7 research outputs found
Analysis of acoustic emission during the melting of embedded indium particles in an aluminum matrix: a study of plastic strain accommodation during phase transformation
Acoustic emission is used here to study melting and solidification of
embedded indium particles in the size range of 0.2 to 3 um in diameter and to
show that dislocation generation occurs in the aluminum matrix to accommodate a
2.5% volume change. The volume averaged acoustic energy produced by indium
particle melting is similar to that reported for bainite formation upon
continuous cooling. A mechanism of prismatic loop generation is proposed to
accommodate the volume change and an upper limit to the geometrically necessary
increase in dislocation density is calculated as 4.1 x 10^9 cm^-2 for the
Al-17In alloy. Thermomechanical processing is also used to change the size and
distribution of the indium particles within the aluminum matrix. Dislocation
generation with accompanied acoustic emission occurs when the melting indium
particles are associated with grain boundaries or upon solidification where the
solid-liquid interfaces act as free surfaces to facilitate dislocation
generation. Acoustic emission is not observed for indium particles that require
super heating and exhibit elevated melting temperatures. The acoustic emission
work corroborates previously proposed relaxation mechanisms from prior internal
friction studies and that the superheat observed for melting of these
micron-sized particles is a result of matrix constraint.Comment: Presented at "Atomistic Effects in Migrating Interphase Interfaces -
Recent Progress and Future Study" TMS 201
Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows
International audienceThis paper reviews solar flows and magnetic fields observed at the photospheric level. We first present the context in which these observations are performed. We describe the various temporal and spatial scales involved, and the coupling between them. Then we present small-scale flows, mainly supergranulation and flows around active regions. Flows at the global scale are then reviewed, again with emphasis on the flows, i.e. differential rotation, torsional oscillation and meridional circulation. In both small- and global-scale we discuss the coupling between flow fields and magnetic field and give an overview of observational techniques. Finally, the possible connection between studies of solar activity and stellar activity is briefly discussed