Dislocation loop formation by swift heavy ion irradiation of metals

Galvin S Khara,Samuel T Murphy,Dorothy M Duffy

doi:10.1088/1361-648x/aa74f8

Abstract

A coupled two-temperature, molecular dynamics methodology is used to simulate the structural evolution of bcc metals (Fe and W) and fcc metals (Cu and Ni) following irradiation by swift heavy ions. Electronic temperature dependent electronic specific heat capacities and electron–phonon coupling strengths are used to capture the full effects of the variation in the electronic density of states. Tungsten is found to be significantly more resistant to damage than iron, due both to the higher melting temperature and the higher thermal conductivity. Very interesting defect structures, quite different from defects formed in cascades, are found to be created by swift heavy ion irradiation in the bcc metals. Isolated vacancies form a halo around elongated interstitial dislocation loops that are oriented along the ion path. Such configurations are formed by rapid recrystallization of the molten cylindrical region that is created by the energetic ion. Vacancies are created at the recrystallization front, resulting in excess atoms at the core which form interstitial dislocation loops on completion of crystallization. These unique defect structures could, potentially, be used to create metal films with superior mechanical properties and interesting nanostructures.

Highlights

The modification of materials by ion and laser irradiation has the potential to introduce novel nanostructures and properties not achievable by any other material processing methods
For the bcc metals, in contrast to the commonly held belief that metals are insensitive to such irradiation, interesting defect structures are created along the ion path, which bear a striking resemblance to the defects observed by TEM two decades ago
In this study we have considered stopping powers ranging from 10 keV nm−1 to 100 keV nm−1, with increments of 10 keV nm−1

Summary

Introduction

The modification of materials by ion and laser irradiation has the potential to introduce novel nanostructures and properties not achievable by any other material processing methods. Very energetic ions can induce elongated features with nanometre width and micron depth, usually referred to as ion tracks, that have properties quite distinct from the bulk material. Since their observation in lithium flouride [1] in 1958, ion tracks have been observed in many other insulators [2–5], semi-conductors [6–12], and even amorphous semiconductors [13]. Metals show a remarkable resistance to ion track formation, with damage (if any) taking the form of small defect clusters

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