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