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
Glass forming ability of the ternary Ni-Nb-Mo system was studied by ion beam mixing of the Ni-Nb-Mo multilayered films.In the experiment,metallic glasses i.e.amorphous alloys were formed in the Ni51Nb19Mo30,Ni52Nb35Mo...Glass forming ability of the ternary Ni-Nb-Mo system was studied by ion beam mixing of the Ni-Nb-Mo multilayered films.In the experiment,metallic glasses i.e.amorphous alloys were formed in the Ni51Nb19Mo30,Ni52Nb35Mo13,Ni61Nb15Mo24 and Ni72Nb20Mo8 multilayered films,while only solid solutions were obtained in the Ni24Nb29Mo47 and Ni26Nb53Mo21 multilayered films.It turned out that the Ni concentration played a dominating role in affecting the glass-forming ability of the system.Besides,thermodynamic calculations predicted a favored composition region for metallic glass formation,matching well with the observations from ion beam mixing.展开更多
For the Pd-Ta system characterized by a negative heat of formation of -78 kJ/mol, 200 keV xenon ion beam mixing with nano-sized Pd-Ta multilayered films was conducted to study the non-equilibrium phase formation. The ...For the Pd-Ta system characterized by a negative heat of formation of -78 kJ/mol, 200 keV xenon ion beam mixing with nano-sized Pd-Ta multilayered films was conducted to study the non-equilibrium phase formation. The results showed that uniform amorphous alloys can be formed within a composition range of 25 at%-78 at% Ta, which falls in the maximum possible amorphization range of 22 at%-80 at% Ta predicted by the empirical model. Moreover, two metastable crystalline phases both of FCC structure, yet with different lattice constants were obtained. Interestingly, a self-assembled fractal pattern was observed in the Pd52Ta48 multilayered films after irradiation to a dose of 1×1015 Xe+/cm2 and its dimension was determined to be 1.75±0.05. The possible mechanisms for the formation of amorphous and metastable crystalline phases as well as for the growth of the fractal pattern were discussed.展开更多
Single-phase and dual-phase metallic glasses as well as metallic glass based composites were synthesized in the Cu-Mo-Hf ternary metal system by 200 keV xenon ion beam mixing of far-from-equilibrium. It was found that...Single-phase and dual-phase metallic glasses as well as metallic glass based composites were synthesized in the Cu-Mo-Hf ternary metal system by 200 keV xenon ion beam mixing of far-from-equilibrium. It was found that Mo-Hf-based and Cu-Mo-based single-phase metallic glasses could be obtained at compositions around CulTMo20Hf63 and Cu34Mo57Hf9, respectively. Interestingly, at the nearly equal-atomic stoichiometry of Cu38Mo31Hf3i, a dual-phase Cu-Mo-Hf metallic glass, consisting both of the Mo-Hf-based and Cu-Mo-based phases, was first obtained at relatively low irradiation doses ranging from （1-5）×10^15 Xe＋/cm2, and a single-phase metallic glass was eventually obtained at a dose of 7×10^15 Xe＋/cm2. In addition, two glass-based composites were obtained at the compositions of Cu14Mo62Hf24 and Cu77Mo14Hf9, and they consisted of the Mo-Hf based and Cu-Mo based metallic glasses, dissolved with some uniformly distributed BCC Mo-based and FCC Cu-based crystalline solid solutions, respectively. The formation mechanism of the above described non-equilibrium alloy phases was also discussed in terms of the atomic collision theory.展开更多
Four sets of ternary Ni-Nb-Ta multilayered samples with overall compositions of Ni69Nb8Ta23,Ni55Nb13Ta32,Ni42Nb16Ta42 and Ni29Nb18Ta53,respectively were prepared and subjected to 185 keV xenon ion beam mixing.The expe...Four sets of ternary Ni-Nb-Ta multilayered samples with overall compositions of Ni69Nb8Ta23,Ni55Nb13Ta32,Ni42Nb16Ta42 and Ni29Nb18Ta53,respectively were prepared and subjected to 185 keV xenon ion beam mixing.The experimental results showed that in the four Ni-Nb-Ta multilayered samples,metallic glasses could all be obtained at appropriate doses,supporting the prediction directly from a proven realistic Ni-Nb-Ta interatomic potential through molecular dynamics simulations,and that two different atomic structures were observed,as in the corresponding selected area diffraction patterns,the locations of the diffused bands reflected from the metallic glass phases were observed at different angles for the Ni69Nb8Ta23 and Ni29Nb18Ta53 metallic glasses.Interestingly,Voronoi tellessation analysis indicated that the observed difference in atomic structures could be attributed to the distinct coordinate number spectra,i.e.,the spectrum of the Ni69Nb8Ta23 metallic glass has its coordinate number(CN) equal to 13 as dominating atomic configuration(with a weight of about 27%),whereas for the Ni29Nb18Ta53 metallic glass,CN=14 is the dominating atomic configuration(also about 27%).Moreover,the distinct atomic configurations of the obtained Ni-Nb-Ta metallic glasses could be correlated to the structures of the constituent metals of the ternary Ni-Nb-Ta system,as the first neighbor of fcc is 12 and the sum of the first and second neighbors of bcc is 14,implying the structural heredity did play a role in metallic glass formation.展开更多
