A high C high Si bainitic steel was continuously cooled from the austenitization temperature and the resulting microstructure observed in a high-resolution transmission electron microscope (HRTEM). It was observed that several alloy carbides precipitated from austenite during cooling, these carbides affect the bainitic microstructure and are thought to substantially improve the steel’s abrasive wear resistance.

Nanostructured zinc oxide (ZnO) particles were synthesized by the one step Ultrasonic Spray Pyrolysis (USP) process from nitrate salt solution (Zn(NO3)2·6H2O). Various influential parameters, from Zn(NO3)2·6H2O concentrations (0.01875–0.0375 M) in the initial solution, carrier gas (N2) flow rates (0.5–0.75 L/min) to reaction temperature (400–800 °C), were tested to investigate their role on the final ZnO particles’ morphology. For this purpose, Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM) and (Selected Area Electron Diffraction) SAED techniques were used to gain insight into how the ZnO morphology is dependent on the USP process. It was revealed that, by certain parameter selection, different ZnO morphology could be achieved, from spherical to sphere-like structures assembled by interwoven nanoplate and nanoplate ZnO particles. Further, a more detailed crystallographic investigation was performed by XRD and Williamson-Hall (W-H) analysis on the ZnO with unique and non-typical planar morphology that was not reported before by USP synthesis. Moreover, for the first time, a flexible USP formation model was proposed, ending up in various ZnO morphologies rather than only ideal spheres, which is highly promising to target a wide application area.

The aim of the study was to assess the influence of adding Al2O3 nano-particles of 0.5 wt. % with the mean particle size of 500 nm on the mechanical properties and wear behaviour of the austenitic stainless steel matrix reinforced with nano-particles produced by conventional ingot casting. The focus was on the methods and possibilities of homogeneous and uniform distribution of the particles within the steel matrix using conventional casting routes. The main drawback of the casting method used is the agglomeration of the particles and poor interface between the particles and the metal matrix. The results show that through a proper insertion method, nano-particles can be successfully introduced into the metal matrix. The Al2O3 nano-particles were successfully incorporated into the steel matrix with no signs of clustering and intermetallic reactions taking place between the nano-particles and the steel matrix. This led to improved mechanical properties as well as the wear behaviour of the stainless steel, achieved by using conventional casting routes.

This article studies the synthesis of bimetallic Fe/Au submicron particles with Ultrasonic Spray Pyrolysis (USP). The combination of Fe oxide particles' ferromagnetism with Au nanoparticles' (AuNPs) surface plasmon resonance has gained high interest in biomedical and various other applications. Initial investigations for producing Fe/Au particles with USP were carried out in order to study the particle formation mechanisms. Firstly, three precursor salt solutions (Fe acetate, Fe nitrate and Fe chloride) were used to produce Fe oxide particles and to study their effect on particle morphology through characterization by Scanning and Transmission Electron Microscopy (SEM and TEM) with Energy Dispersive X-ray spectroscopy (EDX). These precursor salts produce three types of submicron particles, a mesh of primary nanoparticles, spherical particles and irregular particles, respectively. Next, different solution combinations of precursor salts of Fe and Au were used with the USP. The obtained particles were characterized, and similarities were then examined in the particle formation of pure Fe oxide and Fe/Au particles. The effects of using different salts were analyzed for the formation of favorable morphologies of Fe/Au particles. The combinations of Fe chloride/Au chloride and Fe chloride/Au nitrate in the precursor solution indicate potential in synthesizing bimetallic Fe/Au submicron particles with the USP process.

The aim of this article was an explanation of the gold nanoparticle (AuNP) formation mechanisms which take place in a redesigned Ultrasonic Spray Pyrolysis (USP). Depending on the synthesis parameters of gold concentration in the precursor solution, gas flow and reaction temperature, we have previously obtained a combination of spherical, irregular and cylindrical AuNPs. Two parameters (gold concentration and gas flow) were determined to be the most influential on the shapes and sizes of the produced AuNPs. The effects of these two influential synthesis parameters were evaluated on controlling the formation mechanisms: Gold concentration (2.5 and 0.5 g/l Au) in the precursor solution of HAuCl4 dissolved in water and gas flows of (i) aerosol carrier gas N-2 (1.5, 3.0 and 4.5 l/min) and (ii) reduction gas H-2 (1.0, 1.5 and 2.0 l/min). Depending on the parameter conditions, the AuNPs are formed from a combination of the liquid/solid phase (Droplet-to-Particle mechanism, DTP), the gas phase (Gas-to-Particle mechanism, GTP) and from intermediate secondary droplets, formed from primary droplet explosions. Increasing the gas flow affected the evaporation of the solvent (water) and diffusion of the solute ([AuCl4](-)) in the aerosol droplets, which resulted in the formation of more uniformly shaped AuNPs and with narrower size distributions than before. With favorable parameter conditions increased control over AuNP synthesis with USP has been achieved. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V.

