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Overview of Materials Used in Additive Manufacturing
D.L. Bourell Temple Foundation Professor
The University of Texas at Austin
NSF Workshop: Environmental Implications of Additive Manufacturing Arlington VA
October 14, 2014
Material Demands for AM
• Form Proper Feedstock
• Fabricator Processability
• Post-Processability as Needed
• Acceptable Service Properties
“Roadmap for Additive Manufacturing: Identifying the Future of Freeform Processing”, D.L. Bourell, M.C. Leu, D.W. Rosen, eds, The University of Texas at Austin, 2009, 92 pages.
SL
LS, FDM SLM, EBM, DED
Material for Additive Manufacturing
Material for Additive Manufacturing
• Composites • Binders
Transient Permanent
• Support Structures • Graded Structures • Multi-Materials
“Roadmap for Additive Manufacturing: Identifying the Future of Freeform Processing”, D.L. Bourell, M.C. Leu, D.W. Rosen, eds, The University of Texas at Austin, 2009, 92 pages.
Materials Grand Challenge in AM
• Quality • Process Consistency, Repeatability • Reliability • Wide Diversity of Compositions • Superior Structure and Properties • Low (Feedstock and Processing) Cost
Materials for Fused Deposition Modeling (Amorphous Thermoplastics)
• ABS [Acryonitrile Butadiene Styrene] $7-115/lb • Polycarbonate $113/lb • PC/ABS Blend • PLA [Polylactic Acid] $7-25/lb • Polyetherimide (PEI) [Stratasys ULTEM] $220/lb • Nylon Co-Polymer (new in 2012) Source: 2012 Wohlers Report
Materials for Stereolithography and Material Jetting
(Proprietary Thermosets, ~$100/lb)
• Acrylics • Acrylates • Epoxies • “ABS-like” (Material Jetting)
Source: 2012 Wohlers Report
Materials for Laser Sintering (Crystalline/Semi-Crystalline Thermoplastics)
• Polyamide (Nylon) 11 and 12 ~$40/lb Neat Glass Filled Carbon Filled Metal (Al) Filled
• Polystyrene (Lost Wax Patterns) • Polypropylene • Polyester (“Flex”) • Polyetheretherkeytone (PEEK) ~$200/lb • Thermoplastic Polyurethane (new in 2012) • Nylon 6 (new in 2012)
Source: 2012 Wohlers Report
Metals for AM (BJ, DED, PBF, SL)
• Tool Steel ~$50/lb • Stainless Steel ~$50/lb • Aluminum Alloys ~$50/lb • Co-Cr Alloys ~$55-250/lb • Nickel Alloys ~$95-125/lb • CP Titanium ~$150-400/lb • Ti-6Al-4V ~$150-400/lb • Gold • Silver
Source: 2012 Wohlers Report
Most Popular: SLM EBM BJ (ExOne) DED (LENS, POM, etc.) LOM (UAM)
AM Materials/Properties Summary
Property AM Parts Compared to Conventional Processing Stiffness Equal Strength As Strong or Stronger Hardness Harder or as Hard Ductility Less Ductile Fatigue (Cyclic) Weaker Toughness Less Tough Post-processing to remove porosity (e.g., hot isostatic pressing) restores all properties if the interfaces are properly destroyed
Summary of AM Mechanical Behavior
Metals Polymers Non-Metallics
Modulus of Elasticity
Porosity Driven (Power Law)
Porosity Driven (Power Law)
Porosity Driven
Strength/Ductility Porosity Driven Isotropic (High ∆)
Porosity Driven Anisotropic (Ductility)
Porosity Driven Weibull Mod.
Fatigue σe<0.5UTS or no σe -
Fracture Toughness
Less or equal to bulk -
ερρ
−==∆ 1th
Processing Effects on Porosity in SLM Processed 17-4 Stainless Steel
A.B. Spierings, K. Wegener, G. Levy, “Designing Material Properties Locally with Additive Manufacturing Technology SLM”, Proc. SFF Symposium (2012), pp. 447-455.
Power = 190 W Vscan = 1.30 m/s Tlayer = 50 µm
Power = 190 W Vscan = 0.80 m/s Tlayer = 30 µm
Khalid Rafi, H., Karthik N.V., Thomas L. Starr, Brent E. Stucker, “Defect formation in EBM parts built in horizontal orientation”, Proc. SFF Symposium (2012), pp. 456-467.
