Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat ...Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat on structural uniformity as well as average porosity, pore morphology of porous metals was studied. The experimental results show that, when the superheat is higher than a critical value (ΔTc), the bubbling or boiling phenomenon will occur and the gas bubbles will form in the melt and float out of the melt. As a result, the final porosity will decrease. In addition, a higher superheat will simultaneously cause a non-uniform porous structure due to the pores coalescence and bubbling phenomenon. Finally, a theoretical model was developed to predict the critical superheat for the hydrogen to escape from the melt and the corresponding escapement ratio of hydrogen content. Considering the escapement of hydrogen, the predicted porosities are in good agreement with the experimental results.展开更多
The distributions of local structural units of calcium silicate melts were quantified by means of classical molecular dynamics simulation and a newly constructed structural thermodynamic model. The distribution of fiv...The distributions of local structural units of calcium silicate melts were quantified by means of classical molecular dynamics simulation and a newly constructed structural thermodynamic model. The distribution of five kinds of Si-O tetrahedra Qi from these two methods was compared with each other and also with the experimental Raman spectra, an excellent agreement was achieved. These not only displayed the panorama distribution of microstructural units in the whole composition range, but also proved that the thermodynamic model is suitable for the utilization as the subsequent application model of spectral experiments for the thermodynamic calculation. Meanwhile, the five refined regions mastered by different disproportionating reactions were obtained. Finally, the distributions of two kinds of connections between Qi were obtained, denoted as Qi-Ca-Qj and Qi-[Ob]-Qj, from the thermodynamic model, and a theoretical verification was given that the dominant connections for any composition are equivalent connections.展开更多
The effectsof melt overheating degree on the undercooling degree and resultant solidification structures of Nd9Fe85-xTi4C2Bx（x=10, 12） glass-forming alloyswerestudied by differential thermal analysis combining with ...The effectsof melt overheating degree on the undercooling degree and resultant solidification structures of Nd9Fe85-xTi4C2Bx（x=10, 12） glass-forming alloyswerestudied by differential thermal analysis combining with solidification structure analysis. The results indicate that the undercooling degree of Nd9Fe85-xTi4C2Bx（x=10, 12） alloys significantly increaseswith the rise of melt overheating degree, and two overheating degree thresholds corresponding to the drastic increase of the mean undercooling degree are found for each of the alloys. The existence of two turning points of the mean undercooling degreescan be linked to the structure transitions inside the overheated melts, which result in the evident increase of volume fraction of amorphous phasein the solidified structures.展开更多
New experimental data are presented on the density and thermal expansion of solid and liquid magnesium and ultralight magnesium–lithium alloys containing 23.03 and 30.02 at.% Li, respectively. The measurements were p...New experimental data are presented on the density and thermal expansion of solid and liquid magnesium and ultralight magnesium–lithium alloys containing 23.03 and 30.02 at.% Li, respectively. The measurements were performed using the dilatometer method and the gamma-ray attenuation technique in the temperature range from 145 to 1244 K for magnesium and from 293 to ~1000 K for the alloys. The density changes during the solid?liquid phase transition were directly measured for Mg and the Mg70Li30 alloy. The temperature dependences and reference tables of the investigated volumetric properties were developed. A comparison of the obtained results with literature data was made. The study showed that the eutectic composition in the magnesium- lithium system differs from 23 at.% Li. The concentration dependence of molar volume of the magnesium-lithium liquid system was found to be almost linear in the interval of 0-30 at.% Li and deviated noticeably from the corresponding dependence for an ideal mixture.展开更多
The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum(ELTA)without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were com...The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum(ELTA)without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower,but the efficiency decreases rapidly when the superheating temperature is higher.The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature,but it also decreases obviously with the increase of the superheating temperature.One important reason is that the TiB2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased,thus decrease the number of the potent heterogeneous nuclei retained in the Al melt.If the Al-4B master alloy is added to the ELTA melt,the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature.This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..展开更多
基金Project(51271096)supported by the National Natural Science Foundation of ChinaProject(NCET-12-0310)supported by the Program for New Century Excellent Talents in University,Ministry of Education,China
文摘Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat on structural uniformity as well as average porosity, pore morphology of porous metals was studied. The experimental results show that, when the superheat is higher than a critical value (ΔTc), the bubbling or boiling phenomenon will occur and the gas bubbles will form in the melt and float out of the melt. As a result, the final porosity will decrease. In addition, a higher superheat will simultaneously cause a non-uniform porous structure due to the pores coalescence and bubbling phenomenon. Finally, a theoretical model was developed to predict the critical superheat for the hydrogen to escape from the melt and the corresponding escapement ratio of hydrogen content. Considering the escapement of hydrogen, the predicted porosities are in good agreement with the experimental results.
