•Obvious monotectic reaction occurs at 575 °C on ρ-T curves of Al63Cu27Sn10 alloy.•The range of the immiscible area is from 530 °C to 635 °C.•The changes of ρ-T curves reflect accurately the electronic transport properties and solidifying process.•Al63Cu27Sn10 alloy tends to form the core-shell structure of Al-Cu rich phase package on the Sn rich phase.Liquid structure of alloys has a remarkable influence on the microstructure and mechanical properties of solidifying alloy. Resistivity, as one of the sensitive physical properties to microstructure and macrostructure, plays a very important role in the research of liquid structure and can reflect the electronic transport properties. In this paper, the liquid structure and electronic transport properties of Al63Cu27Sn10 alloy have been investigated to explore its liquid phase separation and solidification process.In the heating and cooling process, there is good superposition and consistency of the ρ-T curves and DSC curves, which verifies the accuracy of resistivity method. The results show that monotectic reaction occurs at 575 °C, and the range of the immiscible area is from 530 °C to 635 °C for Al63Cu27Sn10 alloy. Under conventional casting condition, the microstructure of Al63Cu27Sn10 immiscible alloy melt and the solidifying process were discussed by differential scanning calorimetry (DSC), thermal analysis method (TAM), X-ray diffraction (XRD), scanning electron microscopy (SEM). The results show that: Al63Cu27Sn10 alloy dose occur liquid phase separation at the range from 530 °C to 635 °C, and the small volume phase rich Sn droplets tends to gather to the middle to form the core-shell structure.

•MST can promote the formation of core-shell structure.•Action mechanisms of MST were expounded from thermodynamics and kinetics.•Solidification process were studied with calorimetric and resistivity methods.•Resistivity method is a more effective method to investigate L-LPS.In this paper, the liquid-liquid phase separation (L-LPS) and solidification process of the Al75Bi9Sn16 immiscible alloy were studied with calorimetric and resistivity methods to ascertain the melt superheated treatment process. The impact of melt superheating treatment (MST) on the phase constitution and solidification microstructures were investigated using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to determine the structural sensitivity to the melt superheated degree, and find a new strategy for improving the forming ability of the core-shell structure of the Al75Bi9Sn16 alloy. The results show that: resistivity method is a more sensitive, intuitive, and effective method to investigate the liquid-liquid phase separation, and the liquid-liquid phase separation and precipitation of primary (Sn) phase occur in 1039 K–880 K and 460 K–403 K respectively. In addition, the core-shell structure with Sn-Bi-rich core and Al-rich shell can be formed under conventional casting conditions; the melt superheating treatment (MST) can promote the formation of core-shell structure by increasing solidification time t0 and decreasing the average solidification rate v and viscosity η.Download high-res image (150KB)Download full-size image

•Obvious difference can be observed on figures of Al75Bi9Sn16 alloy solidification with different cooling rates.•The Al75Bi9Sn16 alloy which is cast in copper and sand mold at 860 °C has liquid-liquid phase separation.•Exploration of correlation between cooling rate and micro mechanism of solidification.In this paper, the impact of cooling rate on solidification microstructures of Al75Bi9Sn16 alloy was studied for obtaining AlBiSn core-shell organizations by SEM under normal casting conditions. The results show that the core-shell structure is composed of SnBi-rich core and Al-rich shell and outermost thin layer of SnBi phase when Al75Bi9Sn16 alloy melt is cast in a copper mold; when Al75Bi9Sn16 alloy melt is cast in sand mold, alloy does not form the typical core-shell structure.

