Investigating the sink efficiencies of interfaces under irradiation

Interfaces play an important role in material properties such as strength, cracking/fracture, work hardening, corrosion, and damage evolution under irradiation and deformation. Understanding interface-defect interactions that underlie these properties is a core motivation for studying interface phenomenon and is important in engineering design of next generation materials. Among all aspects, interface-vacancy interactions are an important building block to understand many classical structural-property relationships in polycrystals. Interfaces serve as sinks, sources or trap sites for vacancies, which facilitate creep, can drive interface migration, or serve as a vacancy-interstitial recombination site that results in an ideal lattice. This latter role provides a general approach to design radiation-tolerate materials. Previous works qualitatively investigated the ability of an interface to absorb non-equilibrium vacancies on different interfaces and grain boundaries via void denude zone (VDZ) experimental methods. However, a very limited number of quantitative studies of sink efficiency exist, and few systematic investigations comparing interfaces with different crystallography/orientation have been conducted. The importance of these phenomena and the limited experimental data in this area is the motivation of this thesis. Chapter 1 and Chapter 2 introduce the motivation and basic knowledge as well as details of the experimental techniques related to this work. Chapter 3 describes the experimental design for measuring the vacancy concentration profile in the vicinity of a Cu-Nb interface and explains how to extract the sink efficiency by comparing with a chemical rate equation. Chapter 4 is a systematic study for investigating the sink efficiency of different planar interfaces varying from semi/coherent to incoherent interfaces (Cu-Ni, Cu-V, Cu-Nb), demonstrating that sink efficiency varies as the coherency changes. Chapter 5 attempts to study the sink strength of the uniform distributed W nanoclusters/nanoprecipitates in Cu matrix produced by RT irradiation. The sink efficacy per unit area of nanoparticle-matrix interface is low relative to planar interfaces, but the high density of particles result in a similar reduction in non-equilibrium vacancy concentration in both the planar and nanoprecipitate systems. Chapter 6 describes an in-situ TEM nanocompression experiment designed to investigate the mechanical shear strength of a Cu-Nb interface as a function of irradiation dose at different temperatures. This property is used as a proxy for understanding the degree to which irradiation affects the interface structure, and suggests that steady-state behavior is established by a dose of 5 dpa