Microstructures and mechanical properties of a

Science and Technology of Welding and Joining

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Microstructures and mechanical properties of a welded CoCrFeMnNi high-entropy alloy Z. Wu, S. A. David, D. N. Leonard, Z. Feng & H. Bei To cite this article: Z. Wu, S. A. David, D. N. Leonard, Z. Feng & H. Bei (2018): Microstructures and mechanical properties of a welded CoCrFeMnNi high-entropy alloy, Science and Technology of Welding and Joining, DOI: 10.1080/13621718.2018.1430114 To link to this article: https://doi.org/10.1080/13621718.2018.1430114

Published online: 25 Feb 2018.

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SCIENCE AND TECHNOLOGY OF WELDING AND JOINING, 2018 https://doi.org/10.1080/13621718.2018.1430114

Microstructures and mechanical properties of a welded CoCrFeMnNi high-entropy alloy Z. Wu, S. A. David, D. N. Leonard, Z. Feng and H. Bei Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA ABSTRACT

ARTICLE HISTORY

The response of the CoCrFeMnNi high-entropy alloy to weld thermal cycles was investigated to determine its applicability as an engineering structural material. Two processes were used: high-energy-density, low-heat-input electron beam (EB) welding and low-energy-density, highheat-input gas tungsten arc (GTA) welding. Weldability was determined through comprehensive microstructural and mechanical property characterisation of the welds. The welds did not develop solidification cracking or heat-affected zone cracks. The microstructures in weld fusion zones are similar to that in the as-cast materials, consisting of large columnar grains with dendrite. The dendrite arm spacing and the extent of elemental segregation were less in the welds than in the cast ingot, and also were less pronounced in the EB weld than in the GTA weld. Compositional microsegregation between dendritic cores and interdendritic regions of the welds was insignificant. Both welds exhibited slightly higher yield strengths than the base metal. The EB weld possessed comparable tensile strength and ductility to that of the base metal. In comparison, the GTA weld maintained ∼ 80% of the base metal’s tensile strength and 50% of the ductility.

Received 3 November 2017 Accepted 14 January 2018

Introduction High-entropy alloys (HEAs) are receiving an increasing amount of academic attention in the materials science field [1–21]. The emergence of the HEA concept has shifted the focus of alloy developers from conventional alloys with one or two principal elements, such as aluminium alloys and steel, to alloys with multiple (more than four) dominant elements. Mixing multiple (five or more) elements with different crystal structures would be expected to produce compounds that have properties similar to those of intermetallics (i.e. complex microstructures and various phases). However, castings of already-made HEAs [1–15] generally solidify with much simpler microstructures than expected. The microstructures of some HEAs normally consist of single-phase solid solutions with either facecentred-cubic (fcc) or body-centred-cubic (bcc) crystal structure. The simple microstructures often produce remarkable material properties, including high strength and ductility [3,9,15] and good wear and corrosion resistance [5]. An alloy made of equiatomic amounts of cobalt, chromium, iron, manganese, and nickel has been widely investigated. That alloy, first discovered in 2004 [7], is a single-phase solid solution with fcc crystal structure. It possesses good mechanical properties, including strength and ductility, especially at temperatures far below the room temperature [6,9]. Its CONTACT H. Bei

[email protected]

KEYWORDS

High-entropy alloy; welding; weldability; mechanical properties; microstructure

strength and ductility simultaneously increase when the temperature is decreased from room temperature to liquid nitrogen temperature [3,8,9]. This is contradictory to the typical strength-ductility-trade-off in conventional alloys. Very high fracture toughness at crack initiation has also been reported (exceeding 200 MPa m1/2 ) [9], which is comparable to that of the best cryogenic steels [22–29], results partly from mechanical twinning during plastic deformation between room temperature and liquid nitrogen temperature (77 K). The promising low-temperature properties make the HEA a potential candidate for engineering applications at cryogenic temperatures, where many conventional materials would experience ductile-to-brittle transition. Metallic structures are rarely assembled from single alloys or as a simple part. In manufacturing, structures are fabricated from various engineering materials made of alloys with designated compositions and specific properties. Welding is the means by which the components are joined into integrated structures. During the welding process, microstructures and properties can change considerably, depending on the nature of the weld thermal cycle and on the composition of the base metals and fillers [30–34]. Thus the effect of the weld thermal cycle on the new CoCrFeMnNi HEA needs to be investigated before it can be adopted for application as an engineering material.

