USING A MULTI-SCALE APPROACH TO ASSESS THE MECHANICAL PROPERTIES AND DEFORMATION MECHANISMS OF HIGH DOSE INCONEL X-750

摘要

In a high thermal neutron flux, Inconel X-750transmutates, producing displacement damage andhelium and hydrogen generation rates more severe thanother structural materials. To characterize mechanicalproperties and deformation mechanisms incurred byradiation, a multi-scale approach from nanometer scaleTransmission Electron Microscopy (TEM) to componentscale testing is employed. Material irradiated with twodistinct temperature histories, up to 315 °C, irradiated todoses 5-84 dpa, containing up to 2.6 at% He and 0.6 at%H gases is presented. Component testing measures loadbearing capacity, but cannot yield engineeringmechanical properties. Fracture surfaces indicate highlyintergranular failure, but don’t provide mechanisticinformation. Microhardness quantifies hardness and flowstress of the material as a function of radiation damage.Single-grained and bi-crystalline micro-tensile tests in theelectron microscope reveal trans-granular deformationinitiation mechanisms and quantify critical resolved shearstress, σy, and σUTS. Higher resolution fracture surfacesexhibit similar trans-granular facets within graininteriors, along with intergranular features, indicatingmixed-mode failure. TEM investigations of deformed bulkfracture surfaces and micro-tensiles show helium bubbleswithin grain interiors shear along the direction of localplasticity and in some cases coalesce prior to shearingligaments between bubbles. Micro-tensiles with verticallyoriented grain boundaries develop voids at theintersections of boundaries and dislocation channels afteryielding, immediately before failure. In bulk material,these interactions may drive fracture propagation alonggrain boundaries. Meso-scale tensiles with severalconstrained grains are proposed to investigate this.