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Current Applied Physics 12 (2012) 1131e1138

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Current Applied Physics

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Hydrogen permeation characteristics of rolled V85Al10Co5 alloys

Eric Fleury a,*, Jin-Yoo Suh a, Dong-ik Kim a, Chan Hoon Jeong a, Jung Hoon Park b

aCenter for High Temperature Energy Materials, Korea Institute of Science and Technology, Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of KoreabGreenhouse Gas Research Center, Korea Institute of Energy Research, 71-2 Jang-dong, Yuseong-gu, Daejeon 305-343, Republic of Korea

a r t i c l e i n f o

Article history:Received 24 August 2011Received in revised form10 January 2012Accepted 2 February 2012Available online 8 February 2012

Keywords:Hydrogen separationVanadium alloyCold rollingAnnealing treatmentLow angle boundary

* Corresponding author. Tel.: þ82 2958 5456; fax:E-mail address: efleury@kist.re.kr (E. Fleury).

1567-1739/$ e see front matter � 2012 Elsevier B.V.doi:10.1016/j.cap.2012.02.007

a b s t r a c t

Thin sheets of V85Al10Co5 alloy were produced by a thermo-mechanical treatment consisting insuccessive hot rolling, cold rolling steps and annealing treatment at high temperature followed by eitherair cooling or water quenching. Though the values of hydrogen permeability measured for these sheetswere significantly reduced as a consequence of the rolling process, the annealing treatment restoredalmost the hydrogen permeation properties to those of the alloy in the cast condition. EBSD analysessuggested that the post-annealing treatment performed at 1100 �C for 3 min after cold rolling induceda recrystallization of the grains resulting in a preferred orientation along the {002} planes. For the sampleannealed and water quenched, the value of the hydrogen flux reached about 45 ml/cm2.min, which ismore than twice the value of the flux obtained for thin foils of Pd alloys tested under identical conditions.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

The method of separation and purification of hydrogen froma mixed gas based on the permeation of hydrogen through a solidmetallicmembrane appears as an attractivemean of producing highpurity hydrogen at a large scale [1]. However the widespreadcommercialization of this gas separating process is limited owing tothe high cost of Pd, which is the main element in the current alloysproposed as candidate materials for hydrogen membrane applica-tions [2,3]. Alternative materials such as vanadium, niobium andtantalum, i.e., group 5 elements of the periodic table, exhibitattractive properties in terms of the hydrogen permeation propertyhowever these elements are relatively prone to hydrogen embrit-tlement [3,4]. The hydrogen permeability (Q) through a solidmembrane can be separated into the product of the diffusivity (D)and solubility (K), Q ¼ D$K. Though the hydrogen diffusivity of thegroup5 elements is about the same range as that of Pd, the solubilityis however significantly larger [5]. One of the approaches proposedto reduce the sensitivity to hydrogen embrittlement in these alloysmade of group 5 elements consists in adding elements that wouldreduce the hydrogen solubility [1,4,6e9]. The PCT data published byYukawa et al. [10] indicated that the change in the hydrogen solu-bility is stronglydependenton the alloyingelementwith the smaller

þ82 2958 5449.

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the atomic size of the alloying element, the larger the reduction insolubility. In their earlier studies, Nishimura and colleagues haveshown that the resistance to the hydrogen embrittlement of vana-dium can be successfully enhanced in vanadium alloys owing to theaddition of a few atomic percent of Ni and Al though the hydrogenpermeability was significantly reduced [4,6,9]. While studying theeffect of element addition on the hydrogen solubility, the hydrogenpermeability and durability of ternary V85Ni10TM5 alloys[TM¼ transitionmetals], Dolan et al. [11] reported recently that theaddition of a minor element can affect significantly the micro-structure andhydrogen solubility, though thevaluesof thehydrogendiffusivity were found to be less sensitive to the composition.Further improvement could thus be expected for ternary or multi-component alloy systems with a proper alloy design.

