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Abstract Complex alumina parts were printed using vat photopolymerization (VPP), which is a stereolithography‐based additive manufacturing (AM) technique used to shape ceramic preforms, or green parts. The critical flaw size was determined using classical fracture mechanics techniques. The strength and fracture toughness were measured and compared to flaws detected in x‐ray computed tomography (XCT or CT) distributions as well as the fracture surfaces. The strength was lower compared traditionally made alumina, and that is due to layering effects, slurry defects, and printing defects. The critical flaw size from fracture mechanics was 206 µm. XCT has high enough resolution to detect the critical flaw size and much smaller features, where the average flaw size observed in CT scans was around 80–100 µm. The fracture surfaces indicate that flaws causing failure are larger than that of the critical flaw size (∼300 µm), but fracture surfaces do not show definitive features compared to traditionally made ceramics. Since XCT can observe flaws smaller than the critical flaw size, this method can be used as a screening technique.

Abstract Many energy systems demand heat transfer at high temperatures to keep up with high demand for power, so high‐temperature material that can perform and last under these harsh conditions is needed for heat exchangers. The engineering requirements for these high‐temperature heat exchanger material call for high thermal conductivity, high resistance to fracture, high resistance to creep deformation, environmental stability in environments associated with the application, and high modulus of elasticity while maintaining low cost to make and maintain. Naturally, ceramics are a good solution for this endeavor. In the past, high‐temperature heat exchangers made from ceramics have been used. We provide examples of ceramics in relevant heat exchange applications and provide motivation where additive manufacturing (AM) can improve efficiency. AM for the relevant material is under development, and we provide insight on the AM of ceramic materials and examples of AM heat exchangers keeping cost in mind. The motivation of the review paper is to provide a framework for material and manufacturing selection for high‐temperature heat exchangers for AM to keep up with the demand for better efficiency, better material, better manufacturing, and cost moving forward with AM technology in high‐temperature ceramic heat exchangers.

W–ZrC composites were successfully fabricated by reacting amounts of Zr2Cu alloy with powder mixtures of varying composition including stoichiometric WC, WC with additional/W (WC/W), and WC with additional/C (WC/C). The use of WC/C powders to reactively form W–ZrC composites with increased ZrC phase content is a new approach that shows potential for ultra-high temperature applications where higher ZrC content, relative to W, is preferred such as land and aeroengines, aerospace thermal protection, and nuclear. The focus of this work was to stabilize diffusion between W and ZrC during formation, limit interfacial phases, and increase the ZrC content. This was done by varying reactant powder compositions while understanding the final phase composition and microstructure. The composites were prepared by heating the powder mixtures to 1400 °C for 8 h in a furnace with 96% Ar - 4% H2 gas atmosphere. The W–ZrC sample prepared using WC/C powders gave the W–ZrC composite with the highest ZrC phase compared to W and showed promise for phase stabilization. Additionally, there was no W2C, or residual WC identified in the final composite indicating complete conversion from WC to ZrC when adding additional carbon to the WC powder. WC/C sample had the highest hardness due to the increased ZrC phase content. This research addresses the critical comparison of carbon addition on the W–ZrC composites and produced composite with high ZrC content, limited interfacial phases and interlocking microstructure.

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.

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 %).

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.

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