Metastable phase formation in nickel-aluminum alloys during ion beam mixing

ABSTRACTThe effect of ion beam mixing of nickel-aluminum alloys with 500 keV krypton ions has been investigated over a range of temperature, composition, ion dose, and post-irradiation thermal treatments. Samples were formed by aternate evaporation of layers of aluminum and nickel. A portion of these samples was subsequently annealed to form intermetallic compunds. Irradiations were performed at both room temperature and 80 K using the 2 MV ion accelerator at Argonne National Laboratory. Phase transformations were observed during both in situ irradiations in the High Voltage Electron Microscope(HVEM) at Argonne and also in subsequent analysis of an array of irradiated samples. Electron diffraction indicates the presence of metastable crystalline structures not present in the conventional nickel-aluminum phase diagram. Transformations occur at doses as low as 5×1014 cm−2 and continue to develop as the irradiation progresses up to 2×l016 cm−2. Layer mixing is followed through Rutherford Backscattering analysis. Samples are also checked with x-rays and Electron Energy Loss Spectroscopy (EELS). A thermodynamic argument is presented to explain the phase transformations in terms of movements on a free energy diagram. This analysis explains the interesting paradox concerning the radiation hardness of the NiAl[l] phase and the amorphous structure of mixed Ni-50% Al layers[2].

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On the Phase Formation During Ion-Beam Mixing

MRS Proceedings ◽

10.1557/proc-157-187 ◽

1989 ◽

Vol 157 ◽

Cited By ~ 1

Author(s):

L.-U. Aaen Andersen ◽

J. Bøttiger ◽

k. Dyrbye

Keyword(s):

Phase Formation ◽

Elevated Temperatures ◽

Driving Forces ◽

Metastable Phase ◽

Ion Beam ◽

Heat Of Mixing ◽

Preliminary Measurement ◽

Ion Beam Mixing ◽

Glass Forming ◽

Amorphous Structures

ABSTRACTThe phase formation during ion-beam mixing of binary transition-metal alloys has been studied by use of Xe* , Ar* , and Ne* as a function of temperature and composition. Especially the composition ranges, where only amorphous phases occur, i.e., the glass-forming ranges, have been investigated. Based on semiempi-rical data on free energies, metastable phase diagrams have been constructed and glass-forming ranges estimated for the case of negative heat of mixing. Taking into account the quite large uncertainties of the applied thermodynamic data, reasonable agreement is observed between estimated and experimental glass-forming ranges. In the case of positive heat of mixing, the initial thin-film structure is near thermodynamic equilibrium. However, for small values of the heat of mixing, it is still possible to form amorphous structures. In the absence of chemical driving forces, this formation cannot be explained in a similar way as in the case of negative heat of mixing. As the nucleation of crystalline phases may differ with and without irradiation, irradiation of amorphous structures at elevated temperatures may create new metastable phases. Preliminary measurement of crystallization of metallic-glass films during irradiation are reported.

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