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Tension-Compression Asymmetry and Orientation Creep Anisotropy of a Ni
Based Turbine Disk Alloy
Dan Butler
JHU Mechanical Engineering MEANS2 Update Meeting
April 4, 2007
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Our Goals
• Through high temperature microsample testing we aim to:
• Determine creep anisotropy and tension-compression asymmetry.
• Measure activation energies and stress dependencies.
• Enhance fidelity of mechanism map for turbine disk alloys.
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Analyzing Grain Size• 700-800µm thick circular slices were cut perpendicular to longitudinal axis of each rod using a wire EDM.
• Slices were polished to remove residual recast layer from the EDM process.
• Faces of the slices were polished to a mirror finish using 400 grit SiC through 0.05µm colloidal silica.
• A modified waterless Kalling's etch is applied to reveal grain structure. This etchantconsists of 4g CuCl2, 50mL methanol (95%), and 40mL HCl (37%) and is applied using a cotton swab for 30 seconds.
1 cm
One of four bars received from University of Michigan
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Analyzing Grain Size in Crystals
2 mm
Polishing and etching show that the majority of each slice is single crystalline with typical slice containing two grains.
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An Observed Grain Boundary
0.35 mm
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Verifying Chemical AnalysisICP Results*
ElementNominal
compositionOriginal sample(R104)
“Single”crystal
(4-bar mold)
Single crystal
(Crystalox)
Ni 50.1 50.9 50.06 51.2
Co 20.6 20.76 21.40 20.84
Cr 13 12.65 12.55 12.52
Al 3.4 3.11 3.19 3.01
Ti 3.1 3.62 3.53 3.49
W 2.1 2.07 2.06 2.11
Ta 2.4 2.34 2.38 2.33
Nb 0.9 0.77 0.86 0.73
Mo 3.8 3.74 3.81 3.70
C - 0.044 0.04 0.055
Fe - 0.09 0.08 0.08
Zr - 0.05 0.04 0.05
* Analysis of 4-bar mold alloy conducted at Sherry Labs, Daleville, IN. All others after Mills.
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Determining Crystal Orientation
Transmission
Back reflection
http://www.matter.org.uk/diffraction/x-ray/laue_method.htm
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X-Ray Set-up at Hopkins
Replace photo multiplier tube with Polaroid cassette and film to capture Laue patterns.
Photo multiplier tubeX-
Ray
sou
rce
Sample
Collimator
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Calibrating Laue Experiments using Si Wafer
LauePT simulation (5.1 cm image distance)
{100} Si
<011>
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Si {100} Transmission Laue: Theory vs. Experiment
-60 -40 -20 0 20 40 60
-40
-30
-20
-10
0
10
20
30
40
Blue circles are from LauePt simulations, red stars are the diffraction spots taken from the image on the left. Measurements confirm image distance of 5.1cm.
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Ni-Superalloy Transmission Laue
Sample A03Sample A01 Sample A02
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Ni-Superalloy Transmission Laue Analysis
Spot ϕ δ
1 14 48
2 16 28
3 17 15
4 17 9
5 18 -1
6 19 -20
7 21 -39
8 23 -49
9 30 -64
1* 13 50
2* 17 40
3* 20 20
4* 80 -75
5* 55 -69
6* 48 -64
1
23
45
67
8
9
1*2*
3*
4*5*
6*
Data from Leonhardt ChartSample A02
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Stereographic Projection
Poles θ
P to P* ~45
Planes θ
(100) to (110) 45
(130) to (210) 45
(211) to (113) 42
(111) to (171) 43
P
P*
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Example Sample Layout
4mm
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Tension-Compression Sample Geometry
Original Sample Geometry – 5mm
New Sample Geometry – 4.25mmshorter length saves material and allows one to test even smaller volumes of material
Courtesy of Dan Gianola
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Elastic Buckling Analysis
2
22
12LEt
APcr
crπσ ==The Euler buckling load, is given by: , then
2
2
LEIPcr
π=
3
121 wtI = wtA =where
oldcrnewcr __ 0625.3 σσ ∗=mmLnew 0.1=mmLold 75.1=
GPa
GPa
oldcr
newcr
36.3
28.10
_
_
=
=
σ
σLet: and then:mmt 250.0=GPaE 200=
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A Study of T-C Yield Asymmetry in Ti-6Al
• Orient single crystal samples for a-type basal slip (hcp).
• Expect tension-compression asymmetry based on observed asymmetry in polycrystalline material even at very small strains.
Courtesy of Matt Brandes
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Capacitance Strain (%)
Stre
ss (M
Pa)
764 MPa
-504 MPa
Video rate = 90x testing rate
Measuring T-C Asymmetry in Ti-6Al
With Matt Brandes Sample 005a
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Measuring T-C Asymmetry in Ti-6Al
-50 0 50 100-1000
-500
0
500
1000
Capacitance Strain (%)
Stre
ss (M
Pa)
679 MPa
-575 MPa
Video rate = 90x testing rate
With Matt Brandes Sample 005e
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Capacitance Strain (%)
Stre
ss (M
Pa)
Video rate = 30x testing rate
Measuring T-C Asymmetry in Ti-6Al
With Matt Brandes Sample 005c
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Using Image Analysis to Measure Strain
Sample 005eWith Matt Brandes, Chris Eberl
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Stress-Strain Response from Image Analysis
-0.035 -0.03 -0.025 -0.02 -0.015 -0.01 -0.005 0 0.005-600
-500
-400
-300
-200
-100
0
100
Eng. strain [ ]
Eng
. stre
ss [M
Pa]
Image analysis clearly shows a plastic strain has occurred in compression of the sample.
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Extending the Technique to Elevated Temperature
Tension test of RuNiAl at 900oC
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Extending the Technique to Elevated Temperature
Tension test of RuNiAl at 900oC
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Maintaining Constant Temperature vs. Time
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Action Items
• Heat treatment:• What temperature?• How long?• Under what conditions?• When?• Where?
• Precise long-term temperature control of resistive heating set-up:• Have EuroTherm feedback controller• Working out bugs• Need to synchronize timing with optical pyrometer
• Start testing• Orient• Cut samples• Polish
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Questions?