The present investigation reports the first-time successful synthesis of AuNPs using a new precursor salt of Au(III) acetate through USP. An aqueous solution of this salt was prepared with very limited solubility with H2O. HCl and HNO3 were then added separately to increase the solubility, resulting in a clear, yellowish solution. This enabled the successful formation of AuNPs with USP. In order to improve AuNPs synthesis, NaOH and Na2CO3 were added into the precursor to increase its pH (6–7). With such approach, it was possible to perform USP synthesis using varying concentrations of [Au] in the precursor. Evaporation and reaction temperatures (100 and 300 °C) of USP were chosen based on detected decomposition temperatures of Au(III) acetate with TGA-DT. TEM confirmed the presence of circular shaped, unagglomerated AuNPs having an Fm-3m space group with diameter range of 15–30 and circularity value range of 0.89–0.92. The UV–Vis spectroscopy showed absorbance peaks at 528 and 532 nm. ICP-MS indicated the highest concentration of AuNPs, 79 ppm, by the precursor with the lower initial concentration of [Au]. This could be due to the smallest sedimentation and turbulent losses of larger AuNPs in transport tubes and reaction USP zones.

This article explains the mechanism of the metal/oxide core-shell Ag/TiO2 and Au/TiO2 nanoparticle formation via one-step ultrasonic spray pyrolysis (USP) by establishing a new model. The general knowledge on the standard “droplet-to-particle” (DTP) mechanism, nucleation, and growth processes of noble metals, as well as physical and chemical properties of core and shell materials and experimental knowledge, were utilized with the purpose of the construction of this new model. This hypothesis was assessed on silver (Ag)/titanium oxide (TiO2) and gold (Au) TiO2 binary complex nanoparticles’ experimental findings revealed by scanning electron microscopy (SEM), focused ion beam (FIB), high-resolution transmission electron microscopy (HRTEM), and simulation of crystal lattices. It was seen that two mechanisms run as proposed in the new model. However, there were some variations in size, morphology, and distribution of Ag and Au through the TiO2 core particle and these variations could be explained by the inherent physical and chemical property differences of Ag and Au.

Achieving a uniform distribution of reinforcement particles within a matrix is one of the challenges that impacts directly on the properties and quality of a composite material. Therefore, the aim of the present work was to investigate the influence of the reinforcing Al2O3 particles’ concentration and size on their distribution in reinforced austenite stainless steel. Austenitic stainless steel reinforced with (0.5, 1.0 and 2.5) % of mass fractions of Al2O3 particles was produced by a conventional casting route. In this study, an innovative pre-dispersion approach for the addition of particles into a steel melt was designed. The results of this investigation indicate that the concentration and size of the Al2O3 particles has an impact on the distribution of the reinforcement within the matrix. When the weight percent increased to 2.5 the concentration ratio of the particles’ distribution decreases towards the bottom of the cast ingot. In this case also the size of particles starts to play a role, with the larger particle size leading to an increased degree of incorporating particles into the steel matrix. The larger the particles the more particles are found in the cast ingot.

The manufacturing and properties of the AE44 magnesium alloy reinforced with SiC-Al2O3-SiO2 ceramic foam were studied. The interpenetrating phase composite was manufactured by gravity casting at different preheating temperatures of the ceramic foam. The samples were investigated using optical and electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and compression testing. The interfacial reaction products (AISiRE and AIMgSiRE) between the metal phase and ceramics were influenced by the preheating temperatures of ceramic foam and reduced the compression strength significantly.

