Advanced Processing Techniques: Additive, Porous, and Others: Session 1
Program Organizers: Aaron Stebner, Colorado School of Mines

Monday 2:00 PM
July 10, 2017
Room: Gold Coast
Location: Hyatt Regency Chicago

Session Chair: Reginald Hamilton, The Pennsylvania State University

2:00 PM  Invited
Direct Extrusion 3D Printing of NiTi-Nb Shape Memory Alloy Micro-trusses: Shannon Taylor1; Ramille Shah1; David Dunand1; 1Northwestern University
    Shape memory and superelastic NiTi micro-truss structures are attractive for biomedical applications such as actuators and bone replacements because of their unique combination of low density and stiffness and high surface area, biocompatibility, compressive strength, and ductility. Extrusion-based 3D printing (3DP) of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is difficult due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb and NiTi powders are incorporated into the inks. Micro-truss struts, upon annealing, exhibit improved densification, as a result of a low-melting eutectic NiTi-Nb phase which bonds unreacted NiTi powders. This new additive manufacturing method combines extrusion 3DP and simple liquid-phase sintering of the struts to produce NiTi-Nb micro-trusses. The effects of 3DP and sintering parameters on the microstructure and shape recovery properties of the NiTi-Nb micro-trusses are presented.

2:40 PM  
Hydriding-Pulverization-Dehydriding Method of Preparing Shape Memory Alloy Powders: Silvia Briseņo Murguia1; Arielle Clauser1; Heather Dunn1; Wendy Fisher1; Laura Mello1; Yoav Snir2; Raymond Brennan2; Marcus Young1; 1University of North Texas; 2Other
    With growing interest in additive manufacturing, improved methods of producing powders are needed. Shape memory alloys (SMAs), which exhibit unique properties: the shape memory effect and pseudoelasticity, present significant processing challenges due to their compositional sensitivity, where only a 0.1 at.% difference in Ni content in NiTi SMAs can result in a 25 °C drop in transformation temperature. SMA powders can be used for applications such as “smart” sensors and actuators. Powder morphology, i.e. shape, size, and size distribution, and exact composition determine the effectiveness of the application. In this study, a low temperature and low pressure hydriding-pulverization-dehydriding method for preparing well-controlled compositions of SMA powders from wires is presented. The wires and the resulting powders are characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Lastly, a method for producing spiral patterns in SMA wires will be presented.

3:00 PM  
Direct Laser Deposition of Ni-Co-Mn-Sn Magnetocaloric Material: Erica Stevens1; Katerina Kimes1; Jakub Toman1; Anna Wojcik2; Wojciech Maziarz2; Volodymyr Chernenko3; Markus Chmielus1; 1University of Pittsburgh; 2Polish Academy of Science; 3University of Basque Country
    Harnessing the geometrical advantages of additive manufacturing for use in magnetocaloric materials could increase efficiency in magnetic refrigeration and pave the way for novel applications. Through a process involving a phase and magnetic state change, magnetocaloric materials in an adiabatic environment change temperature when a magnetic field is applied. Depending on the balance of entropy effects, there may be a +ΔT or a -ΔT with the applied field; in the case of Ni43Co7Mn39Sn11, a -ΔT has been observed, a function of the martensitic transformation and ferromagnetic austenite. Ni43Co7Mn39Sn11 powder was used in a direct laser deposition additive manufacturing system to fabricate small samples. Two types of samples were observed: properly built and overbuilt. Sample microstructures and properties were characterized using microscopy, VSM, and DSC. Twinning was found to exist within as-built samples, though localized due to microsegregation. To alleviate microsegregation and encourage large-scale twinning, samples were homogenized through heat treatment.

3:15 PM  
Tailored Process and Properties of CuAlMn Shape Memory Foams by Silica-gel Beads Infiltration Method: Hua Li1; Yan Gao1; 1South China University of Technology
     CuAlMn shape-memory foams with spherical pore size of 0.4~2.5mm and porosity of 63%~83% was manufactured by the silica-gel beads infiltration method.The expansion feature of silica-gel beads upon heating was creatively exploited to adjust the sintering bonding between adjacent beads by coordinating the bead density and argon gas pressure, making it feasible to control the foam morphology and porosity. With uniformly distributed thin struts, the typical foam with pore size of 0.7~1mm and porosity of 70% formed an oligocrystalline structure. This oligocystalline structure highly released the grain constraints for martensite movements and accommodations, thus significantly improving the damping, superelasticity and shape-memory effect of the foam material which even overmatched that of the bulk sample. It showed a 25% loss factor of damping at strain amplitude of 1.6%. It also obtained a high superelastic strain of 5.9% and recovered up to 90% despite high shape-memory effect deformation of 10%.

3:30 PM Break