N. Ding

Nonequilibrium alloy formation in the immiscible Cu–Mo system studied by thermodynamic calculation and ion beam mixing

For the equilibrium immiscible Cu–Mo system characterized by a positive heat of formation (+19 kJ mol−1), thermodynamic calculation showed that by adding an adequate interfacial free energy, the Gibbs free energy of the Cu–Mo multilayered films could be elevated up to a higher level than the convex-shaped free energy curve of the amorphous phase and supersaturated solid solutions. Accordingly, ion beam mixing of the Cu–Mo multilayered samples did result in forming a unique amorphous phase with an alloy composition around 80 at. % Mo and two supersaturated solid solutions of fcc and bcc structures at around 27 at. % and 90 at. % Mo, respectively, matching well with the thermodynamic calculation.

Synthesis of amorphous alloys and amorphous-crystalline composites in the Cu-Nb-Hf system by ion beam mixing

Seven sets of Cu-Nb-Hf multilayered films were designed and prepared with the overall compositions of Cu21Nb65Hf14, Cu33Nb49Hf18, Cu34Nb34Hf32, Cu34Nb10Hf56, Cu50Nb23Hf27, Cu58Nb10Hf32, and Cu70Nb8Hf22, and an ion beam mixing experiment was then conducted using 200 keV xenon ions. It is found that the Cu-Nb-Hf system is a metallic glass forming one, and the single amorphous alloys could be synthesized in the Cu-Nb-based alloys with less than 18 at.% of Hf as a third addition. Also, when the Hf concentration is greater than 18 at.%, i.e., at the compositions of Cu34Nb34Hf32, Cu34Nb10Hf56, Cu50Nb23Hf27, Cu58Nb10Hf32, and Cu70Nb8Hf22, ion beam mixing resulted in the formation of amorphous-crystalline composites, which might have better mechanical properties than single-phase glassy alloys. In addition, a detailed discussion was presented for the formation mechanism of the amorphous alloys and amorphous-crystalline composites.

Formation of Metastable Phases Observed in the Zr-Co-Nb Multilayers upon Ion Beam Irradiation

Six multilayered films with overall compositions of Co10Zr80Nb10, Co10Zr70Nb20, Co20Zr70Nb10, Co30Zr60Nb10, Co20Zr60Nb20 and Co10Zr60Nb30 were first prepared by alternatively depositing high pure metals onto the NaCl single crystal substrates and then irradiated by 160 keV xenon ions with the doses ranging from 2×1014 Xe+/cm2 to 9×1015 Xe+/cm2. It turns out that several metastable phases, e.g. amorphous phase, were formed in these metallic multilayered films upon irradiation. Meanwhile, some interesting phase transformations were also observed with increasing irradiation doses. Besides, the phase formation and transformation mechanism of non-equilibrium alloy phases are discussed in terms of thermodynamics of solids and atomic collision theory. KEYWORDS: Zr-Co-Nb system, metastable alloys, phase transformation, ion beam irradiation

Glass forming ability of the Mo-Pd system studied by thermodynamic modeling and ion beam mixing

Glass forming ability/range of the Mo-Pd binary metal system was studied by thermodynamic calculations employing Miedema’s model and ion beam mixing of multiple metal layers. The thermodynamic calculations predict a narrow composition range of 8–26 at% Pd, within which metallic glass formation is energetically favored, whereas the experimental results showed that ion beam mixing was able to synthesize metallic glasses within a composition range 13–30 at% Pd, which was well in accordance with the prediction. Besides, in the Mo70Pd30 multilayered films, with varying the irradiation dose, a dual-phase metallic glass was formed, and it could be considered as an intermediate state. The possible mechanism for the formation of the metallic glasses was also discussed in terms of the atomic collision theory.