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

© 2018 This material is published by permission of the Oak Ridge National Laboratory, operated by UT-Battelle, LLC., for the US Department of Energy under Contract No. DE-AC0500OR22725. The US Government retains for itself, and others acting on its behalf, a paid-up, non-exclusive, and irrevocable worldwide licence in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

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Previously, the autogenous electron beam (EB) welding process was used to determine the weldability of the equiatomic CoCrFeMnNi HEA [35], showing promising weldability of the alloy. During welding, no weld defects (cracks or porosity) were observed, in the heat-affected zone (HAZ) or in the solidification (fusion) zone. The fusion zone exhibited a columnar grain structure that is typical for welds with singlephase polycrystalline materials. More importantly, the autogenous EB cross-weld specimens maintained the base material’s strength and ductility levels. In this study, we further investigated the weldability of the HEA when two sheets are welded together. Sheet alloys were butt-welded using two different welding techniques, including high-energy-density and lowheat-input EB welding and low-energy-density and high-heat-input gas tungsten arc (GTA) welding. The alloy’s weldability was assessed through comprehensive microstructural and mechanical property characterization.

Experimental procedures Material preparation, processing, and welding Raw elemental materials Co, Cr, Fe, Mn, and Ni ( > 99.9% pure) were arc-melt in a water-cooled copper crucible under an Ar atmosphere to produce the equiatomic CoCrFeMnNi alloy. Similar to [6], additional Mn was added to compensate its loss during casting. The melts were drop-cast into copper moulds to produce ingots measuring 25.4 × 12.7 × 127 mm. The ingots were then homogenised for 24 h at 1200°C to improve the chemical homogeneity and then aircooled. Longitudinal rolling was performed in air at room temperature to reach a final thickness of 1.6 mm. The sheets were annealed at 900°C for 1 h to obtain an equiaxed microstructure. EB and GTA welding methods were then used to butt-weld two pieces of the sheet alloys. The EB welds were made at a power level of 125kV, 2.2 mA, and at a welding speed of 38 mm min–1 . The GTA welds were made at a power level of 8.4 V, 75 A at a welding speed of 25.4 mm min–1 . Metallurgical characterisation Comprehensive microstructural characterisation of the as-cast material, base metal, and weldment were examined by using various types of microscopic techniques, including a JEOL 6500 FEG-SEM scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD) and a JEOL JXA-8200X electron microprobe analyzer (EPMA) equipped with five crystal-focusing spectrometers for wavelength dispersive X-ray spectroscopy (WDS). For the as-cast material and the welds, back-scattered electron (BSE) micrographs and EBSD were used to characterise grain

structure. Microprobe analyses were utilised to examine the elemental segregation behaviour through Xray dot mapping and quantitative line scans using the EPMA instrument. During EPMA mapping, a spot size of ∼ 20 nm was used with a 15 kV accelerating voltage and an EB current of 100 nA. In addition to the five constituent elements, oxygen was also analysed utilising pure elemental standards. A JEOL JCM-500 desktop microscope operated at 10 kV was used to observe the fracture surfaces of tensile-tested specimens. Mechanical properties characterisation Both base metal and cross-weld specimens were used to measure mechanical properties under quasi-tensile conditions. Electrical discharge machining (EDM) was used to cut 10 mm gage length dog-bone-shaped specimens. Before the tensile tests, all faces of the sample gage sections were polished with SiC paper (through 600 grit), and nine Vickers microhardness indents spaced 1 mm apart were made along the gage lengths using the LECO LM 100AT Vickers Hardness tester with a force of 200 g. The uniform elongations to fracture (ef ) were determined by averaging the change in the distance between adjacent indents. Tensile tests were performed with a screw-driven mechanical testing machine (Instron) at an engineering strain rate of 10−3 s–1 and at temperatures of 77 and 293 K. For the tests at 77 K, the specimens and grips were first fully immersed in a bath of liquid nitrogen for about 15 min. During the tests, the baths were filled as needed to keep the specimen and grips fully immersed at all times. Room temperature tests were performed in ordinary ambient air. For each test condition, three separate specimens were tested; one was interrupted at the time of necking so that their microstructures could be examined after deformation and their failure locations could be identified.