•The resistivity of Sn–Bi melts increases with the increase of temperature and Bi content.•Obvious turning points can be observed on ρ–T and viscosity–temperature curves.•Temperatures of turning points decrease with the increase of Bi content.•Temperature-induced liquid–liquid structure change occurs at 700–800 °C.•Large cooperative motions for molecular rearrangements result in structure change.In this paper, the liquid structure of Sn100 − xBix alloys (x = 0, 7, 30, 43, 80, 100) was studied with resistivity and viscosity method. The resistivity of liquid alloy increases with the increase of the temperature and Bi content, and obvious turning point is observed on resistivity–temperature and viscosity–temperature curves of different Sn–Bi alloy, while the resistivity increases linearly with increasing temperature before the turning point. Moreover, different compositions of alloy show different turning temperatures. These results indicate that temperature-induced liquid–liquid structure change occurs at 700–800 °C and is reversible, which may be formed by large cooperative motions for molecular rearrangements. Based on these results explored the melt structure from different aspects, Sn–Bi melt structure can be described and the nature of discontinuity of structural phase transition can be explored.

•The resistivity and DSC experiments were done at different heating rates to characterize the melt structure transition.•The methods of Kissinger and Ozawa were used to the study of the melt structure transition.•By comparing the calculated activation energy with the heat of vaporization of Sn, which further verified the fracture of Sn–Sn covalent bond in the melt structure transition.In this paper, the temperature dependence of electrical resistivity (ρ–T), the thermodynamic and kinetic characteristics of Sn57Bi43 eutectic alloy melt structure transition were investigated; the activation energy of structure transition (Ea) and the continuous heating transformation curve (CHT curve) were calculated by a thermal analysis method. The results showed that, both resistivity and thermal parameters of Sn57Bi43 alloy changed abnormally at the range of 850–1100 K, and their characteristic transition temperatures matched well each other, which verifies the existence of liquid–liquid structure transition(L–LST) in Sn57Bi43 alloy and the effectiveness of the resistivity and DSC experimental results, and the method of Kissinger and Ozawa can be applied to study the kinetic characteristics of Sn–Bi alloy melt structure transition.

•The resistivity of Al–Ni alloy melt increases with temperature and Ni content.•Certain temperature-induced liquid–liquid structure change occurs at 850–950 °C.•The melt-spun Al–Ni alloys contain amorphous structure at rotation speed of 2500 rpm.•The favorable melt structure can enhance corrosion resistance and hardness of alloy.•Results of melt-spun alloy verify the liquid aspect and show that this method is useful.In this paper, the liquid structure of Al100 − xNix alloys (x = 0, 2, 2.7, 5) was mainly studied with resistivity and rapid solidification method, the resistivity of liquid alloy increases with the increase of the temperature and Ni content, and shows the linear and nonlinear change successively; the various tests on melt-spun Al–Ni alloy show that the alloys, which contained amorphous structure and treated with higher melt temperature, have a favorable corrosion resistance and hardness, which can reflect and verify the liquid feature from rapidly solidified alloy and amorphous structure. These results indicate that the melt structure becomes homogeneous and disordered with rising temperature, and temperature-induced liquid–liquid structure change occurs at 850–950 °C. Based on these results explored the melt structure from different aspects, we describe this melt structure and discuss shallowly the relationship between the melt and amorphous structure.

Although the effect of overheating treatment on solidification is due to the liquid structure state, its nature and rule are still unclear. In this article, the effect of melt overheating on the melt structure transition and solidified structures of Al100−xLax alloys (x = 2, 3, 5) was mainly studied with resistivity and rapid solidification methods. The resistivity of liquid Al-La alloy increases with the temperature and La content, and it shows the linear and nonlinear changes successively. The corrosion resistance and hardness of melt-spun alloy improves with the increase in melt temperature and La content. These results indicate that the melt structure becomes homogeneous, dense, and disordered with the increase in melt temperature, and a temperature-induced liquid–liquid structure change occurs at 880–960°C. The homogeneous and dense melt structure features are remained partly in this melt-spun alloy and have a beneficial influence on its corrosion resistance and hardness. It is useful to study on the melt structure and solidified structures with the rapid solidification and resistivity method.