To prevent the evaporation of alkali elements during the calcination of the lead-free piezoelectric K0.50Na0.50NbO3 (KNN), lower temperatures for the solid-state synthesis of the KNN from a mixture of Na2CO3, K2CO3 and Nb2O5 were investigated with a variety of powder-characterization techniques. The collected data suggested 550°C as a possible low calcination temperature, as well as being sufficiently high for a completed synthesis of the KNN. The XRD and TEM analyses of double-calcined KNN powder at 550°C revealed nanocrystalline, cube-shaped particles with a perovskite structure, but without noticeable unreacted precursors or secondary phases. Our investigations revealed that the morphology of the calcined powders underwent a dramatic change from small, differently shaped particles at 600°C/6h, to fully rounded, large, spherical agglomerates produced at 1000°C/6h. To explain this behavior, a mechanism involving the formation of a liquid phase during the reaction of the alkali elements with the moisture and CO2 in the atmosphere is proposed.

Potassium sodium niobate K0.5Na0.5NbO3 (KNN) was synthesized by the double calcination of a homogenized mixture of potassium and sodium carbonates and niobium pentoxide for 4 h at 625 degrees C. The calcination temperature was chosen on the basis of the thermal analyses of the mixture of precursors, where the weight loss being the function of the temperature reaches the plateau. The calcined powder was investigated by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) and was found to be without unreacted materials or secondary phases. Before sintering, the powder compacts were annealed for 4 h at 450 degrees C, while the sintering was carried out for 2 h at 1115 degrees C using two different configurations: 1) in a closed crucible where the KNN pellets were in close physical proximity to, but not in direct contact with, the KNN packing powder, and 2) in a completely open crucible without any packing powder. The Archimedes' density of the sintered samples was 91.5 % of theoretical density for the first configuration, while it was 93.4 % for the second configuration. The Field-Emission Scanning Electron Microscopy (FE-SEM) and XRD analyses of the sintered ceramics showed that by using a calcination temperature as low as 625 degrees C a typical sintered microstructure of KNN could be achieved with both sintering configurations.

This article reports about a new synthesis approach by the Ultrasonic Spray Pyrolysis of Au nanoparticles which consists of a separate heating zone for evaporation and subsequent connection of reduction gas by entering directly into the reaction zone. This redesign was made in order to control each step of the USP to find those influential parameters which dictate final gold nanoparticles' morphology and size. For the precursor a starting solution of HAuCl4 and water was used with various concentrations of Au (0.625 g/l, 1.25 g/l and 2.5 g/l). Other variable parameters were evaporation temperatures (75 degrees C, 80 degrees C and 85 degrees C) and time of synthesis (3 h, 6 h, 9 h), while the temperature in the heating zone was constant (350 degrees C) during performing all the experiments. Characterization of synthesized Au nanoparticles was carried out by Transmission Electron Microscopy (TEM). It was found that Au nanoparticles have bimodal size distribution. An investigation of the Au nanoparticles' electron diffractions enabled us to find the possible growth of Au nanocrystal types which was finally the base for setting up the synthesis mechanisms of Au nanoparticles. The cytocompatibility investigations of the Au nanoparticles suggested that they were not cytotoxic for L929 cells in vitro, but they can exhibit anti-proliferative properties, depending on their size distribution.

Microstructure, phase constitution and hardness of Cr-V ledeburitic steel Vanadis 6 subjected to subzero treatment with a soaking time of 4 h and at a temperature of -196 degrees C have been examined with reference to the same material after conventional heat treatment. Microstructures have been characterized using light microscopy, scanning electron microscopy, transmission electron microscopy and Xray diffraction. Hardness has been evaluated by Vickers method. As-annealed material consists of the ferritic matrix and of two carbide phases, namely M7C3 and MC. After the heat treatment, the matrix is martensitic with certain amount of retained austenite. Sub-zero treatment results in more complete martensitic transformation. The martensite contains areas with extremely enhanced carbon content. Sub-zero treatment refines the size of martensitic domains and increases the dislocation density inside the domains. Microstructure of sub-zero treated steel contains enhanced amount of small globular carbides, as compared to conventionally heat treated material. These particles have a size of around 100 nm in most cases. Small globular carbides are of the cementitic nature for both the no sub-zero treated steels and the sub-zero treated material. Bulk hardness manifests a moderate increase due to the sub-zero treatment. The increase in hardness is more significant when higher austenitizing temperature is used for the treatment, which is associated with more pronounced reduction of the retained austenite content. (C) 2014 Elsevier Ltd. All rights reserved.

