Using a multi-scale approach to assess the mechanical properties and deformation mechanisms of high dose Inconel X-750

In a high thermal neutron flux, Inconel X-750 transmutates, producing displacement damage and helium and hydrogen generation rates more severe than other structural materials. To characterize mechanical properties and deformation mechanisms incurred by radiation, a multi-scale approach from nanometer scale Transmission Electron Microscopy (TEM) to component scale testing is employed. Material irradiated with two distinct temperature histories, up to 315 ^oC, irradiated to doses 5-84 dpa, containing up to 2.6 at% He and 0.6 at% H gases is presented. Component testing measures load bearing capacity, but cannot yield engineering mechanical properties. Fracture surfaces indicate highly intergranular failure, but don’t provide mechanistic information. Microhardness quantifies hardness and flow stress of the material as a function of radiation damage. Single-grained and bi-crystalline micro-tensile tests in the electron microscope reveal trans-granular deformation initiation mechanisms and quantify critical resolved shear stress, σ_y, and σ_UTS. Higher resolution fracture surfaces exhibit similar trans-granular facets within grain interiors, along with intergranular features, indicating mixed-mode failure. TEM investigations of deformed bulk fracture surfaces and micro-tensiles show helium bubbles within grain interiors shear along the direction of local plasticity and in some cases coalesce prior to shearing ligaments between bubbles. Micro-tensiles with vertically oriented grain boundaries develop voids at the intersections of boundaries and dislocation channels after yielding, immediately before failure. In bulk material, these interactions may drive fracture propagation along grain boundaries. Meso-scale tensiles with several constrained grains are proposed to investigate this.