Volume 111, Issue 4

The enthalpies of mixing in liquid alloys of the binary Cu-Eu and ternary Al-Cu-Eu systems were determined over a wide range of compositions by means of isoperibolic calorimetry in the temperature range 1 300 - 1450 K. The enthalpies of mixing in the Cu-Eu system demonstrate small exothermic effects (ΔH min = -4.1 ± 0.5 kJ · mol -1 at x Cu = 0.70). The measurements for the liquid ternary Al- Cu-Eu alloys were performed along five sections (x Cu / x Eu = 0.70/0.30; 0.50/0.50 and 0.27/0.73 for x Al changed from 0 up to 0.30 and x Al /x Eu = 0.20/0.80 and 0.47/0.53 for x Cu changed from 0 up to 0.30). The enthalpies of mixing in the ternary system were found to be exothermic and increasing in absolute values from the Al corner towards the Al 0.40 Cu 0.60 -Al 0.60 Eu 0.40 section and from the constituent binary Cu-Eu system towards the same section. The minimum value of the integral enthalpy of mixing is expected in the vicinity of the Al 0.6 Eu 0.4 composition of the binary constituent Al-Eu system (about -23.00 kJ · mol -1 ).

Experimental investigations have been undertaken to determine the effect of Al 2 O 3 in slag on the gas/slag/matte/tridymite equilibria in the multi-component Cu-Fe-O-S-Si-Al system at 1 200 8C, and P(SO 2 ) = 0.25 atm. The experimental technique involves high temperature equilibration of synthetic samples on the open silica substrate in controlled gas atmospheres (CO/CO 2 /SO 2 /Ar), rapid quenching after a designated equilibration time followed by the compositional analysis of the condensed phases with electron probe X-ray microanalyzer. The experimental data of the present study provide information on the effect of alumina on the slag composition, such as the chemically dissolved copper, dissolved sulphur, and Fe/SiO 2 ratio in slag at tridymite saturation at different Cu in matte. The new data have been used as inputs for the optimization of the thermodynamic databases for the copper-containing systems and can also be used to evaluate the fluxing strategy in the copper smelting operation.

Phase transformations during the oxidation of fayalite (Fe 2 SiO 4 ) are investigated for the recovery of iron from iron-rich nickel slag by oxidation-magnetic separation. The proportions of various phases calculated by FactSage 7.1 show that augite and spinel are the major phases in the FeO-SiO 2 -MgO-CaO-O 2 system in air atmosphere. The decreased content of Fe 2+ shows that Fe 2 SiO 4 is gradually oxidized into Fe 3 O 4 with increasing oxidation time. XRD patterns demonstrate that Fe 3 O 4 and Ca(Mg,Fe)Si 2 O 6 are the dominant phases after the oxidation. The Mössbauer spectrum indicates that 93.1 wt.% of iron in oxidized nickel slag is in magnetic minerals, while a limited amount of iron is contained in non-magnetic minerals. Ca(Mg,Fe)Si 2 O 6 was formed during the heating stage in Ar atmosphere through the polymerization of SiO 4 4- and also via peritectic reaction after the isothermal oxidation.

In this study, hot deformation behavior of SP-700 titanium alloy was investigated by hot compression tests in the temperature range of 700-9508C and at strain rates of 0.001, 0.1, and 1 s-1. Final mechanical properties of the alloy (hot compressed at different strain rates and temperatures) were investigated using a shear punch testing method at room temperature. The flow curves of the alloy indicated that the yield point phenomenon occurs in the temperature range of 800- 9508C and strain rates of 0.1 and 1 s -1 . The microstructural analysis showed that dynamic globularization of the lamellar α phase starts at 7008C and completes at 8008C. The alpha phase was completely eliminated from b matrix due to deformation- induced transformation at 8508C. The microstructure of specimens compressed at 8508C and strain rates of 0.001 and 0.1 s -1 showed the serration of beta grain boundaries, whereas partial dynamic recrystallization caused a necklace structure by increasing strain rate up to 1 s -1 . The specimen deformed at 7008C and strain rate of 1 s -1 was located in the instability region and localized shear bands formed due to the low thermal conductivity of the alloy. The processing map of the alloy exhibited a peak efficiency domain of 54% in the temperature range of 780-8108C and strain rates of 0.001- 0.008 s -1 . The hot deformation activation energy of the alloy in the α/β region (305.5 kJ mol -1 ) was higher than that in the single-phase β region (165.2 kJ mol -1 ) due to the dynamic globularization of the lamellar a phase.

