Compliant morphing structures from twisted bulk metallic glass ribbons

In this work, we investigate the use of pre-twisted metallic ribbons as building blocks for shape-changing structures. We manufacture these elements by twisting initially flat ribbons about their (lengthwise) centroidal axis into a helicoidal geometry, then thermoforming them to make this configuration a stress-free reference state. The helicoidal shape allows the ribbon to have preferred bending directions that vary throughout its length. These bending directions serve as compliant joints and enable several deployed and stowed configurations that are unachievable without pre-twist, provided that compaction does not induce material failure. We fabricate these ribbons using a bulk metallic glass (BMG), for its exceptional elasticity and thermoforming attributes. Combining numerical simulations, an analytical model based on shell theory and torsional experiments, we analyze the finite-twisting mechanics of various ribbon geometries. We find that, in ribbons with undulated edges, the twisting deformations can be better localized onto desired regions prior to thermoforming. Finally, we join together multiple ribbons to create deployable systems. Our work proposes a framework for creating fully metallic, yet compliant structures that may find application as elements for space structures and compliant robots

Measured optical constants of Pd_(77.5)Cu_6Si_(16.5) bulk metallic glass

Optical constants of Pd_(77.5)Cu_6Si_(16.5) alloy were determined experimentally using spectroscopic ellipsometry measurements on bulk specimens. Values of the complex refractive index of the glassy metallic alloys are compared to their crystalline counterparts and to pure crystalline Pd. The presence of Cu and Si increase the occurrence of defects in the crystal lattice resulting in reduced refractive index in the crystalline alloy when compared to pure crystalline Pd. Moreover, we show the conduction band energy of each specimen using Tauc’s plot. The obtained complex refractive index across the spectrum (250 – 1500nm) allows for accurate prediction of optical performance within the investigated spectral range providing optimal design for optical devices

3D printing metals like thermoplastics: Fused filament fabrication of metallic glasses

Whereas 3D printing of thermoplastics is highly advanced and can readily create complex geometries, 3D printing of metals is still challenging and limited. The origin of this asymmetry in technological maturity is the continuous softening of thermoplastics with temperature into a readily formable state, which is absent in conventional metals. Unlike conventional metals, bulk metallic glasses (BMGs) demonstrate a supercooled liquid region and continuous softening upon heating, analogous to thermoplastics. Here we demonstrate that, in extension of this analogy, BMGs are also amenable to extrusion-based 3D printing through fused filament fabrication (FFF). When utilizing the BMGs’ supercooled liquid behavior, 3D printing can be realized under similar conditions to those in thermoplastics. Fully dense and amorphous BMG parts are 3D printed in ambient environmental conditions resulting in high-strength metal parts. Due to the similarity between FFF of thermoplastics and BMGs, this method may leverage the technology infrastructure built by the thermoplastic FFF community to rapidly realize and proliferate accessible and practical printing of metals

Developing Processing Parameters and Characterizing Microstructure and Properties of an Additively Manufactured FeCrMoBC Metallic Glass Forming Alloy

Powder bed fusion (PBF) processing parameters are developed for a FeCrMoBC glass‐forming alloy. Although bulk metallic glass parts are successfully fabricated using additive manufacturing, the porosity is too high for imparting good mechanical properties. The processing is tuned to create a fully‐dense, dendrite‐reinforced metal‐matrix composite with low hardness and high indentation fracture toughness. Microstructures and properties of the printed alloy are compared to bulk amorphous samples made through thermal spray additive manufacturing (TSAM). The work shows that printing glass‐forming alloys can result in tunable properties based on the cooling rate, porosity, and composite microstructures

Developing Processing Parameters and Characterizing Microstructure and Properties of an Additively Manufactured FeCrMoBC Metallic Glass Forming Alloy

Powder bed fusion (PBF) processing parameters are developed for a FeCrMoBC glass‐forming alloy. Although bulk metallic glass parts are successfully fabricated using additive manufacturing, the porosity is too high for imparting good mechanical properties. The processing is tuned to create a fully‐dense, dendrite‐reinforced metal‐matrix composite with low hardness and high indentation fracture toughness. Microstructures and properties of the printed alloy are compared to bulk amorphous samples made through thermal spray additive manufacturing (TSAM). The work shows that printing glass‐forming alloys can result in tunable properties based on the cooling rate, porosity, and composite microstructures

Determination of critical cooling rates in metallic glass forming alloy libraries through laser spike annealing

The glass forming ability (GFA) of metallic glasses (MGs) is quantified by the critical cooling rate (R C). Despite its key role in MG research, experimental challenges have limited measured R C to a minute fraction of known glass formers. We present a combinatorial approach to directly measure R C for large compositional ranges. This is realized through the use of compositionally-graded alloy libraries, which were photo-thermally heated by scanning laser spike annealing of an absorbing layer, then melted and cooled at various rates. Coupled with X-ray diffraction mapping, GFA is determined from direct R C measurements. We exemplify this technique for the Au-Cu-Si system, where we identify Au56Cu27Si17 as the alloy with the highest GFA. In general, this method enables measurements of R C over large compositional areas, which is powerful for materials discovery and, when correlating with chemistry and other properties, for a deeper understanding of MG formation