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Characterization of Residual
Stress in Additively
Manufactured Ti‐6Al‐4V Material
After Laser Shock Peening
S. Zabeen, A. Alibe, M. M. Attallah, D. Proud,
and M. E. Fitzpatrick
6th International Conference on Laser Peening and Related Phenomena
06/11 - 11/11/2016 Pretoria and Skukuza, South Africa
Rocket Science?
Rocket Engine Turbopump by NASA
This pump has 45 percent fewer parts than
pumps made with traditional manufacturing
Aim
1.  To investigate the effect of scanning strategy on
the residual stresses in selectively laser melted
Ti-6Al-4V.
2.  To determine whether laser shock peening is
effective in introducing compressive residual
stresses at the surface.
Experimental Methods
Surface Profile
Residual Stress Characterization
(by Incremental Hole Drilling )
With and
without removal
of the base
plate
After Hot
Isostatic
Pressing
After laser
shock peening
Mechanical
Properties
after HIP+LSP
Mechanical
Properties and
texture after
HIPing
Selectively Laser Melted Ti-6Al-4V
Specimen 1 Continuous Unidirectional
Specimen 2 Continuous Bidirectional
Specimen 3 Island Scan Bidirectional
Specimen 4 Chess Scan Bidirectional
Physical Observation
IslandScan
ChessScan
Cont.Uni.
Cont.Bi.
Residual Stress Characterization
Incremental Hole Drilling
Hole Diameter 2 mm
X
Z
Surface Profile of Continuous Unidirectional
Surface Profile of Continuous Bidirectional
Surface Profile of Island Scan
Surface Profile of Chess Scan
Comparison of surface profiles
Residual Stresses in as-built with Base Plate
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi σz
Cont. Bi σx
Chess Scan σz
Chess Scan σx
Residual Stresses in as-built with BP
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi σz
Cont. Bi σx
Chess Scan σz
Chess Scan σx
Residual Stresses in as-built with Base Plate
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi σz
Cont. Bi σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
IslandScan
ChessScan
Cont.Uni.
Cont.Bi.
Residual Stresses in as-built without Base
Plate
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
Residual Stresses in as-built without BP
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni σx
Cont. Bi. σz
Cont. Bi. σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi σz
Cont. Bi σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
Comparison of residual stresses between
specimens with and without BP
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni σx
Cont. Bi. σz
Cont. Bi. σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
With Base Plate Without Base Plate
IslandScan
ChessScan
Cont.Uni.
Cont.Bi.
Effect of Delamination
With Base Plate Without Base Plate
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σx L
Cont. Uni σx R
Cont. Bi. σx L
Cont. Bi. σx R
Island Scan σx L
Island Scan σx R
Chess Scan σx L
Chess Scan σx R
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Cont. Uni. σz L
Cont. Uni σz R
Cont. Bi. σz L
Cont. Bi. σz R
Island Scan σz L
Island Scan σz R
Chess Scan σz L
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Island Scan σx L
Island Scan σx R
Chess Scan σx L
Chess Scan σx R
-200
0
200
400
600
800
1000
1200
1400
1600
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Island Scan σz L
Island Scan σz R
Chess Scan σz L
Chess Scan σz R
-200
-150
-100
-50
0
50
100
150
0 100 200 300 400 500 600 700 800 900 1000
ResidualStress/MPa
Depth /micron
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi. σz
Cont. Bi σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
Residual Stresses after HIPing
With Base Plate
Residual Stresses after HIPing
With Base Plate Without Base Plate
-200
-150
-100
-50
0
50
100
150
0 100 200 300 400
ResidualStress/MPa
Depth /micron
0 200 300 400 500 600 700 800 900 1000
Cont. Uni. σz
Cont. Uni. σx
Cont. Bi. σz
Cont. Bi σx
Island Scan σz
Island Scan σx
Chess Scan σz
Chess Scan σx
-200
-150
-100
-50
0
50
100
150
0 100 200 300 400
ResidualStress/MPa
Depth /micron
Laser Shock Peening
Four Ti-6Al-4V AM specimens were patch peened on
one surface
Peening Parameters
Power Density : 10 GW/
cm2
Time : 18 ns
Number of layers: 2
Spot Shape: Square
Spot Size: 3 x 3 mm2
50% overlap and 200%
coverage
Ablative Layer : Yes
Base
Peening location and strategy
Base
BuildDirection
5 mm
Laser
Peened
Area
Figure: peening location with respect to the Base
Peening starts exactly from the base.