A new nanocrystalline Fe 71 B 23 Nb 6 alloy powder was prepared by mechanical alloying. The phase transformation and morphological and microstructural properties of the as-prepared alloy were investigated by scanning electron microscopy, laser granulometry, and X-ray diffraction with respect to the milling time (0- 200 h). During the milling process, it was observed that the dissolution of Nb and B atoms into the Fe matrix formed solid solutions of Fe (Nb), Fe (B), Fe 23 B 6 , Fe 2 B, and Fe (Nb, B). Moreover, the insertion of B atoms into the Nb network generated the Nb (B) phase. Furthermore, the minimum crystallite size was measured as approximately 1 nanometer. In addition, the dislocation density gradually increased with the extension of the milling time, and the crystallization of the partially amorphous phase occurred after 200 h of milling.

The dynamic recrystallisation behaviour of high-titaniumcontent 6061 aluminium alloy was investigated by hot compression tests within the temperature range of 623- 783 K and at strain rates of 0.01 -10 s -1 . The characteristics of the true stress-strain curves acquired in the hot compression tests were investigated, and it was observed that the dynamic recrystallisation of high-titanium-content 6061 aluminium alloy occurs within the range of deformation temperatures of 623 -783 K, with strain rates of 0.001 - 0.1 s -1 as evinced by a physically-based constitutive analysis. The kinetic model of dynamic recrystallisation was deduced to describe the dynamic recrystallisation behaviour of high-titanium-content 6061 aluminium alloy, and the dynamic recrystallisation grain size model was also constructed.

High-strength 690-MPa steel was prepared using a wire + arc additive manufacturing (WAAM) technology. The phase composition, microstructure, and crystal structure of highstrength 690-MPa steel samples were analysed, and the results show that a sample prepared using WAAM technology achieves a good formation quality. The metallographic structure was mainly acicular ferrite, massive ferrite, and granular bainite. The microhardness distribution of the vertical and horizontal sections of the samples is uniform. Excellent mechanical properties of the specimen were shown, including a horizontal yield strength of 536 MPa, a tensile strength of 760 MPa, an elongation of 23.5%, a Charpy impact value of 70 J at -508C, a vertical yield strength of 486 MPa, a tensile strength of 758 MPa, an elongation of 21.5%, and a Charpy impact value of 51 J at -508C.

Samples of Fe 82 Ga 18-x Al x (1.5 £ x £ 15) alloys were prepared using a high vacuum arc melting system and homogenized at 1100 8C for 3 h, 1 000 8C for 120 h, and 730 8C for 168 h. The Fe 82 Ga 18-x Al x (3 £ x £ 13.5) alloys were annealed at 550 8C for 15 min, while being exposed to a low magnetic field. The structure of the alloys was analysed by X-ray diffraction and optical microscopy. The magnetostriction coefficient of each of the samples was measured. It was found that the magnetostriction values of Fe 82 Ga 18-x Al x (3 £ x £ 13.5) alloys were enhanced by magnetic field annealing. The magnetostrictive growth rate of the Fe 82 Ga 15 Al 3 sample was particularly large at 165%, and the Fe 82 Ga 9 Al 9 sample showed the highest magnetostrictive coefficient (up to 114 · 10 -6 ) without compressive stress.

The effect of Sr addition on the microstructure and time-dependent corrosion properties of the AlSi12 eutectic alloy was investigated. The modified alloy contained 90 ± 3 ppm Sr. The microstructural differences in the eutectic structure of AlSi12 alloys were assessed in terms of the Si particle size and a-Al volume fraction. The unmodified and Sr-modified alloys were immersed for 1, 24, 72 and 120 h in 3.5 wt.% NaCl. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were performed to analyze the corrosion characteristics of the alloys. Sr addition led to a decrease in the Si particle size, and the formation of long dendritic a-Al. It was found that the presence of Sr resulted in more stable corrosion behavior up to 24 h. The deterioration of the corrosion behavior of Sr-modified alloy was observed with the further increase of immersion time.

This paper reports the synthesis of monodisperse spherical LiCoO 2 particles in a wide range of average diameter using a urea-based-uniform-precipitation method. The average diameter of LiCoO 2 particles can be varied from 2 to 14 lm with a uniform size distribution. The effective approach to maintain the size uniformity while changing the average size of LiCoO 2 particles is to keep the ratio of [CO(NH 2 ) 2 ] to [CoSO 4 ] at 8 even when the CoSO 4 and urea concentrations are changed.

The oxidation behavior of porous Ni-Cr-Fe materials prepared by reactive powder synthesis with different open porosity was studied in air at 6008C, 800 8C and 1 0008C. The differences in surface morphology, phase and pore structure parameters between material oxidized and non-oxidized were characterized by means of scanning electron microscopy, X-ray diffraction analysis and mercury intrusion. The results show that the oxidation rate of the samples which were oxidized at 600 8C for 340 h, for 560 h at 800 8C and for 560 h at 1 000 8C were 0.00027% 2 h -1 , 0.0558% 2 h -1 , and 0.64412% 2 h -1 , respectively. All the oxidation kinetics curves obeyed the parabolic law, exhibiting excellent high temperature oxidation resistance.