Elsevier

Intermetallics

Volume 134, July 2021, 107202
Intermetallics

Temperature- and strain-dependent thermally-activated deformation mechanism of a ferrous medium-entropy alloy

https://doi.org/10.1016/j.intermet.2021.107202Get rights and content

Highlights

  • Thermally activated behaviors of a ferrous medium-entropy alloy were investigated.

  • High strain rate sensitivity and low activation volume were obtained at 77 K.

  • The unique rate-controlling mechanisms were identified upon temperature and strain.

  • Inhibited cross-slip supports superior cryogenic tensile properties of the alloy.

Abstract

In this study, quasi-static tensile properties of Fe60Co15Ni15Cr10 (at%) ferrous medium-entropy alloy at 298 K and 77 K were investigated in terms of thermally-activated deformation mechanism. Relatively high strain rate sensitivity and low activation volume were estimated using strain rate jump tests at 77 K where deformation-induced martensitic transformation took place, compared to those at 298 K. Different rate-controlling mechanisms were identified for early and latter deformation at both temperatures considering the plastic strain. Dislocation behaviors, e.g., cross-slip or dislocation accumulation, based on the thermally-activated deformation mechanism, support the outstanding cryogenic tensile properties of the present alloy.

Introduction

During the last decade, a great deal of attention has been focused on multi-component high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) with single-phase solid solution for their outstanding mechanical properties according to large configurational entropy [[1], [2], [3], [4], [5], [6], [7]]. Recently, the studies on these alloy groups with dual-phase [[8], [9], [10]], metastability-engineering of near-single phase [11,12], or utilization of precipitation phases [[13], [14], [15], [16]] have been spotlighted for extending the scope of alloy design strategies. Meanwhile, superior tensile strength and ductility with outstanding strain hardening rate of HEAs/MEAs have been achieved through martensitic transformation from face-centered cubic (FCC) to hexagonal close-packed (HCP) and/or body-centered cubic (BCC) at cryogenic temperature (77 K) [11,[17], [18], [19], [20]]. Notably, recent studies on MEAs dealing with the phase transformation of single or near-single FCC phase [11,17] exhibit an exceptional combination of strength and ductility at cryogenic temperatures.

In particular, a ferrous medium-entropy alloy (FeMEA) corresponding to near-single FCC-structured Fe60Co15Ni15Cr10 (at%) alloy is highly expected to possess superior mechanical properties at 77 K [11]. In designing FeCoNiCr-based alloy system, low Cr concentration of 10 at% can suppress the formation of intermetallic compounds, such as Cr-rich σ phase, which degrade the mechanical properties of the alloy [11]. Besides, the FeMEA shows beneficial effects on both cost-effectiveness and tunable FCC phase stability for metastability-engineering with an increase in Fe and decreases in Co and Ni concentrations [11,17]. As shown in the previous work [11], the FeMEA exhibits excellent tensile properties at cryogenic temperatures due to the sequential operation of BCC martensitic transformation along the grain boundaries and the shear bands within FCC grains.

The analyses on thermally-activated deformation have figured out the rate-controlling mechanisms fairly related to dislocation behaviors of HEAs [[21], [22], [23], [24], [25], [26]]. An equiatomic CoCrFeMnNi HEA with a single FCC phase was discussed on the thermally-activated deformation behavior elaborating that planar dislocation slip is the rate-controlling mechanism, while Peierls lattice friction stress stands for BCC alloys [21]. By investigating the plastic strain dependence of strain rate sensitivity of CoCrFeMnNi HEA [22], nanoscale heterogeneities were revealed. Basu et al. [23] investigated the strain rate sensitivity of transformation-induced plasticity (TRIP)-assisted dual-phase HEA at room temperature, demonstrating that FCC to HCP martensitic transformation accompanied with dislocation glide is a primary deformation mechanism. Despite a few reports, there are still insufficient attempts to figure out the thermally-activated mechanism based on the on-going deformation of multi-component alloys that exhibit metastability-engineering.

In this work, we investigated the temperature and strain dependence of deformation behavior of an FeMEA based on the thermally-activated deformation mechanism. Since the primary rate-controlling deformation mechanism considerably depends on the crystal structure [21], the present TRIP-assisted alloy with a change in the crystal structure through quasi-static deformation at 77 K has a coupling effect on the rate-controlling mechanism due to multi-phase microstructure. Thus, revealing the rate-controlling mechanism leads to a deeper understanding of temperature and strain rate dependence of the present alloy. In particular, predominant rate-controlling mechanisms with respect to plastic strain were elucidated through strain rate jump tests and the corresponding microstructural analyses at both 298 K and 77 K.

Section snippets

Experimental procedure

An ingot of Fe60Co15Ni15Cr10 (at%) FeMEA was cast in a dimension of 70 × 35 × 7 mm3 using vacuum induction melting equipment (MC100V, Indutherm, Walzbachtal-Wossingen, Germany) under an argon atmosphere. Purity of the elemental metals was at least 99.95%. The rectangular ingot was homogenized at 1373 K for 6 h, followed by water quenching. The homogenized ingot was cold-rolled at 298 K from 7 to 1.5 mm with a thickness reduction ratio of 78.6%. After that, the tensile specimens were obtained

Tensile properties and microstructures

Fig. 1 shows true and engineering stress-strain curves and strain hardening rate (SHR) of the alloy at 298 K and 77 K. At 77 K, tensile properties exhibit exceptional yield strength (YS) of 383 ± 36 MPa, ultimate tensile strength (UTS) of 1357 ± 30 MPa, and elongation of 63.5 ± 0.55% with substantial strain hardening compared to those at 298 K.

