Center for Additive Materials (CAM)

The unique solidification conditions during metal additive manufacturing drastically limit the number of alloys that can be processed today.  This has hindered metal additive manufacturing from reaching its full potential to transform design and fabrication and disrupt multiple industries. HRL has developed a metallurgical approach to drastically expand the alloys amenable to processing with existing additive manufacturing hardware. Our approach is based on manipulating solidification mechanisms via functionalization of feedstock powders with nanoparticle nucleants selected using crystallographic informatics. We have demonstrated the effectiveness of this approach by successfully selective laser melting aluminum alloy Al7075 and Al6061 powders resulting in crack-free, equiaxed, fine-grained microstructure and yield strength comparable to wrought material.

Selected Publications:

• J.H. Martin et al. “3D Printing of High Strength Aluminum Alloys” Nature 549, 365-369 (2017)
• “Thin-walled high temperature alloy structures fabricated from additively manufactured polymer templates” Materials and Design 120 (2017)

The extremely high melting point of many ceramics adds challenges to additive manufacturing as compared with metals and polymers. Because ceramics cannot be cast or machined easily, 3D printing enables a big leap in geometrical flexibility. HRL has developed preceramic resin systems that can be cured with ultraviolet light in commercially available stereolithography 3D printers or through a patterned mask. Polymer structures with complex shape can be formed and then pyrolyzed to a ceramic with uniform shrinkage and virtually no porosity. Silicon oxycarbide structures fabricated with this approach exhibit high strength and withstand temperatures up to 1700C.

Selected Publications:

• Z.C. Eckel et al. “Additive Manufacturing of Polymer-derived Ceramics” Science 351 (2016)
• J.M Hundley et al. “Geometric Characterization of Additively Manufactured Polymer Derived Ceramics” Additive Manufacturing 18, 95-102 (2017)

HRL has developed a platform technology to rapidly and scalably manufacture architected lattice materials based on polymers, metals, and ceramics suitable for a variety of applications. Architected materials with periodic cellular structure exhibit unprecedented properties that cannot be achieved with conventional materials. A self-propagating polymer waveguide process invented at HRL is used to additively manufacture architected polymer lattice structures 100-1000x faster than conventional 3D printing approaches such as stereolithography. HRL’s process is inherently scalable to large areas in addition to offering high throughput. HRL has developed photo polymer formulations for a broad range of applications including:

1. High strength and stiffness formulations for low-density sandwich panel cores
2. Viscoelastic formulations for padding and impact protection
3. Bio compatible formulations for biomedical and cellular scaffoldings
4. Dissolvable formulations for sacrificial templates essential for hollow microlattices
5. Preceramic formulations for polymer derived ceramic lattices and honeycombs

Selected Publications:

• A.L. Corrion et al. “Architected Microlattice Materials by Self-Propagating Waveguide Processing” TechConnect Briefs 2017, Advanced Manufacturing Innovation, Chapter 10 p.359 (2017)
• A.J. Jacobsen et al. “Micro-scale Truss Structures formed from Self-Propagating Photopolymer Waveguides” Advanced Materials 19 (2007)
• J. A. Kolodziejska et al. “Enabling ultra-thin lightweight structures: Microsandwich structures with microlattice cores” APL Materials 3 (2015)

Selected Publications:

• C.S. Roper et al. “Scalable 3D Bicontinuous Fluid Networks: Polymer Heat Exchangers Toward Artificial Organs” Advanced Materials 27 (2015)
• K. J. Maloney et al. “Multifunctional heat exchangers derived from three-dimensional micro-lattice structures” International Journal of Heat and Mass Transfer 55 (2012)

Sandwich structures are unique enablers of lightweight design, as they offer an exceptional combination of low density and high bending rigidity. Lightweight sandwich structures are widespread in aerospace applications (e.g. winglets, flaps, rudders, rotor blades) but are also used in many other industries. State-of-the-art sandwich panels are created by attaching thin, stiff composite or aluminum alloy facesheets to thick, lightweight honeycomb or foam cores. HRL has developed advanced core materials based on hollow metallic truss structures that offer improved compressive and shear strengths versus honeycombs. Hollow truss structures are preferably fabricated by coating a polymer template of the truss structure, which is subsequently removed. This approach converts a 2D thin film or coating into a 3D cellular material, thereby redefining the applications of a range of thin film/coating materials.

Selected Publications:

• T.A. Schaedler et al. “Ultralight metallic microlattices” Science 334 (2011)
• E.C. Clough et al. “Mechanical performance of hollow tetrahedral truss cores “ Int. J. of Solids and Structures 91 (2016)
• T.A. Schaedler et al. “Nanocrystalline Aluminum Truss Cores for Lightweight Sandwich Structures“ JOM (2017)