Volume 34, Issue 8 -

The effects of Y on microstructure and mechanical properties of as-cast AZ80–2Sn magnesium alloys were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. Y addition not only changes the as-cast microstructure but also influences the mechanical properties of AZ80–2Sn alloy. Unmodified AZ80–2Sn alloys under casting state show that Mg 17 Al 12 eutectic phase is semicontinuous and reticulated shape and distributes mainly at grain boundaries. Moreover, there are numerous Mg 2 Sn precipitate particles dispersing in Mg 17 Al 12 eutectic phases. Y addition to as-cast AZ80–2Sn alloys has an important influence on the precipitation phase. But there has no obvious effect on grain refinement with Y addition. The results show that the AZ80–2Sn alloys with variable Y contents all contain Al 2 Y phase. By adding Y, the amount of Mg 17 Al 12 is decreased and the dimension of that is reduced. Mg 17 Al 12 eutectic phase turns to discontinuous, and the more disperse phases occur with the increase of Y content. The tensile tests indicate that a minor addition of Y can contribute to the formation of the dispersed small polygonal Al 2 Y particles and the improvement in the room-temperature strength. However, excessive Y addition leads to the coarsening of Al 2 Y phases, and thus results in the decline of strength and ductility.

In this study, production of sponge iron by direct reduction of oxides and the effect of reductant on metallization were investigated. In the first stage of the study, scale formed during hot rolling of slabs was reduced in a rotating furnace using solid and gas reductants. Coal was used as solid reductant and hydrogen released from the combustion reaction of LNG was used as the gas one. The sponge iron produced by direct reduction was melted and solidified. In the second stage, Hematite ore in the form of pellets was reduced using solid carbon in a furnace heated up to 1,100°C for 60 and 120 minutes. Reduction degree of process was evaluated as a function of time and the ratio of C fix /Fe total . In the third stage, final products were examined using scanning electron microscope and microanalysis was carried out by energy dispersive x-ray spectrometer attached to the electron microscope. It is concluded that (i) direct reduction using both solid and gas reductants caused higher metallization compared to using only solid reductant, (ii) as the reduction time and ratio of C fix /Fe total increased %-reduction of ore increased.

BaCO 3 powders have been successfully synthesized by the microwave homogeneous precipitation method, using BaCl 2 · 2H 2 O, NaOH and (NH 2 ) 2 CO as raw materials with variety of different guide reagents. The phases and morphologies of raw materials after microwave homogeneous precipitation were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that 85°C of reaction temperature, 2 h of reaction time, 0.8 mol/L of Ba 2+ concentration, 2.5 of amount of sodium hydroxide and 6 of amount of urea were used in the further research work , and the optimum conditions for preparation of BaCO 3 powders were obtained. The XRD results show that the well-crystallized BaCO 3 powder synthesized has an orthorhombic unit cell. The characterization results show that different guide reagents play a significant role in determining uniform morphology of products. Based on the mentioned results, microwave homogeneous precipitation method can be applied effectively and efficiently for preparing BaCO 3 powders.

The deflected mode (DM) during the preparation of the broach in the flat and combined baizes and also on radial forging machine (RFM) was investigated for creating the rational technology of a broach and determining the optimum size of the angles of rotation and single squeeze reduction. The quantitative data was obtained by the method of final elements and the MSC.Super Forge program; the main consistent patterns of stress–strain state (SSS) distribution and temperature while modeling forging in flat and combined baizes, also on RFM with various angles of rotation and sizes of squeeze reduction were determined. The rational trial technology of forging of biphasic titanium alloys was developed and tested.

Failure of boiler tubes is the main cause of unit outages of the plant, which further affects the reliability, availability and safety of the unit. So failure analysis of boiler tubes is absolutely essential to predict the root cause of the failure and the steps are taken for future remedial action to prevent the failure in near future. This paper investigates the probable cause/causes of failure of the primary superheater tube in a thermal power plant boiler. Visual inspection, dimensional measurement, chemical analysis, metallographic examination and hardness measurement are conducted as the part of the investigative studies. Apart from these tests, mechanical testing and fractographic analysis are also conducted as supplements. Finally, it is concluded that the superheater tube is failed due to graphitization for prolonged exposure of the tube at higher temperature.

The paper reports metal loss data and general overview of steam oxidation behaviour of the selected alloys in water steam under atmospheric pressure in temperature range of 675–725°C. In this research, T22, T23, TP347HFG, HR3C and 718+ alloys were used. In this study, kinetics and metal loss data were obtained for better understanding corrosion degradation of the exposed materials. All the samples after 500-h exposure were characterized using environmental scanning electron microscopy (ESEM) in backscattered mode (BSE) with energy-dispersive x-ray spectroscopy (EDX). The results indicate that the highest corrosion degradation and metal loss were observed in T22, T23 alloys, moderate degradation was found in TP347HFG, whereas HR3C and 718+ nickel-based alloy showed good corrosion resistance.

In this study, an Al thin film interlayer of 80 nm thick has been applied on FeCoNi alloy substrate which possesses a low coefficient of thermal expansion, to enhance the interfacial adhesion of diamond films produced by microwave plasma-enhanced chemical vapor deposition. Characterization of the top deposit, interlayer and the underlying substrate was performed by Raman spectroscopy, energy dispersive X-ray analysis, X-ray photoelectronic spectroscopy, X-scanning electron microscopy and X-ray diffraction. The Al interlayer has effectively inhibited the formation of graphitic carbon and markedly enhanced the nucleation, growth and adhesion of diamond films. The beneficial role Al plays is primarily attributed to the formation of an alumina barrier layer on the substrate surface, as verified by interfacial analysis.