Results and discussion Microstructure of base metal Microstructural investigations of the CoCrFeMnNi HEA have been conducted previously to understand its evolution during thermomechanical processing [36]. As-cast materials yield coarse columnar grains, and that microstructure can be broken down by appropriate thermomechanical processing, such as hot or cold working and subsequent annealing above the recrystallization temperature to produce a fine-grain structure and uniform composition without any texture [3,9,36]. To date, limited attention has been paid to the solidification behaviour of the CoCrFeMnNi HEA. A weld can be considered to be a small-scale casting, and thus an understanding of the solidification behaviour of this

SCIENCE AND TECHNOLOGY OF WELDING AND JOINING

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Figure 2. (a) BSE image of the base metal after rolling and annealing; (b) compositional profile along the red arrow (as marked).

Figure 1. (a) The grain structure of as-cast equiatomic CoCrFeMnNi alloy; (b) the EPMA compositional mapping of the marked area in (a); and (c) the compositional profile along the black line shown in (b).

new class of material will allow us to better understand the behaviour of the alloy when it is exposed to a weld thermal cycle. The as-cast microstructure of the CoCrFeMnNi alloy was reassessed by focusing on the microstructure within individual grains to reveal the solidification structure and elemental segregation that resulted from casting and processing. The as-cast microstructure that we observed is similar to what has been reported in the literature [37]. It consists of large, elongated grains extending from the edge to the centre of the rectangular cross-section mould, parallel to the heat flow direction during solidification (Figure 1(a)). EPMA was used to map the composition of a 100 × 100 μm area inside one of the elongated grains (Figure 1(a)). A clear dendritic

microstructure with dendrite arm spacings of ∼ 15 μm was revealed (Figure 1(b)). The X-ray mapping shows that the dendrite core is enriched with Co, Cr, and Fe; and that the interdendritic region is enriched with Mn and Ni. A 50 μm line scan with a step size of 1 μm was made to quantify the compositional differences between these two regions (Figure 1(c)). Mn underwent the most severe segregation during casting ( ∼ 16 at.% in the dendrite core and ∼ 26 at.-% in the interdendritic regions). The segregation of Ni was minor ( ∼ 18% in the dendrite cores and ∼ 22% in the interdendritic regions). Co, Cr, and Fe behaved similarly to each other (21% in the dendrite cores and ∼ 15% in the interdendritic regions). Thermomechanical processing (24 h homogenis ation at 1200°C, cold rolling, and 1 h annealing at 900°C) yielded a homogeneous microstructure with equiaxed grains (Figure 2(a)). That result is consistent with the results of previous studies [6,8]. Annealing twins having micrometer-scale thicknesses are visible in many grains. The average grain size without twin boundaries, as determined by a linear intercept method, was found to be ∼ 30 μm. The base metal composition was consistent with the designated nominal composition without compositional variations (Figure 2(b)). The small dark particles (e.g. the particle labelled #1

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Figure 3. (a and c) BSE images and (b and d) EBSD maps (superposition of image quality and inverse pole figure) of the EB welds showing the grain structure. Since the mapped area is large, part of the areas (i.e. the edges) were out of focus during imaging, leading to the relative darkness.

Figure 4. (a and c) BSE images and (b and d) EBSD maps (superposition of image quality and inverse pole figure) of the GTA welds showing the grain structure. Since the mapped area is large, part of the areas (i.e. the edges) were out of focus during imaging, leading to the relative darkness.

in Figure 2(a)) have an atomic composition of ∼ 53.6% O, 31% Cr, 15% Mn, 0.2% Co, and 0.2% Ni. These Crand Mn-rich oxides were also observed in the as-cast specimens (Figure 1(a)), resulting from the oxygen in the raw materials and possibly from contamination during arc melting.

Microstructures of the welds The microstructures of the top and transverse sections of EB and GTA welds in the CoCrFeMnNi HEA are shown in Figures 3 and 4, respectively. Similar to the as-cast specimen (Figure 1(a)), both welds yield columnar grain microstructures. This similarity is expected because a weld can be interpreted to be a small ingot cast in a metallic mould. Another important finding was that no solidification cracks or HAZ cracks were observed for either weld, indicating good weldability of the HEA.