Based on the Cu-Zr-Ti ternary phase diagram,four sets of Cu-Zr-Ti multilayered films with various compositions of Cu20Zr36Ti44,Cu36Zr31Ti33,Cu49Zr24Ti27,and Cu67Zr16Ti17 were prepared and then the ion beam mixing was ...Based on the Cu-Zr-Ti ternary phase diagram,four sets of Cu-Zr-Ti multilayered films with various compositions of Cu20Zr36Ti44,Cu36Zr31Ti33,Cu49Zr24Ti27,and Cu67Zr16Ti17 were prepared and then the ion beam mixing was carried out.It turned out that the increase of Cu content doesn't always have a positive effect on the glass forming ability.The glass forming ability of Cu49Zr24Ti27 was degraded due to the appearance of a Cs Cl-type B2 structure Cu Zr phase in the eutectic region.The experimental observations justify the existence of the Cu Zr phase under the non-equilibrium condition.Possible formation mechanisms for the crystalline phase were also discussed in terms of the atomic collision theory.展开更多
The positive temperature coefficient resistance ( PTCR) barium titanate ceramic samples have been prepared by the standard solid-state reaction method, and the ceramic samples have been treated by depositing copper fi...The positive temperature coefficient resistance ( PTCR) barium titanate ceramic samples have been prepared by the standard solid-state reaction method, and the ceramic samples have been treated by depositing copper films with magnetron sputtering method. The metallic copper films deposited on the ceramic substrates have been mixed at room temperature with argon ions in energy of 400 keV. Ion beam mixing induced modification of PTCR behavior of the ceramics was studied by using the ac complex impedance method and the resistance vs. temperature measurements . The results showed that room temperature resistance dramatically decreased and Curie point shifted toward higher temperature side for the ion beam mixed samples.展开更多
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.
基金supported from the National Natural Science Foundation of China (Grant Nos. 50971072 and 51131003)the Ministry of Science and Technology of China ("973" Program) (Grant Nos. 2011CB606301 and 2012CB825700)+1 种基金the Ministry of Education of China (Grant No. 200800030054)the Administration of Tsinghua University
文摘Glass forming ability of the ternary Ni-Nb-Mo system was studied by ion beam mixing of the Ni-Nb-Mo multilayered films.In the experiment,metallic glasses i.e.amorphous alloys were formed in the Ni51Nb19Mo30,Ni52Nb35Mo13,Ni61Nb15Mo24 and Ni72Nb20Mo8 multilayered films,while only solid solutions were obtained in the Ni24Nb29Mo47 and Ni26Nb53Mo21 multilayered films.It turned out that the Ni concentration played a dominating role in affecting the glass-forming ability of the system.Besides,thermodynamic calculations predicted a favored composition region for metallic glass formation,matching well with the observations from ion beam mixing.
基金supported by the National Natural Science Foundation of China (Grant No. 50971072)the Ministry of Science and Technology of China (Grant No. 2006CB605201)the Administration of Tsinghua University
文摘For the Pd-Ta system characterized by a negative heat of formation of -78 kJ/mol, 200 keV xenon ion beam mixing with nano-sized Pd-Ta multilayered films was conducted to study the non-equilibrium phase formation. The results showed that uniform amorphous alloys can be formed within a composition range of 25 at%-78 at% Ta, which falls in the maximum possible amorphization range of 22 at%-80 at% Ta predicted by the empirical model. Moreover, two metastable crystalline phases both of FCC structure, yet with different lattice constants were obtained. Interestingly, a self-assembled fractal pattern was observed in the Pd52Ta48 multilayered films after irradiation to a dose of 1×1015 Xe+/cm2 and its dimension was determined to be 1.75±0.05. The possible mechanisms for the formation of amorphous and metastable crystalline phases as well as for the growth of the fractal pattern were discussed.
