Volume 99, Issue 12

Based on the critically reviewed experimental data available in the literature, new phase transition temperatures and phase equilibria at 800 °C close to the Cu-Fe side of the Cu-Fe-Mn system were measured in the present work. The composition-invariant (γFe, γMn) → (αFe) massive transformations were observed in the two quenched alloys in the Fe-rich region. A set of consistent thermodynamic parameters of the Cu-Fe-Mn system was then obtained by taking into account all kinds of experimental data. Comparisons between the calculated and measured phase diagrams indicate that most of the experimental information is satisfactorily described by the present thermodynamic modeling. The liquidus isolines, liquidus projection and reaction scheme of this ternary system are also presented. Significant improvements have been made, compared with the previous assessments. The presently obtained parameters were applied in successfully solving the !surface fissure" during hot rolling of steel and controlling the micro-structure of the Cu-Fe based alloys in rapid solidification.

Following new findings by Y. Du et al. (Int. J. Mater. Res. 98 (2007) 855), the Al-Mn phase diagram was re-examined in the compositional range of ∼4 to 27 at.% Mn using scanning and transmission electron microscopy, energy-dispersive X-ray analysis and differential thermal analysis. The corrections to the Al-Mn phase diagram concerning the reactions involving the Al 6 Mn and Al 4 Mn phases reported in the above-mentioned contribution were not confirmed. Instead, our results were in agreement with those reported earlier by Murray et al. (Metall. Trans. A18 (1987) 385): the reaction Al 6 Mn + μ ↔ λ occurs at 695 °C, and L + μ ↔ Al 6 Mn at 705 °C. At higher Al concentrations, the reactions μ ↔ L + T, μ + v ↔ T and T ↔ L + γ 1 were revealed at ∼923, 913°C and 1001 °C, respectively, in good agreement with the literature data. Kinetic effects during phase transitions of the Al-Mn alloys are discussed on the basis of experimental results.

Ultra-pure AI 2 O 3 ceramics doped with 2000 ppm of Y 2 O 3 were sintered at 1500 °C or 1650 °C for 2 or 12 h. The re-sulting microstructure consisted of alumina matrix grains and second-phase precipitates. Y-doped alumina samples sintered at 1550 °C for shorter times (<2 h) contained primarily YAIO3-YAP precipitates. This is in contradiction of the binary equilibrium phase diagram for AI 2 O 3 and Y 2 O 3 , which predicts Y3AI5O12- YAG to be the first phase to appear, as the Y-concentration exceeds the solubility limit of α-A1 2 O 3 . The formation of YAG in co-existence with the YAP precipitates was observed in samples sintered at 1550°C for 12h and 1650°C for 2 h. The excess of yttrium in the grain boundary was 5.5 ± 0.9 Y-atoms/nm 2 for the specimen containing primarily YAP and 4.2 ± 1.2 Y-atoms/nm 2 in samples where YAP and YAG co-existed. The study demonstrates that in samples containing multiple precipitates, the grain-boundary excess concentration of Y atoms is controlled by the composition of the precipitates.

The EMF of galvanic cells with zirconia solid electrolytes was measured to determine the activity of gallium in liquid Ga-Bi-Sn alloys in the temperature range of 1000–1250 K along three pseudo-binary lines of (Bi y , Sn 1−y )-Ga where y = 0.25, 0.50 and 0.75. A mixture of Ga and Ga 2 03 was used as a reference electrode. The activity curves of Ga show positive deviations from ideality in the whole composition range. The excess free energies of mixing for Ga-Bi-Sn alloys have been calculated using the general solution model in the same temperature range and along same pseudo-binary lines. The gallium activities obtained by the EMF method and calculated using the general solution model at 1100 K were compared with literature data.

The present study shows that the hot deformation behavior of boron microalloyed steels can be quantitatively described by constitutive equations. These equations take into account both dynamic recovery and recrystallization phenomena. They have been fitted using experimental data taken from hot compression tests of four boron microalloyed steels in order to determine their characteristic parameters. The tests were carried out over a wide range of temperatures (950, 1000, 1050 and 1100°C) and strain rates (10 −3 , 10 −2 and 10 −1 s −1 ). The analysis of the characteristic parameters of the constitutive equations describing the hot flow behavior of these steels shows that boron additions play a major role in softening mechanisms rather than on hardening. A quantification of the boron effect is also presented. The experimental data were compared with the predictions of the proposed model and an excellent agreement between measured and predicted values for all boron micro-alloyed steels over a wide range of temperatures and strain rates was obtained.

The oxidation kinetics of β-SiA10N (Si 3 Al 3 O 3 N 5 ) powder prepared by reaction sintering have been investigated from both experimental and theoretical aspects. In the oxidation experiments, X-ray diffraction, optical microscopy and thermogravimetry were used to study the oxidation mechanism and kinetics of β-SiAlON powder. Based on the ex-perimental data, a new model for predicting the oxidation process of β-SiAlON powder has been developed, which offers an analytic form expressing the oxidation mass change as a function of time and temperature. The effect of particle size distribution on oxidation has especially been discussed. The new model was used to predict the oxidation behavior of β-SiAlON powder and the calculated results agreed well with the experimental data with the activation energy to be 253 kJ · mol −1 .

Fe-(17∼25)Mn alloys have been systematically investigated by means of X-ray diffraction, optical microscopy, differential scanning calorimetry and dilatometry. Such parameters of martensitic transformation as transformation temperatures, enthalpy, phase composition and microstructural changes are discussed taking into account the effect of thermocycling. A special focus is laid on the incompleteness of the γ → ∊ transformation that is attributed mainly to the antiferromagnetic → paramagnetic transition of austenite. The volume fraction of epsilon martensite has been determined using the results from X-ray diffraction and dilatometry tests.