The observed centreline grain structures (grain growth from the fusion lines to a distinct centreline) for the EB and GTA welds are related to their weld pool geometries which are determined by the welding speed. Welding speed also has a profound effect on the weld microstructure [31,32,38–46]. In the current study, the weld speed of the EB process was 38 mm min–1 ; the welding speed for the GTA welding process was 25.4 mm min–1 . For welds made at such moderate to low speeds, the weld pools on the weld surfaces tend to have an elliptical shape. In fusion welding, the initial solidification commonly occurs epitaxially at the partially melted grains in the base metal in contact with liquid. The grain growth of the epitaxially oriented solids that form initially is strongly influenced by both the thermal gradient and crystallographic effects. The grains tend to grow in the direction of the maximum temperature gradient, toward the solid–liquid interface. Their growth direction is also affected by the materials’ preferred


Figure 5. (a) Microstructure of the EB weld zone area marked in Figure 3(a); (b) EMPA compositional mapping of the marked area in a; (c) compositional profile along the arrow shown in (a).

direction of growth, called the ‘easy’ growth direction (e.g. < 100 > for cubic materials). Therefore, during welding, the initial growth of partially melted grains in the base metal is followed by a competitive growth process. The most favourably oriented grains grow faster and soon outgrow the less favourably oriented grains. In polycrystalline materials, the selection takes place among grains of different orientations, and the grains that survive are those with their easy growth directions optimally aligned. The trailing boundary of an elliptical weld pool is curved, leading to a continuously changing direction of the maximum temperature gradient from the fusion line to the weld centre. Thus a given grain will not be favourably orientated during

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Figure 6. (a) Microstructure of the for GTA weld zone area marked in Figure 4(a); (b) EMPA compositional mapping of the marked area in (a); (c) compositional profile along the arrow shown in (a).

the entire solidification process. Therefore, many of the grains at the fusion line that are initially of unfavourable orientations may become more favourably oriented before they are completely eliminated, and thus they may survive and continue to grow toward the centreline. Consequently, no grain from the fusion line experiences preferred growth for an extended period of time, and a continual appearance of new grains toward the centreline is observed as shown in Figures 3 and 4. Many of these grains grow a considerable distance before they are restricted by the appearance of a new grain, and thus they are not equiaxed but elongated. In an EB weld, there are also continuous grains in the welding direction at the weld centre. Those grains initiate in the weld trailing edge and grow along the length of the weld.

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Element redistribution during weld pool solidification is also an important phenomenon that can significantly affect weldability and, in particular, hot-cracking

Figure 7. Representative engineering stress–strain curves of base metal, EB weld, and GTA weld at 293 and 77 K. Table 1. Mechanical properties of the CoCrFeMnNi high-entropy alloy base metal, and of EB and GTA welds Yield strength (MPa)

Base metal EB weld GTA weld

UTS (MPa)

Elongation (%)

293 K

77 K

293 K

77 K

293 K

77 K

273 320 297

481 567 510

633 617 530

1095 1057 880

38 ± 6.2 27 ± 4.8 15 ± 3.7

59 ± 7.2 39 ± 4.4 33 ± 6.1

behaviour, weld microstructure, and other properties. EPMA compositional mapping of the areas marked in Figure 3(a) and Figure 4(a) was performed to determine whether elemental segregation took place during weld solidification. The results are shown in Figures 5 and 6 for the EB and GTA welds, respectively. It is clear that the compositional microsegregations in the fusion zone of the welds are similar to that of the base material (Figure 1) with the exhibition of a dendritic microstructure consisting of Co-, Cr-, and Fe-rich dendrite cores and Mn- and Ni-rich interdendrite regions. Differences between the as-cast and weld microstructures included the dendrite arm spacing and the extent of elemental segregation. The dendrite arm spacing and the extent of elemental segregation were less in the welds than in the cast ingot and were less pronounced in the EB weld than in the GTA weld. This microstructural difference is thought to relate to the different cooling rates in each process. Typical solidification rate of arc welding is orders of magnitude higher than that found in ingot castings and that of EB welding is higher than that of arc welding. Various studies have shown that high cooling rates and the associated larger undercooling would, in general, lead to reduced diffusion distances and increased nucleation rates. Together, the two effects lead to finer and more homogeneous structures (i.e. reduced dendrite arm spacings [47–52] and reduced scale of

Figure 8. EBSD images of (a) base metal; (b) EB weld; and (c) GTA weld tensile-fractured at 77 K; (d) misorientation profile along the black arrow shown in (a).


