Three-dimensional Analysis of Microstructures by nak14542

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									                      Naval Research Laboratory - Office of Naval Research
                              Materials Science and Technology
                                                  http://mstd.nrl.navy.mil


                               Science and Technology Success Stories
    Three-dimensional Analysis of Microstructures
      An understanding of the true three-dimensional (3-D) morphology and
   distribution of fine-scale solid-state precipitates is very important for control of
   microstructural evolution and mechanical properties of advanced materials used in a
   variety of Naval and commercial applications. Conventional optical and electron
   microscopy techniques used for microstructural characterization typically provide
   only two dimensional (2-D) sections from which the 3-D information must be
   inferred. Serial sectioning in combination with advanced computer reconstruction
   and visualization techniques are being employed at the Naval Research Laboratory
   (NRL) to obtain many new findings about the true three-dimensional characteristics
   of solid-state microstructures in opaque materials. These techniques are also
   supplemented by deep etching experiments wherever possible.
      These methods are being used to provide important new qualitative and
   quantitative information about the development of fine-scale solid-state precipitates
   during the thermomechanical treatment of alloys. In particular, the true three-
   dimensional morphology and connectivity of ferrite and cementite precipitates in
   steels have been revealed, and these observations demonstrate that erroneous
   conclusions are often made based on 2-D observations alone.


                                     0.2 m




                                     5 m
                                                                                             5 m
Individual sections (with fiducial marks): used for             3-D reconstruction of cementite
3-D reconstruction, & viewed as video sequences                 precipitates in an austenite grain
 3-D Analysis & Visualization of Microstructures

              New Findings                                                                                                                                                          Impact
                                                                                                                                                                   • When feature shapes and/or interconnectivities
 •High carbon steels                                                                                                                                                 are complicated or variable, 2-D methods give
   •No intragranular cementite precipitates                                                                                                                          erroneous results and 3-D analysis is required
   in 3-D (all connected somewhere to                                                                                                                              • A number of previous findings in the materials
   matrix grain boundaries)                                                                                                                                          community based on 2-D microscopy
   •Both lath & plate morphologies                                                                                                                                   techniques are incorrect
   extending into matrix grain interiors                                                                                                                           • The true 3-D microstructure strongly dictates
   •Plates have a constant thickness                                                                                                                                 the mechanical and other properties of steels
   •Grain boundary precipitates are not                                                                                                                              and other materials
   conventional allotriomorphs - actually                                                                                                                          • Predictive materials processing models must
   solid-state dendrites                                                                                                                                             take into account the true 3-D microstructure
 •Low carbon steels
   •No intragranular precipitates in 3-D
   (all connected somewhere to matrix                                                                                                                                      Point of Contact
   grain boundaries)                                                                                                                                               George Spanos
   •Ferrite primary “sideplates” are often                                                                                                                         Code 6324, Naval Research Laboratory
   not plate shaped, but are spikes in 3-D                                                                                                                         Washington D.C. 20375-5343
   •Ferrite secondary “sideplates” are not                                                                                                                         Ph: (202)767-5799
   plate shaped, but are fingers/tentacles                                                                                                                         Email: spanos@anvil.nrl.navy.mil
                                                                                                                                                                   Web: http://mstd.nrl.navy.mil/6320/6324




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                                                                          LOG(LENGTH/WIDTH)




    Quantification of 3-D microstructure                                                                                                                                  Visualization of 3-D microstructure
Frequency histogram of logarithm of the ratio                                                                                                                       Cave-like fully immersive virtual reality
of precipitate length to width for many                                                                                                                             environment at NRL, with user (pictured) inside
cementite precipitates                                                                                                                                              a matrix grain, studying precipitates

								
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