基金the financial support from 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Single-phase and dual-phase metallic glasses as well as metallic glass based composites were synthesized in the Cu-Mo-Hf ternary metal system by 200 keV xenon ion beam mixing of far-from-equilibrium. It was found that Mo-Hf-based and Cu-Mo-based single-phase metallic glasses could be obtained at compositions around CulTMo20Hf63 and Cu34Mo57Hf9, respectively. Interestingly, at the nearly equal-atomic stoichiometry of Cu38Mo31Hf3i, a dual-phase Cu-Mo-Hf metallic glass, consisting both of the Mo-Hf-based and Cu-Mo-based phases, was first obtained at relatively low irradiation doses ranging from （1-5）×10^15 Xe＋/cm2, and a single-phase metallic glass was eventually obtained at a dose of 7×10^15 Xe＋/cm2. In addition, two glass-based composites were obtained at the compositions of Cu14Mo62Hf24 and Cu77Mo14Hf9, and they consisted of the Mo-Hf based and Cu-Mo based metallic glasses, dissolved with some uniformly distributed BCC Mo-based and FCC Cu-based crystalline solid solutions, respectively. The formation mechanism of the above described non-equilibrium alloy phases was also discussed in terms of the atomic collision theory.
基金supported from the National Natural Science Foundation of China (Grant Nos. 50971072,51131003)the Ministry of Science and Technology of China (973 Program) (Grant Nos. 2011CB606301,2012CB825700)the Administration of Tsinghua University
文摘Four sets of ternary Ni-Nb-Ta multilayered samples with overall compositions of Ni69Nb8Ta23,Ni55Nb13Ta32,Ni42Nb16Ta42 and Ni29Nb18Ta53,respectively were prepared and subjected to 185 keV xenon ion beam mixing.The experimental results showed that in the four Ni-Nb-Ta multilayered samples,metallic glasses could all be obtained at appropriate doses,supporting the prediction directly from a proven realistic Ni-Nb-Ta interatomic potential through molecular dynamics simulations,and that two different atomic structures were observed,as in the corresponding selected area diffraction patterns,the locations of the diffused bands reflected from the metallic glass phases were observed at different angles for the Ni69Nb8Ta23 and Ni29Nb18Ta53 metallic glasses.Interestingly,Voronoi tellessation analysis indicated that the observed difference in atomic structures could be attributed to the distinct coordinate number spectra,i.e.,the spectrum of the Ni69Nb8Ta23 metallic glass has its coordinate number(CN) equal to 13 as dominating atomic configuration(with a weight of about 27%),whereas for the Ni29Nb18Ta53 metallic glass,CN=14 is the dominating atomic configuration(also about 27%).Moreover,the distinct atomic configurations of the obtained Ni-Nb-Ta metallic glasses could be correlated to the structures of the constituent metals of the ternary Ni-Nb-Ta system,as the first neighbor of fcc is 12 and the sum of the first and second neighbors of bcc is 14,implying the structural heredity did play a role in metallic glass formation.
基金The National Natural Science Foundation of China(Grant No.51131003)The National Basic Research Program of China("973"Project)(Grant Nos.2011CB606301,2012CB825700)The Administration of Tsinghua University
文摘Based on the Cu-Zr-Ti ternary phase diagram,four sets of Cu-Zr-Ti multilayered films with various compositions of Cu20Zr36Ti44,Cu36Zr31Ti33,Cu49Zr24Ti27,and Cu67Zr16Ti17 were prepared and then the ion beam mixing was carried out.It turned out that the increase of Cu content doesn't always have a positive effect on the glass forming ability.The glass forming ability of Cu49Zr24Ti27 was degraded due to the appearance of a Cs Cl-type B2 structure Cu Zr phase in the eutectic region.The experimental observations justify the existence of the Cu Zr phase under the non-equilibrium condition.Possible formation mechanisms for the crystalline phase were also discussed in terms of the atomic collision theory.
文摘The positive temperature coefficient resistance ( PTCR) barium titanate ceramic samples have been prepared by the standard solid-state reaction method, and the ceramic samples have been treated by depositing copper films with magnetron sputtering method. The metallic copper films deposited on the ceramic substrates have been mixed at room temperature with argon ions in energy of 400 keV. Ion beam mixing induced modification of PTCR behavior of the ceramics was studied by using the ac complex impedance method and the resistance vs. temperature measurements . The results showed that room temperature resistance dramatically decreased and Curie point shifted toward higher temperature side for the ion beam mixed samples.
