Metallic glasses (MGs) are very attractive for structural applications due to their large elastic strain, high strength and hardness, resulting from their unique atomic structure. However, MGs are brittle. Preparing metallic glass–crystal composites (MGCCs) from parent glass through thermal treatment is a useful method to induce ductility and work hardening. Thus, besides the direct applications of as-prepared MGs, the glasses can be used as a starting material to be processed, for example, by thermoplastic forming or thermal treatment to design components with desired shape and/or properties. In this view, it is of high importance to know the phase- transformation mechanisms and kinetics upon heating MGs, especially for rapid heating, which has not been sufficiently studied yet.
CuZrAl-based alloys, with near CuZr equimolar compositions, are suitable for producing MGCCs with improved plasticity owing to their good glass-forming ability and the formation of ductile B2 CuZr phase upon crystallization. However, the crystallization mechanism(s) and products have mainly been elucidated by extrapolating the available knowledge of the binary CuZr system. In the present work, a set of complementary techniques including resistive (Joule) heating, in situ high-energy synchrotron X-ray diffraction, conventional and ultrafast differential scanning calorimetry and containerless solidification during electromagnetic levitation is used to map the phase evolution ― crystallization and solid-state phase transformations ― in Cu₄₇.₅Zr₄₇.₅Al₅, Cu₄₇.₅Zr₄₈Al₄Co₀.₅ and Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MGs during isokinetic and isothermal annealing. The resistive heating devices, custom-built at the Leibniz Institute for Solid State and Materials Research Dresden – IFW Dresden, enable heating rates Φ to range from 10¹ up to 10⁵ K s⁻¹ in a vacuum.
Using the obtained experimental data, continuous-heating-transformation (CHT) diagrams for a heating rate range exceeding six orders of magnitude, covering the entire supercooled liquid region, and time-temperature-transformation (TTT) diagrams are constructed. The transformation maps reveal the competition between the Cu₁₀Zr₇, B2 CuZr and τ4 (Cu₂ZrAl) phases during crystallization. The formation of the primary phase and transformation sequence depends on the MG composition as well as on the heating rate. The critical heating rate to bypass the crystallization increases from ~30 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG to ~40 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG and to ~90 000 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, reflecting their glass-forming ability. The optimum heating rate to obtain glass–crystal composites with the predominant and desired B2 CuZr phase is evaluated to be Φ > 1 000 K s⁻¹ for Cu₄₇.₅Zr₄₇.₅Al₅ MG, Φ > 1 500 K s⁻¹ for Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MG, and Φ > 4 000 K s⁻¹ for Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG. Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ MG shows an increased propensity for the formation of brittle Cu₁₀Zr₇ intermetallic phase, compared to Cu₄₇.₅Zr₄₇.₅Al₅ and Cu₄₇.₅Zr₄₈Al₄Co₀.₅ MGs. The TTT diagram for the isothermal heating of Cu₄₆.₅Zr₄₈Al₄Nb₁.₅ shows an apparent double-nose shape which corresponds to the primary crystallization of Cu₁₀Zr₇ at lower temperatures and B2 CuZr at higher temperatures.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:88955 |
| Date | 11 January 2024 |
| Creators | Han, Xiaoliang |
| Contributors | Nielsch, Kornelius, Kaban, Ivan, Wang, Gang, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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