Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. ...Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry （XRD） and high resolution transmission electron microscopy （HRTEM）. The results show that, the whole devitrification of rapidly solidified Al87NiyCu3Nd3 amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, EIso and EKis and growth activation energies Eg are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the a（Al） particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α （Al） particles. For secondary crystallization, EIso, EKis and Eg of the first reaction are about 291,208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.展开更多
Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg_(24)Ni_(10)Cu_2)_(100-x)Nd_x(x=0, 5, 10, 15, 20) were prepared by melt spinning technology and their structures as well as gaseous h...Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg_(24)Ni_(10)Cu_2)_(100-x)Nd_x(x=0, 5, 10, 15, 20) were prepared by melt spinning technology and their structures as well as gaseous hydrogen storage characteristics were investigated. The XRD, TEM and SEM linked with EDS detections reveal that the as-spun Nd-free alloy holds an entire nanocrystalline structure but a nanocrystalline and amorphous structure for the as-spun Nd-added alloy, implying that the addition of Nd facilitates the glass forming in the Mg_2Ni-type alloy. Furthermore, the degree of amorphization of the as-spun Nd-added alloy and thermal stability of the amorphous structure clearly increase with the spinning rate rising. The melt spinning ameliorates the hydriding and dehydriding kinetics of the alloys dramatically. Specially, the rising of the spinning rate from 0(the as-cast was defined as the spinning rate of 0 m/s) to 40 m/s brings on the hydrogen absorption saturation ratio(R_5~a)(a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increasing from 36.9% to 91.5% and the hydrogen desorption ratio(R_(1 0)~d)(a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) rising from 16.4% to 47.7% for the(x=10) alloy, respectively.展开更多
Ti/Cr (atomic ratio 3:4) amorphous alloy was prepared by ball milling the rapidly quenched Ti/Cr ribbons for 30h, and then milled with MgH_2 for 50 h under Ar atmosphere to obtain MgH_2-30wt. % Ti/Cr composite. The XR...Ti/Cr (atomic ratio 3:4) amorphous alloy was prepared by ball milling the rapidly quenched Ti/Cr ribbons for 30h, and then milled with MgH_2 for 50 h under Ar atmosphere to obtain MgH_2-30wt. % Ti/Cr composite. The XRD results indicate that MgH_2 decomposed partly during ball milling process. The brittle MgH_2 and the mechanical driving force resulted in a highly dispersive distribution of the Ti/Cr amorphous phase in the Mg matrix. The favorable hydrogenation performance is mainly attributed to the com...展开更多
Structural evolution of alloys by ball milling during solid state amorphization were studied by means of XAFS technique. The first one is amorphization process of Fe and B powder mixtures by mechanical alloying (MA), ...Structural evolution of alloys by ball milling during solid state amorphization were studied by means of XAFS technique. The first one is amorphization process of Fe and B powder mixtures by mechanical alloying (MA), and the second one is amorphization process of ordered B2 CoZr intermetallic compound by mechanical milling (MM). The mixing process of Fe and B and disintegration process of ordered B2 CoZr intermetallic compound crystal were observed clearly in atomic level by XAFS method. The micro mechanism of amorphization process of alloy by ball milling was discussed.展开更多
The crystallization kinetics of amorphous (Nd3.6Pr5.4Fe83Co3B5) and the preparation of α-Fe/Nd2Fe14B nanocomposite magnets by controlled melt-solidification of (Nd3.6Pr5.4Fe83Co3B5) was investigated by employing DTA,...The crystallization kinetics of amorphous (Nd3.6Pr5.4Fe83Co3B5) and the preparation of α-Fe/Nd2Fe14B nanocomposite magnets by controlled melt-solidification of (Nd3.6Pr5.4Fe83Co3B5) was investigated by employing DTA, XRD, and TEM. The results show that a metastable intermediate phase (Nd8Fe27B24) prior to α-Fe and Nd2Fe14B phases is crystallized as the amorphous Nd3.6Pr5.4Fe83Co3B5 is heated to 1 223 K. The crystallization activation energy of α-Fe and Nd8Fe27B24 phases is larger at the beginning stage of crystallization, and then it decreases with crystallized fraction x for the former and has little change when x is below 70% for the latter, which essentially results in an α-Fe/Nd2Fe14B microstructure with a relatively coarse grain size about 20-60 nm and a non-uniform distribution of grain size in the annealed alloy. The α-Fe/Nd2Fe14B nanocomposite magnets with a small average grain size about 14 nm and a quite uniform grain size distribution were prepared by controlled melt-solidification of (Nd3.6Pr5.4Fe83Co3B5) at a wheel speed of 20 m·s-1 during melt-spinning. The magnets show a high maximum energy product of （BH）max = 194 kJ·m-3, which is nearly twice of that of the nanocomposite magnets made by annealing the amorphous Nd3.6Pr5.4Fe83Co3B5 precursor alloy.展开更多
基金Project(2005-5) supported by the Postdoctoral Foundation of Central South University, ChinaProject(2005038560) supported by the Postdoctoral Science Foundation of China
文摘Rapidly solidified Al87Ni7Cu3Nd3 amorphous alloy was prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter in a continuous or isothermal heating mode. phase transformation was investigated, with a special interest in primary crystallization, by using an in-situ examination of X-ray diffractometry （XRD） and high resolution transmission electron microscopy （HRTEM）. The results show that, the whole devitrification of rapidly solidified Al87NiyCu3Nd3 amorphous alloy involves two main processes of primary crystallization and secondary crystallization that consist mainly of two reactions. For primary crystallization, the apparent activation energies, EIso and EKis and growth activation energies Eg are about 153, 166 and 288 kJ/mol, respectively. The interdiffusion of Al atoms is a rate-controlled step of formation of the a（Al） particles, but slow diffusion of Ni and Nd atoms plays a significant role in retarding growth of the α （Al） particles. For secondary crystallization, EIso, EKis and Eg of the first reaction are about 291,208 and 290 kJ/mol, and those of the second reaction are about 367, 269 and 372 kJ/mol. The two reactions of secondary crystallization are controlled mainly in an interface-controlled three-dimensional mode, depending mainly on slow diffusion of Ni and Nd atoms.
