Microstructure and mechanical behavior of cast Ti-6Al-4V ...
Characterization of Additively Manufactured Ti-6Al-4V for ... Poster.pdf · Characterization of...
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Characterization of Additively Manufactured Ti-6Al-4V for Use in Pacemaker Shields Alexander Antonuccio, Charlie Meisel, Fiona O’Dowd, Alyssa Stubbers Faculty Advisors: Dr. David F. Bahr, Dr. Ernesto E. Marinero Industrial Sponsors: Jordan Balmer (Medtronic), Dr. Peter Tortorici (Medtronic) & Dr. John Barnes (The Barnes Group) Acknowledgements: David Brice (Purdue), PulseTech Products Corp. Medtronic evaluated two suppliers to determine if their additive manufacturing process was a suitable replacement for the current method of deep drawing custom pacemaker shields. A heat treatment softened the as-printed fine, brittle microstructure. After heat treatment, 3D Systems shields had a point defect density comparable to the deep drawn samples. After heat treatment, TransMachine shields had a microhardness most like the deep drawn samples. 3D Systems pores had a lower aspect ratio and average pore size (27.9um), with a more predictable pore formation and geometry compared to TransMachine (49.1um). MSE 430 - 440 : Materials Processing and Design Shields from two suppliers, 3D Systems (3DS) and TransMachine (TM), were examined. This work is sponsored by Medtronic plc, (Mounds View, MN) and The Barnes Group (Pittsburgh, PA) Titanium (Ti-6Al-4V) shields provide a barrier between the body and internal pacemaker electronics 1) Characterize shields from suppliers to determine similarities to deep drawn 2) Develop heat treatment for microstructure similar to deep drawn 3) Advise on concerns of porosity, brittleness, and residual stress Current Custom/Prototype: Machine from Solid Block Future Custom/Prototype: Additive Manufacturing Custom shapes are required for prototyping and select patients o Cost ↓ 25% Heat Treatment Rapid cooling characteristic to additive manufacturing leads to fine, brittle microstructure Annealing and cooling slowly results in grain growth Sample Heat Treatment: Hold 3 hours at 1100°C Cool at 5°C/min X-Ray Diffraction (XRD) Diffraction scans on all samples elucidated microstructure Full Width at Half Max (FWHM) analysis gives information on point defects Microscopy SEM - Lineal analysis on BSE micrographs of shield cross sections Optical – Pore size analysis on shield cross sections Knoop Microhardness Long aspect ratio of Knoop tip appropriate for thin shields Hardness scales with strength and will indicate brittleness Project Background Results & Discussion Objectives Procedures Results & Discussion (cont.) Recommendations Heat Treatment Softening Porosity Analysis Conclusions Higher FWHM = Higher density of point defects = Lower ductility Heat treatment reduced the FWHM value for both suppliers. As-deposited, 3DS shields had a higher FWHM than TM. After heat treatment, 3DS shields had a lower FWHM than TM and were closest to the deep drawn shields. Shield thickness and location of scan had no effect. 3DS shields with additional processing steps have higher FWHM values, likely leading to more brittle shields. 3DS TM standard 0.016” standard 0.020” HIP’ed 0.020” standard 0.012” stress relief 0.020” Characterization Shields as deposited had a fine lamellar α + β microstructure. XRD peaks confirmed the above microstructure. No other phases were present. TM shields consistently had a finer microstructure than 3DS shields. Heat treatment increased grain size significantly in all parts, decreasing the grain boundary strengthening effect. This change was greater for 3DS. After heat treatment, only TM shields are statistically softer than the required 365 HK specification; the 3DS shields were not. Location and shield thickness did not effect microhardness. Wide distribution of pore sizes in TM shields make porosity harder to predict. Sharp pore morphology is more likely to lead to crack propagation and part failure. 