Melt spinning technology was used to prepare the Mg2Ni-type(Mg24Ni10Cu2)100–x Ndx(x=0,5,10,15,20)alloys in order to obtain a nanocrystalline and amorphous structure.The effects of Nd content and spinning rate on the structures and electrochemical hydrogen storage performances of the alloys were investigated.The structure characterizations of X-ray diffraction(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM)linked with energy dispersive spectroscopy(EDS)revealed that the as-spun Nd-free alloy displayed an entire nanocrystalline structure,whereas the as-spun Nd-added alloys held a nanocrystalline and amorphous structure and the degree of amorphization visibly increased with the rising of Nd content and spinning rate,suggesting that the addition of Nd facilitated the glass forming of the Mg2Ni-type alloy.The electrochemical measurements indicated that the addition of Nd and melt spinning improved the electrochemical hydrogen storage performances of the alloys significantly.The discharge capacities of the as-cast and spun alloys exhibited maximum values when Nd content was x=10,which were86.4,200.5,266.3,402.5 and 452.8 mAh/g corresponding to the spinning rate of 0(As-cast was defined as the spinning rate of 0 m/s),10,20,30 and 40 m/s,respectively.The cycle stability(S20,the capacity maintain rate at 20thcycle)of the as-cast alloy always rose with the increasing of Nd content,and those of the as-spun alloys exhibited the maximum values for Nd content x=10,which were77.9%,83.4%89.2%and 89.7%,corresponding to the spinning rate of 10,20,30 and 40 m/s,respectively.
The thermal stability of microstructures is crucial for determining the performance of alloys in extreme environments.In the present work,the microstructural evolution and precipitation behavior in a high Nb-containing Ti45Al8Nb alloy during thermal exposure at 950°C were investigated.It was found that excessα2 phases in the as-cast microstructure were unstable and tended to decompose during thermal expo-sure.Hexagonal Ti 2 Al phases precipitated at lamellar interfaces and had a[1¯10]_(γ)[11¯20]_(α2)[11¯20]_(Ti2Al),(002)_(γ)(1¯100)_(α2)(1¯100)_(Ti2Al)crystallographic orientation relationship(OR)with the matrix.Stacking faults(SFs)generated inα2 phases during theα2→γphase transformation provided favorable nucleation sites for Ti 2 Al phases.
Dongxu LiGuoying ZhangGang LuYujie LiuJianjun WangChunming Liu
