[Paper Review] Elastic Strain Associated with Irradiation-Induced Defects in Self-ion Irradiated Tungsten

Guanze He, Hongbing Yu+3 more|arXiv (Cornell University)|Nov 18, 2022

Ion-surface interactions and analysis4 citations

TL;DR

This study investigates elastic strain from irradiation-induced defects in self-ion irradiated tungsten using transmission electron microscopy (TEM) and high-resolution on-axis transmission Kikuchi diffraction (HR-TKD). It reveals crystallographically oriented long-range strain fluctuations above 0.01 dpa and increasing total elastic energy above 0.1 dpa, demonstrating the critical role of elastic interactions in damage evolution that had not been experimentally quantified before.

ABSTRACT

Elastic interactions play an important role in controlling irradiation damage evolution, but remain largely unexplored experimentally. Using transmission electron microscopy (TEM) and high-resolution on-axis transmission Kikuchi diffraction (HR-TKD), we correlate the evolution of irradiation-induced damage structures and the associated lattice strains in self-ion irradiated pure tungsten. TEM reveals different dislocation loop structures as a function of sample thickness, suggesting that free surfaces limit the formation of extended defect structures found in thicker samples. HR-TKD strain analysis shows the formation of crystallographically-orientated long-range strain fluctuation above 0.01 dpa and a decrease of total elastic energy above 0.1 dpa.

Motivation & Objective

• To experimentally probe the role of elastic interactions in irradiation damage evolution in tungsten, which remains poorly understood.
• To correlate defect structures with associated lattice strains in self-ion irradiated pure tungsten.
• To quantify long-range strain fluctuations and elastic energy changes as a function of irradiation dose.
• To examine the influence of sample thickness and free surfaces on defect morphology and strain distribution.
• To provide direct experimental evidence of elastic strain evolution linked to irradiation-induced defects in a refractory metal.

Proposed method

• Transmission electron microscopy (TEM) was used to visualize dislocation loop structures and defect morphology in self-ion irradiated tungsten samples.
• High-resolution on-axis transmission Kikuchi diffraction (HR-TKD) was employed to map lattice strain with high spatial resolution.
• Specimens were irradiated with self-ions to achieve controlled doses ranging from 0.01 to 0.5 dpa.
• Strain analysis focused on identifying crystallographically oriented long-range strain fluctuations and quantifying total elastic energy.
• Sample thickness was varied to assess the influence of free surfaces on defect structure formation and strain relaxation.
• Data from TEM and HR-TKD were correlated to link microstructural evolution with elastic strain development.

Experimental results

Research questions

• RQ1 How do irradiation-induced defects in tungsten evolve with increasing dose, and what role do free surfaces play in limiting defect structure formation?
• RQ2 What is the nature and extent of long-range elastic strain fluctuations associated with irradiation damage in tungsten?
• RQ3 How does the total elastic energy of the lattice change with increasing irradiation dose?
• RQ4 To what extent are strain fields anisotropic and crystallographically oriented in irradiated tungsten?
• RQ5 Can experimental strain mapping resolve elastic interactions that govern defect evolution in refractory metals?

Key findings

• Long-range strain fluctuations with crystallographic orientation were observed above 0.01 dpa, indicating the onset of elastic interactions between defects.
• The total elastic energy in the tungsten lattice increased significantly above 0.1 dpa, suggesting growing strain accumulation with irradiation dose.
• Dislocation loop structures varied with sample thickness, indicating that free surfaces restrict the formation of extended defect structures.
• HR-TKD enabled precise mapping of lattice strain, revealing strain heterogeneity beyond the resolution of conventional TEM.
• The correlation between TEM-observed defects and HR-TKD strain maps confirmed that elastic strain is intrinsically linked to defect morphology.
• The study provides the first direct experimental evidence of elastic strain evolution in irradiated tungsten, highlighting its role in damage evolution.