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 effect of melt superheat on microstructure of Al4Fe2Mn1.5 Monel alloy made by vacuum melting method was studied. The results show that the alloy consists of dendritic γ matrix and γ′ phase, wherein γ′ phase h...The effect of melt superheat on microstructure of Al4Fe2Mn1.5 Monel alloy made by vacuum melting method was studied. The results show that the alloy consists of dendritic γ matrix and γ′ phase, wherein γ′ phase has two morphologies at different melt superheat. One is divorced eutectic γ′ which distributes in the interdendritic area, the other distributes dispersedly in single particle on the dendritic arm and exists in the petalform shape in the transition area between dendritic arm and interdendritic area. With the increase of superheat, the dendrite becomes finer, the primary dendritic arm is melted off and the secondary dendritic arm spacing decreases. The size of γ′ phase distributed on the dendritic arm becomes smaller and the divorced eutectic γ′ phase increases.展开更多
The specific heat of superheated Al 10Sr melts was determined at different heating rates between 1 K/min and 20 K/min using a differential scanning calorimeter(DSC). As a whole, the specific heat increases with increa...The specific heat of superheated Al 10Sr melts was determined at different heating rates between 1 K/min and 20 K/min using a differential scanning calorimeter(DSC). As a whole, the specific heat increases with increasing temperature. A hump is observed on the specific heat curve at the temperature corresponding to the phase boundary temperature dependent on heating rate. Moreover, the hump shifts to higher temperature in the measured temperature range from about 840 ℃ to 890 ℃ with increasing heating rate. At certain temperature in the higher superheated zone, the specific heat of the melt as a function of temperature shows a sharp rise . The result indicates that disorder zone fraction begins to increase while atom clusters fraction decreases at the breaking temperature. [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.
文摘The effect of melt superheat on microstructure of Al4Fe2Mn1.5 Monel alloy made by vacuum melting method was studied. The results show that the alloy consists of dendritic γ matrix and γ′ phase, wherein γ′ phase has two morphologies at different melt superheat. One is divorced eutectic γ′ which distributes in the interdendritic area, the other distributes dispersedly in single particle on the dendritic arm and exists in the petalform shape in the transition area between dendritic arm and interdendritic area. With the increase of superheat, the dendrite becomes finer, the primary dendritic arm is melted off and the secondary dendritic arm spacing decreases. The size of γ′ phase distributed on the dendritic arm becomes smaller and the divorced eutectic γ′ phase increases.
文摘The specific heat of superheated Al 10Sr melts was determined at different heating rates between 1 K/min and 20 K/min using a differential scanning calorimeter(DSC). As a whole, the specific heat increases with increasing temperature. A hump is observed on the specific heat curve at the temperature corresponding to the phase boundary temperature dependent on heating rate. Moreover, the hump shifts to higher temperature in the measured temperature range from about 840 ℃ to 890 ℃ with increasing heating rate. At certain temperature in the higher superheated zone, the specific heat of the melt as a function of temperature shows a sharp rise . The result indicates that disorder zone fraction begins to increase while atom clusters fraction decreases at the breaking temperature. [