For commercialization, these alloys should be produced in theform of large and thin sheets. As the hydrogen flux is inverselyproportional to the thickness [3], the production of thin sheets hasthe advantage of increasing the hydrogen flux, which is an impor-tant parameter for the enhancement of the efficiency and costconsideration to achieve high competitiveness [12]. However theproduction of thin plate from a widely used industrial process suchas rolling induced important microstructural changes that deteri-orate the hydrogen permeation properties [13,14]. Though thiseffect was first reported by Nishimura and co-authors for V85Ni15alloy (concentration expressed in at.%) [1], it has recently beendocumented in details by Song et al. [15]. The reduction in thehydrogen permeability observed for rolled binary V85Ni15 alloy in

10 20 30 40 50 60 70 80

a) as-cast

b) as rolled

c) rolled+AC

d) rolled+QCV (211)

V (200)

Inte

nsit

y (a

.u.)

Diffraction angle, 2θ (degrees)

V (110)

Fig. 1. XRD traces of VeAleCo samples; a) as-cast, b) as-rolled, c) rolled þ AC, and d)rolled þ WQ.

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e11381132

comparison to the as-cast alloy was attributed to an increase in thedensity of defects, particularly to dislocations.

With the aim of understanding the effect of the thermo-mechanical processing on the hydrogen permeation properties at400 �C, the aspect of the annealing treatment performed after coldrolling has been investigated on the ternary V85Al10Co5 alloy [16]. Inthis paper, the change in the microstructure resulting from post-annealing treatment followed by either air-cooling or waterquenching has been examined, and an attempt is made to correlatethe hydrogen permeation properties with the microstructure of theas-rolled and annealed membranes.

2. Experimental procedures

V85Al10Co5 (at.%) ingots in the form of disks, of approximately30 mm diameter and about 3e4 mm thick, were prepared usingvacuum arc melting machine. Membranes of 12 mm diameter and0.5 mm thickness were machined by wire cutting. For theproduction of thin membranes, the V85Al10Co5 ingots were firstheated to 1100 �C then hot-rolled down to about a thickness of1 mm (thickness reduction ratio w66e75%) while maintaining thetemperature at around 1100 �C. The total thickness reduction ratiowas achieved by a succession of steps with a reduction ratio notexceeding 50% per pass. Before performing cold rolling with theaim of further reduction in the thickness, the samples were heat-treated for 3 min at 1100 �C, then air cooled. After removing theoxide scale formed on the surface of the annealed samples, thesubsequent cold rolling step enabled further reduction down to0.2 mm (thickness reduction ratio w80%). The total reduction ratiowas achieved by successive steps which have a reduction ratio ofless than 20%. After cold rolling, 12 � 12 mm2 samples were sealedinto quartz tube vacuumed and filled with argon then annealed at1100 �C during 3 min. The annealed samples were either air cooledor water quenched.

The structure of the as-rolled, air cooled and water quenchedsamples, referred as as-rolled, rolled þ AC and rolled þ WQ,respectively, were investigated by XRD analyses. The crystallo-graphic orientation, grain size and grain boundary characteristics ofthe samples were analyzed by EBSD (Electron BackscatteredDiffraction). Samples for the EBSD analysis were prepared byelectro-polishing with 50 ml HCL and 950 ml Ethanol mixed solu-tion at 48 V for 30 s. Each EBSD pattern was collected under anacceleration voltage of 20 kV and probe current beam condition of4 nA for an integration time 10 ms. The orientation image mapswere acquired with 2.5 mm step size for texture analysis and 1.0 mmstep size for grain size and grain boundary characteristics analysis.The EBSD data were analyzed with the HKL Channel 5 software(Oxford Instruments), and a misorientation of 5� was accepted asthe grain analysis criterion as it has been applied to other BCCmetals [17].

For hydrogen permeation tests, both surfaces of the membranesamples, preliminary polished down to 2000 grade SiC abrasivepaper, were subjected to inductively couple plasma reactive etchingin radiofrequency plasma before the deposition of a thin layer of Pdabout 150 nm thick by RF magnetron sputtering applied for thedissociation and recombination of the H2 molecules [18]. The Pd-coated membranes were then tested to determine the hydrogenpermeation properties at 400 �C under a pressure of 0.2 MPa.

3. Results

3.1. Structure

The XRD traces of the as-cast, as-rolled, rolled þ AC androlled þ WQ samples are shown in the Fig. 1. No significant

difference in the crystal structure can be detected for the as-castand rolled samples however the intensity of the diffraction peakswas found to vary according to the thermo-mechanical processing.As expected for a microstructure composed of randomly orientedgrains, the intensity of the {110} peak is the larger for as-castsample. In contrast rolling induced a pronounced increase in theintensity of the {002} peak. In comparison to the results obtainedby Song et al. [15] for the binary V85Ni15 alloy, it is observed that theintensity of the {002} peak in V85Al10Co5 is further increased bya short post-annealing treatment. This suggests that a preferentialgrowth of the grains along the {002} crystallographic planes tookplace during the recrystallization, which is reinforcing the textureof the cold rolled samples.

Themicrostructure of the rolled sampleswas further analyzed byEBSD. The EBSD observation in the Fig. 2 indicates that the structureof all V85Al10Co5 alloyswere essentially composed of vanadiumsolidsolution (bcc structure) without a large volume fraction of secondphase, as it was expected from the XRD of the as-cast alloy (Fig. 1a)and shown in our previous study [16]. The black areas of the inversepole figure orientation maps of the deformed sample (Fig. 2a,b) areunindexed areas by EBSD. The reason why the cold rolled samplesshow large unindexed areas is that these areas of the cold rolledsample are too highly deformed to compose diffraction patternsclear enough to be indexed. The microstructure of the cold rolledsample observed by EBSD revealed that the grains are elongatedalong the rolling direction (upper direction) and the grain size isaround 100 mm. After post-annealing treatment, the grains have anequiaxed shape, which can be explained by the recrystallizationtaking place at high temperature after cold deformation. The grainsize was found to be about 29.2 mm (aspect ratio: 2.25) and 27.2 mm(aspect ratio: 1.74) for the annealed samples followed by air coolingand water quenching, respectively. After post-annealing treatment,the grain size is rather small in comparison to as-rolled sample, andthe water quenched sample (Fig. 3b) shows a narrower grain sizedistribution in comparison to the air cooled sample (Fig. 3a) owingparticularly to the absence of large grains.

Fig. 2. Inverse pole figure orientation maps; a) ND as-rolled (non filtered image), b) RD as-rolled (non filtered), c) ND rolled þ AC (filtered image), d) RD rolled þ AC (filtered), e) NDrolled þ WQ (filtered), f) RD rolled þ WQ (filtered), and g) standard triangle.

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e1138 1133

The XRD traces shown in Fig. 1 indicated that the orientation ofthe grains was changed as a result of the annealing at hightemperature with the formation of a preferred orientation alongthe {002} planes. With the aim of detecting minor difference in thestructure of the rolled þ AC and rolled þ WQ samples, the polefigures were extracted from the EBSD analyses. For both rolledþ ACand rolled þ QC samples, the pole figures shown in Fig. 4 confirmthat the normal direction of the grains are mainly oriented alongthe {002} crystallographic orientation, indicating that the texture isreinforced during the short post-annealing treatment. However by

looking at the distance between the red contour lines, this figureseems to indicate that the orientation of the rolled þWQ sample isslightly closer to a perfect {002} in comparison to that of roll-ed þ AC sample, which overall orientation is aligned along the {1 212} direction. This is also in agreement with the higher intensity ofthe {002} diffraction peak revealed by the XRD analysis.

Another information provided by the EBSD analysis is themisorientation between neighboring measured points, which isrevealed by different colors in the Fig. 5a and b. A larger number ofadjacent grains are represented with green and blue colors in the

0 20 40 60 80 1000.00

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a b

Fig. 3. Grain size distribution in VeAleCo samples; a) rolled þ AC, and b) rolled þ WQ.

