Fe–Al–O ODS alloy prepared via mechanical alloying was subjected to three different heat treatments. Material basic state exhibited a fine-grained (300–500 nm) microstructure with fine dispersion of aluminum oxide particles (60% up to 20 nm). Heat treatment at 1100 °C for 3 h resulted in local grain and particles coarsening. Prolongation of the heat treatment to 24 h resulted in further grain (50 % up to 5 μm) and particle (25 % with size 25–40 nm) coarsening. Annealing at 1200 °C for 24 h led to a bimodal microstructure (35 % of grains with size 100–250 μm and 45 % of particles with size 30–60 nm) and substantial oxide particle coarsening. Microstructural changes resulted in tensile strength decrease and ductility increase. Tensile tests at 800 °C revealed a 90% decrease of tensile strength while ductility increased 4–6 times when compared to the room temperature tests. The hardening ratio was below 10 % for all the alloys and both test temperatures.

Piezoelectric single crystals based on the perovskite ferroelectric system (K,Na)NbO3 have been widely investigated over the past 20 years due to large piezoelectric coefficients, high transition temperatures, low density, and the nontoxic chemical composition. Various crystal growth methods were examined, including high-temperature solution growth, solid-state crystal growth, Bridgman–Stockbarger method, and the floating zone method. Increased understanding of the crystal growth process and post-growth treatments resulted in improved crystal quality and larger sizes. Recently, crystals with high piezoelectric and electromechanical coupling coefficients exceeding 1000 pC/N and 0.90, respectively, were reported. Moreover, their large potential for high-frequency ultrasonic medical imaging was demonstrated. This work provides a review of the development of piezoelectric (K,Na)NbO3-based single crystals, including their growth, defect chemistry, domain structures, electromechanical properties, and applications. Approaches for reducing growth defects, controlling point defects, and domain engineering are discussed. The remaining open issues are presented and an outlook on the future is provided.

Distinguished by a marked combination of high strength and high fracture toughness, 18Ni-300 maraging steel (MS) is widely used for intricate tool and die applications. MS is also amenable to the powder bed fusion additive manufacturing process, providing unique opportunities to make small features and incorporate cooling channels in molds. In this study, tensile test samples were fabricated using selective laser melting to investigate the effects of built height and orientations on the evolution of the microstructure and the mechanical properties of the samples. The microstructure of the as-fabricated samples consists of the primary α-martensite phase and fine cellular microstructure (~0.66–0.83 μm) with the retained austenite γ-phase aggregated at the boundaries of the cells, resulting in an enhanced mechanical performance compared with traditional counterparts under the same condition (without post-heat treatments). Random grain orientations with weak textures are revealed in all samples. The XY-built samples display better tensile performance when compared to the Z-built samples due to the fine grain sizes and the retained γ phase. The bottom of the Z-built sample exhibits a higher hardness than other parts of the sample, which could be attributed to its finer cellular structure.

In the present work, the effect of annealing temperature on the microstructure, mechanical and tribological properties of NiCr–WC–Co coatings produced by the high-velocity oxy-fuel (HVOF) technique has been investigated. X-ray diffraction and scanning electron microscopy revealed the dissolution of WC into the NiCr matrix to form W2C and Cr3C2 with the annealing process. This dissolution became complete at 800 °C. The mechanical properties of the coatings were investigated using nano-indentation and Vickers fracture toughness measurements. These measurements suggested that the hardness, Young's modulus, and fracture toughness values increased because of the newly formed carbide phases as a result of the dissolution of the WC particles. The overall properties of the coatings were found to be optimum for annealing temperatures of 800 °C. The wear mechanism appears to be abrasive in the as-sprayed coating, and it becomes a combination of an abrasive and oxidative wear with increasing the annealing temperature.

Titanium dioxide (TiO2) is a semiconductor that can be applied in different technological areas. In this work, we investigated the modifications of the electrical properties of thin films composed of TiO2 nanoparticles produced with different morphologies. The solvothermal route used for the synthesis allowed the production of nanoparticles with functionalized surfaces due to oleate groups. It was possible to modulate nanocrystals shape and size due to the detachment crystal growth mechanism, by changing the reaction time. Nanorods were obtained using 4 h of synthesis, and an increase in the reaction time to 64 h led to a bipyramidal morphology. The functionalization by the organic ligand allowed the preparation of stable colloidal solutions, which were used to prepare thin films by the dip-coating method. The films presented a homogeneous surface, an average thickness around 100 nm, and no agglomerations were observed. The electrical resistance measurements indicated a typical behavior of semiconductors, and they were dependent on the nanoparticle morphology. An exploratory test indicated that the thin films prepared using nanorod particles presented a higher electrical response compared with isotropic particles, when exposed in a liquefied petroleum gas vapor atmosphere. Therefore, the morphology of the nanoparticles is a key factor for the further application of these thin films in gas sensing. Employing an easy methodology which required simple apparatus, and by using reaction time modulation only, it was possible to prepare homogeneous thin films with a tunable electrical response.