This work presents the results of the microstructure observation of six different types of NiTi orthodontic wires by using Transmission Electron Microscopy (TEM). Within these analyses the chemical compositions of each wire were observed in different places by applying the EDS detector. Namely, the chemical composition in the orthodontic wires is very important because it shows the dependence between the phase temperatures and mechanical properties. Microstructure observations showed that orthodontic wires consist of nano-sized grains containing precipitates of Ti 2 Ni and/or TiC. The first precipitated Ti 2 Ni are rich in Ti, while the precipitated TiC is rich in C. Further investigation showed that there was a difference in average grain size in the NiTi matrix. The sizes of grains in orthodontic wires are in the range from approximately 50 to 160 nm and the sizes of precipitate are in the range from 0,3 μm to 5 μm.

The objective of this work was to evaluate the influence of martensite fraction on the wear mode and the energy dissipation by friction of dual phase (DP) steel tested under reciprocating sliding conditions. For this purpose, a Ti-Nb microalloyed steel was heat treated in a conventional furnace at temperatures between 780 and 880°C (intercritical annealing temperature) for 3 min to obtain DP microstructures with volume fractions of martensite between 25 and 90%. Wear tests were carried out in both DP and as-received samples, using a reciprocating tribometer with ball-on-flat geometry, at two constant applied loads, 2.5 and 4 N. The wear damage of each sample was measured through volume loss and the dissipated energy during the test. The obtained results evidenced a significant influence of the contact load over the wear mode, because at low load the DP wear was reduced with increased hardness but just up to 75% of martensite. At high load, the sliding process promotes an oxide mixture in the ferritic microstructure that acts as a factor in wear reduction.

Specimens of duplex stainless steel (DSS, the 258-alloy type) were isothermally annealed (aged) at 300 degrees C and 350 degrees C for 10000 h and 30000 h. Spinodal decomposition of the solid solution in ferrite occurs during the thermal ageing of this material with a redistribution of mainly Cr and Ni and a formation of nanocellular domains. This causes significant changes in the mechanical properties (the hardness and the tensile strength increase, while the ductility and the notch toughness decrease). The change in the mechanical properties may be related to the changes in the material's internal structure (stacking faults, the morphology and density of dislocations) or/and internal stresses. Therefore, non-aged and aged specimens were studied using transmission electron microscopy (TEM).

The Cr-V ledeburitic steel Vanadis 6 was vacuum austenitized at different temperatures, nitrogen gas quenched and double tempered at 530 °C for 2 h. For the selected samples, a sub-zero period was inserted between quenching and tempering. The obtained results infer that: I) as-quenched microstructure consisted of martensite, retained austenite and undissolved carbides, II) sub-zero processing reduced the amount of the retained austenite and increased the tetragonality of the martensitic lattice, III) as-quenched hardness of the steel was higher by 2 – 3 HRC due to sub-zero processing, IV) as-tempered hardness increased with increasing austenitizing temperature but it decreased slightly with the sub-zero period, V) no negative impact of sub-zero processing on toughness was recorded, VI) wear resistance increased with sub-zero period when 100Cr6 steel has been used as a counterpart.

The ledeburitic steel Vanadis 6 has been austenitized at the temperatures 1000 – 1075 o C, nitrogen gas quenched and 2x tempered at the temperatures 480 – 600 o C. Each tempering cycle was 2 h. Sub-zero treatment carried out via various regimes has been inserted in-between quenching and tempering, except one set of specimens. The effect of sub-zero treatment on the tempering characteristics of the material has been investigated. It has been found that the martensite after sub-zero processing differs from that of conventionally transformed in terms of substructure. The sub-zero treatment induced a multiple reduction of the volume fraction of retained austenite. This makes a difference between as-tempered microstructure of sub-zero treated and no-sub-zero treated steel, which results in different as-tempered hardness.

Specimens made from P/M Vanadis 6 cold-work steel were austenitized, quenched and tempered for various combinations of the parameters. The selected sets of samples, also in the sub-zero range, were treated at a temperature of -196 degrees C after quenching. The microstructure was investigated as a function of the austenitizing temperature and the parameters of the sub-zero processing using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. It was found that the as-quenched microstructure is composed of martensite, retained austenite and carbides. The sub-zero processing reduced the amount of retained austenite and led to an increase in the tetragonality of the martensitic lattice. As a result, the hardness of the material was higher by 2 HRc before the tempering of the samples after the sub-zero processing, but the hardness of the sub-zero-processed material after tempering is about 2.5 HRc lower than that of the non-sub-zero-processed steel. Based on the facts that the sub-zero-processed steel contained less retained austenite and an unknown amount of the expected nano-precipitates, we expected it to have a lower capability to manifest the secondary-hardening effect.