Theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys

doi:10.1016/j.jmst.2021.05.037

Journal of Materials Science & Technology

Volume 99, 10 February 2022, Pages 161-168

https://doi.org/10.1016/j.jmst.2021.05.037 Get rights and content

Highlights

•
Theoretical framework for connecting the ab initio SFEs and the prevalent deformation mechanism is established.
•
Critical factors affecting the deformation model transitions are identified and established.
•
Deformation mode map with respect to composition in Cr-Co-Ni alloys is constructed.

Abstract

Combined theoretical and experimental efforts are put forward to study the critical factors influencing deformation mode transitions in face-centered cubic materials. We revisit the empirical relationship between the stacking fault energy (SFE) and the prevalent deformation mechanism. With ab initio calculated SFE, we establish the critical boundaries between various deformation modes in the model Cr-Co-Ni solid solution alloys. Satisfying agreement between theoretical predictions and experimental observations are reached. Our findings shield light on applying quantum mechanical calculations in designing transformation-induced plasticity and twinning-induced plasticity mechanisms for achieving advanced mechanical properties.

Graphical abstract

Introduction

In face-centered cubic (fcc) materials, stacking fault energy (SFE) strongly affects the activation of the primary deformation mechanisms, namely, martensitic phase transformation (MT), twinning (TW), and dislocation slips (SL) [1], [2], [3], [4]. Empirically, the relationship between experimental SFE ( $γ_{i s f}^{e x p .}$ ) and the prevalent deformation mode has been well documented in many systems including the medium/high-Mn transformation-induced plasticity (TRIP)/twinning-induced plasticity (TWIP) steels [2,5], TWIP high entropy alloys (HEAs, e.g., Cr₁₀Mn₄₀Fe₄₀Co₁₀ and CrMnFeCoNi) [6,7] and TRIP HEAs (Cr₁₀Mn₃₀Fe₅₀Co₁₀) [8, 9]. For instance, austenitic steels with $γ_{i s f}^{e x p .}$ higher than 10~16 mJ/m² usually deform by extensive twinning, whereas steels with lower $γ_{i s f}^{e x p .}$ exhibit deformation-induced martensitic phase transformation (DIMT) [4]. However, the above empirical relations are considerably rough, leading to weak predictive power. The critical experimental SFE that indicates the TRIP/TWIP transition varies notably in different alloys [10]. On the other hand, ab initio calculations provide an alternative means of accessing the SFE [11]. It becomes feasible to establish the correlation between the theoretical SFE ( $γ_{i s f}^{f c c}$ ) and the prevalent deformation mode. Importantly, a recent revisit to the experimental method for determining the SFE shows that the experimental SFE is limited to positive values due to its underlying approximations, and that the experimental SFE cannot reflect the real thermodynamic stability of the fcc phase in metastable fcc alloys like Co-rich Co-Ni alloys or some CrCoNi-based HEAs [12]; while the ab initio calculated SFE correlates nicely with the thermodynamic phase stability (the free energy difference between the fcc and hexagonal close packed (hcp) phases) in both stable and metastable fcc alloys. In light of the difference in theoretical and experimental SFEs [12], here we put forward combine theoretical and experimental efforts to re-establish the correlation between the prevalent deformation modes and the theoretical SFEs, and investigate the critical factors influencing the deformation mode transition.

Section snippets

Methodology

The room temperature γ-surfaces in the CrCoNi-based alloys were obtained by ab initio calculations using the exact muffin-tin orbitals (EMTO) method with the coherent potential approximation (CPA) [13, 14]. The temperature effect on the SFEs was considered through using the room-temperature lattice parameter and the magnetic entropy contribution. For details of the calculations, readers are referred to our recent work [11]. In this work, we focus on the application of the new plasticity

Theoretical assessment of the critical factors affecting plastic deformation mechanisms

Theoretically, in fcc materials the activation of a specific deformation mode on a slip plane is decided by the competition among the three main deformation modes, a/2<110> dislocation slip, twinning, and fcc→hcp martensitic transformation. All three modes are accomplished through a/6<112> Shockley partial dislocations, but according to different dislocation mechanisms. For instance, on the (111) slip plane, a/2[10–1] dislocation is realized through a leading partial (b_L=a/6[11–2]) followed by

Discussion

The critical values of $γ_{i s f}^{f c c}$ and $δ \approx - γ_{i s f}^{f c c} / γ_{u s f}^{f c c}$ are related by a linear function, indicating that one may use one parameter, $γ_{i s f}^{f c c}$ , to predict the microstructure transition from twinning to fcc→hcp DIMT, but together they provide more physical understanding of the transition [17]. On the one hand, the negative SFE, since it correlates to the relative Gibbs energy difference between fcc and hcp phases, tells the metastability of the fcc phase [12]. It means that the system lowers its

Conclusions

To summarize, the relationship between the ab initio calculated SFEs and deformation mechanisms were re-established based on the classical layer-by-layer twinning mechanism and the novel transformation-mediated twinning route [17]. The critical factors affecting the transition between the TWIP and TRIP effects were identified in the Cr-Co-Ni ternary alloys with both theoretical and experimental efforts. In contrast to using the conventionally measured SFE with a positive value, here we proposed

Data availability

All data needed to evaluate the conclusions in the paper are present in the paper. Additional data related to this paper may be requested from the authors.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The financial support is provided by the Major State Basic Research Development Program of China (2016YFB0701405). This work is also supported by the KTH-SJTU collaborative research and development seed grant, the Swedish Research Council, the Swedish Foundation for Strategic Research, the China Scholarship Council, the Swedish Foundation for International Cooperation in Research and Higher Education, and the Hungarian Scientific Research Fund (research project OTKA 128229), the Fundamental

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Research ArticleTheoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Methodology

Theoretical assessment of the critical factors affecting plastic deformation mechanisms

Discussion

Conclusions

Data availability

Declaration of Competing Interest

Acknowledgements

Prog. Mater. Sci.

Mater. Sci. Eng. A

Mater. Sci. Eng.

Acta Mater.

Acta Mater.

Acta Mater.

Acta Mater.

J. Mater. Sci. Tech.

Mater. Des.

Scr. Mater.

Acta Mater.

Acta Mater.

Mater. Sci. Eng.: A

Adv. Mater.

Scr. Mater.

J. Alloys Compd.

Acta Mater.

Mater. Sci. Eng.

Research Article
Theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys