The phase equilibria and compositions in Mg-rich side at 300 ℃ were investigated in Mg-Zn-Ca ternary system through the equilibrated alloy method by using scanning electron microscopy,electron probe microanalysis,X-r...The phase equilibria and compositions in Mg-rich side at 300 ℃ were investigated in Mg-Zn-Ca ternary system through the equilibrated alloy method by using scanning electron microscopy,electron probe microanalysis,X-ray diffraction and transmission electron microscopy.The results show that two ternary compounds T1 and T2 can be in equilibrium with the Mg-based solid solution in Mg-Zn-Ca system.T1 phase is a linear compound with the composition region（molar fraction） of 15% Ca,20.5%-48.9% Zn and balanced Mg at 300 ℃.Its hexagonal structure parameters decrease with increasing Zn content,i.e.a=0.992-0.945 nm,c=1.034-1.003 nm.T2 phase has hexagonal structure with the composition region of 26.4%-28.4% Mg,63.2%-65.5% Zn and 7.1%-8.4% Ca.At 300 ℃,the solubility of Zn in the Mg-based solid solution increases for the addition of Ca,the maximum solubility of Zn is 3.7%.Three-phase fields consisting of--Mg＋Mg2Ca＋T1,--Mg＋T1＋T2,--Mg＋T2＋MgZn and MgZn＋T2＋Mg2Zn3 exist in the Mg-Zn-Ca system at 300 ℃.展开更多
In the ion beam mixing experiments,eight Fe-Hf-Nb multilayered films,with overall compositions of Fe67Hf22Nb11,Fe67Hf11Nb22,Fe54Hf38Nb8,Fe54Hf30Nb16,Fe54Hf11Nb35,Fe25Hf67Nb8,Fe25Hf50Nb25 and Fe25Hf11Nb64,were irradiat...In the ion beam mixing experiments,eight Fe-Hf-Nb multilayered films,with overall compositions of Fe67Hf22Nb11,Fe67Hf11Nb22,Fe54Hf38Nb8,Fe54Hf30Nb16,Fe54Hf11Nb35,Fe25Hf67Nb8,Fe25Hf50Nb25 and Fe25Hf11Nb64,were irradiated by 200 keV xenon ions to doses ranging from 3×1014 Xe+/cm2 to 7×1015 Xe+/cm2.The results showed that unique amorphous phases were obtained at designed alloy compositions,falling in the favored glass-forming region deduced from three binary metal sub-systems.Interestingly,at some alloy compositions,the crystal-amorphous-crystal transformations were observed back and forth while varying the irradiation doses.In addition,at the alloy composition of Fe25Hf67Nb8,a metastable FCC phase was formed through an HCP-FCC structural phase transformation and it had a large lattice constant identified to be a=4.51 .Besides,the formation mechanism of non-equilibrium alloy phases was also discussed in terms of thermodynamics of solids and atomic collision theory.展开更多
基金Project(50731002) supported by the National Natural Science Foundation of ChinaProject(20082030) supported by the Natural Science Foundation of Liaoning Province,China
文摘The phase equilibria and compositions in Mg-rich side at 300 ℃ were investigated in Mg-Zn-Ca ternary system through the equilibrated alloy method by using scanning electron microscopy,electron probe microanalysis,X-ray diffraction and transmission electron microscopy.The results show that two ternary compounds T1 and T2 can be in equilibrium with the Mg-based solid solution in Mg-Zn-Ca system.T1 phase is a linear compound with the composition region（molar fraction） of 15% Ca,20.5%-48.9% Zn and balanced Mg at 300 ℃.Its hexagonal structure parameters decrease with increasing Zn content,i.e.a=0.992-0.945 nm,c=1.034-1.003 nm.T2 phase has hexagonal structure with the composition region of 26.4%-28.4% Mg,63.2%-65.5% Zn and 7.1%-8.4% Ca.At 300 ℃,the solubility of Zn in the Mg-based solid solution increases for the addition of Ca,the maximum solubility of Zn is 3.7%.Three-phase fields consisting of--Mg＋Mg2Ca＋T1,--Mg＋T1＋T2,--Mg＋T2＋MgZn and MgZn＋T2＋Mg2Zn3 exist in the Mg-Zn-Ca system at 300 ℃.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50871058 and 50971072)the Ministry of Science and Technology of China (Grant No. 2011CB606301)+1 种基金the Ministry of Education of China (Grant No. 200800030054)the Administration of Tsinghua University
文摘In the ion beam mixing experiments,eight Fe-Hf-Nb multilayered films,with overall compositions of Fe67Hf22Nb11,Fe67Hf11Nb22,Fe54Hf38Nb8,Fe54Hf30Nb16,Fe54Hf11Nb35,Fe25Hf67Nb8,Fe25Hf50Nb25 and Fe25Hf11Nb64,were irradiated by 200 keV xenon ions to doses ranging from 3×1014 Xe+/cm2 to 7×1015 Xe+/cm2.The results showed that unique amorphous phases were obtained at designed alloy compositions,falling in the favored glass-forming region deduced from three binary metal sub-systems.Interestingly,at some alloy compositions,the crystal-amorphous-crystal transformations were observed back and forth while varying the irradiation doses.In addition,at the alloy composition of Fe25Hf67Nb8,a metastable FCC phase was formed through an HCP-FCC structural phase transformation and it had a large lattice constant identified to be a=4.51 .Besides,the formation mechanism of non-equilibrium alloy phases was also discussed in terms of thermodynamics of solids and atomic collision theory.