3DS pores had a lower aspect ratio, reducing likelihood of fracture initiation. Pores did not form preferentially in certain areas of the shields of either supplier. Residual stress measurements on two regions of a 3DS shield resulted in measurements of -599 MPa and -668 MPa. Both values are more than half the yield strength of Ti-6Al-4V. Residual Stress o XRD and SEM confirmed additively manufactured shields had a lamellar α + β microstructure. o While heat treatment revealed point defects for both suppliers, the heat treated 3DS shields were most similar to deep drawn shields. o Heat treatment increased grain size which decreases the Hall-Petch effect on hardness, leading to more ductile shields. o The Knoop microhardness data agreed with the SEM and XRD data. o Heat treated TM shields were the only samples below the maximum microhardness of 365 HK o 3DS pores are less likely to initiate crack propagation due to their equiaxed morphology o TransMachine pores are large and unpredictable, making bridging a concern o As-deposited shields have high residual stress o As delivered from suppliers, shields do not have desired properties for use in pacemakers o The designed heat treatment resulted in more favorable shields that were not all within specification 3D Systems • Heat treatment to soften and reduce residual stress TransMachine • Modification of printing parameters to reduce porosity While the designed heat treatment was effective, a shorter process should be researched Current Production: Deep Drawing Medtronic plc, “Our Pacemakers” fast cool = martensite slow cool = α + β TM 3DS as-deposited heat treated T. Ahmed, H.J. Rack. Materials Science and Engineering A. (243) 1998 █ TM (n=197 ; x̄ = 49.1 μm) █ 3DS (n=98 ; x̄ = 27.9 μm) 25 30 35 40 45 50 55 60 65 70 0.0 0.5 1.0 Intensity (Normalized) 2θ Deep Drawn Shield o Lead time 4-6 weeks → 24 hours 20 25 30 35 40 45 50 55 60 65 70 75 80 85 0.0 0.5 1.0 Intensity (Normalized) 2θ TransMachine .020" Back α Titanium Phase Peaks Deep Drawn base 3DS base 3DS HT base TM 0.020" Front Base TM 0.020" Back Base TM 0.012" Front Base TM 0.012" Back Base TM 0.020" Back Base HT TM 0.012" Front Base HT TM 0.012" Back Base HT 3DS SP Base Front 3DS SP Base Back 3DS HIP Base Front 3DS HIP Base Back 0.0 0.5 1.0 1.5 0.14 0.93 0.29 0.73 0.55 0.75 0.74 0.48 0.54 0.51 1.17 1.01 1.13 1.19 3DS Post Process TM HT TM Mean FWHM HT = Heat Treated TM = TransMachine 3DS = 3D Systems 3DS 3DS .016" coupon 3DS .016" base 3DS .016" HT TMA .020" base TMA .020" HT TMA .012" base TMA .012" HT 0 5 10 15 20 25 30 Distance between β grains (µm) 3DS TM Deep Drawn 3DS Std. 3DS HT 3DS Weld Weld Coupon TM .012 in TM .020 in TM HT 0 100 200 300 400 500 Microhardness(HK) 3DS TM dark phase: α light phase: β Instron, “Instron Knoop Test”
Transcript of Characterization of Additively Manufactured Ti-6Al-4V for ... Poster.pdf · Characterization of...
Characterization of Additively Manufactured Ti-6Al-4V for Use in Pacemaker ShieldsAlexander Antonuccio, Charlie Meisel, Fiona O’Dowd, Alyssa Stubbers Faculty Advisors: Dr. David F. Bahr, Dr. Ernesto E. MarineroIndustrial Sponsors: Jordan Balmer (Medtronic), Dr. Peter Tortorici (Medtronic) & Dr. John Barnes (The Barnes Group)Acknowledgements: David Brice (Purdue), PulseTech Products Corp.
Medtronic evaluated two suppliers to determine if their additive manufacturing process was a suitablereplacement for the current method of deep drawing custom pacemaker shields. A heat treatment softenedthe as-printed fine, brittle microstructure. After heat treatment, 3D Systems shields had a point defect densitycomparable to the deep drawn samples. After heat treatment, TransMachine shields had a microhardnessmost like the deep drawn samples. 3D Systems pores had a lower aspect ratio and average pore size(27.9um), with a more predictable pore formation and geometry compared to TransMachine (49.1um).
MSE 430-440: Materials Processing and Design
Shields from two suppliers, 3D Systems (3DS) and TransMachine (TM), were examined.
This work is sponsored by Medtronic plc,(Mounds View, MN) and The BarnesGroup (Pittsburgh, PA)
Titanium (Ti-6Al-4V) shields provide a barrier betweenthe body and internal pacemaker electronics
1) Characterize shields from suppliers to determinesimilarities to deep drawn
2) Develop heat treatment for microstructure similarto deep drawn
3) Advise on concerns of porosity, brittleness, andresidual stress
Current Custom/Prototype:Machine from Solid Block
Future Custom/Prototype:Additive Manufacturing
Custom shapes are required for prototyping and select patients
o Cost ↓ 25%
Heat TreatmentRapid cooling characteristic toadditive manufacturing leadsto fine, brittle microstructureAnnealing and cooling slowlyresults in grain growth
Sample Heat Treatment:Hold 3 hours at 1100°CCool at 5°C/min
X-Ray Diffraction (XRD)Diffraction scans on all sampleselucidated microstructure
Full Width at Half Max (FWHM)analysis gives information onpoint defects
MicroscopySEM - Lineal analysis on BSE micrographs of shieldcross sections
Optical – Pore size analysis on shield cross sectionsKnoop Microhardness
Long aspect ratio of Knoop tipappropriate for thin shields
Hardness scales with strengthand will indicate brittleness
Project Background Results & Discussion
Objectives
Procedures
Results & Discussion (cont.)