Figure: peening Strategy
Material was peened only on one side
50 mm
Laser Shock peened Ti-6Al-4V
Cont. Uni Cont. Bi
Island Scan Chess Scan
Experimental Methods
Depth
µm εz εx τ
32 -2 0 -1
64 -3 0 -1
96
128
8 13 12
28 38 33
Residual Stresses after LSP
-600
-500
-400
-300
-200
-100
0
100
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Peening Condition:10-18-2
Cont. Bi. σz
Cont. Bi. σx
Island σz
Island σx
Comparison of Residual Stresses
-600
-400
-200
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200
ResidualStress/MPa
Depth /micron
Island Scan as built
σz
Island Scan After
HIPing σz
Island Scan HIP+LSP
σz
Combined LSP and SLM Technique
Comparison of residual stresses between the as-built state, and
LSP treated in 316L material made by SLM
(1mm spot size, NO ablative coating)
(Reference LMTM)
Conclusions
1.  A high tensile residual stresses (approximately equal to the yield
stress) were found near the surface in as-built condition in the
build direction.
2.  60% lower residual stresses are found in the horizontal direction.
3.  After HIPing 90% residual stresses are relaxed for all specimens
in both directions.
4.  LSP effectively introduced high compressive residual stresses
(– 450 MPa).
1.  There is no significant effect of scanning strategies found on
residual stresses.
Questions and Comments?
Laser shock peening to enhance the
structural integrity of additively
manufactured material.

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Characterization of residual stress in addtively manufactured ti 6 al-4v after laser shock peening suraiya zabeen

  • 1. Characterization of Residual Stress in Additively Manufactured Ti‐6Al‐4V Material After Laser Shock Peening S. Zabeen, A. Alibe, M. M. Attallah, D. Proud, and M. E. Fitzpatrick 6th International Conference on Laser Peening and Related Phenomena 06/11 - 11/11/2016 Pretoria and Skukuza, South Africa
  • 2. Rocket Science? Rocket Engine Turbopump by NASA This pump has 45 percent fewer parts than pumps made with traditional manufacturing
  • 3. Aim 1.  To investigate the effect of scanning strategy on the residual stresses in selectively laser melted Ti-6Al-4V. 2.  To determine whether laser shock peening is effective in introducing compressive residual stresses at the surface.
  • 4. Experimental Methods Surface Profile Residual Stress Characterization (by Incremental Hole Drilling ) With and without removal of the base plate After Hot Isostatic Pressing After laser shock peening Mechanical Properties after HIP+LSP Mechanical Properties and texture after HIPing
  • 5. Selectively Laser Melted Ti-6Al-4V Specimen 1 Continuous Unidirectional Specimen 2 Continuous Bidirectional Specimen 3 Island Scan Bidirectional Specimen 4 Chess Scan Bidirectional
  • 7. Residual Stress Characterization Incremental Hole Drilling Hole Diameter 2 mm X Z
  • 8. Surface Profile of Continuous Unidirectional
  • 9. Surface Profile of Continuous Bidirectional
  • 10. Surface Profile of Island Scan
  • 11. Surface Profile of Chess Scan
  • 13. Residual Stresses in as-built with Base Plate -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni. σx Cont. Bi σz Cont. Bi σx Chess Scan σz Chess Scan σx
  • 14. Residual Stresses in as-built with BP -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni. σx Cont. Bi σz Cont. Bi σx Chess Scan σz Chess Scan σx
  • 15. Residual Stresses in as-built with Base Plate -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni. σx Cont. Bi σz Cont. Bi σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx IslandScan ChessScan Cont.Uni. Cont.Bi.
