Volume 35, Issue 8 -

Amorphous nanoparticles have attracted a large amount of interest due to their superior catalytic activity and unique selectivity. The Ni-B amorphous nanoparticles were synthesized from aqueous reduction of NiSO 4 by sodium borohydride in microscale interface at room temperature. The size, morphology, elemental compositions, and the chemical composition on the surface of Ni-B amorphous nanoparticles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). All the results showed that the synthesized particles are Ni-B amorphous nanoparticles with uniform in size distribution and having good dispersion. The mean particle diameter of Ni-B amorphous nanoparticles was around 9 nm. The present work provides an alternative synthesis route for the Ni-B amorphous nanoparticles.

Various thermal cycles at the end of solution heat treatment and their influences on microstructure of single crystal superalloy DD6 were studied by experiments. During various thermal cycles, the qualitative and quantitative microstructure of samples quenched of the transformations is microscopically characterized. This completely includes the large changes in volume fraction, size distribution and morphology of gamma prime precipitate experienced in the upper temperature transformation. Noticeable deviation from the equilibrium volume fraction of γ’ phase is detected in both the dissolution and precipitation processes above 1,120°C for both moderate cooling and heating rate; differences were mainly attributed to the unsteady nature of the turbulent flow. The growth and alignment of the γ’ precipitates are deeply influenced by several factors, e.g. ageing time, cooling rate and quenching temperature. In addition, interesting findings such as “labyrinth” and “cluster” morphologies were observed by scanning electron microscope. During precipitation processes, the complicated microstructure evolution is illustrated by considering the consecutive equilibrium shapes of a coherent precipitate, which grows under the interaction with its neighbors and the coherency of the precipitates improves their potential to resist dissolution.

This paper presents the experimental results and analysis of the behaviour of steel 1.4762 at different temperatures. Tensile mechanical properties and creep behaviour were determined using uniaxial tests. Charpy impact test was used to determine impact energies at different temperatures. The mentioned mechanical properties are displayed as engineering stress–strain diagrams while material resistance to creep is presented in the form of creep curves. Based on Charpy impact energy an assessment of fracture toughness is given. Experimental results show that the values of mechanical properties are continuously decreased by increasing the temperature. After the temperature of 623 K (tensile strength: 468 MPa; yield strength: 298 MPa) the decrease of the ultimate strength and yield strength is especially emphasized and the difference between them becomes smaller. The creep resistance is considered quite small, except at low stress levels.

Titanium silicide (Ti 5 Si 3 ) was fabricated by self-propagating high-temperature synthesis (SHS) from the elemental powder compact. With the increase of sample density from 50 to 60% TMD, experiments showed that the flame-front velocity increased from 28 to 50 mm/s and combustion temperature from 1,580 to 1,700°C. Based on their dependence, the activation energy of the synthesis reaction, E a =193 kJ/mol, was deduced. By numerical simulation of combustion wave kinetics, the Arrhenius factor of the rate function, K 0 =3×10 9 s −1 , was determined for the 5Ti + 3Si reaction system. The effect of sample compaction density on the SHS process was correlated to the variation of the effective thermal conductivity ( k eff ) of the powder compact. The ratio of k eff / k bulk =0.02–0.05 was numerically obtained for the 5Ti + 3Si samples with 50–60% TMD and well validated by the experimental data.

In supersonic plasma spraying system (SAPS), heat transfer from arc plasma is characterized by several distinct features, such as transport of dissociation and ionization energy and of electrical charges in addition to mass transport. The thermodynamic and transport properties of plasma jet were influenced by several main parameters such as primary gas flow rate, the H 2 vol.% and current intensity A. This paper first analyzes the effect of these parameters on the temperature and velocity of plasma jet theoretically. Further, the loading particles were melted and accelerated by plasma jet. Effects of several main parameters such as carrier gas flow rate, the H 2 vol.%, the current intensity, the voltage and the spraying distance on temperature and velocity of in-flight particle were studied experimentally. The average maximum temperature and velocity of in-flight particle at any given parameters were systematically quantified. Optimal SAPS process parameters were given in this paper. In general, increasing the particles impacting velocity and surface temperature can improve the maximum spreading factor and decrease the coating porosity.

The aim of the present work is to elucidate crystallization and growing process of rutile crystals in Ti-bearing blast furnace slag. The samples were taken from the liquid slag and quenched at once at elevated temperatures in order to analyze phase transaction of titanium and grain size of rutile crystals. Crystallization and growing kinetics of rutile crystals under elevated temperature conditions were calculated, and the crystallization process of rutile crystals under isothermal conditions was expressed by Avrami equation. The effects of experimental parameters, such as experimental temperatures, SiO 2 addition, cooling rate, crystal seed addition and oxygen flow, were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the optimal conditions for rutile crystals to grow up were obtained. Distribution and movement state of rutile crystals in the slag were analyzed.

One way of controlling alkali chloride-induced corrosion in biomass boilers is by designing new alloy materials used as superheater tubes. Four newly designed Cr–Ni alloy was designed and studied for applicability in biomass power plants. High-temperature oxidation experiments and high-temperature corrosion experiments were carried out for evaluation material characterization. Through analysis and discussion of the corrosion kinetics and oxidation kinetics, it can be concluded that materials with series number of “2xx” and “3xx” had better endurance ability in KCl environment under 650°C and 700°C than TP316 material. In the same conditions, 3xx material had better anticorrosion ability in 700°C with KCl environment.