Recommendations
Heat Treatment Softening
Porosity Analysis
Conclusions
Higher FWHM =
Higher density of point defects
=Lower ductility
Heat treatment reduced the FWHM value for bothsuppliers. As-deposited, 3DS shields had a higherFWHM than TM. After heat treatment, 3DS shieldshad a lower FWHM than TM and were closest to thedeep drawn shields. Shield thickness and location ofscan had no effect. 3DS shields with additionalprocessing steps have higher FWHM values, likelyleading to more brittle shields.
3DS TMstandard 0.016” standard 0.020”HIP’ed 0.020” standard 0.012”stress relief 0.020”
Characterization
Shields as deposited had a fine lamellar α + βmicrostructure.
XRD peaks confirmed the above microstructure. No other phases were present.
TM shields consistentlyhad a finer microstructurethan 3DS shields. Heattreatment increased grainsize significantly in allparts, decreasing the grainboundary strengtheningeffect. This change wasgreater for 3DS.
After heat treatment,only TM shields arestatistically softer thanthe required 365 HKspecification; the 3DSshields were not.Location and shieldthickness did not effectmicrohardness.
Wide distributionof pore sizes inTM shields makeporosity harder topredict.
Sharp pore morphology ismore likely to lead to crackpropagation and part failure.3DS pores had a lower aspectratio, reducing likelihood offracture initiation. Pores didnot form preferentially incertain areas of the shields ofeither supplier.
Residual stress measurements on two regions of a3DS shield resulted in measurements of -599 MPaand -668 MPa. Both values are more than half theyield strength of Ti-6Al-4V.
Residual Stress
o XRD and SEM confirmed additively manufactured shields had a lamellar α + β microstructure.
o While heat treatment revealed point defects for both suppliers, the heat treated 3DS shields were most similar to deep drawn shields.
o Heat treatment increased grain size which decreases the Hall-Petch effect on hardness, leading to more ductile shields.
o The Knoop microhardness data agreed with the SEM and XRD data.
o Heat treated TM shields were the only samples below the maximum microhardness of 365 HK
o 3DS pores are less likely to initiate crack propagation due to their equiaxed morphology
o TransMachine pores are large and unpredictable, making bridging a concern
o As-deposited shields have high residual stresso As delivered from suppliers, shields do not
have desired properties for use in pacemakerso The designed heat treatment resulted in more
favorable shields that were not all within specification
3D Systems• Heat treatment to soften and reduce residual
stressTransMachine• Modification of printing parameters to reduce
porosityWhile the designed heat treatment was effective, a shorter process should be researched
Current Production:Deep Drawing
Medtronic plc, “Our Pacemakers”
fast cool =martensite
slow cool =α + β
TM3DS
as-d
epos
ited
heat
trea
ted
T. Ahmed, H.J. Rack. Materials Science and Engineering A. (243) 1998
█ TM (n=197 ; x̄ = 49.1 μm)█ 3DS (n=98 ; x̄ = 27.9 μm)
25 30 35 40 45 50 55 60 65 700.0
0.5
1.0
Inte
nsity
(Nor
mal
ized
)
2θ
Deep Drawn Shield
o Lead time 4-6 weeks → 24 hours
20 25 30 35 40 45 50 55 60 65 70 75 80 850.0
0.5
1.0
Inte
nsity
(Nor
mal
ized)
2θ
TransMachine .020" Back α Titanium Phase Peaks
Deep Drawn base
3DS base
3DS HT base
TM 0.020" Front Base
TM 0.020" Back Base
TM 0.012" Front Base
TM 0.012" Back Base
TM 0.020" Back Base HT
TM 0.012" Front Base HT
TM 0.012" Back Base HT
3DS SP Base Front
3DS SP Base Back
3DS HIP Base Front
3DS HIP Base Back0.0
0.5
1.0
1.5
0.14
0.93
0.29
0.73
0.55
0.75 0.74
0.480.54 0.51
1.17
1.01
1.131.19
3DS Post ProcessTM HTTM
Mea
n FW
HM
HT = Heat TreatedTM = TransMachine3DS = 3D Systems
3DS
3DS .016" c
oupon
3DS .016" b
ase
3DS .016" H
T
TMA .020" b
ase
TMA .020" H
T
TMA .012" b
ase
TMA .012" H
T
0
5
10
15
20
25
30
Dist
ance
bet
ween
β g
rain
s (µ
m)
3DS TM
Deep D
rawn
3DS S
td.
3DS H
T
3DS W
eld
Weld C
oupo
n
TM .012
in
TM .020
in
TM HT
0
100
200
300
400
500
Mic
roha
rdne
ss(H
K)
3DS TM
dark phase: α
light phase: β
Instron, “Instron Knoop Test”
