Nanostructural Fluctuation in Radiation-Amorphized Alloys
- PDF / 943,670 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 100 Downloads / 207 Views
R8.6.1
Nanostructural Fluctuation in Radiation-Amorphized Alloys Seiichi Watanabe1, Heishichirou Takahashi2, Nghi Q.Lam3 1 Materials Science and Engineering, Hokkaido University, Sapporo 060-8628, Japan 2 CARET, Hokkaido University, Sapporo 060-8628, Japan 3 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA. ABSTRACT Spatio-temporal nanostructural fluctuations brought about by transient, metastable atom-cluster formation and the manifold nature of inherent atomic ordering in electron-irradiation-amorphized NiTi were investigated by using a combination of in situ observations inside a high-resolution high-voltage electron microscope (HR-HVEM) and image analyses of molecular-dynamics-simulated atom configurations. Nanometer-sized clusters were found to appear and disappear in the irradiated region. The random formation and annihilation of such nanoclusters are believed to be responsible for nanostructural fluctuations which appear to be related to transitions among manifold inherent structural states, involving multirelaxation processes. Temporal fluctuations in the amorphized structure were manifested through the dose-dependent local amorphization parameter, potential energy, volume, and inherent cluster bonding. The observed fluctuations obey a universal power law. Within the framework of the multi-Lorentzian picture, the resultant power law describes the distribution of multirelaxation times or cluster lifetimes. In addition, a unified relation for the temporal autocorrelation function for such fluctuation phenomena has been determined. INTRODUCTION Amorphization of intermetallic compounds by energetic particle irradiation has been studied extensively[1,2]. High-resolution high-voltage electron microscopy is a potential technique to investigate the dynamical changes in atomic order that occur during the crystal-to-amorphous transition. When the number of atoms involved is small, one might expect that spatial and temporal stochastic fluctuations play a key role in determining the destination of the reaction system. Recently, using a combination of in situ observations inside a high-resolution high-voltage electron microscope (HVEM) and molecular-dynamics (MD) simulation, the present authors studied the dynamics of electron irradiation-induced amorphizing transformation in the NiTi intermetallic compound [3-6]. Metastable atomic clusters were found to form and
R8.6.2
disappear repeatedly in the irradiated structure, giving rise to nanoscale spatio-temporal fluctuations. It was suggested that these fluctuations represent nonequilibrium open processes that occur during the amorphizing transformation, and that a high-energy particle irradiation field produced in a high-resolution HVEM provides a useful environment in which dynamic structural fluctuations can be investigated on an atomic scale. In this paper we review our recent studies on such spatio-temporal nanostructural fluctuations. We concentrate upon the spatial autocorrelation functional (ACF) analysis [7-9] on structural fluctu
Data Loading...
