Ion Irradiation-Induced Microstructural Evolution of Ni⁻Mo⁻Cr Low Alloy Steels

Area of Science:

• Materials Science
• Nuclear Engineering
• Physical Metallurgy

Background:

• Advanced nuclear reactors require robust materials like Ni-Mo-Cr high-strength low alloy (HSLA) steels.
• Understanding irradiation-induced defects is crucial for material performance and safety.

Purpose of the Study:

• To investigate the distribution and morphology of defects in HSLA steels after ion irradiation.
• To compare defect generation between focused ion beam (FIB) and electroplating and twin-jet electropolishing (ETE) sample preparation methods.
• To analyze the impact of irradiation dose on defect evolution using positron-annihilation spectroscopy (PAS).

Main Methods:

• Irradiation of CNST1, CNST2, and CNSS3 HSLA steels with 400 keV Fe+ ions at varying fluences.
• Transmission electron microscopy (TEM) for defect morphology analysis.
• Positron-annihilation spectroscopy (PAS) for defect characterization and quantification.

Main Results:

• FIB preparation introduced artifact defects, while ETE preparation showed fewer defects, especially in CNSS3.
• PAS detected both small-scale (vacancies, clusters, loops) and large-sized defects.
• The S-parameter saturated with increasing Fe+ dose, with higher values observed in CNST1 and CNST2 compared to CNSS3.

Conclusions:

• Sample preparation methods significantly influence observed defect structures.
• ETE is a more suitable preparation technique for minimizing artifact defects in HSLA steels.
• PAS is effective in characterizing irradiation-induced defects and their evolution in steels for nuclear applications.