Search

Zirconium diboride (ZrB2) and silicon carbide (SiC) composites have long been of interest since it was observed that ZrB2 improved the thermal shock resistance of SiC. However, processing of these materials can be difficult due to high and different sintering temperatures and differences in the thermodynamic stability of each material. ZrB2–SiC composites have been processed in a variety of ways including hot-pressing, spark-plasma sintering, reactive melt infiltration, pack cementation, chemical vapor deposition, chemical vapor infiltration, stereolithography, direct ink writing, selective laser sintering, electron beam melting, and binder jet additive manufacturing. Each manufacturing method has its own pros and cons. This review serves to summarize more than 60 years of research and provide a coherent resource for the variety of methods and advancements in development of ZrB2–SiC composites.

Reaction-bonded SiC-B4C-Si ceramic composites were binder jet 3D-printed and subsequently pressureless-melt-infiltrated with molten Si. The addition of B4C aided the Si infiltration to produce a highly dense composite. The microstructures and phases of these composites were examined. The measured hardness values of each constituent with Vickers and nanoindentation matched the bulk values, and the macro-hardness values with Knoop and spherical indentation represented the bulk, composite hardness values of all three phases together, which was close to a rule of mixtures value. For particulate-based composites, this is a significant finding. The interfacial bonds of SiC and Si were imaged using scanning transmission electron microscopy to view intimacy, whereas the crack propagation was examined with carefully placed indents. This work demonstrated that pressureless melt infiltration with a reactive particle provides a method to shape non-wetting reaction-bonded ceramic composites with limited shrinkage and high density and provides insights into the mechanical behavior with numerous indentation techniques.

Abstract The COVID-19 pandemic triggered a surge in demand for N95 or equivalent respirators that the global supply chain was unable to satisfy. This shortage in critical equipment has inspired research that addresses the immediate problems and has accelerated the development of the next-generation filtration media and respirators. This article provides a brief review of the most recent work with regard to face respirators and filtration media. We discuss filtration efficiency of the widely utilized cloth masks. Next, the sterilization of and reuse of existing N95 respirators to extend the existing stockpile is discussed. To expand near-term supplies, optimization of current manufacturing methods, such as melt-blown processes and electrospinning, has been explored. Future manufacturing methods have been investigated to address long-term supply shortages. Novel materials with antiviral and sterilizable properties with the ability for multiple reuses have been developed and will contribute to the development of the next generation of longer lasting multi-use N95 respirators. Finally, additively manufactured respirators are reviewed, which enable a rapidly deployable source of reusable respirators that can use any filtration fabric. Graphic abstract

TiNxOy (TiNO) thin films with superior electrochemical properties have been synthesized in situ using a pulsed laser deposition method and a varied oxygen partial pressure from 5 to 25 mTorr. The e...

Among engineering materials, ceramics are indispensable in energy applications such as batteries, capacitors, solar cells, smart glass, fuel cells and electrolyzers, nuclear power plants, thermoelectrics, thermoionics, carbon capture and storage, control of harmful emission from combustion engines, piezoelectrics, turbines and heat exchangers, among others. Advances in additive manufacturing (AM) offer new opportunities to fabricate these devices in geometries unachievable previously and may provide higher efficiencies and performance, all at lower costs. This article reviews the state of the art in ceramic materials for various energy applications. The focus of the review is on material selections, processing, and opportunities for AM technologies in energy related ceramic materials manufacturing. The aim of the article is to provide a roadmap for stakeholders such as industry, academia and funding agencies on research and development in additive manufacturing of ceramic materials toward more efficient, cost-effective, and reliable energy systems.

Digital light processing (DLP) stereolithography was used to prepare layers and samples for dimensional calibration from commercial alumina slurries. Single-layer squares were studied to understand the penetration depth and curing behavior, and samples with varying curing time and intensity were printed and sintered. Fourier-transform infrared spectroscopy (FTIR) of the squares was performed to measure the relative amount of curing based on the change of the bond transparency of the polymer during various printing conditions. X-ray computed tomography (XCT) scans were performed after printing of squares and parts as well as after sintering parts. The morphologies and structures of the squares and parts were studied after printing and after sintering. The dimensions were measured, and the differences before and after sintering are reported for the various printing conditions. The study shows how FTIR can monitor curing of printed parts, and dimensional accuracy of 0.20 mm can be achieved.

