Band 34, Heft 3 -

IN100 superalloy castings were vacuum cast with the application of multi-electromagnetic field. The effect of multiple-electromagnetic field on the solidification structure of IN100 superalloy castings has been studied. The results show that with the application of the multiple-electromagnetic field composed of the main frequency rotary electromagnetic field with 60A current and the steady direct current electromagnetic field with 290A current, the shrinkage porosity of IN100 superalloy castings is greatly improved and the fine equiaxed grain fraction of IN100 superalloy castings is increased to 100%. Moreover, the action mechanism of multiple-electromagnetic field is discussed to explain its effect on improving the solidification structure of IN100 superalloy castings.

The effect of 4, 6 and 8 (mass%) Ce additions on the microstructure and creep resistance of the Mg-2.5Zn alloy was investigated by tensile creep test in the temperature of 200 °C, 225°C with the tensile stress of 60 MPa and tensile test in room temperature. The microstructure and phase composition of these alloys were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). The results showed that the grain sizes of Mg-2.5Zn- x Ce alloys were decreased and the creep strength of the base alloy was remarkably improved by increasing Ce addition. This were attributed to the formation of Mg 12 Ce, Mg 2 Ce and (Mg,Zn) 12 Ce compounds that morphology remains relatively stable at moderately elevated temperature which strengthen both matrix and grain boundaries during creep deformation.

An attempt is made to study the hot corrosion behaviour of Inconel 617 under mixed salt environment (Na 2 SO 4 , NaCl and/or V 2 O 5 ) at 900 and 1000 °C. The results were analysed and discussed with respect to mass change, XRD, optical image and SEM/EDAX. The oxide scales are enriched with Ni, Cr, Mo and Co at elevated temperatures. The presence of V 2 O 5 in the salt mixture is found to be the most influencing corrosion species for hot corrosion.

This study used ABAQUS finite element (FE) software to investigate the residual stress distributions of P92 welded pipes in both the as-weld and post weld heat treated (PWHT) condition. Sequential coupling quasi-static thermo-mechanical in conjunction with moving double ellipsoidal heat source and an element add/remove technique to simulate deposition of new weld material, are combined in the 3D FE analysis. To validate the simulation results, the residual stresses in axial direction at the surface of pipe were measured by X-ray diffraction technique and compared with the results of FE analysis. Detailed characteristic distributions of the residual stresses are discussed. Results show that the FE model can predict the residual stress distributions satisfactorily. Highest residual stresses on the outer surface are found in the last weld bead to be deposited. And the highest tensile residual stress for the full welded section take place in heat affected zone (HAZ) near the middle thickness. Larger residual sstress can be found around the welding start point along the pipe circumference. Comparison of heat treated specimen and untreated specimen illustrates that PWHT has a strong effect on the residual stress field.

In this study, the possibility of chromium extraction from Turkish chromite concentrate and the production of chromium oxide were investigated. For the conversion of chromium(III) into chromium(VI), NaOH was employed, as well as air with a rate of 20 L/min. The effects of the base amount, fusing temperature, and fusing time on the chromium conversion percentage were investigated in detail. The conversion kinetics of chromium(III) to chromium(VI) was also undertaken. Following the steps of dissolving the sodium chromate in water and filtering, aluminum hydroxide was precipitated by adjusting the pH level of the solution. The chromium(VI) solution was subsequently converted to Cr(III) by the combination of sulfuric acid and ethanol. Interestingly, it was observed that ethanol precipitated chromium as chromium(VI) at mildly acidic pH levels, although this effect is more pronounced for K 2 Cr 2 O 7 than Na 2 Cr 2 O 7 . On the other hand, in the strongly acidic regime, ethanol acted as a reducing agent role in that chromium(VI) was converted into Cr(III) whereas ethanol itself was oxidized to carbon dioxide and water. Subsequently, chromium hydroxide was obtained by the help of sodium hydroxide and converted to chromium oxide by heating at 800 °C, as indicated in thermo gravimetric analysis (TGA).

Carbon materials should have specific centers for its functionalities. In this study, the specific centers of polybenzoxazine carbides were studied for the first time. Three classical benzoxazine monomers were chose as the object. The transformation of nitrogen configuration of polybenzoxazines carbides was characterized via pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and X-ray photoelectron spectroscopy (XPS). The results showed that the tertiary amine nitrogen converted to pyridinic nitrogen and pyrrolic nitrogen incorporated in graphene residuals during the carbonization, which were the specific centers for the functionality.