Investigation on reduction kinetics of scheelite(CaWO 4 ) provides important fundamental knowledge to control and optimize process of Ferrotungsten manufacturing and direct reduction of scheelite in steelmaking. In this work, the isothermal reduction kinetics of CaWO 4 powder by Si powder at 1,423 K, 1,473 K and 1,523 K, where all reactants and products are in solid state, was investigated by using X-ray diffraction quantitative analysis. Scanning electronic microscopy (SEM) attached with energy dispersive spectra (EDS) was also employed to investigate the microstructure of reaction interface. Both Jander model and Ginstling–Brounshtein model could describe kinetics of reduction of CaWO 4 well, whereas 3D interfacial reaction model could not describe the kinetics of reduction of CaWO 4 . The rate determining step for reduction of CaWO 4 could be diffusion of Si across product layer. The values of activation energies obtained by fitting kinetic data using Jander and Ginstling–Brounshtein model are as great as 379.93 kJ/mol and 387.16 kJ/mol respectively. The oxygen partial pressure during reduction has impact on the kinetics of reduction. The reduction was retarded by increase of oxygen partial pressure.

The effect of boron and titanium addition on the hot ductility of Nb-containing steel was investigated using hot tensile tests. The fracture surface and the quenched longitudinal microstructure were examined by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that both steel samples had the similar change from 1,100°C to 700°C. The hot ductility of Nb-containing steel with boron and titanium addition was higher than the steel without boron and titanium in the temperature range of 900–750°C. Because the formation of intergranular ferrite was inhibited by solute boron segregating on the grain boundary, the formation of TiN changed the distribution of Nb- and boron-containing precipitates and improved the amount of intragranular ferrite.

The microstructure and tensile properties of Incoloy 901 superalloy with various contents of carbon (0.02–0.09 wt%) were studied and a proper amount of carbon was determined to achieve good tensile properties at 650°C. The alloys were produced by vacuum induction melting and electro-slag refining (VIM+ESR) process and then they were hot rolled. After heat treatment, microstructures and 650°C tensile properties of specimens were investigated. Phase analysis with X-ray diffraction (XRD) indicated that Incoloy 901 contained Metallic carbides (MC)-type carbide enriched with Ti and Mo. With increasing carbon content from 0.02 to 0.09 wt%, carbide area fraction increased from 0.73% to 1.2%. Also, increasing of carbon content gave rise to higher amounts of carbide sizes. Using XRD patterns, the lattice parameters of γ and γ ′ phases were determined and the results showed that, with increase of carbon content, the lattice parameters of γ and γ ′ phases decreased and the mismatch between them increased from 0.119% for alloy containing 0.02 wt% to 0.167% for alloy containing 0.09 wt% C. The maximum strength of the alloy was obtained at 0.05 wt% carbon and ductility decreased slightly with increasing carbon.

Type 316L(N) stainless steel (SS) containing 0.02–0.03 wt% carbon and 0.06–0.08 wt% nitrogen is used as the major structural material for the components of fast reactors. Research is underway to improve the high-temperature mechanical properties of 316LN SS by increasing the nitrogen content in the steel above the level of 0.08 wt%. In this investigation, ball indentation (BI) technique was used to evaluate the effect of nitrogen content on the tensile properties of 316LN SS. BI tests were conducted on four different heats of 316LN SS containing 0.07, 0.11, 0.14 and 0.22 wt% nitrogen in the temperature range 300–923 K. The tensile properties such as yield strength and ultimate tensile strength increased with increase in nitrogen content at all the investigated temperatures. These results were consistent with the corresponding uniaxial tensile test results. These studies showed that BI technique can be used to optimize the chemical composition during alloy development by evaluating tensile properties with minimum volume of material.

The effect of Ga addition on alloy macrostructure, morphology and recovery rate of primary Si during the Al–Si–Ga alloy solvent refining process of silicon was studied in this work. The addition of Ga to Al–Si alloy could change the morphology of the primary Si. The average plate thickness of the primary Si increases with increase of Ga content. With the increase of Ga content, the average plate length of the primary Si crystals becomes larger when the Ga content is less than 5% in the Al–30%Si– x Ga alloy, but becomes smaller when the Ga content exceeds 5%. Al–Si–Ga alloys consist of three types, primary Si, Ga x Al 1– x , (α-Al+Si+β-Ga) eutectic. (111) is the preferred growth surface of the plate-like primary Si. The recovery rate of the primary Si increases with the increase of Ga content. When the Ga content increased to 20% in Al–30%Si– x Ga alloy, the relative recovery rate of the primary Si increased to 50.41% than that in Al–30%Si alloy.

This paper focuses on thermal stability of molten salts, operating temperature range and latent heat of molten salts at a high temperature. In this experiment, multi-component molten salts (purified Solar Salt) composed of purified NaNO 3 and purified KNO 3 were prepared by statical mixing method. Compared with unpurified Solar Salt, purified Solar Salt had a higher thermal stability. The optimal temperature would be increased from 500°C to 550°C, and the upper limitation temperature increases from 577.5°C to 593.7°C. Meanwhile, thermal stability and thermal cycling analysis showed the purified Solar Salt had a lower melting point and the deterioration time of molten salts was reduced. The melting point of purified Solar Salt decreases sharply to 223.8°C and the latent heat increases from 74.39 J/g to 80.79 J/g. Besides, the XRD and chemical analysis test indicated that the degree of degradation reduced and the thermal storage efficiency of purified Solar Salt was improved.