Elsevier

Intermetallics

Volume 69, February 2016, Pages 1-9
Intermetallics

Effect of heavy cryo-rolling on the evolution of microstructure and texture during annealing of equiatomic CoCrFeMnNi high entropy alloy

https://doi.org/10.1016/j.intermet.2015.10.005Get rights and content

Highlights

  • Effect of cryo-rolling on annealing texture of HEA is reported.

  • Recrystallized grain size is significantly smaller in cryo- than cold-rolled HEA.

  • Evolution of annealing texture in cryo-rolled is similar to cold-rolled HEA.

  • Absence of preferential nucleation or growth during annealing.

Abstract

The effect of cryo-rolling on the evolution of microstructure and texture during annealing was investigated in equiatomic CoCrFeMnNi high entropy alloy. For this purpose the alloy was cold- and cryo-rolled to 90% reduction in thickness followed by annealing at temperatures ranging from 700 °C to 1200 °C. The two alloys showed the development of predominantly brass type deformation texture consistent with profuse nano-twin formation reported in this alloy. The cryo-rolled material showed significantly finer grain size after different annealing treatments as compared to the cold-rolled alloy. This could be attributed to finer microstructure in the cryo-rolled material providing greater number of available sites for nucleation. The recrystallization texture of cold- and cryo-rolled materials showed the presence of similar texture components indicating that cryo-rolling had limited effect on the formation of annealing texture. The volume fractions of different texture components did not reveal significant dependence on the annealing temperature. The evolution of texture could be explained on the basis of absence of strong preferential nucleation and growth during annealing.

Introduction

High entropy alloys (HEAs) are newly developed multicomponent alloys based on the novel alloy design concept of mixing five or more constituent elements in equiatomic or near equiatomic proportion [1]. Despite having the presence of a large number of components the HEAs often show rather simple crystal structures such as, FCC (e.g. equiatomic CoCrFeMnNi [2]), BCC and FCC + BCC [1]. The research on HEAs has gained considerable attention in recent years and many interesting and unique properties of these materials have been reported [3], [4], [5], [6], [7], [8], [9]. The unique properties of the HEAs are attributed to the core effects of multicomponent solid solution formation, namely distorted lattice structure [3], cocktail effect [3], [4], sluggish diffusion [3], [10] and formation of nanoscale deformation twins [5], [11].

A major area of research in widening the potential applications of HEAs is to understand the thermo-mechanical processing (TMP) behavior of HEAs [12], [13], [14], [15], [16], [17], [18]. Appropriate understanding of the TMP response of HEAs can significantly affect the microstructure and mechanical properties of HEAs [11], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32]. TMP routes usually involve heavy deformation and annealing, which leads to the refinement of microstructure and development of crystallographic texture [33], [34]. Consequently, microstructure and texture of TMP processed materials are crucial aspects which have been intensely researched in different materials [35], [36] and remain topics of much interest in case of HEAs.

Cryo-rolling (i.e. rolling at the liquid N2 temperature) of materials constitutes an interesting TMP route which can introduce significant microstructural refinement and enhance mechanical strength. Consequently, the effect of cryo-rolling has been investigated in a wide variety of materials [37], [38], [39], [40], [41], [42], [43], [44], [45]. Recently, the effect of cryo-rolling has also been investigated in HEAs and significant enhancement in strength has been reported by Stepanov et al. [46]. However, the annealing behavior of the cryo-rolled HEAs has not been reported in the research.

In the present work, we are investigating the effect of cryo-rolling on microstructure and texture formation during annealing for cryo-rolled FCC CoCrFeMnNi HEA which has not been attempted earlier. For comparison purpose the alloy has been cold-rolled and cryo-rolled at room temperature and at the liquid N2 temperature, respectively.

Section snippets

Processing

The equiatomic CoCrFeMnNi alloy used in the present research work was prepared by vacuum arc melting. The as-cast alloy was subjected to a homogenization treatment at 1100 °C for 6 h (hrs) to enhance the chemical homogeneity. The as-cast and homogenized alloy showed a rather coarse microstructure. In order to generate a wrought microstructure suitable for the present research, samples with dimensions 25 mm (length) × 8 mm (width) × 5 mm (thickness) were extracted from the homogenized material

Microstructure and texture evolution during deformation

The microstructure of the starting recrystallized material (Fig. 1(a)) shows the presence of recrystallized grains separated by high angle grain boundaries (HAGBs defined by misorientation angle (θ) ≥ 15° and highlighted in black in Fig. 1(a)) [12]. The average grain size (neglecting annealing twins as separate grains) of the starting material is ∼7 μm. The microstructure also shows the presence of profuse annealing twin boundaries (highlighted in red).

