ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Annealing is an important mechanism of microstructural modification both in rocks andmetals. In order to relate directly changes in crystallographic orientation to migrating boundaries theresearcher has the option to investigate either samples where the grain boundary motion can bedirectly tracked or a series of samples exhibiting successively higher degrees of annealing.Here we present results from rock samples collected from two well characterised contactaureoles (a volume of rock heated by the intrusion of a melt in its vicinity): One quartz sample inwhich patterns revealed by Cathodoluminescence (CL) indicate the movement of grain boundariesand a series of calcite samples of known temperature history. Electron backscatter diffraction(EBSD) analysis is used to link the movement of grain, twin boundaries and substructures with thecrystallographic orientation / misorientation of a respective boundary.Results from the quartz bearing rock show: (a) propagation of substructures and twinboundaries in swept areas both parallel and at an angle to the growth direction, (b) development ofslightly different crystallographic orientations and new twin boundaries at both the growthinterfaces and within the swept area, and (c) a gradual change in crystallographic orientation in thedirection of growth. Observations are compatible with a growth mechanism where single atoms areattached and detached both at random and at preferential sites i.e. crystallographically controlledsites or kinks in boundary ledges. Strain fields caused by defects and/or trace element incorporationmay facilitate nucleation sites for new crystallographic orientations at distinct growth interfaces butalso at continuously migrating boundaries.Calcite samples show with increasing duration and temperature of annealing: (a) systematicdecrease of the relative frequency of low angle grain boundaries (gbs), (b) decrease in latticedistortion within grains, (c) development of distinct subgrains with little internal lattice distortion,(d) change in lobateness of gbs and frequency of facet parallel gbs and (e) change in position ofsecond phase particles. These observations point to an increasing influence of grain boundaryanisotropy with increasing annealing temperature, while at the same time the influence of secondphase particles and subtle driving-force variations decrease.This study illustrates the usefulness of using samples from natural laboratories and combiningdifferent analysis techniques in microprocess analysis
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/16/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.550.333.pdf
Permalink