The effects of Al-P addition on the microstructure and mechanical properties of as-cast Mg-5%Sn-1.25%Si magnesium alloy were investigated. The results show that the phases of the as-cast alloy are composed of α-Mg, Mg2Sn, Mg2Si, little P, and AlP. The Chinese character shape Mg2Si phase changes into a granular morphology by P addition because AlP can act as a heterogeneous nucleation core for the Mg2Si phase. When 0.225wt% of Al-3.5%P alloy is added, the mechanical properties of the Mg-5%Sn-1.25%Si alloy are greatly improved, and the tensile strength increases from 156 to 191 MPa, an increase of 22.4% compared to the alloy without P addition. When the amount of Al-3.5%P reaches 0.300wt%, a segregation phenomenon occurs in the granular Mg2Si phase, and the tensile strength and hardness decrease though the elongation increases.

The influence of cooling rate and addition of La and Ce on the formation of nanoporous copper by chemical dealloying of Cu15Al85 alloy was studied. The components and microstructures of nanoporous copper were characterized by utilizing X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis. N2 adsorption/desorption experiments were used to evaluate specific surface areas of samples. The results showed that, with the increase of cooling rate, phase composition of precursor alloy almost had no change, the ligament size of nanoporous copper had a decrease trend, and specific surface area increased gradually. And it was found that the specific surface area of the nanoporous copper obtained by Cu15Al85 alloy containing La and Ce was 63.258 m2/g, which was more than 11.739 m2/g compared with the nanoporous copper dealloying by Cu15Al85 alloy without La and Ce under the same conditions.Section-view SEM image showing microstructure of NPC through dealloying of the melt-spun Cu15Al85 alloy containing La and Ce

Under the condition of melt thermal-rate treatment (MTRT) and low-temperature pouring (LTP), the tensile properties of Al-15%Si alloy are improved, the average size of primary Si is refined to about 20 μm from about 50 μm, and eutectic silicon can be well modified. The ultimate tensile strength and elongation are 201 MPa and 3.5%, and these values increase by 12% and 25%, respectively, compared with that obtained by conventional casting technique. The Al-15%Si alloy modified with Sr and RE additions was also studied for comparison purposes. The tensile properties of the Al-15%Si alloy treated with MTRT + LTP are superior to those modified with Sr or RE addition individually. The eutectic growth temperature difference between modified and unmodified melts was used to indicate the modification level. The modification effect of MTRT + LTP on Al-15%Si alloy is better than that modified with Sr or RE addition.

In this study, effects of thermalrate treatment (TRT) technique on microstructure and mechanical properties of hypoeutectic Al–Si alloys with addition of Ti were studied. The superheating temperatures of the melt were ascertained based on the DSC result. The results show that when the alloy castings in sand mold were treated with TRT technique at the superheating temperature of 930 °C, α-Al changes into smaller equiaxial crystals from coarse dendrites, and hardness of the alloy increases by 12.7 %, compared to that of the alloy treated with conventional casting technique. In addition, the supercooling increases to 8.5 °C and the characteristic temperatures of eutectic solidification are all the lowest with TRT technique at the superheating temperature of 930 °C. As holding time increases at the pouring temperature of 730 °C in TRT at the superheating temperature of 930 °C, the effects on microstructure and mechanical properties of the alloy casting in sand mold decrease. TRT technique plays a limited role in the alloy casting in permanent mold.

A testing device for the resistivity of high-temperature melt was adopted to measure the l resistivity of In–Bi system melts at different temperatures. It can be concluded from the analysis and calculation of the experimental results that the resistivity of InxBi100−x (x = 0–100) melt is in linear relationship with temperature within the experiment temperature range. The resistivity of the melt decreases with the increasing content of In. The fair consistency of resistivity of In–Bi system melt is found in the heating and cooling processes. On the basis of Novakovic's assumption, we approximately estimated the content of InBi atom clusters in InxBi100−x melts with the resistivity data by equation ρ ≈ ρInBixInBi + ρm(1 − xInBi). In the whole components interval, the content corresponds well with the mole fraction of InBi clusters calculated by Novakovic in the thermodynamic approach. The mole fraction of InBi type atom clusters in the melts reaches the maximum at the point of stoichiometric composition In50Bi50.Highlights► A testing device was adopted to measure the electrical resistivity of In–Bi system melts. ► A basically linear relation exists between the resistivity and temperature of InxBi100−x melts in measured temperature range. ► Based on Novakovic's assumption, the content of InBi atomic cluster in InxBi100−x melt is estimated with ρ ≈ ρInBixInBi + ρm(1 − xInBi) equation.