The microstructure of the 90% cold-rolled

Discussion

The bulk textures of the two materials processed by the two different routes show very similar strong brass type. The development of strong brass type texture after heavy deformation is characteristic of low SFE materials [48] and also consistent with the low SFE of this alloy obtained by theoretical calculations [49] and recent experimental observations [50]. Although the precise mechanism of low SFE of the present HEA has not been clarified, the highly distorted whole-solute matrix of the HEA

Acknowledgment

The authors acknowledge the financial support of DST, India (Grant no. SB/S3/ME/47/2013). The authors also acknowledge Professor I. Samajdar, IIT Mumbai, India for kindly providing access to the national facility for Texture-OIM (DST-IRPHA) at I.I.T. Bombay, India.

References (56)

  • Z. Wu et al.

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

    Acta Mater.

    (2014)
  • J.Y. He et al.

    Steady state flow of the FeCoNiCrMn high entropy alloy at elevated temperatures

    Intermetallics

    (2014)
  • Z. Wu et al.

    Recovery, recrystallization, grain growth and phase stability of a family of FCC-structured multi-component equiatomic solid solution alloys

    Intermetallics

    (2014)
  • Y. Zou et al.

    Size-dependent plasticity in an Nb25Mo25Ta25W25 refractory high-entropy alloy

    Acta Mater.

    (2014)
  • M.A. Hemphill et al.

    Fatigue behavior of Al 0.5CoCrCuFeNi high entropy alloys

    Acta Mater.

    (2012)
  • W.H. Liu et al.

    Grain growth and the Hall–Petch relationship in a high-entropy FeCrNiCoMn alloy

    Scr Mater.

    (2013)
  • Y. Wu et al.

    In-situ neutron diffraction study of deformation behavior of a multi-component high-entropy alloy

    Appl. Phys. Lett.

    (2014)
  • M.J. Yao et al.

    A novel, single phase, non-equiatomic FeMnNiCoCr high-entropy alloy with exceptional phase stability and tensile ductility

    Scr. Mater.

    (2014)
  • C.W. Tsai et al.

    Deformation and annealing behaviors of high-entropy alloy Al0.5CoCrCuFeNi

    J. Alloys Compd.

    (2009)
  • Y.F. Kao et al.

    Microstructure and mechanical property of as-cast, -homogenized, and -deformed AlxCoCrFeNi ((0 ≤ x ≤ 2)) high-entropy alloys

    J. Alloys Compd.

    (2009)
  • N. Nayan et al.

    Hot deformation behaviour and microstructure control in AlCrCuNiFeCo high entropy alloy

    Intermetallics

    (2014)
  • R.D. Doherty et al.

    Current issues in recrystallization: a review

    Mater. Sci. Eng.

    (1997)
  • R.D. Doherty

    Recrystallization and texture

    Prog. Mater. Sci.

    (1997)
  • M. Weiss et al.

    Strength and biaxial formability of cryo-rolled 2024 aluminium subject to concurrent recovery and precipitation

    Acta Mater.

    (2013)
  • S.K. Panigrahi et al.

    Influence of solutes and second phase particles on work hardening behavior of Al 6063 alloy processed by cryorolling

    Mater. Sci. Eng. A

    (2011)
  • H.L. Yu et al.

    Mechanical properties of Al–Mg–Si alloy sheets produced using asymmetric cryorolling and ageing treatment

    Mater. Sci. Eng. A

    (2013)
  • S.V. Zherebtsov et al.

    Formation of nanostructures in commercial-purity titanium via cryorolling

    Acta Mater.

    (2013)
  • R. Kumar et al.

    Enhancement of mechanical properties of low stacking fault energy brass processed by cryorolling followed by short-annealing

    Mater. Des.

    (2015)
  • Cited by (116)

    View all citing articles on Scopus
    View full text