Fig. 2, Fig. 3 reveal the microstructural evolution of the present alloy during deformation at 298 K and 77 K, respectively. In Fig. 2(a), EBSD inverse

Conclusion

The thermally-activated deformation behavior of the Fe60Co15Ni15Cr10 (at%) ferrous MEA was explored using strain rate jump tests. Higher strain rate sensitivity of the present alloy at 77 K than that at 298 K was rationalized by the thermally-activated deformation mechanism. The core findings disclosed in this study are described below:

  • (1)

    At 298 K, dynamic recovery associated with the cross-slip mechanism is predominant at early deformation. As the true plastic strain exceeds 0.1, dislocation

CRediT authorship contribution statement

Jungwan Lee: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft. Jongun Moon: Conceptualization, Formal analysis, Investigation, Methodology, Validation, Writing – review & editing, Supervision. Jae Wung Bae: Methodology, Investigation, Resources. Jeong Min Park: Conceptualization, Methodology, Validation. Hyeonseok Kwon: Methodology, Investigation. Hidemi Kato: Validation, Investigation. Hyoung Seop Kim: Funding acquisition,

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.

Acknowledgments

This work was supported by Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF–2016M3D1A1023384). J.M. acknowledges support from Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education [2020R1A6A3A03037509].

References (63)

  • J.W. Bae et al.

    Towards ferrous medium-entropy alloys with low-cost and high-performance

    Scripta Mater.

    (2020)
  • J. Yang et al.

    Effects of transformation-induced plasticity (TRIP) on tensile property improvement of Fe45Co30Cr10V10Ni5-xMnx high-entropy alloys

    Mater. Sci. Eng. A

    (2020)
  • G.B. Olson et al.

    A mechanism for the strain-induced nucleation of martensitic transformations

    J. Less Common. Met.

    (1972)
  • J.W. Bae et al.

    Enhanced cryogenic tensile properties with multi-stage strain hardening through partial recrystallization in a ferrous medium-entropy alloy

    Scripta Mater.

    (2021)
  • S.I. Hong et al.

    Thermally activated deformation and the rate controlling mechanism in CoCrFeMnNi high entropy alloy

    Mater. Sci. Eng. A

    (2017)
  • A.V. Podolskiy et al.

    Mechanical properties and thermally activated plasticity of the Ti30Zr25Hf15Nb20Ta10 high entropy alloy at temperatures 4.2–350 K

    Mater. Sci. Eng. A

    (2018)
  • S.-H. Joo et al.

    Tensile deformation behavior and deformation twinning of an equimolar CoCrFeMnNi high-entropy alloy

    Mater. Sci. Eng. A

    (2017)
  • J.M. Park et al.

    Synergetic strengthening of additively manufactured (CoCrFeMnNi)99C1 high-entropy alloy by heterogeneous anisotropic microstructure

    Addit. Manuf.

    (2020)
  • S. Curtze et al.

    Dependence of tensile deformation behavior of TWIP steels on stacking fault energy, temperature and strain rate

    Acta Mater.

    (2010)
  • S. Curtze et al.

    Deformation behavior of TRIP and DP steels in tension at different temperatures over a wide range of strain rates

    Mater. Sci. Eng. A

    (2009)
  • D.G. Kim et al.

    Ultrastrong duplex high-entropy alloy with 2 GPa cryogenic strength enabled by an accelerated martensitic transformation

    Scripta Mater.

    (2019)
  • G. Laplanche et al.

    Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

    Acta Mater.

    (2018)
  • Z. Wu et al.

    Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures

    Acta Mater.

    (2014)
  • Z. Wu et al.

    Thermal activation mechanisms and Labusch-type strengthening analysis for a family of high-entropy and equiatomic solid-solution alloys

    Acta Mater.

    (2016)
  • Y.M. Wang et al.

    Temperature-dependent strain rate sensitivity and activation volume of nanocrystalline Ni

    Acta Mater.

    (2006)
  • Z. Li et al.

    Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels

    Int. J. Plast.

    (2019)
  • J. Klepaczko

    Thermally activated flow and strain rate history effects for some polycrystalline f.c.c. metals

    Mater. Sci. Eng.

    (1975)
  • J. Bonneville et al.

    A study of cross-slip activation parameters in pure copper

    Acta Metall.

    (1988)
  • N.V. Malyar et al.

    Dislocation slip transmission through a coherent Σ3{111} copper twin boundary: strain rate sensitivity, activation volume and strength distribution function

    Acta Mater.

    (2018)
  • J.W. Bae et al.

    On the phase transformation and dynamic stress–strain partitioning of ferrous medium-entropy alloy using experimentation and finite element method

    Materialia

    (2020)
  • S.I. Hong et al.

    Mechanisms of slip mode modification in F.C.C. solid solutions

    Acta Metall. Mater.

    (1990)
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