Volume 104, Issue 3

In the refining of solar-grade silicon using slag treatment, boron dissolved in the silicon is oxidized and rejected to a liquid oxide (slag) phase. In this study the partitioning of boron between liquid silicon and SiO 2 –CaO–MgO slags was examined at 1 873 K over a range of slag compositions and oxygen partial pressures. It was found that the distribution of boron is indeed dependent on both the slag composition and the oxygen partial pressure. The concentration of MgO seems to have little impact on the partition ratio.

In this paper, according to the thermal simulation compression test data, relationships for flow stress, temperature, strain rate and strain of semi-solid ZL201 alloy were studied through multiple regressions, and the constitutive equation of the alloy was established. The relationship between apparent viscosity and the shear rate was also researched. The results indicated that the maximum stress increased as strain rates increased at a constant temperature. The peak stress was clearly affected by deformation temperature, strain rate and strain. The plateau stress showed the same characteristics as the peak stress. In general, it increased slightly with increasing of the deformation temperature, except at high strain rates. The relationship between apparent viscosity and the shear rate was in accordance with the power law. The results provided a technological reference for the study of semi-solid die-casting numerical simulation of semi-solid ZL201 alloy parts. The viscosity of other semi-solid alloys could be calculated, as in the case of viscosity estimation of semi-solid ZL201 alloy.

Experimental studies have been conducted to determine the primary phases and liquidus temperatures in the binary “SnO”–SiO 2 and ternary “SnO”–CaO–SiO 2 systems in equilibrium with tin metal between 1 148 and 1 673 K, using a high temperature equilibration and quenching technique followed by measurement of phase compositions using electron probe X-ray microanalysis. The melting temperature of cassiterite (SnO 2 ) in equilibrium with tin metal was found to be between 1 398 and 1 403 K. The following primary phase fields were identified in the system: malayaite (CaSiSnO 5 ), pseudo-wollastonite (CaSiO 3 ), tridymite and cristobalite (SiO 2 ), and cassiterite (SnO 2 ). The liquidus of the “SnO”–CaO–SiO 2 system is dominated by the tridymite or cristobalite (SiO 2 ), and pseudo-wollastonite (CaSiO 3 ) primary phase fields in the range of compositions studied.

An extended unified microsegregation model with solid back diffusion effects and five different dendrite morphologies was used to investigate the solidification path of Al-4.37Cu-27.02Mg (wt.%) ternary eutectic alloy at different cooling rates and solid back diffusion coefficients, coupled with Thermo-Calc. It was indicated that the cooling rates ( R f ) had no obvious effect on the solidification path which was (L + α) → (L + α + T) → (L + α + β + T); but the solid back diffusion coefficient (Φ) had a great effect on the solidification path, which evolved gradually from (L + α) → (L + α + T) → (L + α + β + T) into (L + α) → (L + α + T) when Φ increased from 0 to 1. The volume fractions of primary α phase ( V α ), binary eutectic ( V 2E ) and ternary eutectic ( V 3E ) at each solidification path were calculated. It was shown that V 2E decreased with the increase of R f whereas V 3E increased and V α was almost invariant. The dependence of V 2E , V 3E and R f were determined by linear regression analysis given as: V 2E = −2.5lg R f + 47.5; V 3E = 6.4lg R f + 47. Increase in Φ lead to increases in V α and V 2E and decrease in V 3E . The predicted soldification paths and volume fractions of Al-4.37Cu-27.02Mg ternary eutectic alloy at different cooling rates were in good agreement with experimental results.

In this work, the effective diffusion coefficient of boron in the Fe 2 B phase was evaluated by considering the effect of chemical stresses in the case of paste-boriding of AISI 4140 steel. Two kinetic approaches were proposed to evaluate the diffusion coefficient of boron in the Fe 2 B phase in the temperature range of 1 123–1 273 K, and considering the effect of the boride incubation times. By applying the mass balance equation at the (Fe 2 B/substrate) interface and the theory of elasticity, it is possible to determine the effective diffusion coefficient of boron in the Fe 2 B phase. The obtained value of activation energy of boron diffusion in the presence of chemical stresses was estimated as 158.78 kJ mol −1 using the experimental parabolic growth constants taken from the literature. In addition, the simulated values of effective diffusion coefficients of boron in the Fe 2 B phase are found to be sensitive to the change in the boriding temperature and to the increase in the upper boron content in the Fe 2 B phase within its composition range

GTD-111 is an Ni-based superalloy used in manufacturing of gas turbine blades. The superalloy attains appropriate high temperature strength through precipitation hardening. In this research the effect of isothermal aging on the morphology evolution and characteristics of precipitates was investigated. Two different heat treatment cycles were applied to the specimens. In cycle I all samples were solution-treated at 1 200 °C for 4 h and water quenched to obtain supersaturated solid solution. A microstructure containing fine γ′ precipitates was produced after heat treatment cycle I. The second heat treatment, cycle II, consisted of reheating of the specimens in the precipitate partial dissolution zone at 1 150 °C for 2 h to get coarse primary precipitates, and then water quenching to obtain fine secondary precipitates. The precipitate coarsening in the fine and duplex size precipitate distribution was studied by means of aging of the specimens for various times at 1 000 °C. The results showed that during long-term annealing of the single size distribution (Cycle Ι), precipitates line up to reduce interactive free energy and grow to fairly coarse sizes along a direction. In cycle ΙΙ, the precipitates were split into a group of eight small cuboids or pairs of parallel plates and a large number of γ′ particles were closely aligned along a direction.

The hot forming behavior of a new steel used in manufacturing processes at high temperatures such as hot stamping has been studied in this article. Compression and tensile tests were performed at low and high strain rates in a temperature range of 1 173–1 473 K to simulate forming processing conditions. The deformation data obtained from these experiments were correlated with the Garofalo equation with a stress exponent of 4.4 and an activation energy of 277 kJ · mol −1 . This equation was used to determine the J-factor efficiency and stability of the steel. Temperatures in the range 1 423 to 1 473 K are recommended to conduct the forming process.

Magnetron sputtered freestanding thin films of two modified WE43 alloys (Mg4Y3Nd and Mg4Y3Gd) consist of a supersaturated single phase microstructure with a strong texture in [0001] direction for a wide range of deposition conditions. While the deposition conditions have no significant influence on the corrosion behaviour of these samples, they strongly influence the mechanical properties, which can be tuned between extremely brittle behaviour for high sputtering pressures (2.0 × 10 −2 mbar) and ductile behaviour with a maximum strain of about 18 % at room temperature for low sputtering pressures (8.0 × 10 −4 mbar) for both investigated alloys.

Stellite 6, Colmonoy 56, and SKS3 tool steel are typically the materials used as weld hardfacing claddings or as-cast to provide the needed wear resistance to a base material with the required mechanical properties. In this study, a series of Co- and Ni-based hardfacing alloys are successfully fabricated on a substrate of S45C carbon steel using the plasma transferred arc process with Stellite 6 and Colmonoy 56 powders. An Fe-based hardfacing alloy is used on commercial SKS3 tool steel for comparison. The microstructure, hardness and wear resistance of the three materials are investigated systematically. The two claddings and the as-cast SKS3 examined belong to the categories of Co-, Ni- and Fe-based hardfacing, respectively, with hard carbides/borides in their microstructures. The two different claddings are not only tested against SKS3 tool steel but also against each other using the ring-on-disk wear test. After the wear test, the worn surfaces are examined using scanning electron microscopy and energy dispersive spectroscopy to identify the dominant wear mechanisms. The experimental results show adhesive wear is confirmed by metal transfer from a hard surface to a softer one in Stellite 6 against SKS3, and in Colmonoy 56 against the Stellite 6 specimens, while surface deformation testifies to abrasive wear. The transfer layer formed on the surface prevents direct metal-to-metal contact and reduces the wear loss. For Colmonoy 56 against SKS3, adhesion does not occur; instead, Colmonoy 56 causes serious abrasion on SKS3 due to its greater degree of hardness and causes significant wear loss for SKS3.