基金Project(2012CB722805)supported by the National Basic Research Program of ChinaProjects(50504010,50974083,51174131,51374141)supported by the National Natural Science Foundation of China+1 种基金Project(50774112)supported by the Joint Fund of NSFC and Baosteel,ChinaProject(07QA4021)supported by the Shanghai"Phosphor"Science Foundation,China
文摘The distributions of local structural units of calcium silicate melts were quantified by means of classical molecular dynamics simulation and a newly constructed structural thermodynamic model. The distribution of five kinds of Si-O tetrahedra Qi from these two methods was compared with each other and also with the experimental Raman spectra, an excellent agreement was achieved. These not only displayed the panorama distribution of microstructural units in the whole composition range, but also proved that the thermodynamic model is suitable for the utilization as the subsequent application model of spectral experiments for the thermodynamic calculation. Meanwhile, the five refined regions mastered by different disproportionating reactions were obtained. Finally, the distributions of two kinds of connections between Qi were obtained, denoted as Qi-Ca-Qj and Qi-[Ob]-Qj, from the thermodynamic model, and a theoretical verification was given that the dominant connections for any composition are equivalent connections.
基金Projects(51174121,51274125)supported by the National Natural Science Foundation of ChinaProject(2010R50016-30)supported by Zhejiang Province Science and Technology Innovation Team of Key Projects,ChinaProject supported by the K.C.Wong Magna Fund of Ningbo University,China
文摘The effectsof melt overheating degree on the undercooling degree and resultant solidification structures of Nd9Fe85-xTi4C2Bx（x=10, 12） glass-forming alloyswerestudied by differential thermal analysis combining with solidification structure analysis. The results indicate that the undercooling degree of Nd9Fe85-xTi4C2Bx（x=10, 12） alloys significantly increaseswith the rise of melt overheating degree, and two overheating degree thresholds corresponding to the drastic increase of the mean undercooling degree are found for each of the alloys. The existence of two turning points of the mean undercooling degreescan be linked to the structure transitions inside the overheated melts, which result in the evident increase of volume fraction of amorphous phasein the solidified structures.
基金the study of volume properties of melts and density changes during the solid–liquid transition was financially supported by RFBR (Grant No. 16-38-00669)
文摘New experimental data are presented on the density and thermal expansion of solid and liquid magnesium and ultralight magnesium–lithium alloys containing 23.03 and 30.02 at.% Li, respectively. The measurements were performed using the dilatometer method and the gamma-ray attenuation technique in the temperature range from 145 to 1244 K for magnesium and from 293 to ~1000 K for the alloys. The density changes during the solid?liquid phase transition were directly measured for Mg and the Mg70Li30 alloy. The temperature dependences and reference tables of the investigated volumetric properties were developed. A comparison of the obtained results with literature data was made. The study showed that the eutectic composition in the magnesium- lithium system differs from 23 at.% Li. The concentration dependence of molar volume of the magnesium-lithium liquid system was found to be almost linear in the interval of 0-30 at.% Li and deviated noticeably from the corresponding dependence for an ideal mixture.
文摘The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum(ELTA)without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower,but the efficiency decreases rapidly when the superheating temperature is higher.The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature,but it also decreases obviously with the increase of the superheating temperature.One important reason is that the TiB2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased,thus decrease the number of the potent heterogeneous nuclei retained in the Al melt.If the Al-4B master alloy is added to the ELTA melt,the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature.This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..