Examples of Porosity in EBM Ti-6Al-4V
Modulus of Elasticity
C.E. Majewski and N. Hopkinson, “Effect of section thickness and build orientation on tensile properties and material characteristics of Laser Sintered nylon-12 parts”, SFF Symposium Proceedings, Univ. Texas at Austin, 2010, pp. 422-34.
Nylon 12
200
400
600
0
Stiff
ness
(ksi)
Strength
J.P. Kruth, et al., “Binding Mechanisms in Selective Laser Sintering and Selective Laser Melting”, SFF Symposium Proceedings, Univ. Texas at Austin, 2004, pp. 44-58.
316L Stainless Steel SLM, As Processed
27.5 ksi
70-100 ksi
Strength and Ductility
R.S. Keicher, A.M. Christiansen and K.W. Wurth, “Electron Beam Melted (EBM) Co-Cr-Mo Alloy for Orthopaedic Implant Applications”, SFF Symposium Proceedings, Univ. Texas at Austin, 2009, pp. 428-36.
66Co-28Cr-6Mo EBM, HIP, Homogenized
(ksi) (ksi)
D.K. Leigh, Harvest Technologies, priv. comm., 2011.
LS Bulk* Yield (MPa) 22.6 57.9 Tensile (MPa) 50.0 61.0 % Elongation 27 350
*CES Edupack Matl Selector, Version 7.0.0, Granta Ltd., 2011
Mechanical Behavior of LS Nylon
Strength
1.5
1.55
1.6
1.65
1.7
1.75
1.8
1.85
1.9
-0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0
Log(
H)
Log(∆)
E. Yasa, et al., “Microstructure and Mechanical Properties of Maraging Steel 300 after Selective Laser Melting”, SFF Symp., 2010, pp. 383-396
SLM Maraging Steel 18Ni300 Various Layer Thicknesses
R.M. German, “Powder Metallurgy and Particulate Materials Processing”, MPIF, Princeton NJ, 2005, p. 385.
Strength
M.K. Agarwala, D.L. Bourell, B. Wu, J.J. Beaman, “An Evaluation of the Mechanical Behavior of Bronze-Ni Composites Produced by Selective Laser Sintering”, SFF Symposium Proceedings, H.L. Marcus, J.J. Beaman, J.W. Barlow, D.L. Bourell and R.H. Crawford, eds., Austin TX, 193-203 (1993).
Room-Temperature Tensile Strength of Pre-Mixed SLS (90Cu-10Sn) Bronze and Commercially Pure Nickel Powder as a Function of Relative Density ∆ = 1-ε. (a) As SLS Processed, (b) SLS Processed and Sintered at 900-1100°C for 1 to 10 hr.
Mechanical Properties of AM Parts
Ductility
Relative Ductility as a Function of Fractional Porosity for Pure Iron. Various Particle Sizes and Purity. [From Haynes, Powder Met., 1977, 20, 17-20]
( )( ) 2/12
2/3
11
)0()0(
εε
εε
CDuctilityDuctility
+
−=
=≠
Ductility
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0 0.1 0.2 0.3 0.4 0.5
Elon
gatio
n
Relative Porosity ε
LS Polyamide 12 C = 4000
D.K. Leigh, D.L. Bourell, J.J. Beaman, “Basis for Decreased Mechanical Properties of Polyamide in Selective Laser Sintering” Proc. SFF Symposium, Austin TX, 2011.
R. Haynes, “A Study of the Effect of Porosity Content on the Ductility of Sintered Metals”, Powder Metallurgy 20 (1977) pp. 17-20.
SLM Ti-6Al-4V Based on Post-Process Anneals (Furnace Cooled)
Thöne, M., S. Leuders, A. Riemer, T. Tröster, H.A. Richard, “Influence of heat-treatment on Selective Laser Melting products – e.g. Ti6Al4V”, Solid Freeform Fabrication Proceedings, (2012), pp. 492-498.
Fatigue
Reid, Fatigue of Fused Deposition Modeled (FDM) Acrylonitrile Butadiene Styrene (ABS) Stage Three individual Project MEC 3098, Newcastle University School of Mechanical and Systems Engineering 2011.
Fatigue of FDM Processed ABS polymer
Fatigue
P.A. Kobryn and S.L. Semiatin, “Mechanical Properties of Laser-Deposited Ti-6Al-4V”, SFF Symposium Proceedings, Univ. Texas at Austin, 2001, pp. 179-186.
LENS Processed Ti-6Al-4V, Stress Relieved or HIPped
Fracture Toughness
P.A. Kobryn and S.L. Semiatin, “Mechanical Properties of Laser-Deposited Ti-6Al-4V”, SFF Symposium Proceedings, Univ. Texas at Austin, 2001, pp. 179-186.