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solute segregation [53–61]). To quantify the microsegregation, line scans across multiple dendrite arms and interdendritic regions with 1 μm step size were performed within the mapped area. For the EB weld, the average content of Mn is below the nominal composition of 20 at.-%. The maximum concentration of Mn in the interdendrite region is 16.8 at.-%. Similar depletion behaviour of Mn in the weld zone has been reported for other Mn-containing alloys [62–67], such as high-Mn stainless steels. One possible cause in this study would be the evaporation of Mn (the element that has lowest melting temperature and highest evaporation pressure) due to the high power density associated with the EB welding process. Due to the loss of Mn, the average atomic percent of the other four elements (Co, Cr, Fe, and Ni) are slightly above the nominal composition (20 at.-%). With regard to the segregation behaviour of individual elements, the absolute differences between the two regions are rather small. Mn was determined to be ∼ 13 at.-% in dendrite core and ∼ 16 at.-% in the interdendritic region. The differences between the two regions for the other four elements (Co, Cr, Fe, and Ni) were all less than 2%. Those differences are much less than that observed in the as-cast specimens (10% difference for Mn, 4% for Ni, and 6% for Co, Cr, and Fe). The GTA weld exhibited similar microsegregation behaviour in the Mn- and Ni-rich interdendritic region and Co-, Cr-, and Fe-rich dendrite cores, but the depletion of Mn was not observed. The compositional differences between the two regions are also small (4% difference of Mn and less than 3% difference for Co, Cr, Fe, and Ni). The above observations indicated that the investigated CoCrFeMnNi alloy exhibited only minimal compositional microsegregation during EB weld solidification.

Mechanical properties Different weld microstructures, including grain structure and elemental segregation, compared with those of the base metal, would lead to differences in mechanical properties. The mechanical properties of cross-weld specimens were characterised and were compared to those of base metal. Figure 7 shows the representative engineering stress–strain curves, and Table 1 summarises the mechanical properties, including 0.2% yield strength, ultimate tensile strength (UTS) and uniform elongation of fracture of the base metal, EB, and GTA cross-weld specimens. The results were consistent with previous findings [9]; the base metal exhibits a good combination of strength and ductility. Its strength and ductility simultaneously increase when test temperature is decreased from 293 to 77 K. These strength- and ductility-temperature sensitivities were also observed for both EB and GTA welds. Quantitatively, the yield strength and UTS for all samples of base metal, EB

Figure 9. Back-scattered images showing the necking regions and local macrostructure of EB and GTA samples tested at 77 and 293 K.

weld, and GTA weld increased by ∼ 70% when the temperature was decreased from 293 to 77 K. Compared with the base metal, both welds exhibit enhanced yield strength (by ∼ 10% for GTA and 20% for EB) compared with that of base metal at both 293 and 77 K. The EB welds maintained all of the tensile strength of the base metal and retained ∼ 70% of its ductility; GTA weld maintained ∼ 80% of the tensile strength of the base metal and ∼ 50% of its ductility. Extensive microstructural characterisations were performed to identify the possible causes for the differences in mechanical properties and to understand their

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Figure 10. Fracture surfaces of (a) base metal, (b) EB weld, and (c) GTA weld tensile-deformed to fracture at 77 K.

deformation mechanisms. Figure 9 shows EBSD maps of the microstructures of tensile-deformed to fracture at 77 K of (a) the base metal, (b) the EB weld, and (c) the GTA weld. Many of the grains of base metal that tensile-fractured at 77 K contained parallel bands with various thickness and spacings. A black line crossing a few band features was drawn, and misorientations along the line were measured and plotted (Figure 8(d)). The plot shows that there will be a ∼ 60o misorientation whenever the line passes the individual band, indicating that the bands are composed of 3 twins. The twin-band features have been reported extensively for the CoCrFeMnNi HEA and for other fcc metals and alloys with low stacking fault energy [68–73]. Each band is expected to consist of numerous nano-scaled twins [13]. The nano-twins and twin bundles formed during deformation have significantly beneficial effects on mechanical properties such as tensile strength and ductility, attributing to the ‘dynamic Hall-Petch’ effects [68–73] caused by the twin-dislocation interactions, which will reduce the effective grain size and hence

