Elsevier

Intermetallics

Volume 143, April 2022, 107463
Intermetallics

Microstructure and texture development in CoCrNi medium entropy alloy processed by severe warm cross-rolling and annealing

https://doi.org/10.1016/j.intermet.2022.107463Get rights and content

Highlights

  • Warm cross-rolling and annealing behavior of CoCrNi investigated.

  • Profuse intersecting shear bands in different cross-rolled materials.

  • Development of rotated-brass texture after cross-rolling.

  • Smaller grain size and weak recrystallization texture in cross-rolled materials.

  • Considerable effect of cross-rolling on microstructure and texture formation.

Abstract

The effect of cross-rolling on microstructure and texture evolution in equiatomic CoCrNi medium entropy alloy (MEA) was investigated in the present work. For this purpose, the MEA was warm-rolled to 90% reduction in thickness at 400 °C by unidirectional and different cross-rolling routes. The heavily deformed specimens were further annealed at temperatures varying from 700 °C to 1200 °C. The development of fine-scale microstructures and profuse shear band formation was confirmed in all the processed materials. Compared to unidirectional processed material, the different cross-rolled materials showed greater propensity for forming intersecting shear bands. Higher hardness in the different cross-rolled materials was consistent with finer microstructure and abundant shear bands. Unidirectional processed material showed weak brass ({110}<112>) component, whereas the different cross-rolled material showed rotated brass components. Upon annealing, the different cross-rolled materials showed smaller grain sizes than the unidirectional processed material due to more abundant potential nucleation sites. The recrystallization texture of the different processed materials showed retention of the deformation texture components. High fractions of random components indicated weak recrystallization texture, contributed by the absence of preferential nucleation and growth and profuse annealing twin formation.

Introduction

High entropy alloys (HEAs) are multicomponent alloys synthesized based on the novel alloy design strategy of mixing a large number (usually greater than five) of constituents with concentrations varying from 5 to 35 at.% [1]. Defying the classical metallurgical expectation of microstructures dominated by various intermetallic phases, several HEAs have simple solid-solution phases such as FCC [2], BCC [3], FCC + BCC dual structure [1], or even HCP [4,5]. It has been presumed that the decrease in free energy is affected by the large configurational entropy (ΔSconf) of mixing of a large number of elements could stabilize these solid solution phases [1]. Consequently, the new paradigm in alloy design based on the configurational entropy evolved, resulting in the grouping of alloys into high (HEAs with ΔSconf1.5R), medium (MEAs with 1RΔSconf1.5R), and low entropy (ΔSconf1R) alloys. HEAs [[6], [7], [8], [9], [10], [11], [12], [13], [14], [15]] and MEAs [[16], [17], [18]] have attracted unprecedented attention due to their intriguing structural and functional properties.

It can hardly be overemphasized that thermo-mechanical processing (TMP) treatments can considerably enhance the microstructure and properties of a wide range of metallic materials. Consequently, research focusing on tailoring microstructure and properties of single- and multiphase HEAs using TMP treatments has gained considerable momentum [[19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]]. Towards this direction, TMP studies of FCC equiatomic CoCrNi MEA by different routes, including cold- [31,32], cryo- [33], and warm-rolling [31], have been initiated. Among these different treatments, warm-rolling is featured by lower flow stress than cold-rolling (due to the elevated deformation temperature) and superior surface finish than hot-rolling (due to lower temperature of deformation). The efficacy of warm-rolling in attaining fine-grained microstructure, controlling texture, and enhancing mechanical properties has already been reported [31]. In effect, these results encourage researchers to study the effect of different processing parameters on microstructure and texture evolution during warm-rolling.

A key thermo-mechanical processing parameter affecting microstructure and texture formation is strain path, apart from imposed strain, starting grain size, and deformation temperature. The effect of strain path change can be executed by cross-rolling, i.e., by mutually interchanging the rolling direction (RD) and transverse direction (TD) by the rotation of the sample around the normal direction (ND) [34]. The effect of cross-rolling has been highlighted in cold-rolled FCC materials [[34], [35], [36], [37], [38], [39], [40], [41]], which show significant differences with conventional unidirectional rolled counterparts. Development of ND-rotated brass texture after cross-rolling has been observed in cross-rolled aluminum and copper alloys [[35], [36], [37], [38], [39]], and also in nickel [40,42]. Development of unusual recrystallization texture (ND//<111>) fiber texture in nickel [42]), weakening, and even complete randomization of texture [43] are possible in cross-rolled materials. Despite these interesting outcomes, the effect of cross-rolling has been investigated only to a limited extent in HEAs, which nonetheless reveal considerable influence on microstructure and texture formation [44,45].

In the current study, we investigate the effect of different cross-rolling routes on the evolution of microstructure and texture in FCC equiatomic CoCrNi MEA after severe warm-rolling and subsequent recrystallization. The purpose of this study is two-fold; firstly, to clarify the effect of cross-rolling on the MEAs and secondly, to complete the landscape of various processing variables on microstructure and texture formation of MEAs during warm-rolling.

Section snippets

Processing

The equiatomic CoCrNi MEA was synthesized by vacuum arc melting in a controlled argon-filled inert atmosphere starting with high purity elements (≥99.9% purity). The arc-melted buttons (∼100 gm weight) were flipped and subjected to multiple remelting and solidification cycles (4–5 times) before being finally cast into a water-cooled copper mold. The as-cast ingots were subsequently homogenized at 1100 °C for 6 hours (h)).

To attain a wrought starting microstructure, samples having dimensions of

Effect of cross-rolling on microstructure and texture evolution

The microstructure of the starting material (obtained after 50% cold-rolling and treated at 800 °C/1 h) (Fig. 2(a)) shows fully recrystallized grains bounded by high angle boundaries (HAGBs; misorientation angle (θ)≥15°; highlighted in black) containing annealing twin boundaries (TBs; highlighted in red). The grain size distribution (Fig. 2(b)) shows a large fraction of fine grains with average grain size (excluding the TBs) ∼5–7 μm. A comparison of the (111) PF (Fig. 2(c)) with the ideal (111)

Warm-rolled microstructure and texture

The microstructural development in UWR and different cross-rolled materials is featured by the gradual evolution of elongated microstructures, further grain refinement, and finally, forming deformation-induced ultrafine microstructures. The grain subdivision mechanism mainly contributes to the ultrafine microstructure formation in all the differently processed materials. The starting equiaxed recrystallized grains are progressively subdivided on an increasingly finer scale [46]. Remarkably, the

Conclusions

The CoCrNi MEA was processed by unidirectional and cross-rolling routes and further annealed at different temperatures to understand the microstructure and texture formation. The following conclusions may be drawn.

  • (i)

    The MEA processed by the UWR and different cross-rolling routes developed fine-scale deformation-induced microstructures. The different cross-rolled materials showed a greater propensity for forming complex intersecting shear bands than the UWR specimen.

  • (ii)

    Greater hardness in the

Author statement

1. J. Saha: Investigation, Analysis, Validation, Writing-Original draft.

2. R. Saha: Investigation (Bulk texture measurement).

3. P.P. Bhattacharjee*: Methodologies, Writing-Original draft, Review and Editing, Supervision, Fund acquisition, Project administration.

Data availability

The dataset analyzed in this work will be made available by the corresponding author upon reasonable requests. Some dataset may not be shared he raw/processed data required to reproduce these findings cannot be shared at this time as the dataset also forms part of an ongoing study.

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. (We declare no conflict of interest).

Acknowledgment

The financial supports of DST-SERB, India (CRG/2020/00665), the DST-FIST program (SR/FST/ETI-421/2016), and the DRDO (ER&IPR) (ERIP/ER/2002002/M/01/1773) are sincerely acknowledged.

References (57)

  • G.D. Sathiaraj et al.

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

    Intermetallics

    (2016)
  • N. Stepanov et al.

    Effect of cryo-deformation on structure and properties of CoCrFeNiMn high-entropy alloy

    Intermetallics

    (2015)
  • G.D. Sathiaraj et al.

    The effect of heating rate on microstructure and texture formation during annealing of heavily cold-rolled equiatomic CoCrFeMnNi high entropy alloy

    J. Alloys Compd.

    (2016)
  • Z. Wang et al.

    Effects of annealing and thermo-mechanical treatment on the microstructures and mechanical properties of a carbon-doped FeNiMnAl multi-component alloy

    Mater. Sci. Eng., A

    (2017)
  • T.S. Reddy et al.

    Severe plastic deformation driven nanostructure and phase evolution in a Al0.5CoCrFeMnNi dual phase high entropy alloy

    Intermetallics

    (2017)
  • G.D. Sathiaraj et al.

    Texture formation in face-centered cubic high-entropy alloys

    J. Alloys Compd.

    (2020)
  • N. Haghdadi et al.

    On the hot-worked microstructure of a face-centered cubic Al0.3CoCrFeNi high entropy alloy

    Scripta Mater.

    (2020)
  • I.S. Wani et al.

    Evolution of microstructure and texture during thermo-mechanical processing of a two phase Al0.5CoCrFeMnNi high entropy alloy

    Mater. Char.

    (2016)
  • J. Saha et al.

    Microstructure and texture of CoCrNi medium entropy alloy (MEA) processed by severe cryo-rolling: a study vis-a-vis cold-rolling

    Intermetallics

    (2021)
  • S. Suwas et al.

    Role of strain path change in texture development

    Mater. Sci. Eng., A

    (2003)
  • T. Öztürk

    Deformation and recrystallization textures in cross-rolled sheets of copper and α-brass

    Scripta Metall.

    (1988)
  • N.P. Gurao et al.

    Effect of strain path change on the evolution of texture and microstructure during rolling of copper and nickel

    Mater. Sci. Eng., A

    (2011)
  • P.P. Bhattacharjee et al.

    The effect of starting grain size on the evolution of microstructure and texture in nickel during processing by cross-rolling

    Mater. Char.

    (2013)
  • M. Zaid et al.

    Electron backscatter diffraction study of deformation and recrystallization textures of individual phases in a cross-rolled duplex steel

    Mater. Char.

    (2014)
  • M.Y. Huh et al.

    Randomization of the annealing texture in aluminum 5182 sheet by cross-rolling

    Mater. Sci. Eng., A

    (2001)
  • S.R. Reddy et al.

    Effect of strain path on microstructure and texture formation in cold-rolled and annealed FCC equiatomic CoCrFeMnNi high entropy alloy

    Intermetallics

    (2017)
  • A. Patel et al.

    Strain-path controlled microstructure, texture and hardness evolution in cryo-deformed AlCoCrFeNi2.1 eutectic high entropy alloy

    Intermetallics

    (2018)
  • T. Konkova et al.

    Effect of cryogenic temperature and change of strain path on grain refinement during rolling of Cu–30Zn brass

    Mater. Des.

    (2015)
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