基金Projects(51161015,51371094)supported by the National Natural Science Foundation of China
文摘Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg_(24)Ni_(10)Cu_2)_(100-x)Nd_x(x=0, 5, 10, 15, 20) were prepared by melt spinning technology and their structures as well as gaseous hydrogen storage characteristics were investigated. The XRD, TEM and SEM linked with EDS detections reveal that the as-spun Nd-free alloy holds an entire nanocrystalline structure but a nanocrystalline and amorphous structure for the as-spun Nd-added alloy, implying that the addition of Nd facilitates the glass forming in the Mg_2Ni-type alloy. Furthermore, the degree of amorphization of the as-spun Nd-added alloy and thermal stability of the amorphous structure clearly increase with the spinning rate rising. The melt spinning ameliorates the hydriding and dehydriding kinetics of the alloys dramatically. Specially, the rising of the spinning rate from 0(the as-cast was defined as the spinning rate of 0 m/s) to 40 m/s brings on the hydrogen absorption saturation ratio(R_5~a)(a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increasing from 36.9% to 91.5% and the hydrogen desorption ratio(R_(1 0)~d)(a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) rising from 16.4% to 47.7% for the(x=10) alloy, respectively.
基金supported by the Special Funds for Major States Basic Research Project (No. TG20000264-06) of MOST, China
文摘Ti/Cr (atomic ratio 3:4) amorphous alloy was prepared by ball milling the rapidly quenched Ti/Cr ribbons for 30h, and then milled with MgH_2 for 50 h under Ar atmosphere to obtain MgH_2-30wt. % Ti/Cr composite. The XRD results indicate that MgH_2 decomposed partly during ball milling process. The brittle MgH_2 and the mechanical driving force resulted in a highly dispersive distribution of the Ti/Cr amorphous phase in the Mg matrix. The favorable hydrogenation performance is mainly attributed to the com...
文摘Structural evolution of alloys by ball milling during solid state amorphization were studied by means of XAFS technique. The first one is amorphization process of Fe and B powder mixtures by mechanical alloying (MA), and the second one is amorphization process of ordered B2 CoZr intermetallic compound by mechanical milling (MM). The mixing process of Fe and B and disintegration process of ordered B2 CoZr intermetallic compound crystal were observed clearly in atomic level by XAFS method. The micro mechanism of amorphization process of alloy by ball milling was discussed.
文摘The crystallization kinetics of amorphous (Nd3.6Pr5.4Fe83Co3B5) and the preparation of α-Fe/Nd2Fe14B nanocomposite magnets by controlled melt-solidification of (Nd3.6Pr5.4Fe83Co3B5) was investigated by employing DTA, XRD, and TEM. The results show that a metastable intermediate phase (Nd8Fe27B24) prior to α-Fe and Nd2Fe14B phases is crystallized as the amorphous Nd3.6Pr5.4Fe83Co3B5 is heated to 1 223 K. The crystallization activation energy of α-Fe and Nd8Fe27B24 phases is larger at the beginning stage of crystallization, and then it decreases with crystallized fraction x for the former and has little change when x is below 70% for the latter, which essentially results in an α-Fe/Nd2Fe14B microstructure with a relatively coarse grain size about 20-60 nm and a non-uniform distribution of grain size in the annealed alloy. The α-Fe/Nd2Fe14B nanocomposite magnets with a small average grain size about 14 nm and a quite uniform grain size distribution were prepared by controlled melt-solidification of (Nd3.6Pr5.4Fe83Co3B5) at a wheel speed of 20 m·s-1 during melt-spinning. The magnets show a high maximum energy product of （BH）max = 194 kJ·m-3, which is nearly twice of that of the nanocomposite magnets made by annealing the amorphous Nd3.6Pr5.4Fe83Co3B5 precursor alloy.