An additive manufacturing process for fabricating ceramic matrix composites has been developed based on the C/C-SiC system. Automated fiber placement of the continuous carbon fibers in a polyether ether ketone matrix was performed to consolidate the carbon fibers into a printed preform. Pyrolysis was performed to convert the polymer matrix to porous carbon, and then Si was introduced by reactive melt infiltration to convert a portion of the carbon matrix to silicon carbide. The densities and microstructures were characterized after each step during the processing, and the mechanical properties were measured. The C/C-SiC composites exhibited a porosity of 10–20%, characteristic flexural strength of 234.91 MPa, and Weibull modulus of 3.21. The composites displayed toughness via a significant displacement to failure.

In-situ formation of ZrB2–SiC composites was investigated by reactive spark plasma sintering of precursor powders according to the reaction B4C + 2ZrC + 3Si → 3SiC + 2ZrB2. The reaction and process presented here involves a diffusion reaction between B4C and ZrC which facilitates the formation of ZrB2, while liquid phase sintering of silicon facilitates atomic diffusion and combines with free C from the B4C and ZrC reaction to form SiC within minutes of heating and there were some residual unreacted precursor materials. An interpenetrating matrix of ZrB2–SiC was formed that shows increased fracture toughness (6.03 ± 0.45 MPa m1/2) despite relatively low density (95 %).

Traditionally, WC-based composites use Co as the metal binder phase to consolidate using liquid-phase sintering with a small percentage of Co, but a potentially lower cost binder phase can be made with a different approach when using large amount of metal binder phase. FeNi as a metal binder material is much cheaper than Co. WC can be liquid-phase sintered and melt infiltrated with FeNi, but by making FeNi in situ, costs lower even further. Composites of WC-(Fe-Ni) were made by first pressing a mixture of WC and Fe powders and subsequently melt infiltrating Ni in an amount corresponding to less volume than the porosity of the preform to ensure high WC content. The research objective was to make highly dense composites via melt infiltration with a low-cost metal binder phase in situ. This method has the potential to make fully dense composites, rather than hardmetals, with suitable properties at lower costs. The density and hardness are 97.4%TD and 6.72 GPa, respectively.

Additive manufacturing (AM) of tungsten carbide-cobalt (WC-Co) is explored starting with WC preforms shaped with binder jet additive manufacturing (BJAM) followed by melt infiltration of Co. The research objective is to demonstrate the ability to net-shape WC-Co composites through BJAM of a WC preform followed by backfilling with cobalt via pressureless infiltration. This method also has the potential to minimize shrinkage and grain growth compared to other AM techniques. The effects of sintering, Co content, and infiltration time on the net shaping and properties of processed composites are shown. The best shaped material had an average grain size of 5.1 μm, 32 vol.% Co, density of 98.54% theoretical, fracture toughness of 23.2 MPa m1/2, and hardness of 9.0 GPa. Data presented illustrates that the proposed approach results in favorable ceramic-metal (cermet) properties and is viable for fabricating cermets of other material combinations. Successful AM of cermets provides complex geometries, high throughout, and low costs.

Lightweight ceramic–metal (cermet) composites combine stiffness and hardness with fracture toughness and ductility. TiC and Al are ideal pairs among lightweight cermet composites because of their relatively high strength-to-weight ratios, but these materials are hard to process in solid state or with Al melt infiltration without making an aluminum carbide phase, which is detrimental to mechanical properties. In this research, Fe is added to a TiC powder preform to reduce the activity of Al with TiC during Al melt infiltration and to aid in pressing TiC preforms, making a lightweight TiC–(Fe–Al) composite while avoiding other, unwanted phases. The composites are made by first pressing TiC powder mixed with Fe followed by Al melt infiltration; the result is a composite with high TiC content in a two-phase matrix, both of which are Fe–Al-based. The composite has low density, low porosity, high hardness, no detectable Al4C3 phase with X-ray diffraction and retains shape well during infiltration.

This article focuses on binder-jetting technologies in additive manufacturing (AM) that produce metal artifacts either directly or indirectly. The intent is to focus on the most strategic and widespread uses of the binder jetting technology and review some of the challenges and opportunities for that technology. The discussion includes a historical overview and covers the major steps involved and the advantages of using the binder jetting process. The major steps of the process covered include printing, curing, de-powdering, and sintering.