To detect the suitability of the American Iron and Steel Institute grade 304, 309, 310, 316L steels and Hastelloy C276 substrates for thin film deposition using spray pyrolysis, the substrates were pre-heated between 400–700°C and soaked for one hour. American Society for Testing and Materials standards A262-A, E and G28-A were then applied. The substrates of 304 heated at 400, 600–700°C, the 310 heated between 450–700°C and the as-received 310 were not found suitable. However it was found that the 304, 309, and 310 substrates were suitable up to 550°C, the 316L up to 700°C and the C276 up to 550°C.

Nanostructured zinc oxide (ZnO) has been synthesized via a one step solution based wet chemical method. Zinc acetate dihydrate (Zn (CH 3 COO) 2 · 2H 2 O) was used as the precursor and its growth conditions were optimized for the formation of nanostructured ZnO. The powder pattern X-ray diffraction data of synthesized ZnO confirm particles of radius of about 20 nm with wurtzite hexagonal phase and preferential growth along (101) plane. Transmission electron microscopic results support the particle size value obtained through X-ray diffraction study. Clusters of nanostructured ZnO in agglomerated form are observed in scanning electron micrographs. The absorption bands observed at 509 cm −1 and 406 cm −1 in infrared spectra are assigned to ∊ M-O of the synthesized compound. The absorption spectrum shows a narrow peak near the band edge in the exciton absorption region at about 371 nm and a blue shift is observed with respect to the bulk exciton absorption, 375 nm. Thermo-gravimetric analysis indicates weight loss corresponding to the formation of ZnO. The mechanism for the growth of nanostructured ZnO in solution has also been discussed.

Experiments and numerical results are presented to demonstrate the adverse effects of a zone melting method in (Bi 2 Te 3 ) 0.25 (Sb 2 Te 3 ) 0.75 thermoelectric crystallization, on mass transport. The zone melting method shows a considerable effect from the deflection of the solid–liquid interface, and the Bi 2 Te 3 stoichiometry changes significantly. Electrical conductivity measurements of the crystallized ingot were carried out at stepped intervals of length (each step is 7 mm). A considerable gradient was observed in the readings from the tip to the end of the ingot. To understand this variation taking into account all empirical aspects of crystal growth, we conducted a numerical study because it gives vast information on the crystal growth process. Simulating the crystallization process and characterization of the ingot reveals a variation in the measured values of the thermoelectric parameters, which was attributed to the deviation of Bi 2 Te 3 concentration along the ingot.

The X-ray absorption near edge structure technique was employed for studies of coordination environments and valence states of impurity atoms (Mn, In and Ga) in a series of narrow band gap PbTe-based semiconductors. Impurity atoms' absorption data were analysed with the help of the Real Space Full Multiple Scattering FEFF8.2 code. These results are complemented with band structure calculations using the full potential augmented plane waves method extended by local orbitals using WIEN2k code. Impurity atoms are found to be off-centred from the regular lattice positions each in a specific manner, which leads to formation of significantly different local structures from that expected in host PbTe. Observed structural modifications are accompanied by the change in the impurity atoms' valence states. These findings support and extend our previous results obtained with various techniques on this class of materials.

Investigations were carried out to grain refine the aluminium alloys Al-6Si (all compositions given in wt.%) and Al-12Si as well as pure silicon by means of inoculation using boron nitride nano-particles. Comparative tests were performed using both conventional grain refiners based on titanium as well as without inoculants. Analyses were performed using scanning electron microscopy, tensile testing, thermographic and metallographic techniques. In doing this, a significant effect on grain refining is verified by inoculating using boron nitride which exceeds the effect of conventional grain refiners.