Qiang Jianbing

Ni-Hf metallic glasses and their atomic cluster formulas

Ni-Hf binary alloys are merely known as a category of marginal glass formers. In this system, the assessment of glass-forming abilities has not been made and the optimal glass-forming composition remains unclear. In the present work, Ni-Hf glass-forming compositions are explored using the atomic cluster plus glue atom model. Ni-Hf phase diagram shows a deep eutectic point at Ni65Hf35 which is associated two intermetallic phases, namely, Ni7Hf3 and Ni10Hf7. A predominant atomic cluster was first derived from the crystalline structures of the deep eutectic related phases, and several glass-forming compositions were determined considering the one or three glue atoms constraint condition. Rapid quenching results show that Ni71.43Hf28.57 and Ni68.75Hf31.25 metallic glasses can be made fully glassy. The latter can be well described with the model composition formula as [Ni-Ni7Hf5]Ni3. Among the melt-spun alloys, the Ni68.75Hf31.25 glass which locates in between the deep eutectic point and the Ni7Hf3 phase in the phase diagram, exhibited a highest crystallization temperature of 877 K and a lowest liquidus of 1482 K, and hence is suggested to be the optimal Ni-Hf glass former by the high reduced glass temperature criterion.

Ar12+ Induced Irradiation Damage in Bulk Metallic Glass (Cu47Zr45Al8)98.5Y1.5

The highly charged ion Ar12+ with an energy of 3 MeV is used for irradiating metallic glass (Cu47Zr45Al8)98.5Y1.5 and polycrystalline metallic W at the irradiation fluences of 1 × 1014 ions/cm2, 1 × 1015 ions/cm2 and 1 × 1016 ions/cm2. The main structure of metallic glass remains an amorphous phase under different irradiation fluences according to x-ray diffraction analysis. The scanning electron microscope observation on the morphologies indicates that no significant irradiation damage occurs on the surface and cross section of the metallic glass sample after different fluences of irradiation, while a large area of irregular cracks and holes were observed on the surface of metallic W at a fluence of 1 × 1016 ions/cm2, with cracks and channel impairments at a certain depth from the surface. The root-mean-square (rms) roughness of metallic glass increases with increasing fluence of Ar12+, while the reflectance decreases with increasing irradiation fluence. A nano-hardness test shows that the hardness of metallic glass decreases after irradiation. Under certain conditions, metallic glass (Cu47Zr45Al8)98.5 Y1.5 exhibits a higher capability of resistance to Ar12+ irradiation in comparison with polycrystalline W.

COMPOSITION DESIGN OF Ni–Nb–(Zr, Ta, Ag) TERNARY BULK METALLIC GLASSES BASED ON CLUSTER FORMULA OF Ni–Nb EUTECTIC

A cluster-plus-glue atom model was employed to design Ni-Nb based ternary bulk metallic glasses.The binary eutectic point Ni_(59.5)Nb_(40.5) was first interpreted by the model in form of a cluster formula[(Ni_(0.5)Nb_(0.5))-Ni_6Nb_6]Ni_3,where the cluster is(Ni_(0.5)Nb_(0.5))-centered icosahedron derived from a eutectic phase Ni_6Nb_7(Fe_7W_6 type).It was then pointed out that the best binary glass former Ni_(62)Nb_(38) could be interpreted based on the eutectic cluster formula by replacing the cluster center Nb_(0.5) with Ni_(0.5,namely[Ni-Ni_6Nb_6]Ni_3=Ni_(62.5)Nb_(37.5).To further improve the glass-forming ability,Zr,Ta and Ag are selected as alloying additions to partially replace Nb in the[Ni-Ni_6Nb_6]Ni_3 cluster formula,and glassy rods with a critical size of 3 mm are achieved at appropriate ternary compositions by copper-mould suction-casting.DTA measurements indicate these bulk metallic glasses exhibit high thermal stabilities,among which the[Ni-Ni_6Nb_5Ta]Ni_3 alloy has the highest T_g(glass transition temperature)of 935 K and T_x(crystallization temperature) of 952 K. Room-temperature compressive curves of[Ni-Ni_6Nb_5Zr]Ni_3 and[Ni-Ni_6Nb_5Ta]Ni_3 alloys show they have limited plasticity with a elongation of about 0.3%,fracture strength of the[Ni-Ni_6Nb_5Zr]Ni_3 and [Ni-Ni_6Nb_5Ta]Ni_3 BMGs are about 3.2 GPa and 3.4 GPa,respectively.