This work investigates the feasibility of a binderless, extrusion-based additive manufacturing approach to fabricate alumina ( A l 2 O 3 ) parts from nanopowder. Traditional manufacture of ceramics with subtractive methods is limited due to their inherent hardness and brittleness, inevitably leading to ceramic parts with less-than-optimal geometries for the specific application. With an additive manufacturing approach, ceramic parts with complex 3D geometries, including overhangs or hollow enclosures, become possible. These complex ceramic parts are highly valuable in heat exchanger, condenser, biomedical implant, chemical reactant vessel, and electrical isolation applications. This research employed direct coagulation of alumina nanopowder slurries with the polyvalent salt tri-ammonium citrate providing the solidification mechanism in an extrusion-based printing process. The viscosity of the slurries was adjusted from ∼35 Pa-s to ∼1000 Pa-s by adjusting pH from ∼9 to ∼4, resulting in a paste that is suitable for extrusion, which retains near-net geometry. It was shown that the direct coagulation approach can be used to create a suspension with tuneable flow characteristics and coagulation rate, and a mechanism describing the process was proposed. The direct coagulation printing (DCP) method is described in detail, including how slurry is extruded, solidified, and printed in complex geometries, and sintered to full density. Parts were printed with a sintered resolution of 450 μm and green densities as high as 65%. After sintering at 1550 °C for up to 2 h, parts were shown to be fully dense (>97%) with an average grain size of ∼2 μm. Mechanical properties were characterized with a comparison to different materials and methods from literature, showing hardness and flexural modulus up to ∼1800 HV and 400 GPa, respectively.

Direct energy conversion using thermoelectric generators (TEGs) is a research area of growing interest because of its potential for increasing energy efficiency. Bulk thermoelectric modules are used widely in industry as Peltier cooling devices. Currently, only bismuth telluride modules are commercially available for power generation. Significant efforts have been put into exploring promising materials and techniques to improve the figure of merit (zT) at laboratory scale (5–20 g). A variety of techniques have been investigated to improve the output and useful temperature range for common industrial TEGs made from bulk polycrystalline materials including segmentation, geometric pinning, and property gradients. However, the improvement in zT at device level (500–1000 g and up) is exceptionally limited. In addition, the thermal degradation of TEGs occurs when cracks form due to thermal stresses that arise from transient heat sources, which consequently lead to a decreased lifetime. Functionally graded material (FGM) thermoelectrics in bulk and polycrystalline form have been developed to mitigate some of these issues by improving the temperature bandwidth, current output range, and lifetime. The present work provides a review of functionally graded TEGs, including their manufacturing, usage and current techniques for improving their performance. This article also provides a pathway to additional research and approaches for improving the efficiency and temperature range, as well as reducing the property degradation of bulk polycrystalline TEGs.

A functionally graded material (FGM) in terms of grain size gradation is fabricated using zinc oxide (ZnO) with spark plasma sintering and an additive manufacturing technique by diffusion bonding layers of material sintered at different temperatures to achieve a thermoelectric generator (TEG) material that can dissipate heat well and retain high energy conversion efficiency for longer-lasting and comparably efficient TEGs. This FGM is compared to a previously made FGM with continuous grain size gradation. Uniform and graded grain size conditions are modeled for thermoelectric output by using thermoelectric properties of the uniform grain size as well as the varying properties seen in the FGMs. The actual thermoelectric output of the samples is measured and compared to the simulations. The grain size has a large effect on the efficiency and efficiency range. The samples are thermally cycled with a fast heating rate to test the thermal stress robustness and degradation, and the resistance at the highest temperature is measured to indicate degradation from thermal stress. The measured efficiency after cycling shows that the FGMs survive longer lifetime than that with uniform small grains.

As a non-beam-based additive manufacturing (AM) method, binder jet 3D printing (BJ3DP) is a process in which a liquid binder is jetted on layers of powdered materials, selectively joined, and then followed by densification process. Among AM technologies, binder jetting holds distinctive promise because of the possibility of rapid production of complex structures to achieve isotropic properties in the 3D printed samples. By taking advantage of traditional powder metallurgy, BJ3DP machines can produce prototypes in which material properties and surface finish are similar to those attained with traditional powder metallurgy. Various powdered materials have been 3D printed, but a typical challenge during BJ3DP is developing printing and post-processing methods that maximize part performance. Therefore, a detailed review of the physical processes during 3D printing and the fundamental science of densification after sintering and post–heat treatment steps are provided to understand the microstructural evolution and properties of binder jetted parts. Furthermore, to determine the effects of the binder jetting process on metallurgical properties, the role of powder characteristics (e.g., morphology, mean size, distribution), printing process parameters (e.g., layer thickness, print orientation, binder saturation, print speed, drying time), sintering (e.g., temperature, holding time), and post-processing are discussed. With the development of AM technologies and the need for post-processing in 3D printed parts, understanding the microstructural evolution during densification is necessary and here, processing steps are explained. Finally, opportunities for future advancement are addressed.

