Volume 35, Issue 5 -

In order to predict the creep life of a component at high temperature both accurately and economically, continuum damage mechanics approach is used based on experimental creep data. However, material constants used in the models have a great relationship with the performed stress range of creep tests. In this paper, several sets of material constants were obtained from a wide range of stresses on P91 steel. The creep damage tolerance parameter was used to classify these sets, and the modified continuum damage mechanics model was used to investigate a pipe under closed-end condition. Results have illustrated the main difference lies on the tertiary stage while slight difference on the primary and secondary stages, and the contribution of the tertiary stage to the total damage decreased when using material constants from higher stress region.

A novel electroslag furnace with the ultrasonic treatment was fabricated in this study. The effect of ultrasonic treatment on the compact density and segregation degree of alloys were studied. Results show that the distribution of carbon, silicon, manganese, chromium and phosphorus become uniform with increase of the ultrasonic power when the ultrasonic power is between 0 and 700 W. But when the ultrasonic power increases to 1,000 W, segregation of alloy elements increases instead. The reasonable ultrasonic power is favorable for improvement of compact density of electroslag remelting (ESR) ingots. When the ultrasonic power increases to 700 W from 0, compact density of ESR ingots increases to 0.9618 from 0.9479 and decreases to 0.9517 when the ultrasonic power increases to 1,000 W. This occurrence is attributed to the cavitation and acoustic flows effect of the ultrasonic which break off the dendritic crystal in the mushy zone and increase crystal nucleus. At the same time, the heat transfer and mass transfer are accelerated which make the distribution of temperature and alloying element more homogeneous. But the excessive ultrasonic power is not conducive to the improvement of solidification structure.

Posnjakite nanoparticles, Cu 4 SO 4 (OH) 6 · H 2 O, were synthesized by utilizing a new thio-Schiff base ligand as new capping agent via a microwave approach. The effects of molar ratio, surfactants, heating time and microwave power on morphology of the product were investigated. The as-synthesized posnjakite nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and energy dispersive X-ray analysis (EDAX). The effects of different parameters such as the molar ratio, surfactants, microwave power and irradiation time on the morphology of the products were investigated. Moreover, adsorption of methylene orange dye on posnjakite nanoparticles was considered and the uptake percent was determined to be >65% in 200 min.

The microstructure of as-cast and as-HIPed (hot isostatic pressed) K403 superalloy was investigated using a scanning electron microscopy (SEM), as component analysis was conducted by energy dispersive x-ray spectrometer (EDS). It was found that the microstructure of the alloy was improved significantly through HIP. Firstly, the microporosity and micropores in as-cast alloy were ameliorated effectively and the morphology of grains tended to be uniform. Moreover, the morphology of carbides at grain boundaries transformed from thread-like to granular. Uppermost, the size, shape and volume fraction of γ ′ phase were significantly optimized and γ ′ precipitates in two different sizes were generated in matrix. Nanoindentation experiment was then carried out to obtain the nanohardness and elastic modulus of as-cast and as-HIPed K403 superalloy. The results revealed an obvious increase in both nanohardness and elastic modulus after HIP. Conclusions could be drawn from the research that HIP could improve the microstructure of as-cast K403 superalloy, which could enhance the mechanical properties of the alloy positively.

Oxide dispersion strengthened (ODS) ferritic steels are the leading candidates of fuel cladding for Generation IV nuclear reactors due to their excellent properties such as excellent radiation tolerance and high-temperature creep strength. Mechanical milling with the aim of a fine dispersion of oxides in the metal matrix becomes the main process for the production of ODS steels. In order to clarify the influence of milling time on the precursor powders for 15Cr-ODS steel, the morphology and properties of mechanical alloying (MA) powders with different milling time were investigated by scanning electron microscopy (SEM), laser diffraction particle size analyzer, X-ray diffraction (XRD) and Vickers hardness tester. The experimental results showed that the powder was fractured and welded with rotation and vibration of container during mechanical milling. The mean powder size increased (0–1 h) firstly then decreased (2–60 h). Extending milling time to 70 h, the mean powder size increased again. The grain size decreased quickly at the initial stage of milling process (0–2 h) then trended to reach a saturation value. The Vickers hardness increased rapidly at the initial stage of milling, then reached a saturation value.

The clean utilization of the CuCl residue containing chloride produced from zinc hydrometallurgy residue is very important for the recycle of valuable metals. A new method of microwave roasting under oxygen enriched condition was put forward to strengthen the process of dechlorination. It was demonstrated that the dechlorination rate of CuCl residue by microwave roasting was higher than that of conventional roasting by tubular resistance furnace under the same conditions (temperature, holding time and atmosphere). After roasting at a temperature of 450°C for 120 min under an oxygen flow rate of 150 mL/min in microwave field, the dechlorination rate of CuCl residue was as high as 97%, increasing 17% compared to that of conventional roasting using tubular resistance furnace. The characterizations of phase variation of CuCl residue in microwave field by means of X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and Raman spectroscopy indicated that the process of dechlorination by microwave roasting under the oxygen enriched condition was much more efficient than conventional roasting.

The wear behavior of cast A7075 and A7075/SAF 2205 composite material fabricated by vacuum-assisted investment flask casting was investigated under dry sliding condition. The wear tests were carried out using a “ball-on-disc” type tribometer. In the wear tests, 100Cr6 and ZrO 2 balls were used as counterparts and the load, total distance and rotating speed were selected as 10 N, 100 m and 100 rpm, respectively. The results were evaluated using the friction coefficient–distance diagram, weight loss and wear rate. All worn surfaces were examined by scanning electron microscope and wear characteristics of the materials were discussed as a function of the microstructural features. It was concluded that composite material had lower friction coefficient, less weight loss and slower wear rate than that of cast material.