  • 16. Residual Stresses in as-built without Base Plate -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx
  • 17. Residual Stresses in as-built without BP -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni σx Cont. Bi. σz Cont. Bi. σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx
  • 18. -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni. σx Cont. Bi σz Cont. Bi σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx Comparison of residual stresses between specimens with and without BP -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni σx Cont. Bi. σz Cont. Bi. σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx With Base Plate Without Base Plate IslandScan ChessScan Cont.Uni. Cont.Bi.
  • 19. Effect of Delamination With Base Plate Without Base Plate -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σx L Cont. Uni σx R Cont. Bi. σx L Cont. Bi. σx R Island Scan σx L Island Scan σx R Chess Scan σx L Chess Scan σx R -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Cont. Uni. σz L Cont. Uni σz R Cont. Bi. σz L Cont. Bi. σz R Island Scan σz L Island Scan σz R Chess Scan σz L -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Island Scan σx L Island Scan σx R Chess Scan σx L Chess Scan σx R -200 0 200 400 600 800 1000 1200 1400 1600 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Island Scan σz L Island Scan σz R Chess Scan σz L Chess Scan σz R
  • 20. -200 -150 -100 -50 0 50 100 150 0 100 200 300 400 500 600 700 800 900 1000 ResidualStress/MPa Depth /micron Cont. Uni. σz Cont. Uni. σx Cont. Bi. σz Cont. Bi σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx Residual Stresses after HIPing With Base Plate
  • 21. Residual Stresses after HIPing With Base Plate Without Base Plate -200 -150 -100 -50 0 50 100 150 0 100 200 300 400 ResidualStress/MPa Depth /micron 0 200 300 400 500 600 700 800 900 1000 Cont. Uni. σz Cont. Uni. σx Cont. Bi. σz Cont. Bi σx Island Scan σz Island Scan σx Chess Scan σz Chess Scan σx -200 -150 -100 -50 0 50 100 150 0 100 200 300 400 ResidualStress/MPa Depth /micron
  • 22. Laser Shock Peening Four Ti-6Al-4V AM specimens were patch peened on one surface Peening Parameters Power Density : 10 GW/ cm2 Time : 18 ns Number of layers: 2 Spot Shape: Square Spot Size: 3 x 3 mm2 50% overlap and 200% coverage Ablative Layer : Yes Base
  • 23. Peening location and strategy Base BuildDirection 5 mm Laser Peened Area Figure: peening location with respect to the Base Peening starts exactly from the base. Figure: peening Strategy Material was peened only on one side 50 mm
  • 24. Laser Shock peened Ti-6Al-4V Cont. Uni Cont. Bi Island Scan Chess Scan
  • 25. Experimental Methods Depth µm εz εx τ 32 -2 0 -1 64 -3 0 -1 96 128 8 13 12 28 38 33
  • 26. Residual Stresses after LSP -600 -500 -400 -300 -200 -100 0 100 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Peening Condition:10-18-2 Cont. Bi. σz Cont. Bi. σx Island σz Island σx
  • 27. Comparison of Residual Stresses -600 -400 -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 ResidualStress/MPa Depth /micron Island Scan as built σz Island Scan After HIPing σz Island Scan HIP+LSP σz
  • 28. Combined LSP and SLM Technique Comparison of residual stresses between the as-built state, and LSP treated in 316L material made by SLM (1mm spot size, NO ablative coating) (Reference LMTM)
  • 29. Conclusions 1.  A high tensile residual stresses (approximately equal to the yield stress) were found near the surface in as-built condition in the build direction. 2.  60% lower residual stresses are found in the horizontal direction. 3.  After HIPing 90% residual stresses are relaxed for all specimens in both directions. 4.  LSP effectively introduced high compressive residual stresses (– 450 MPa). 1.  There is no significant effect of scanning strategies found on residual stresses.
  • 31. Laser shock peening to enhance the structural integrity of additively manufactured material.