W-ZrC composites were successfully prepared by reactive melt infiltration (RMI) of stoichiometric and excess amounts of Zr2Cu into sintered and un-sintered WC preforms made from binder jet 3D printing. The focus of this work was to study the conversion of reactant powders and liquid infiltrant with varying preform density and infiltrant amount by controlling the processing time to reach high conversion yield while understanding the phase composition, microstructure, and hardness. To investigate the effect of time, the reactive melt infiltration was conducted at 1400 °C for 2, 4 and 8 h in a furnace with 96% Ar - 4% H2 gas atmosphere. The increase in reaction time from 2 to 8 h increased the W and W2C phase contents and decreased the ZrC phase content when using sintered WC preforms. Samples prepared from un-sintered WC preforms exhibited improved reactive melt infiltration compared to sintered samples, and there was no detectable W2C phase and nearly full consumption of WC. Similar to sintered WC samples, the content of W and ZrC phases increased with the increase in time from 2 to 8 h. The interfaces and phases at reaction interfaces were investigated using electron diffraction analysis and S/TEM-EDS to understand material stability; the phases were identified and consistent with XRD analysis. Additionally, there was no Cu present at the interfaces. Increasing the amount of infiltrant led to better reactive melt infiltration. In general, the hardness increased with reaction time and the highest Vickers hardness was found in the W-ZrC sample formed from sintered WC reacted with excess Zr2Cu. This research addresses the critical comparison of sintering and RMI time and shows that by using un-sintered samples for 8 h we are able to achieve W-ZrC composites with fewer undesired phases.

High-density WC-FeNi ceramic-metal (cermet) composites were fabricated using liquid-phase spark plasma sintering/field-assisted sintering technology (SPS/FAST) with in-situ formation of metal binder phase. The precursor materials were micron-sized powders of WC, Fe, Ni, and C. A low melting point from a eutectic reaction of the powders enabled the in-situ formation of FeNi alloy and facilitates liquid-phase sintering of the WC. The carbon powder was added to stabilize the formation of the binder phase. Electron backscatter diffraction (EBSD) was performed to measure grain size and orientation. The composite exhibited a 99% theoretical density and a microstructure consisting of rounded and contiguous WC grains. The average grain size is 10.5 μm. The composite has a maximum hardness of 16.1 GPa. This research provides a fast and cost-effective approach to fabricate hard metals.

WC-Co was made via binder jet additive manufacturing of tungsten carbide followed by melt infiltration with a Co-WC infiltrant. The goal of the study was to achieve fully densified parts in near-net shape with minimal shrinkage while keeping the Co content low. The exact amount of infiltrant was determined in order to fully densify with minimum shrinkage based on the actual volume taken up by WC powder in the preform based on theoretical density, the bounding volume of prints after shrinkage, and the volume from the infiltrant. The eutectic nature of the infiltrant enabled melting at much lower temperature compared to the melting temperature of pure Co. The density, microstructure, grain size, hardness, and fracture toughness were characterized. The shrinkage and net shaping were assessed with light scans. A detailed look at the fracture mechanics was assessed. This approach achieved highly dense WC-Co parts in net-shape with Co vol% of near 29 (Co wt% ~19), density of 96.2% theoretical, hardness of 8.34 GPa, grain size of 7.7 μm, magnetic saturation of 0.5 T, room temperature thermal conductivity of 125 W/mK, and fracture toughness of 24.7 MPa·m1/2.

High silicon (Si) electrical steel has the potential for efficient use in applications such as electrical motors and generators with cost-effective in processing, but it is difficult to manufacture. Increasing the Si content beyond 3 wt.% improves magnetic and electrical properties, with 6.5 wt.% being achievable. The main goal of this research is to design, develop, and implement a scalable additive manufacturing process to fabricate Fe with 6.5 wt.% Si (Fe–6Si) steel with high magnetic permeability, high electrical resistivity, low coercivity, and low residual induction that other methods cannot achieve because of manufacturing limitations. Binder jet additive manufacturing was used to deposit near net shape components that were subsequently sintered via solid-state sintering to achieve near full densification. Here, it is shown that the use of solid-state sintering mitigates cracking since no rapid solidification occurs unlike fusion-based additive technologies. The Fe–6Si samples demonstrated an ultimate tensile strength of 434 MPa, electrical resistivity of 98 μΩ cm, and saturation magnetization of 1.83 T with low coercivity and high permeability. The results strongly supports to replace the only available 0.1 mm thick chemical vapor deposition (CVD) produced Si steel using the cost effective AM method with good mechanical and magnetic properties for motor applications., Electromagnetism, Soft magnetic alloy, Fe–6Si, Binder jet additive manufacturing, DC and AC magnetic properties, Stators