LENS Processed Ti-6Al-4V, Stress Relieved or HIPped
Ceramics AM Processing Weibull Behavior
𝑆 = 𝑒𝑒𝑒 −𝜎𝜎�𝑓
𝑚
Γ1 + 𝑚𝑚
𝑚𝑆𝑐𝑆𝑠
S = Probability of Survival σ = Applied Stress 𝜎�𝑓 = Average Fracture Stress Γ(x) = Gamma Function = ∫ 𝑠𝑥−1𝑒−𝑠𝑑𝑠∞
0 ≅ 0.6 Sc = Effective Surface Area of a Component Ss = Effective Surface Area of the Test Specimen m = Weibull Modulus
Ceramics AM Processing Weibull Behavior
𝑆 = 𝑒𝑒𝑒 −𝜎𝜎�𝑓
𝑚
Γ1 + 𝑚𝑚
𝑚𝑆𝑐𝑆𝑠
1𝑆
= 𝑒𝑒𝑒 +𝜎𝜎�𝑓
𝑚
Γ1 + 𝑚𝑚
𝑚𝑆𝑐𝑆𝑠
𝐿𝐿𝐿𝐿1𝑆
= 𝐿𝐿 +𝜎𝜎�𝑓
𝑚
Γ1 + 𝑚𝑚
𝑚𝑆𝑐𝑆𝑠
𝐿𝐿𝐿𝐿1𝑆
= 𝑚 𝐿𝐿 𝜎 + [ −𝑚 𝐿𝐿 𝜎�𝑓 + 𝐿𝐿 𝐶 ]
Weibull Plot and Modulus
Weibull Plot, Sintered Alumina
Tieshu Huang, Michael S. Mason, Xiyue Zhao, Gregory E. Hilmas, Ming C. Leu, (2009) "Aqueous-based freeze-form extrusion fabrication of alumina components", Rapid Prototyping Journal, Vol. 15 Iss: 2, pp.88 – 95
Al2O3 powder, 0.4 μm Freeform Extruded Freeze-dried Sintered at 1,550°C for 2 h Weibull Modulus = 5
S = 50%
S = 10%
S = 90%
150 MPa 300 MPa
Weibull Plot, Sintered FDM Silicon Nitride
R. Clancy, V. Jamalabad, P. Whalen, P. Bhargava, C. Dai, S. Rangarajan, S. Wu, S. Danforth, N. Langrana, A. Safari, “Fused Deposition of Ceramics: Progress Towards a Robust and Controlled Process for Commercialization”, Proc. SFF Symposium, 1997, Austin TX, pp. 185-94.
Less than 1 micron Si3N4 FDM Binder Burnout and non-disclosed HT sinter
Vintage 1 – Starting Control Vintage 2 – After processing quality improvements to minimize large porosity
Weibull Modulus, LOM Silicon Carbide
Don Klosterman, Richard Chartoff, Nora Osborne, George Graves, “Automated Fabrication of Monolithic and Ceramic Matrix Composites via Laminated Object Manufacturing (LaM)”, Proc SFF Symposium, Austin TX, 1997, pp. 537-550.
Weibull Modulus EFF Alumino-Silicate/Fused Silica
Qingbin Liu, Ming C. Leu, ,Harish Jose, Von L. Richards, “Study of Ceramic Slurries for Investment Casting with Ice Patterns”, Proc SFF Symp, Austin TX, 2004, pp. 602-11.
• Materials will be demanded in a quantity to justify volume production with concomitant reduction in unit cost for the user. Material cost will drop.
• Lower cost will increase usage, engendering greater demand,…
• Several “mini-suppliers” or niche product companies have appeared in the last 5-10 years and seem to be surviving.
Materials Forecast
• Common 3DP materials are generally not patent protected
• Material cost is high for consumers, but new suppliers do not seem to be entering the marketplace
• Perhaps the price will come down as material usage volume increases due to adoption
• My impression is that there is little consumer loyalty to a specific brand of material
Materials Perspectives
Summary of AM Mechanical Behavior
• Mechanical behavior is predictable based on the traditional understanding of microstructure and processing.
• Porosity and inter-layer interfaces have a strong influence on the mechanical behavior.
• Anisotropy is not generally an issue if parts are built with low porosity and good layer interface.
• As processed parts are stronger than conventionally processed material but have lower elongation and poorer dynamic properties.
• Polymers produced using best practice have isotropic strength and anisotropic ductility.
Thank you