated by tailoring the process parameters.

A combination of in situ high-temperature neutron diffraction and synchrotron X-ray diffraction was used to study the evolution of the residual stresses and precipitation in nickel based Alloy 718 for a temperature range from 600°C to 1000°C. Samples with cylindrical symmetry were prepared and by using the 2-bank detector system at the Engin-X beamline, ISIS UK, it was possible to follow the evolution of residual stresses. Rietveld analysis on the X-Ray diffraction data was used to evaluate the initial phase composition and its evolution during the annealing. These results allow for the optimisation of one-step annealing treatments to relieve residual stresses and, in the meantime, control the microstructure and improve the mechanical properties of the final material.