Executive Summary : | The increasing demand for energy production and safety in critical energy facilities has led to a growing interest in developing new structural alloys like nickel-based superalloys and austenitic stainless steels. However, these materials often suffer from degradation due to weakening of grain boundaries, leading to poor thermal stability and intergranular cracking. To improve the service life of these materials, the project proposes using grain boundary design or grain boundary engineering (GBE) to enhance the mechanical properties of two FCC alloys: Ni-base alloy (Inconel 718) and austenitic stainless steels (316L). GBE involves imparting a high fraction of special boundaries, such as coincident site lattice (CSL) boundaries, through sequential deformation and annealing. This allows sufficient migration of grain boundaries during annealing, leading to improved grain boundary-related phenomena like precipitation, intergranular corrosion, and grain boundary diffusion. Limited literature exists on the systematic understanding of the effect of GBE on achieving a good combination of strength and ductility, especially at elevated temperatures. In-depth understanding of micro-mechanisms involved in improving high temperature mechanical properties is crucial. Ni base alloys used in high temperature applications have a high propensity for precipitation at elevated temperatures, making the role of γ and γ' precipitates on grain boundary migration at high temperatures critical. Optimization of GBD will be done using thermo-mechanical processing, electron back scatter diffraction, and ultimate tensile machine (UTM) equipped with a high temperature furnace. |