The use of lubricant is the key of warm compaction technology. Because of admixed different lubricants, the optimal parameters of warm compaction process were also different. This paper investigated the effect of two kind of lubricants (zinc stearate and polystyrene) on the parameters of warm compaction process by compared properties of Cu-based composite. It was shown that with the rise of compacting pressure, the density and hardness of the Cu-based composite increased, but the resistivity and gaining weight reduced. With increasing compacting temperature, the density and hardness first increased and then decreased, but the trend of resistivity and gaining weight just reversed. For the samples admixed zinc stearate (ZS), the optimal admixed concentration was 0.4 wt%, and the sample prepared at 120 °C and 650 MPa had the highest density and hardness, the lowest resistivity and gaining weight. For the samples admixed polystyrene (PS), these parameters were 0.7 wt%, 140 °C and 650 MPa, respectively. The properties of samples admixed PS were superior to that of admixed ZS.

The SiC gradiently coated carbon fiber/carbon (Cf/C) composites were prepared by a two-step rapid chemical liquid deposition (RCLD) method. The microstructure and properties of the composites were investigated using X-ray diffraction, scanning electron microscopy together with energy dispersive X-ray analysis, bending tests, and oxidation tests. The experimental results show that the surface layer of the composites is composed of SiC, pyrocarbon, and carbon fibers. Their inner area consists of pyrocarbon and carbon fibers. The SiC content gradiently decreases with increasing distance from the outer surface to the center of the composites. Furthermore, the thickness of the SiC layer increases with increasing tetraethylorthosilicate content and deposition time. SiC coatings have no significant influence on the bending strength of the composites. However, the oxidation resistance of the composites increases with increasing thickness of the SiC layer.

The behavior of GaSb melt with tellurium addition was investigated using viscometer and differential scanning calorimetry (DSC). Normally, the viscosity of all melts measured decreased with the increasing temperature. However, anomalous transition points were observed in the temperature dependence of viscosity for Ga–Sb–Te system. Corresponded with the abnormal points on the viscosity–temperature curves, there were thermal effect peaks on the DSC curves. Furthermore, viscous activation energy and flow units of these melts and their structural features were discussed in this paper.

Viscosity of SbBi melts under different magnetic induction intensity was investigated by using RHEOTRONI C VIII torsional oscillation viscometer with 0–0.27 T horizontal magnetic field. The viscosity of all melts measured decreased with increasing temperature under different magnetic intensity. Furthermore, the viscosity increased as horizontal magnetic intensity enhanced. The effect of magnetic induction intensity on the viscosity of melts increased with the content of Sb in the melts. The viscosity–temperature curves can be well fitted with Equation η = η0 + AB2.

The densities of Sb and Bi melts were investigated by an improved Archimedean method. The results show that the density of the Sb melt decreases linearly with increasing temperature, but the density of the Bi melt firstly increases and then decreases as the temperature increases. There is a maximum density value of 10.002 g/cm3 at 310°C, about 39°C above the melting point. The temperature dependence of the Sb melt is well fitted with the expression ρ=6.8590−5.8105×10−4T, and that of the Bi melt is fitted with ρ=10.3312−1.18×10−3T. The results were discussed from a microstructure viewpoint.

TiO2 modified Al2O3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO2–Al2O3 catalyst in CO2 methanation reaction was investigated. Compared with Ru/Al2O3 catalyst, the Ru/TiO2–Al2O3 catalytic system exhibited a much higher activity in CO2 methanation reaction. The reaction rate over Ru/TiO2–Al2O3 was 0.59 mol CO2·(g Ru)− 1·h− 1, 3.1 times higher than that on Ru/Al2O3 [0.19 mol CO2·(g Ru)− 1·h− 1]. The effect of TiO2 content and TiO2–Al2O3 calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO2–Al2O3 support is 2.8 nm, smaller than that on Al2O3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO2–Al2O3 catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO2 support, which hindered the aggregation of Ru nano-particles.Download full-size image