On fabricating magnetorheolgoical elastomer, the mixture of iron particles and un-vulcanized rubber is placed under a curing magnetic field for some time so that iron particles are driven by the magnetic force to form a columnar structure; this process is called the pre-structure process. The microstructure of a magnetorheological elastomer sample is influenced by the pre-structure process, however, few reports address this problem in detail. This paper aims to study the effect of the pre-structure process on the magnetorheological elastomer performance. The pre-structure process is dominated by three influencing factors: magnetic field, curing time and temperature. A variety of magnetorheological elastomer samples were fabricated under different pre-structure conditions and their shear moduli were measured by using a dynamic mechanics analyzer machine. Scanning electron microscope images of these samples were also taken. The results demonstrated the magnetic field-induced modulus shows an increasing trend with magnetic strength before the magnetorheological elastomer samples reach magnetic saturation. The relative magnetorheological effect has an optimal value when the pre-structure field is 110 mT. The effects of the pre-structure time and temperature on the magnetorheological effect were also addressed by using the optimal pre-structure field. These three pre-structure conditions also affect each other. Thus, to fabricate higher-performance magnetorheological elastomer, these pre-structure conditions should be optimized. These results were also explained by study of the particle motion within the matrix.

A Cr + TiN double layer was coated on an SS-420 substrate using a hollow cathode discharge gun. The compositional analysis of the samples carried out by glow discharge optical emission spectroscopy confirmed the Cr/TiN constituents. X-ray diffraction pattern studies showed that due to the presence of chromium in the TiN matrix, preferential growth of TiN was changed from (200) to (111) reflection plane, leading to formation of a Cr + TiN double layer hard composite. However, at the same time, the hard coating layers exhibited unavoidable defects exposing them to corrosive environments. In this work, the corrosion protective behaviour of the Cr + TiN double layer was examined by potentiodynamic measurements in sodium chloride solution. It was inferred from this study that the increase in corrosion potential from −505 mV to −452 mV corresponding to the bare substrate and Cr + TiN coatings, respectively, led to the formation of more corrosion protective layers. The electrochemical impedance spectra analysis of the SS-420 substrate, TiN and Cr + TiN layers revealed that corrosion resistance increased and the electrochemical impedance of the Cr + TiN layer decreased. This is attributed to the corrosion protective properties of the resultant coating and its reduced permeability to the corrosive environment.

This article is devoted to experimental investigation of the influence of chemical composition on surface properties of inorganic oxidic systems. Through its contents it belongs to a broader area of investigation of systems that form a basis of refining metallurgical slags. The experiment itself was realised on equipment using the sessile drop method modified for high temperatures. The results were compared with theoretical concepts about intrinsic structural relations in melts. Due to the occurrence of anomalies in the temperature dependence of surface tension in the systems investigated and ensuing disagreement with theories, we have used high-temperature X-ray phase analysis. This analysis determined precipitation of individual phases during thermal load and added information for theoretical exploration and consideration about physico-chemical properties of melts working only with binary or ternary systems.

In order to obtain fine-microstructure magnesium alloys with superior mechanical properties, AZ61 alloy is processed by friction stir processing combined with rapid heat sinking in this study. Ultrafine-grain microstructure with average size less than 300 nm was observed in the resultant AZ61 alloy. The mean microhardness of the ultrafine-grain region reached 120 ∼ 130 HV, twice that of the AZ61 substrate. All these results demonstrate clearly that under a cooling rate high enough, ultrafine-grain structure in AZ 61 alloy with superior mechanical properties can be produced by one pass friction stir processing via dynamic re-crystallization.

Two refinement methods for Al-50Si alloy are presented in this article: one way is using a newly developed Si-20P alloy at 1573 K; another technique is using the Si-20P alloy in company with Al-TiO 2 -C mixture powder at 1473 K. Compared to the first method, the second one not only has better refinement effect on primary Si but also lower refinement temperature. These results are due to the combined effect of TiC and AlP on the refinement process, and the duplex TiC/AlP nucleus of primary silicon has been demonstrated using electron probe micro-analysis. Moreover, the reaction of Al-TiO 2 -C mixture powder with increasing temperature was investigated using differential scanning calorimetry, which shows that the TiC particles are produced at about 1473 K. AlP particles combine with the in-situ TiC particles in the melt, which is the main reason for the formation of a duplex nucleus, and the disregistry between TiC and AlP in low-index planes is also discussed.

The effect of the thickness of strips and cooling rates on the macro- and micro-structural features such as grain size, secondary dendrite arm spacing, and intermetallic phases, were studied for AA6111 aluminum alloy cast on a simulator of a horizontal single belt strip casting process. Different strips were investigated. As strip thickness decreased from 2.49 mm to 0.55 mm, the grain size decreased about 56 % and secondary dendrite arm spacing decreased about 56.7 %. An equation was developed based on the results obtained via thermal analysis which relates secondary dendrite arm spacing to cooling rate in this process. The formation and behavior of various complex intermetallic compounds in AA6111 were studied using scanning electron microscopy. The compositions of the precipitates were analyzed using electron probe microanalysis and their most likely stoichiometries determined.

Far infrared reflectivity spectra of single crystal Pb 0.85 Sn 0.15 Te doped with Ni were measured in the temperature range between 10 K and 300 K. Analysis of the experimental spectra was made using a fitting procedure based on the modified model of plasmon-phonon interactions and the optical parameters were calculated. Two local modes were observed and their origin was discussed.