Nanocrystalline 3 mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) ceramic powder containing 5 wt.% Al₂O₃ with 64 m²/g specific area was synthesized through precipitation method. Different amounts of Co (0–3 mol%) were introduced into synthesized powders, and ceramic materials were obtained by heat treatment in the air for 2 h at 1350–1550 °C. The influence of Co addition on the sintering temperature, phase composition, microstructure, mechanical and biomedical properties of the obtained composite materials, and on the resolution of the digital light processing (DLP) printed and sintered ceramic samples was investigated. The addition of a low amount of Co (0.33 mol%) allows us to decrease the sintering temperature, to improve the mechanical properties of ceramics, to preserve the nanoscale size of grains at 1350–1400 °C. The further increase of Co concentration resulted in the formation of both substitutional and interstitial sites in solid solution and appearance of CoAl₂O₄ confirmed by UV-visible spectroscopy, which stimulates grain growth. Due to the prevention of enlarging grains and to the formation of the dense microstructure in ceramic based on the tetragonal ZrO₂ and Al₂O₃ with 0.33 mol% Co the bending strength of 720 ± 33 MPa was obtained after sintering at 1400 °C. The obtained materials demonstrated the absence of cytotoxicity and good cytocompatibility. The formation of blue CoAl₂O₄ allows us to improve the resolution of DLP based stereolithographic printed green bodies and sintered samples of the ceramics based on ZrO₂-Al₂O₃. The developed materials and technology could be the basis for 3D manufacturing of bioceramic implants for medicine.

The microstructure, texture, and mechanical properties of Inconel 718 fabricated via hybrid wire-arc additive manufacturing (WAAM) with inter-pass forging, and the subsequent modified post-deposition heat treatment (PDHT), were investigated. The modified PDHT included homogenization at 1185 °C and double ageing at 720 °C, with furnace-cooling to 620 °C; this process was first used for Inconel 718 obtained via WAAM and inter-pass forging. In the as-printed material, two characteristic zones were distinguished, as follows: (i) columnar grains with a preferable orientation and (ii) fine grains with a random crystallographic orientation. The development of static recrystallization induced via inter-pass forging and further heating during the deposition of the next (upper) layer provoked the formation of the fine-grained zone. In the as-printed material, particles of (Nb,Ti)C and TiN, and precipitates of a Nb-rich Laves phase that caused premature cracking and failure during mechanical testing, were detected. In the PDHT material, two zones were found, as follows: (i) a zone with coarse uniaxial grains and (ii) a zone with a gradient grain size distribution. PDHT resulted in the precipitation of γ″ nanoparticles in the γ-Ni matrix and the dissolution of the brittle Laves phase. Therefore, significant hardening and strengthening, as well as increases in ductility and impact toughness, occurred.

Zirconia-toughened alumina (ZTA) powders with 20.0 wt.% of ZrO₂ were synthesized using the coprecipitation method. Transmission electron microscopy indicated that the powders contained needle-like particles 15–30 nm long and 50–70 nm flake-like particles with a uniform component distribution. Effects of different Y₂O₃ concentrations (3.0, 4.0, or 5.0 mol.%) and 0.5 wt.% of MnO on the phase composition, microstructure, and physicomechanical properties of the composites were evaluated after sintering at 1600 °C. The microhardness of 5ZTA-Mn samples (5.0 mol.% of Y₂O₃ and 0.5 wt.% of MnO) was 1653 ± 50 HV when density reached 4.18 g/cm³. For digital light processing on a commercial 3D printer Anycubic Photon S, acrylate-based homogeneous slurries were obtained. Compositions based on ZTA powder stabilized with 5.0 mol.% of Y₂O₃ and containing 0.5 wt.% of MnO were studied. MnO in the materials improved polymerization depth during the UV-curing process as compared to 5ZTA materials. The microstructure and mechanical properties of the 5ZTA-Mn composites were investigated at the sintering temperature of 1600 °C. Compared with 5ZTA, the 5ZTA-Mn composites showed higher density (4.0 g/cm³) and microhardness (1409 ± 50 HV). According to in vitro experiments, the newly developed materials are promising for biomedical applications and can serve as a basis for the production of personalized implants via digital light processing printing.

The influence of hafnium on high-magnesium alloys doped with transition metals during heat treatment Влияние гафния на высокомагниевые сплавы, легированные переходными металлами, при термической обработке

Nanopowders of hydroxyapatite (HA) and Fe-substituted hydroxyapatite (HAFe) were synthesized by wet precipitation on either MCM-41 (a synthetic, mesoporous aluminosilicate material) or an aluminum-containing MCM-41 (AlMCM) support. According to X-ray diffraction data, all of the synthesized materials are composite powders consisting of amorphous silicate and an HA phase with low crystallinity. The presence of aluminum and iron in the structure of the powders resulted in further amorphization. The obtained samples showed high specific surface areas (SSAs), ranging from 162.3 to 186.6 m²/g for MCM-41-HA and from 112.6 to 127.2 m²/g for AlMCM-HA. The hysteresis loops were found to be of type H3, indicating the formation of slit-like pores in the intercrystalline space, as confirmed by transmission electron microscopy, which revealed the presence of lamellar and flake-like particles. Catalytic activity tests showed that the conversion of dibenzothiophene depended on the iron concentration in the material and the acidity of the support. To further improve the catalytic activity of the materials, they were impregnated with molybdenum compounds. Active molybdenum peroxo complexes formed under these conditions enabled 100% conversion of dibenzothiophene. To our knowledge, this is the first study on the influence of MCM-41-HA- or AlMCM-HA-based materials on dibenzothiophene conversion via oxidative desulfurization using hydrogen peroxide as an oxidant.

Magnesium-rich aluminum alloys with small scandium additives are widely used in many branches of modern industry due to the high level of their mechanical properties. However, the issue of low thermal stability of Al3Sc particles, which does not allow performing deformation processing of this group of alloys at a temperature above 400 °С, continues to be relevant. Hafnium addition can become one of the ways to solve this problem as hafnium forms a shell around the Al3Sc particles and, due to the low diffusion coefficient in the aluminum matrix, reduces their coagulation rate. The paper studies the influence of addition of 0.2 % and 0.5 % Hf on the electrical conductivity and the process of supersaturated solid solution decomposition, as well as on the size and quantity of nanoparticles in the 1570 magnesium-rich aluminum alloy at its thermal treatment. The authors studied the kinetics of supersaturated solid solution decomposition in the 1570, 1570–0.2Hf, and 1570–0.5Hf alloys by the electrical conductivity measuring and constructed C-curves describing the supersaturated solid solution decomposition in the studied alloys in the temperature range of 260–440 °С. Besides, using transmission electron microscopy, the strengthening nanoparticles of the 1570 and 1570–0.5Hf alloys were studied during heating to 370 °C and 4-hour soaking. The study showed that hafnium addition significantly slows down the supersaturated solid solution decomposition in the 1570 alloy. The authors identified that in the alloys with hafnium additives, the supersaturated solid solution decomposition is the most intense at a temperature of 350 °С, and in the alloys without hafnium – at a temperature of 430 °С. The transmission microscopy data confirm that the 1570 alloy without hafnium contains 3–4.5 times more nanoparticles than the 1570–0.5Hf alloy.