Relaxor ferroelectrics have drawn attention for possible applications in solid-state cooling and thermal energy harvesting, owing to their electrothermal energy conversion properties. Here, we have synthesized and characterized the structure–property correlations of a new Sn- and Nb-doped (Ba,Ca)TiO3 relaxor ferroelectric with large pyroelectric and electrocaloric effects over a broad temperature range. We observed two peaks for the temperature-dependent pyroelectric coefficient: (i) -(∂P/∂T) ∼ 563 μC/(m2 K) at T∼ 270 K and (ii) -(∂P/∂T) ∼ 1021 μC/(m2 K) at T∼ 320 K. In addition, a broad peak for electrocaloric temperature change is observed near 320 K with a relative cooling power of ∼17 J/kg. These properties could be correlated to structural changes observed using X-ray diffraction at two different temperature ranges in the material. Analysis of high-energy X-ray scattering and specific heat capacity data revealed a transition from the cubic to tetragonal phase near Tm∼ 320 K, whereas an additional increase in the tetragonality (c/a) of the polar phase is observed below Ts∼ 270 K.

SiC and Ga2O3 are promising wide band gap semiconductors for applications in power electronics because of their high breakdown electric field and normally off operation. However, lack of a suitable dielectric material that can provide high interfacial quality remains a problem. This can potentially lead to high leakage current and conducting loss. In this work, we present a novel atomic layer deposition process to grow epitaxially MgxCa1−xO dielectric layers on 4H-SiC(0001) and β-Ga2O3$\left( {\bar 201} \right)$ substrates. By tuning the composition of MgxCa1−xO toward the substrate lattice constant, better interfacial epitaxy can be achieved. The interfacial and epitaxy qualities were investigated and confirmed by cross-sectional transmission electron microscopy and X-ray diffraction studies. Mg0.72Ca0.28O film showed the highest epitaxy quality on 4H-SiC(0001) because of its closest lattice match with the substrate. Meanwhile, highly textured Mg0.25Ca0.75O films can be grown on β-Ga2O3$\left( {\bar 201} \right)$ with a preferred orientation of (111).

Honeycomb phononic crystal can obtain wider band gaps in the low frequency based on local resonance theory. Its band structure can be adjustable if we change the height of the cores, which means different kinds of honeycomb phononic crystal can be selected on the basis of different damping demands. Meanwhile, the point defects and line defects affect the localized modes of sound waves and propagation characteristics, the dispersion relations and the displacement fields of the eigenmodes are calculated in the defected systems, as well as the propagation behaviors in the frequency ranges of the band structure, which are also discussed in detail. We constructed the model based on the periodic boundary condition and calculated the band structure according to Bloch theory, and also performed a series of simulation through the COMSOL software, showing that honeycomb has excellent features in reducing noise and vibration, which has a far-reaching influence in designing the new type of acoustic wave devices.

Pop-in during indentation testing is a term used to indicate the sudden displacement burst during loading. Experimental data are measured during an indentation pop-in event, using displacement sensors with 20 μs time constant at 100 kHz data acquisition rate. The load–depth response during the pop-in event that occurs within 160 μs is determined after accounting for the instruments' dynamic response. Unlike the response reported in the literature for force-controlled tests, wherein the load on the sample remains constant during the pop-in, a steep load drop is observed after the onset of pop-in, followed by a significant increase in the load well beyond the load at the onset of pop-in. A model for the material and instrument's dynamic response is presented that agrees well with the experimental observations. The implications of these findings for determination of pop-in length or velocity and for performing displacement-controlled testing involving closed loop control are discussed.

To reveal the thermal shock resistance of double-layer thermal barrier coatings (TBCs), two types of TBCs were prepared via atmospheric plasma spraying, i.e., Gd2Zr2O7/yttria-stabilized zirconia (GZ/YSZ) TBCs and La2Zr2O7 (LZ)/YSZ TBCs, respectively. Subsequently, thermal cycling tests of the two TBCs were conducted at 1100 °C and their thermal shock resistance and failure mechanism were comparatively investigated through experiments and the finite element method. The results showed that the thermal shock failure of the two TBCs occurred inside the top ceramic coating. However, the GZ/YSZ TBCs had longer thermal cycling life. It was the mechanical properties of the top ceramic coating, and the thermal stresses arising from the thermal mismatch between the top ceramic coating and the substrate that determined the thermal cycling life of the two TBCs together. Compared with the LZ layer in the LZ/YSZ TBCs, the GZ layer in the GZ/YSZ TBCs had smaller elastic modulus, larger fracture toughness, and smaller thermal stresses, which led to the higher crack propagation resistance and less spallation tendency of the GZ/YSZ TBCs. Therefore, the GZ/YSZ TBCs exhibited superior thermal shock resistance to the LZ/YSZ TBCs.