Abstract
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.
Highlights
Bulk metallic glasses (BMGs) are metastable alloys, which are commonly produced through rapid solidification of metallic melts[1,2,3,4]
Developing novel bulk metallic glass composites (BMGCs) comprising a glassy matrix with an exceptional high glass-forming ability (GFA) is needed from a practical point of view and, simultaneously, a more advanced and detailed understanding of the solidification process in these particular BMGCs is required in order to produce novel BMGCs with custom-made microstructures
“BT48” for example represents a composition, which contains 48% mole of crystals and 52% mole of glass. This estimation is based on the lever rule for the quasi-equilibrium phase diagram
Summary
Bulk metallic glasses (BMGs) are metastable alloys, which are commonly produced through rapid solidification of metallic melts[1,2,3,4]. CuZr-based BMGCs have two drawbacks: they are relatively poor glass formers, which severely restricts the dimensions of the samples and, simultaneously, it is rather difficult to control the morphology (volume fraction, size and distribution of the B2 phase) of the microstructure[12,13]. Both factors negatively affect the reproducibility of microstructures and the respective mechanical properties[12,13]. The two-phase quasi-equilibrium has strong implications on designing and understanding the evolution of typical microstructures found in cast BMGCs containing the β -phase
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