Manganese oxyhydroxide (MnOOH) nanoparticles were synthesized by the reaction of [Mn(Hsal) 2 ] complex and NaOH in the presence of ultrasound irradiation. In this study, the effect of different reaction parameters such as type of solvent, sonication time and type of surfactant on the morphology and the particle size of product were studied. The as-synthesized nanoparticles, with an average size of 10–15 nm, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and energy dispersive spectrometry (EDS). To the best of author’s knowledge, it is the first time that [Mn(Hsal) 2 ] complex is used as manganese source for the synthesis of MnOOH nanoparticles.

Barium–samarium titanate nanopowder (Ba 0.85 Sm 0.1 TiO 3 ) was synthesized through tartrate precursor route. The effect of annealing temperature on the formation, crystalline size, morphology and magnetic properties was systematically studied. The annealing temperature was varied from 600°C to 1,100°C. Thermal analysis measurement (TG-DSC, thermogravimetry-differential scanning calorimetry) was carried out on the precursor to characterize the thermal decomposition behavior. The results showed that the precursor of Ba–Sm–Ti mixture decomposed thermally in multistep weight loss up to about 480°C and perovskite Ba 0.85 Sm 0.1 TiO 3 started to form at ~520°C. X-ray diffraction and Fourier transform infrared (FTIR) spectroscopic measurements showed that the synthesized Ba 0.85 Sm 0.1 TiO 3 has a tetragonal dominant structure with the presence of intermediate SmTi 2 O 3 at lower annealing temperature. The ratio of SmTi 2 O 3 was decreased and completely disappeared at higher annealing temperatures. The tetragonality, the theoretical density and the crystalline size were increased by increasing annealing temperature. The crystalline size is still in nano-range of 12.4–19.9 nm even after annealing at 1,100°C. The morphology of the produced sample transferred from nano-cubes to nano-whisker to nano-mace (nano-aggregates) with the increase of annealing temperature.

The reduction tests of pellet were carried out from room temperature to 1,373 K in the condition of traditional blast furnace (TBF) and oxygen blast furnace (OBF) by thermogravimeter measurement. The apparent activation energy E , pre-exponential factor A and the controlling steps of reaction were determined by the non-isothermal method of Coats–Redfern. In the condition of TBF, the reduction is controlled by solid diffusion to interfacial chemical reaction at initial stage, and gas diffusion at final stage. In the condition of OBF, the controlling step switched from solid diffusion to gas diffusion + interfacial chemical reaction in the beginning and the interfacial chemical reaction at the late stage. Meanwhile, the transition temperature points of the controlling step were predicted. The transition temperatures are 750℃ and 900℃ in TBF and 630℃ (earlier 120℃ than in TBF) and 900℃ (after the insulation) in OBF.

Different properties of nanostructured materials such as physical, chemical and catalytic properties based on metal nanoparticles for various applications have been studied extensively on account of their attraction these days. Nanocrystalline tungsten oxide (WO 2 ) can chemically break down adsorbed organic contaminants in sunlight. In this research work, a novel photocatalyst of WO 2 /glass mat nanocomposite has been prepared by hot filament chemical vapor deposition (HFCVD) method, which is used for the degradation of dyestuff from dyes wastewater. Morphology of treated mat was observed using a scanning electron microscope (SEM). The amounts of tungsten oxide on glass mat were examined using the energy dispersive X-ray (EDX) method. Electrical surface resistivity was also measured. It is concluded that oxidant sedimentation has been done physically without any structural changes and increasing of reaction time led to an increase in deposition of tungsten oxide and finally led to a decrease in the electrical resistance of glass mat. The photocatalytic activities of tungsten-oxide-deposited glass mat were assessed by analyzing the decrease in concentration of the methylene blue (MB) as a colorant after exposure to ultraviolet (UV) irradiation. The MB concentration decreases continuously, concomitant with the UV irradiation time up to 240 min. The results show that the WO 2 /glass mat nanocomposite exhibits high photocatalytic activity and provides a good way in the degradation field of dyes wastewater.

Si 3 N 4 /nano-carbon black (CB) composite ceramics with boron nitride (BN) as interphase were fabricated by gelcasting. The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that the structures of BN interphase and BN coated CB were formed and were uniform distributed in the Si 3 N 4 ceramic. The permittivity ( ε ′ ε ″) of BN-coated CB was obviously lower than that of the pure CB, and the impedance of the BN-coated CB particles was close to the Z 0 ( Z 0 = 1, Z 0 is impedance under vacuum) compared with that of the CB particles; therefore, electromagnetic wave can enter into the BN-coated CB particles and be dissipated due to the high conductivity of CB particles. When incorporating the BN(CB) into Si 3 N 4 substrate, the electromagnetic wave can pass through Si 3 N 4 /nano-CB composite ceramics easily and be absorbed by CB, so the tg δ of the composite ceramic increased as the mass content of BN(CB) increased. The tg δ of the composite ceramic was about 0.43 when the content of BN(CB) increased to 15 wt%.

Cr-substituted Ni 0.2 Cu 0.2 Zn 0.6 Fe 2– x Cr x O 4 ferrites (where x = 0–1.0) were prepared by solid-state reaction. The effects of Cr content on structural and magnetic properties were investigated. X-ray diffraction (XRD) revealed the formation of ferrite particles with cubic spinel structure. The lattice parameter and average crystallite sizes are much dependent on the chromium content and are found to decrease with its increasing. The initial permeability ( μ i ) and saturation flux density ( B s ) decrease with the increasing Cr content. In addition, without substituted ceramic samples possess lower quality factor ( Q factor) than the NiCuZn ferrites with Cr substituted.