The present study using a single-particle softening under a load equipment was designed to better understand the softening and melting process of pellet, sinter and a mixture of both under a high reduction potential condition. Additionally, the experiment was interrupted at different shrinkage stages, and the evolvement of particle structure was analyzed. The softening and melting behavior of ferrous burden in high reduction potential compared with the general conditions was ascertained. In comparison with the general case, the thickness of the iron shell and the fineness of the metallic iron phase increased in high reduction potential. In the general condition the melting process is impacted by the low melting point of the slag with wustite outflow from the metallic iron shell, while in high reduction potential, the higher melting point of the slag without wustite exuded from the metallic iron phase. Under high reduction potential, the liquid slag was distributed in the metallic iron phase, which hindered the interaction between pellet and sinter. Thus, the temperature of interaction in high reduction potential is obviously higher than that in the general condition. The thicker iron shell and the higher melting point of slag lead to the improvement of the softening behavior under high reduction potential.

Microwave heating has been applied in the field of drying rare earth carbonates to improve drying efficiency and reduce energy consumption. The effects of power density, material thickness and drying time on the weight reduction (WR) are studied using response surface methodology (RSM). The results show that RSM is feasible to describe the relationship between the independent variables and weight reduction. Based on the analysis of variance (ANOVA), the model is in accordance with the experimental data. The optimum experiment conditions are power density 6 w/g, material thickness 15 mm and drying time 15 min, resulting in an experimental weight reduction of 73%. Comparative experiments show that microwave drying has the advantages of rapid dehydration and energy conservation. Particle analysis shows that the size distribution of rare earth carbonates after microwave drying is more even than those in an oven. Based on these findings, microwave heating technology has an important meaning to energy-saving and improvement of production efficiency for rare earth smelting enterprises and is a green heating process.

The experiments were operated for the cylindrical sample (cement/steel) in high temperature and high pressure (HTHP) CO 2 environment to simulate surrounding CO 2 attack in oil and gas well. The interfacial evolutions between well cement and casing steel were measured, including mechanical property, structure alteration, chemical change and electrochemical character. The interfacial behaviors are attributed to the competition of hydration and degradation of Portland cement. The damage at the interface was faster than the cement bulk deterioration by carbonation. Thus, the interface provided a potential flow leakage pathway for the HTHP gas and fluid in the well, so improving interfacial stability between well cement and casing steel is the key issue to long-term zonal isolation.

The dissolution process of solid Cu in liquid Al influences the compound quality directly when fabricating the copper cladding aluminum (CCA) composite castings utilizing the casting aluminum method. Dissolution rate of solid Cu is investigated utilizing the method of quenching rapidly. Effects of liquid Al temperature and the contact time between solid Cu and liquid Al on the dissolution rate of Cu are investigated; meanwhile, the dissolution mechanism of Cu is explored. Subsequently, the influences of processing parameters on the dissolution thickness of Cu are examined. The results indicate that chemical compounds, such as AlCu 2 , Cu 5 Al, CuAl 2 and Cu 2 Al 3 , may form on the contact surface between solid Cu and liquid Al. These chemical compounds are contributed to decompose the solid Cu, Cu 5 Al exerts the greatest effect. The dissolution of Cu is affected by the contact time between solid Cu and liquid Al, temperature and cooling method of Cu plate. The dissolution of Cu cannot terminate immediately even though the Cu plate is cooled by the spray. The experimental results will provide a reference for controlling the composite layer thickness.

Two novel small specimen creep testing techniques are presented in this paper. The pin-loaded small one-bar specimen (OBS) and the small notched specimen with four loading pins (SNS4) are designed to determine the remaining lifetime for the high-temperature components. The small OBS is suitable for use in obtaining both uniaxial creep strain and creep rupture life data and the SNS4 is designed to obtain the multiaxial behaviour using small material samples. The specimens can be made from small material samples removed from the component surface or from the heat-affected zone. The specimens can be loaded through pin connections for testing. A conversion relationship and conversion factor have been obtained and used to convert the OBS creep data to the corresponding uniaxial data. For validation two materials have been used, P92 and P91 steels at 650°C. The advantages of these testing techniques are highlighted; the recommendations for future research are also given.

Vertical compensation friction stir welding (VCFSW) was proposed in order to solve the adverse effect caused by a big gap at the interface between two welded workpieces. VCFSW was successfully applied to weld 6061-T6 aluminum alloy with the thickness of 4 mm, while 2024-T4 aluminum alloy was selected as a rational compensation material. The results show that VCFSW is difficult to get a sound joint when the width of strip is no less than 1.5 mm. Decreasing the welding speed is beneficial to break compensation strip into pieces and then get higher quality joint. When the width of strip is 1 mm, the tensile strength and elongation of joint at the welding speed of 50 mm/min and rotational velocity of 1,800 rpm reach the maximum values of 203 MPa and 5.2%, respectively. Moreover, the addition of 2024-T4 alloy plays a strengthening effect on weld zone (WZ) of VCFSW joint. The fracture surface morphology of joint consisting of amounts of dimples exhibits ductile fracture.