will increase the strain-hardening capabilities and will postpone the necking instability. The twin-bands were also observed in the fusion zones of the EB and GTA welds. A direct comparison between the twin densities of the fusion zones and the base metal is not available due to the limited number of grains covered in the EBSD maps. However, it has been shown that grain coarsening favours the formation of mechanical twins. A critical stress needs to be reached for the initiation of mechanical twins. In single-phase solid solutions, the ease to reach the critical stress is affected by the dislocation substructures formed during deformation [74]. Fine-grain materials contain more grain boundaries and thus more nucleation sites for twinning; however, under deformation, dislocations in fine-grain materials tend to have a more homogeneous distribution and form dislocation cell structures that do not twin upon deformation. In contrast, coarse-grained (materials tend to form high-density dislocation substructures, such as high-density dislocation wall, and the critical stress for twin initiation is reached more easily. Thus areas with much larger grain size, such as the


fusion zones in the welds, could favour the formation of mechanical twins. The expected ease of twin formation tends to cause more significant strain hardening and postpone this area’s necking instability. The coarsened grain structure can also reduce the grain boundary area that can act as dislocation-movement barriers and thus sacrifice the local strength through the well-known Hall–Petch effects. The large grain sizes in the fusion zones of the welds are also more difficult at accommodating plastic deformation than is the base metal far from the fusion zone. In order to identify the weakest part (where failure starts) under each condition, the tensile test was interrupted slightly after the onset of necking, after which the stress–strain curve starts to drop. The microstructures of the necking region of both welds at 293 and 77 K are shown in Figure 9. It is clear that for all tests necking occurs within the fusion zone. The reduction of tensile strength and elongations of the weld compared to base metal indicates that the effect of grain size on the strain accommodation outweighs the effects of the twinning activities. Figure 10 shows the fracture surfaces of base metal, EB and GTA welds at 77 K. It is clear that the fracture takes place by the nucleation of microvoids followed by their growth and eventual coalescence to form cracks, resulting in a fracture surface consisting of numerous micro-sized ‘equiaxed dimples.’ Those features are typical of a fracture surface in ductile materials under uniaxial loading. The dimples have a larger average size in the EB weld than in the base metal, and the dimples in the GTA weld are larger than those in the EB weld. The differences in dimple size are consistent with the observed ductility reductions. Another finding from the fracture surfaces is that, for the GTA weld, the microvoids on the fracture surface are mostly associated with particle inclusions. EDS compositional analysis shows that the composition of the inclusions is similar to that of the oxides observed in the base metal and in the welds. Only a small number of microvoids on the EB fracture surface were associated with oxide inclusions. Base metal fracture surfaces had much cleaner microvoids and no inclusions. The presence of inclusions in the welds indicates that the weld properties, such as the ductility, could be improved by controlling the atmosphere during welding. Other factors that may cause the observed mechanical property differences between the welds and base metal include the loss of Mn and microsegregation; however, further studies are needed to differentiate the effects from individual factors.

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its engineering applicability. EB and GTA welding processes were used to join thin sheets of the alloy. Extensive microstructural and mechanical property characterisation on cast ingots, base metal, and the welds were conducted to examine the alloy’s weldability. Welds without cracks or significant microsegregation were produced. The weld fusion zones yielded insignificant microsegregation and exhibited a centreline grain structure of large columnar grains grown from the fusion lines to the centrelines. The yield strength, UTS, and ductility of the base metal specimens and the cross-weld specimens increased considerably with the decreasing of temperature due possibly to the formation of nano-twinning. Both welds exhibit enhanced yield strength when compared to the base metal. The EB weld possessed comparable tensile strength and ductility to that of base metal. The GTA weld maintained ∼ 80% of the base metal’s tensile strength and 50% of its ductility. Properties of the welds could be further improved by better control of the oxygen level in the atmosphere during welding. Although the current welding tests on small laboratory-scaled coupons indicated that the CoCrFeMnNi alloy exhibited good weldability, further work needs to be done on fully industry-scaled coupon using qualitative and quantitative welding analyses.

Acknowledgement This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http:// energy.gov/downloads/doe-public-access-plan).

Disclosure statement No potential conflict of interest was reported by the authors.

Funding This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

ORCID H. Bei

http://orcid.org/0000-0003-0283-7990

References Summary and conclusions The current study assessed the response of equiatomic CoCrFeMnNi HEA to weld thermal cycles to identify

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