Discussion

Data collected here will aid researchers in creating a more accurate crystal

plasticity finite element model that can predict the lattice rotations of

individual grains. After 25% compression, there exists a stark difference

between the grains. Compression creates more regions of low CI,

indicating a degradation of the grain substructure. Minor misorientations

are introduced in larger quantities as well. However, the average number

of grain boundary misorientations

decreases. We are currently

engineering a finite element model

to help manufacturers generate

higher quality products by

exploring how the microstructural

lattice of aluminum creates the

properties seen today.

Acknowledgements

I am sincerely grateful for all the time and effort that Dr. David P. Field,

Zhe Leng, and Dr. Amy Wo have spent helping me pursue my research. I

truly appreciate the advice that Erin Patterson, John Young, Khaled

Adam, and other important individuals have given me about the essentials

of research.

Linda L. Vo1, David P. Field2, and Zhe Leng2

1Princeton University, 2Washington State University Materials Science Engineering Department, Washington State University

This work was supported by the National Science Foundation’s REU program under grant number DMR-1062898.

Introduction Although various crystal plasticity finite element models (CPFEMs)

exist for predicting lattice rotations caused by channel-die compression on

aluminum 1050-O, most models require an easily accessible experimental

component to confirm their predictions. Models generally have difficulty

incorporating non-ideal conditions such as uneven load and grain-to-grain

interactions. Issues also arise when models are limited in their capability to

predict individual grain rotation (Panchanadeeswaran, 1996). This

experimental work provides the statistical basis to support the modeling

of plasticity algorithms to predict lattice rotations of individual grains

accurately. Using backscattered electrons to form Kikuchi patterns,

orientation images can be used to study the lattice rotations of individual

grains before and after each compression. Characterizing individual grain

rotations is significant because these grains collectively create the different

properties that manufacturers can manipulate to create consumer goods.

Objectives

• Deform samples using channel-die compression

• Study the lattice rotations of individual grains before and after each

deformation

Utilize EBSD to create orientation maps

• Provide data for researchers to create crystal plasticity finite element

models (CPFEM) that characterize lattice rotations of individual grains

in aluminum 1050-O due to channel die compression

Important for manufacturing purposes

• Help to reveal the heterogeneities that occur at grain boundaries

Procedures

Sample Preparation

• Samples were cut from an aluminum 1050 plate (7.5 x 17.5 x 25 mm)

• Annealed for 2 hours at 600°C to generate grain growth

• Grinded with successively finer grit paper (from 320 grit paper to 1200

grit paper) to prepare sample surfaces for EBSD

• Polished using various materials including 1.0 µm diamond paste, 0.05

µm alumina polish, and a 0.02 µm colloidal silica finish

Channel Die Compression

• Deformed using channel die compression at a rate of 0.001 in/sec

• Channel die compression provides unique conditions that hold stress

constant while limiting the expansion to plane strain, similar to deformation

in an industrial rolling mill.

• In order to avoid edge effects that produce shearing, which is not

characteristic of plane strain deformation, samples are split to analyze a

pseudo-internal interface.

• Compressions occurred at 10%, 15%, and 25%.

Results

Average Grain Size: 2.0 um

Specimen 1:

Initial: 7 mm X 15 mm X 25 mm

Final: 7 mm X 11 mm X 33 mm

Specimen 2:

Initial: 8 mm X 15mm X 25mm

Final: 8 mm X 11 mm X 33 mm

As specimens were compressed and became

more elongated, the surfaces began to display

deformation planes.

Although the compressions caused most grains to rotate, changes were minor for some and

more pronounced for others. This reflects the difficulty in creating an accurate plasticity model

that can take into account the varying levels of strain upon different regions of the sample in

experimental conditions. Neighboring grains often rotated in similar orientations as seen in the

upper portion of the EBSD map.

Electron Backscatter Diffraction (EBSD)

Spot size: 6

Accelerating Voltage: 20 kV

Mounted using conductive carbon tape in the scanning

electron microscope(SEM), sample surfaces can be studied

using the diffracted backscattered electrons to form

Kikuchi patterns. EBSD images reveal the lattice

orientations of individual grains before and after each

compression. Fiducial marks were used to annotate

different regions of study.

Specimen 1 Specimen 2 Load Applied

0% Compression 15 mm 15 mm N/A

10% Compression 13.25 mm 13.25 mm ~8,000 pounds

15% Compression 12.5 mm 12.8 mm ~8,400 pounds

25% Compression 11 mm 11 mm ~12,500 pounds

Table 1: Load Applied and Height of Specimens at Varying Compression Percentages

0% Compression

Figure 2: Samples are tilted at 70° to

allow the phosphor screen to capture

backscattered electrons to form EBSD

images.

10% Compression 15% Compression 25% Compression

Above: Channel die compression apparatus:

Above: Mechanical testing machine to

perform channel die compression

Grain D Compressio

n Percentage

Orientation

Coordinates

Angle

0 % 296.5 46.0 342.0 46.0

10 % 272.1 127.9 251.5 41.5

15 % 13.4 105.9 124.1 37.2

25 % 187.9 76.9 329.4 33.0

Above: Inverse Pole Figure showing the varying locations and rotation angles of Grain D

at 0%, 10%, 15%, and 25% compressions. Although grains did rotate and change in shape,

the rotations were minor. The grains studied showed rotations between 7.2° and 13 °.

Table: Orientation Coordinates and Angles at Varying Compression Levels

0% Compression 25% Compression

Left: Kernel Average

Misorientation Map before

compression

Right: Kernel Average

Misorientation Map after 25%

compression

Above: Specimen before deformation (left) and after 25% deformation (right)

At 0% Compression At 25% Compression

Average Number: 9.36746 Average Number: 5.47254

Localized Strain Component E22

Grain D

Grain D

Grain D

Average C.I.=0.92

Above: EBSD maps portraying varying grain shapes and orientations at 0%,

10%, 15%, and 25% compression (left to right). Different colors represent

different orientations while black regions represent areas with a Confidence

Index (CI) of 0.20 or less. Maps were scanned with a step size of 0.04 μm.

Left: Legend displaying reference direction

Right: Legend for interpreting color-coded orientations above

Average C.I.=0.92 Average C.I.=0.76

Grain D

Average C.I.=0.88