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The main goal of this work was to obtain dense Al2O3–Y3Al5O12 ceramic composites by reactive sintering of three-dimensional samples, built by direct ink writing from a paste containing a mixture of Al2O3 and Y2O3 powders. To obtain a ceramic ink with proper rheological properties for extrusion-based printing, highly pure Al2O3 and Y2O3 powders in a percentage–weight ratio of 64:36 was mixed with 0.2 wt% MgO in a total solid loading of 42 vol% in aqueous media, adding carboxymethyl cellulose and polyethyleneimine solution as additives. The dried printed samples were sintered at final temperatures in the range of 1550 °C and 1650 °C; thus, relative densities of 83.7 ± 0.8%, 95.4 ± 0.4%, and 96.5 ± 0.5% were obtained for 1550 °C, 1600 °C, and 1650 °C, respectively. Rietveld refinement performed on the X-ray diffraction patterns indicated the presence of Al2O3 (42 to 47%) and Y3Al15O12 (58 to 61%) as crystalline phases, while micrographs showed the presence of equiaxial micrometric grains with average sizes of 1.8 ± 0.6 μm, for both phases and all sintering conditions. Samples sintered at 1600 °C and 1650 °C presented similar average Vickers hardness values of 14.2 ± 0.27 GPa and 14.5 ± 0.25 GPa, respectively. A slight increase in fracture toughness as sintering temperature increases was also stated, consistent with the densification.

Significant advances have been made in recent years in the materials development of liquid-based 4D printing. Nevertheless, employing additive materials such as nanoparticles for enhancing printability and shape memory characteristics is still challenging. Herein, we provide an overview of recent developments in liquid-based 4D printing and highlights of novel 4D-printable polymeric resins and their nanocomposite components. Recent advances in additive manufacturing technologies that utilise liquid resins, such as stereolithography, digital light processing, material jetting and direct ink writing, are considered in this review. The effects of nanoparticle inclusion within liquid-based resins on the shape memory and mechanical characteristics of 3D-printed nanocomposite components are comprehensively discussed. Employing various filler-modified mixture resins, such as nanosilica, nanoclay and nanographene, as well as fibrous materials to support various properties of 3D printing components is considered. Overall, this review paper provides an outline of liquid-based 4D-printed nanocomposites in terms of cutting-edge research, including shape memory and mechanical properties.

Activated carbon (AC) and multiwalled carbon nanotubes (MWCNTs) have been extensively investigated in recent decades as electrical double-layer capacitor (EDLC) electrode materials for supercapacitors, owing to their superior capacitive properties and cycling stability performance. However, in the modern electronics industry, ternary electrode materials have been designed to develop high-performance and efficient energy storage devices. EDLC-based ternary materials are of great importance, where all the present components participate both individually and as a multicomponent electrode system to promote high-electrochemical performance electrode materials. In this study, we have incorporated an optimized content of boron nitride nanotube (BNNT) powder into a binary material composed of AC and MWCNTs to enhance their electrochemical performance using a pneumatic printer. The printed MWCNTs/AC/BNNTs ternary composite electrode material has shown a maximum specific capacitance of 262 F g−1 at a minimum current density of 1 A g−1, with a capacitance retention of 49.61% at a maximum current density of 10 A g−1. These results demonstrate that the printable MWCNTs/AC/BNNTs ternary composite electrode material is a potential candidate for the development of high-performance supercapacitors.