Tramp elements in steels such as tin have been thought harmful because of the hot brittleness at grain boundaries and will be enriched in new steels because of difficulty of removal. It has been an important and difficult matter for metallurgist to use these elements. In the present paper, the as-cast steel containing high concentration of tin is prepared in laboratory and tin precipitates at the manganese sulphide inclusions have been found. A theoretical model is established to calculate the size of manganese sulphide inclusions acted as the heterogeneous nucleation site of tin precipitation. The results show that the inclusions with the smaller contact angle between tin precipitate is more advantageous to be the nucleus of tin heterogeneous nucleation. In this experiment, the manganese sulphide inclusions whose size is 2~4 μm in diameter can act as the nuclei of the nucleation of tin precipitation.

New refining technology of soda-calcium-silicon glass surfaces with inorganic compounds nano-molecules has been presented in the study. In order to determine modification of the glass surface SEM observation and EDX analysis have been carried out. The UV-VIS, photo-elasticity and ellipsometry examinations were carried out on glass samples. The results of investigations that have been conducted show that refining process of the glass surface by use of nanopowder inorganic compounds deposited electrostatically on glass surface provides forming of very thin (about 50 nm) surface layers [1]. This method of surface modification improves physical and chemical glass properties. In this paper results of microhardness test of refined glass were also presented.

A new approach to separate britholite phase from the rare-earth-rich slag by super gravity was investigated. With the parameter of G = 500, t = 5 min, T = 1423 K, almost all britholite phase is enriched in the concentrate, while the tailing is made up of CaF 2 phase. Under the hypothesis that the RE exists in the slag in terms of RE 2 O 3 , with the gravity coefficient G = 500, t = 5 min and T = 1423 K, the mass fraction of RE 2 O 3 in the concentrate is up to 24.67%, while the mass fraction of CaF 2 in the tailing is 50.01%. Considering that the mass fraction of RE 2 O 3 is 12.01% in the parallel sample, the recovery ratio of rare earth in the concentrate is up to 76.47% by centrifugal separation.

Effects of quenching plus tempering and intercritical annealing plus quenching heat treatments on the impact toughness properties of 1.7Ni-1.5Cu-0.5Mo pre-alloyed powder metallurgy steels with 0.2 (in mass%) graphite were investigated. Specimens were prepared by pressing at 670 MPa and sintering at 1250 °C. Different heat treatments, namely quenching and tempering, directly intercritically annealing and fully austenization plus intercritically annealing were carried out on the sintered specimens. The results showed that the impact toughness decreased with increasing intercritical annealing temperature in ferrite plus martensite dual phase powder metallurgy steels and with increasing tempering temperature in the quenched plus tempered specimens. Besides, impact toughness of fully austenizated plus intercritically annealed specimens was higher than those of quenched plus tempered and directly intercritically annealed specimens at the same hardness levels.

In this study, Al-Co-Ni ternary alloys were synthesized, in order to obtain low-cost starting material for Ni-based superalloy production, by a self-propagating high temperature synthesis (SHS) both under normal gravity conditions (a = 9.81 m/s 2 ) and under high gravity conditions (up to 1000 g-force) by using a centrifugal machine. The mixture of Co 3 O 4 -NiO powder were reduced by Al powder for the production of SHS alloys with the estimated compositions of 5–10 mass% Al, 20–65 mass% Co, 25–75 mass% Ni. The effect of green mixture compositions and centrifugal overload on combustion temperature, alloy/slag separations, chemical composition and microstructure of final alloys were investigated. The chemical analysis results showed that production of SHS alloys were achieved by having up to 86.12% of Co and 92.32% of Ni recoveries. The highest metal recovery value was obtained in SHS alloy with the estimated composition of 10%Al-65%Co-25%Ni by the addition of 20% Al 2 O 3 into the green mixture. The metal/slag separation efficiency increased by increasing the centrifugal overload.

The Electro-Coagulated Thermal Waste (ECTW) sample of the impedance spectroscopy investigation for electrical modulus and conductivity are presented. Electrical properties via temperature and frequency dependent impedance spectroscopy were investigated. Real and imaginary parts of electrical modulus were measured at various frequencies and a related Cole-Cole plot was acquired as well. The surface resistivity of the ECTW was measured by the four-point probe measurement technique, yielding a relatively high surface resistivity. As a result of this study, an effective building shielding material, which is a cost effective alternative, is proposed. The activation energy values were calculated from the Arrhenius plots at different frequencies. The transition region in this plot may be attributed to activation of ionic conductivity at lower temperatures.

The new technology of dechlorination from zinc oxide dust by microwave roasting was investigated, combined with the advantages of microwave selective heating and based on a thermodynamic analysis of zinc and lead halides. The associated dechlorination reactions were discussed in details and the effect of all the influencing parameters such as roasting temperature, holding time, stirring speed and air flow were systematically investigated. Experimental results showed that zinc oxide dust dechlorination rate could reach over 95% and meet the requirements of wet smelting electrolysis, given an air flow of 300 L/h, a stirring speed of 60 r/min, a roasting temperature of 650 °C and a holding time of 30 min. Microwave roasting provided a new solution to the dechlorination from zinc oxide dust.