Titanium carbide-nickel aluminide (TiC-Ni x Al y ) intermetallic matrix composite materials were fabricated with additive manufacturing and pressureless melt infiltration for applications intended for high-wear and corrosive environments while maintaining low density. Here, two compositions of nickel aluminide are infiltrated into porous, printed TiC preforms. Net shaping of a nickel-rich infiltrant is less compared to the net shaping of the aluminum-rich infiltrant due to dissolution of TiC in the molten infiltrant. The microstructures and porosity of the two infiltrants with TiC are examined after processing. The explanation of shape retention from infiltration is explained, and the excellent shape retention in an Al-rich infiltrant system is thought to be from peritectic behavior and a metered infiltration of different phases during cooling and solidification without significant dissolution. The metered infiltration contributed to some porosity, microcracking, and segregated Ni x Al y phases. This work demonstrates that TiC can be shaped and infiltrated with intermetallics to provide a method of making composites with limited shrinkage and controlled geometry.

Complex collimator geometries are desired for custom neutron scattering applications. Boron carbide (B4C) is a suitable candidate collimator material because its high boron content results in a large neutron-absorbing cross section and it can be safely processed with powders and subsequent melt infiltrations. High-density collimator geometries of boron carbide-aluminum metal matrix composites were fabricated using binder jet additive manufacturing followed by pressureless melt infiltration with Al alloys. Infiltration of three different Al alloys was demonstrated and the effects of processing time on one alloy were analyzed. During processing, additional reactant phases were produced, and the resulting microstructure was analyzed. Collimator samples produced had high densities and hardness as well as favorable neutron scattering results. Keywords: Neutron collimation, B4C-Al composite, Binder jet additive manufacturing, Pressureless melt infiltration

Additive manufacturing (AM) of complex tungsten carbide-cobalt (WC-Co) parts was achieved using binder jet additive manufacturing (BJAM) of WC powders followed by Co infiltration. The intent of the study is to explore the shape retention, infiltration height, and properties of parts made with this method. Using BJAM with infiltration of the metal phase can limit shrinkage and grain growth in ceramic-metal (cermet) composites compared to other additive manufacturing (AM) methods. Knowledge of previous infiltration studies was used to help process parts to imitate production of parts. The properties such as density, microstructure, grain size, and hardness of the parts are characterized along the infiltration height. Fracture toughness is measured where applicable. This approach has the potential to achieve highly dense WC-Co parts that are net-shaped with some ternary phase and z-direction distortion.

Functionally graded material (FGM) in terms of grain size gradation is fabricated from ZnO with a combination of modified Spark Plasma Sintering (SPS) graphite tooling, water sintering enhancements through transient liquid phase surface transport, and strategic SPS mechanical loading. The grain size gradation of the ZnO FGM spans from 180 nm grains to 1.2 micrometers in a fully dense material. This is the first semiconductor or ceramic to be graded microstructurally to this extent. Predictions of the microstructure with a Master Sintering Curve (MSC) approach were done with a series of isothermal experiments on two different FGM conditions revealing a slight offset due to a constrained mechanism. The mechanical properties were tested with Vickers micro hardness across the sample, showing a gradient in hardness from 2.6 GPa to 4.2 GPa. In addition, the thermoelectric properties of the FGM were measured and show a zT of 2 × 10−5 at 100 °C compared to uniform small- and large-grained samples of 1 × 10−6. This is an order of magnitude difference making a new path for improvements of bulk thermoelectric material.

Molybdenum oxide (MoOx) and molybdenum oxynitride (MoON) thin film back contacts were formed by a unique ion-beam sputtering and ion-beam-assisted deposition process onto CdTe solar cells and compared to back contacts made using carbon–nickel (C/Ni) paint. Glancing-incidence x-ray diffraction and x-ray photoelectron spectroscopy measurements show that partially crystalline MoOx films are created with a mixture of Mo, MoO2, and MoO3 components. Lower crystallinity content is observed in the MoON films, with an additional component of molybdenum nitride present. Three different film thicknesses of MoOx and MoON were investigated that were capped in situ in Ni. Small area devices were delineated and characterized using current–voltage (J-V), capacitance–frequency, capacitance–voltage, electroluminescence, and light beam-induced current techniques. In addition, J-V data measured as a function of temperature (JVT) were used to estimate back barrier heights for each thickness of MoOx and MoON and for the C/Ni paint. Characterization prior to stressing indicated the devices were similar in performance. Characterization after stress testing indicated little change to cells with 120 and 180-nm thick MoOx and MoON films. However, moderate-to-large cell degradation was observed for 60-nm thick MoOx and MoON films and for C/Ni painted back contacts.