Microstructure development and mechanical properties of cast and thermo-mechanically treated eutectic high-entropy alloys
Doktorsavhandling, 2021

The recently emerging high-entropy alloys (HEAs) present a novel alloying strategy, significantly expanding the scope of metal alloy design. Single-phase HEAs, nevertheless, suffer from the strength-ductility trade off as seen in conventional metallic materials. A possible solution is found in the recently developed eutectic HEAs (EHEAs), which borrow the concept of using lamellar structures as in-situ composites to balance mechanical properties. The first such alloy, AlCoCrFeNi2.1, with an FCC(L12) + BCC(B2) lamellar microstructure, remains the most studied EHEA. Despite much work put into its characterization, much remains to be understood. For example, more efforts have been given to optimize the mechanical properties while less are given to quantitatively describe the microstructure. Various thermo-mechanical treatments have been used to modify the mechanical properties of the AlCoCrFeNi2.1 alloy, however, previous studies mainly focused on the fully recrystallized materials, while a clear understanding of the recrystallization process is still missing, and the potential of partial recrystallization remains to be explored.

The first part of this thesis work focuses on the as-cast microstructures of the eutectic and near-eutectic compositions of the AlCoCrFeNi2.1 system. Quantification of the phase volume and lamellar spacing is performed as a function of the Ni content. Orientation relationship and misorientation angle-axis changes in the five investigated alloys are also studied, with the previously unknown dependency of misorientation angle on the Ni content revealed. Some attention is also given to irregular microstructures in eutectic and near-eutectic compositions, which have not been discussed in previous studies.

In the second part of this thesis work, a systematic study of the recrystallization process and the correlation between microstructure and mechanical properties in the thermo-mechanically treated AlCoCrFeNi2.1 alloy is undertaken. Distinctive behavior of the constituent phases during recrystallization, with varying rates of recrystallization and grain growth are observed, providing new insights to the recrystallization process in this alloy. Furthermore, it is shown that by controlling the annealing temperature and time, hetero-deformation induced hardening could lead to abnormal hardening in the as-rolled alloy, providing a new strategy to achieve high-strength with acceptable ductility in EHEAs.

high-entropy alloys

EBSD

eutectic alloys

recrystallization

heterogeneous structure

strength-ductility trade-off

Virtual Development Laboratory (VDL), Chalmers Tvärgata 4C
Opponent: Professor Pasi Peura, Tampere University, Tampere, Finland

Författare

Adrianna Lozinko

Chalmers, Industri- och materialvetenskap, Material och tillverkning

Quantification of microstructure in a eutectic high entropy alloy AlCoCrFeNi2.1

IOP Conference Series: Materials Science and Engineering,; Vol. 580(2019)

Paper i proceeding

Microstructural characterization of eutectic and near-eutectic AlCoCrFeNi high-entropy alloys

Journal of Alloys and Compounds,; Vol. 822(2020)

Artikel i vetenskaplig tidskrift

A. Lozinko, R. Gholizadeh, Y. Zhang, U. Klement, N. Tsuji, O. V. Mishin, S. Guo, Evolution of microstructure and mechanical properties during annealing of a heavily rolled AlCoCrFeNi2.1 eutectic high-entropy alloy

A. Lozinko, R. Gholizadeh, L. Han, U. Klement, N. Tsuji, S. Guo, Effect of annealing temperature on microstructure and mechanical properties of a partially recrystallized AlCoCrFeNi2.1 eutectic high-entropy alloy,

A. Lozinko, R. Gholizadeh, L. Han, U. Klement, N. Tsuji, S. Guo, Rapid annealing induced hardening in a cold-rolled AlCoCrFeNi2.1 eutectic high-entropy alloy

Compositionally complex alloys, better known as high-entropy alloys (HEAs), present a paradigm-shifting strategy when it comes to designing metallic materials. Unlike steels, where iron is the dominant element, there exists no dominant element in HEAs and all elements are the major elements. The compositional complexity that is brought by the concept of HEAs not only opens up an enormously large compositional space but also holds the potential to lead to novel structural and functional properties that are not available in existing metallic materials. Nevertheless, there are still many obstacles between the potential and reality. For example, HEAs are no exception to the known trade-off between strength and ductility for metallic materials, i.e., materials with high strength are usually less ductile. Here, we use a composite approach to address the strength-ductility trade-off in HEAs by designing them to have two components (known as phases), with one soft phase providing the ductility while the other hard phase provides the strength. These two-phase HEAs show a decent balance of strength and ductility, but that is not all. We further show that inhomogeneity can be engineered in a selected two-phase HEA for improved strength, with still acceptable ductility. The inhomogeneity can be conveniently introduced by deformation and subsequent heat treatments, which are routine processing conditions for metallic materials. What is truly impressive is how versatile this two-phase HEA can be, regarding its mechanical performance, simply by changing its processing conditions, and it provides a convincing case that complexity and inhomogeneity can be fine-tuned to make HEAs better structural materials.

Eutektiska högentropilegeringar : en lovande ny klass av högtemperaturlegeringar

Vetenskapsrådet (VR) (2015-04087), 2016-01-01 -- 2020-12-31.

Ämneskategorier

Materialteknik

Metallurgi och metalliska material

Infrastruktur

Chalmers materialanalyslaboratorium

Styrkeområden

Materialvetenskap

ISBN

978-91-7905-602-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5068

Utgivare

Chalmers tekniska högskola

Virtual Development Laboratory (VDL), Chalmers Tvärgata 4C

Online

Opponent: Professor Pasi Peura, Tampere University, Tampere, Finland

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Senast uppdaterat

2021-11-30