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SUMMARY:Quantifying deformation under indentations by TEM diffraction - Ki
 rsten McLaughlin\, Department of Materials Science and Metallurgy\, Univer
 sity of Cambridge
DTSTART:20061114T150000Z
DTEND:20061114T160000Z
UID:TALK5907@talks.cam.ac.uk
CONTACT:Edmund Ward
DESCRIPTION:This talk will describe a quantitative diffraction technique i
 n the transmission electron microscope (TEM) to measure crystal lattice ro
 tations in materials deformed by low-load indentation.  These rotations ar
 e equivalent to the accumulation of an excess of dislocations of a particu
 lar sign [1]\, known as geometrically necessary dislocations.\n\nA variety
  of soft metals and hard ceramics have been deformed with low-load indenta
 tions using a Berchovich tip (nanoindentation) or a Knoop tip (microindent
 ation).  The crystals are then cut perpendicular to the indentation surfac
 e and thinned using a focused ion beam workstation so that the deformed re
 gion under the indentation can be studied in the TEM.  The electron transp
 arent foils are about 200 nm thick.\n\nConvergent beam electron diffractio
 n patterns are generated from spots with a 1 nm diameter in EF-STEM.  The 
 orientation of the local crystal lattice is measured from the Kikuchi line
 s in the diffraction patterns.  These Kikuchi lines become blurred if the 
 plastic or elastic strain gradients are high within the diffracting volume
 \, but in-plane rotations can still be collected with selected area diffra
 ction patterns.\n\nBy applying this technique to metals (Cu\, W)\, ceramic
 s (MgAl2O4\, Al2O3\, SiC)\, and a semi-conductor (GaN)\, it is possible to
  compare the size and intensity of rotations due to geometrically necessar
 y dislocations.  The results for the Cu and W can be compared to indent- i
 nduced lattice rotations measured with other techniques\, such as EBSD and
  Synchrotron-source X-ray diffraction.  New results have been found for th
 e other materials\, showing kinking in the hexagonal materials and rotatio
 ns associated with the cracking around larger indents.\n\n[1] J.F. Nye. Ac
 ta metall. 1\, 153 (1953). \n
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
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