LONG THERMAL EXPOSURE EFFECTS ON RENÉ 80 AND CM247 LC NICKEL SUPER ALLOYS MANUFACTURED BY LASER BEAM POWDER BED FUSION

Nickel base super alloys (NBSs) are the class of material which are mainly used in harsh working environments where they are subjected to high temperatures for a long duration. They are used in the fields of energy production and aeronautics, where they find particular space in the production of blades and casings for turbines. As compared to other classes of super alloys, they are preferred due to their greater mechanical stability at high temperatures; in fact, Nickel super alloys can work at temperatures up to 80% of the melting point without suffering a significant loss of strength, which is relatively a very high percentage. They have excellent resistance to oxidation which is essential in sectors involving extreme thermal conditions and possible contact with corrosive fluids. Conventional techniques have been in use for a long period of time & have therefore been optimized to a greater extent. However, these technologies have their own limitations in production of complex shape components. With the advent of technology, the manufacturing processes have also evolved. Latest technologies can produce parts with complex geometries but still they are under development and optimization is still going on. This thesis has the main objective of characterizing the microstructure of two poor to weld NBSs (Renè 80 and CM247 LC) made by PBF-LB (Laser Beam Powder Bed Fusion) which are treated with two different recipes. After treatment samples are thermally exposed at 900 &#8451; for 100, 250, 500 and 750 hours. Along with analysis of as-built & as-treated conditions, samples undergone long thermal exposure are also analyzed. These alloys are characterized by an austenitic matrix &#947; reinforced both by the precipitate called &#947;' of stoichiometry Ni3(Al,Ti), and by different types of carbides. In recipe 1, as-built sample will undergo sand blasting (SB), stress relieving (SB), HIP done under T<Tsolvus &#947;', solution annealing and then two step ageing. In recipe 2, as-built samples will undergo SB, SR, HIP and solution annealing is done in combined one step and then two step ageing. After all these treatments and long thermal exposure, defects and microstructural analysis will be done. The evolution of grains, precipitates and oxide layer are analyzed. Hardness test is performed to evaluate material resistance to deformation. Obtained results for both recipes are compared with each other and checked which recipe give better properties of super alloys under research.