Impurity Role In Mechanically Induced Defects

Howell, R.H. ; Asoka-Kumar, P. ; Hartley, J. ; Sterne, P.

Lawrence Livermore National Laboratory

关键词: 71 Classical And Quantum Mechanics, General Physics;    43 Particle Accelerators;    Atoms;    Dislocations;    Positron Beams;   

DOI  :  10.2172/793454
RP-ID  :  UCRL-ID-137732
RP-ID  :  W-7405-Eng-48
RP-ID  :  793454

美国|英语

来源: UNT Digital Library

【 摘 要 】

An improved understanding of dislocation dynamics and interactions is an outstanding problem in the multi scale modeling of materials properties, and is the current focus of major theoretical efforts world wide. We have developed experimental and theoretical tools that will enable us to measure and calculate quantities defined by the defect structure. Unique to the measurements is a new spectroscopy that determines the detailed elemental composition at the defect site. The measurements are based on positron annihilation spectroscopy performed with a 3 MeV positron beam [1]. Positron annihilation spectroscopy is highly sensitive to dislocations and associated defects and can provide unique elements of the defect size and structure. Performing this spectroscopy with a highly penetrating positron beam enables flexibility in sample handling. Experiments on fatigued and stressed samples have been done and in situ measurement capabilities have been developed. We have recently performed significant upgrades to the accelerator operation and novel new experiments have been performed [2-4] To relate the spectrographic results and the detailed structure of a defect requires detailed calculations. Measurements are coupled with calculated results based on a description of positions of atoms at the defect. This gives an atomistic view of dislocations and associated defects including impurity interactions. Our ability to probe impurity interactions is a unique contribution to defect understanding not easily addressed by other atomistic spectroscopies.