Sandia Fracture Challenge Microstructure Characterization

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Sandia Fracture ChallengeMicrostructure
Characterization

• Yuxiong Mao, PhD
• Mark Horstemeyer, CAVS Chair Professor
• Center for Advanced Vehicular Systems Mississippi
  State University

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15-5PH Stainless Steel Plate

• Six samples were made from the received specimen
  to observe the Longitudinal-Transverse (LT1LT2),
  Longitudinal-Thickness (LS1LS2),
  Transverse-Thickness (TS1TS2) sections.
• Samples were mounted and polished. Then etched
  with Vilella's reagent for 90 seconds.

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LT1 LT2 Before Etch
LT sections are homogeneous. Very few inclusions
can be found in these sections. Note the lines
here are polish scratches.
Inclusions
LT1 Overview
LT2 Overview
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LT1 Before Etch
High Resolution View
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LS1 Before Etch
Near Surface
Banding and inclusions can be observed in LS
sections. The inclusions are aligned along the
longitudinal direction. The bands run through the
entire sample and are clustered in the center
region.
Inclusions
Center
Overview
High Resolution View
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LS2 Before Etch
Near Surface
Center
Overview
High Resolution View
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TS1 Before Etch
Near Surface
Banding and inclusions can also be observed in TS
sections. The bands are shorter compared to those
in LS sections.
Center
Overview
High Resolution View
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TS2 Before Etch
Near Surface
Center
Overview
High Resolution View
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Quantitative Analyses of the inclusions observed
in LS and TS un-etched sections
Area Fraction() Number Density(/um2) Average Area (um2) Average NND(um)
LS1 0.1014 4.261E-04 2.379 18.578
LS2 0.0825 3.164E-04 2.608 20.318
TS1 0.1534 7.093E-04 2.162 16.138
TS2 0.1649 8.394E-04 1.965 14.474
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LT1 After Etch Martensite Dominated
Homogenous Martensitic matrix covers the entire
LT sections.
Martensitic matrix
Overview
High Resolution View
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LT2 After Etch
Overview
High Resolution View
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LS1 After Etch Ferrite Banding is an Issue
Near Surface
Banding/segregations can be observed in LS
sections. The bands run through the entire sample
and are clustered in the center region. The bands
are aligned along the longitudinal direction.
These segregations may have detrimental effects
on the mechanical properties(a).
Ferrite Stringer
Center
Banding
Overview
(a) B. Potter, NDT of Precipitation Hardened
Steels Using Fluorescent Magnetic Particle
Testing, NDT Solution, December 2003
High Resolution View
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LS2 After Etch
Near Surface
Center
Overview
High Resolution View
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TS1 After Etch
Near Surface
Banding/segregations can also be observed in TS
sections. The bands are aligned along the
transverse direction and are shorter than those
in LT sections.
Center
Banding
Overview
High Resolution View
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TS2 After Etch
Near Surface
Center
Overview
High Resolution View
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Grain Boundary Segmentation
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Grain Size Distributions Change Hardening
Behavior Locally
Sample LT1 LT2 LS1 LS2 TS1 TS2
Average Grain Size (um) 4.54 4.80 4.01 4.30 3.71 3.56