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- ItemGlass-forming ability, phase formation and mechanical properties of glass-forming Cu-Hf-Zr alloys(Amsterdam : Elsevier B.V., 2019) Kosiba, K.; Song, K.; Kühn, U.; Wang, G.; Pauly, S.The influence of Hf additions on the glass-forming ability (GFA), phase formation and mechanical properties of Cu50HfxZr50-x (x = 2,5,10,20 at.%) alloys has been systematically investigated. We report on a distinct correlation between phase formation and GFA of Cu50Zr50-based alloys. Increasing additions of Hf reduce the thermal stability of the high-temperature B2 Cu(Hf,Zr) phase, while the thermal stability of the corresponding undercooled melt is enhanced. The GFA of these alloy series gradually raises up to 10 at.% Hf, whereas at 20 at.%Hf, the GFA is drastically lowered, since the B2 Cu(Hf,Zr) phase becomes unstable and the precipitation of the low-temperature equilibrium phases is favoured. This interrelation determines the microstructure and results in the formation of Cu-Hf-Zr-based bulk metallic glass composites. These composites not only show appreciable macroscopic plastic strain, but also high yield strength.
- ItemTwo-phase quasi-equilibrium in β-type Ti-based bulk metallic glass composites(London : Nature Publishing Group, 2016) Zhang, L.; Pauly, S.; Tang, M.Q.; Eckert, J.; Zhang, H.F.The microstructural evolution of cast Ti/Zr-based bulk metallic glass composites (BMGCs) containing β-Ti still remains ambiguous. This is why to date the strategies and alloys suitable for producing such BMGCs with precisely controllable volume fractions and crystallite sizes are still rather limited. In this work, a Ti-based BMGC containing β-Ti was developed in the Ti-Zr-Cu-Co-Be system. The glassy matrix of this BMGC possesses an exceptional glass-forming ability and as a consequence, the volume fractions as well as the composition of the β-Ti dendrites remain constant over a wide range of cooling rates. This finding can be explained in terms of a two-phase quasi-equilibrium between the supercooled liquid and β-Ti, which the system attains on cooling. The two-phase quasi-equilibrium allows predicting the crystalline and glassy volume fractions by means of the lever rule and we succeeded in reproducing these values by slight variations in the alloy composition at a fixed cooling rate. The two-phase quasi-equilibrium could be of critical importance for understanding and designing the microstructures of BMGCs containing the β-phase. Its implications on the nucleation and growth of the crystalline phase are elaborated.