ICMCTF2014 Session G2: Additive Manufacturing

The deposition of thick films of nano-crystalline barium hexaferrite (BaFe₁₂O₁₉) (BaM) and Yttrium Iron Garnet

(Y­₃Fe₅O₁₂) (YIG) for application in high power passive rf electronic components and ZnS/Diamond composites for IR transparent protective coatings by the aerosol deposition method (ADM) is presented.

The advantages of the ADM include the ability to form dense ceramic films up to hundreds of microns thick at room temperature and at a high deposition rate on a variety of substrates. Deposition is achieved by creating a pressure gradient that accelerates particles in an aerosol to a velocity up to 400 m/s. Upon impact with the target the particles fracture and embed [1]. Continual deposition forms the thick compacted film.

BaM and YIG films are characterized for their microstructural, morphological and magnetic properties by scanning electron microscopy, profilometry, and vibrating sample magnetometry, respectively. For BaM, magnetic saturation of the film is 80 % of the bulk value of 68 emu/g, but a significant increase in coercive field suggests significant particle fracturing. All samples have a squareness value near ½ indicating randomized orientation of the magnetization. YIG and BaM film stripes of 10 mm in length deposited for 5 minutes resulted in an approximately 200 micron thick film or a deposition rate of 40 microns/min.

In contrast to this high deposition rate, deposition from a mixture of ZnS/diamond onto sapphire results in linear trend from sputter erosion of the substrate at 100% diamond to formation of a film with increasing fractions of ZnS. The crossover from abrasion to film formation occurs at about 50 – 60 % ZnS and a mixture of 80% ZnS and diamond forms a well-adhered film of about 0.6 microns thickness at 0.12 microns/min. Fourier Transform Infrared Spectroscopy transmission measurements of these films indicate good transparency in the far infrared making the system a promising candidate for infrared window protective coatings.

[1] J. Akedo, J. Thermal Spray Technol.17 (2), 181 (2008).

Nature armors, such as abalone nacre and crustacean exoskeleton are hierarchically-structured multilayer composites of inorganic minerals and organic proteins which possess excellent mechanical properties and superior toughness. The organic and inorganic interfaces resist or deflect crack propagation and prevent the composites from catastrophic failure. Ceramic-based protective coatings with high hardness, wear and corrosion resistance have been extensively investigated and applied widely in the area of constructional instruments. However, their brittle mechanical behavior and poor toughness limit the commercial applications. Mimicking the exocuticle and endocuticle in crab exoskeletons, a functional graded composite of harder outer layers and tougher inner layers was designed and synthesized, resulting in a hybrid coating with both good abrasion resistance and high impact toughness. By combining a hybrid coating system of reactive RF sputtering and pulsed laser deposition, multilayer coatings with various thickness, organic/inorganic ratio and surface roughness were synthesized. The fatigue behavior with different thickness ratio and hardness of outer and inner layer has been discussed. Microstructural features were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). Nano-indentation and nano-scratch tests were conducted to evaluate the mechanical performance of multilayer films. The fracture toughness was determined by an energy-based method to eliminate the influence of substrates. The impact resistance of protective coatings can be measured by thin film impact test, which applies dynamic loads on specimens. The graded microstructure can significantly enhance the damage tolerance of periodic impact. Toughening mechanisms at the organic/inorganic interfaces were elucidated, which may lead to optimal designs for multifunctional protective coatings. This research is funded by the National Science Council, Taiwan (NSC-100-2218-E-007-016-MY3).

Since the commercial introduction of Additive Manufacturing (AM) technologies more than two decades ago, considerable advancements in processing speed, accuracy, resolution and capacity have been achieved and the available AM materials have expanded considerably, enabling customized end-use products to be directly manufactured for a range of applications. Many AM technologies have been released that use different processes for fabricating the individual layers from a variety of liquid, solid, and powder-based materials ranging from photoreactive polymers to metals. In 2000, the University of Texas at El Paso identified AM as an emerging technology and invested strategically in establishing the W.M. Keck Center for 3D Innovation (Keck Center). The Keck Center has grown to occupy over 13,000 sq. feet (1200 sq. meters) with nearly 50 commercial and experimental AM machines. One particular focus of Keck Center research is on developing the methods and systems required to have spatial control over material placement and structure creation, leading to, for example, the realization of complex 3D devices that integrate electronics and thus intelligence within mechanical structures as well as 3D spatially complex bioactive, implantable, tissue engineered constructs. There are myriad issues associated with combining multiple materials to create functional products – from the deposition and processing of different materials to the combined performance of the materials in the resulting product. These efforts have resulted in demonstrations of multi-material, multi-functional products that were fabricated using multiple technologies operating in integrated manufacturing environments at different levels of automation, and although these product demonstrations exemplify the potential for AM to transform the human condition, significant progress is still required to make this future a reality.