Fig. 4. Pole figures from VeAleCo samples; a) (002) rolled þ AC), b) (110) rolled þ AC, c) (002) rolled þ WQ, and d) (110) rolled þ WQ.

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e11381134

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e1138 1135

rolled þ WQ sample, suggesting a larger proportion of adjacentgrains with a misorientation in the range 5e15�. If the misorien-tation between adjacent grains is plotted as a function of thenumber fraction as it is shown in Fig. 5c and d, it clearly appearsthat most of the grains in rolled þ WQ sample have a misorienta-tion between 5 and 25� while the largest volume fraction of grainsin the rolled þ AC sample have a misorientation between 30 and60�. The black line in the Fig. 5c and d indicates the Mackenziedistribution [19], which shows the misorientation fraction of cubicmaterials when they have a random orientation. The rolled þ ACsample shows a misorientation distribution rather closer toa random distribution, but the rolled þ WQ sample shows rathera larger fraction of low angle misorientation.

3.2. Hydrogen permeation properties

The Fig. 6a shows the values of the hydrogen permeabilitymeasured at 400 �C for the rolled samples with and without post-treatment, and these values are compared to those of cast sampleand Pd-based membranes tested under identical conditions. As ithas been shown for many compositions of vanadium alloys[1,4,6,11,16], the value of the hydrogen permeability of the VeAleCoalloy is larger than those of the Pdmetal and PdeCu alloy. The Fig. 6indicates that the rolling process results in a significant reduction inthe hydrogen permeability with value about 58.9% lower than thatof sample in the as-cast condition. Similar results have beenobtained by Ishigawa et al. [20] for duplex alloys and Song et al. [15]for V85Ni15 alloy. These variations in the hydrogen permeabilitywere attributed to microstructural changes, and particularly to thechange in the density of dislocations in V85Ni15 alloys. Afterannealing treatment, the values of the hydrogen permeabilitymeasured for the V85Al10Co5 annealed samples were found to

Fig. 5. Map showing the neighboring grain misorientation (green : 2e5� , blue : 5e15� , rrolled þ AC, and d) rolled þ WQ. (For interpretation of the references to colour in this figu

increase and to reach for the rolled þ AC and rolled þ WQ samples(Fig. 6a) values, respectively, 49.1% and 18.4% lower than that of theas-cast sample.

The values of the hydrogen flux for the cold rolled samples havebeen plotted in Fig. 6b and are compared with those of pure Pd,PdeCu alloy and as-cast V85Al10Co5 alloy. The hydrogen flux isrelated to the hydrogen permeability, Q, the hydrogen pressure atthe retentate side, Pin, and permeate side, Pout, and to the thicknessof the membrane, t, by the expression: J ¼ Q[Pin1/2 � Pout1/2]/t [2].Owing to the difference in the thickness of the materials tested inthis study, the values of the hydrogen flux measured for the 70 mmand 45 mm thickmembranes made of, respectively, Pdmetal PdeCualloy were larger than that of the 0.5 mm (500 mm) thick castVeAleCo membrane tested under similar conditions. This figureindicates also that, though the value of the hydrogen permeationwas lower, the reduction in the thickness during rolling processfrom approximately 500 to 200 mm results in a value of thehydrogen flux for the as-rolled sample superior to that of the as-cast membrane. Finally, as it could be expected from the differ-ence in the hydrogen permeation properties, the post-annealingtreatment applied to the as-rolled sample results in furtherincrease in the hydrogen flux with values exceeding 40ml/cm2.minfor the rolled þ WQ membrane.

4. Discussion

The hydrogen permeation tests conducted at 400 �C onV85Al10Co5 samples show a dependence of the properties on thestates of the samples, i.e., as-cast, as-rolled, rolled þ AC, androlledþWQ. The deformation by cold rolling reduced the hydrogenpermeability while a short time annealing at 1100 �C tends torestore the hydrogen permeation properties. However our results

ed: >15�); a) rolled þ AC, b) rolled þ WQ, frequency of the grain misorientation; c)re legend, the reader is referred to the web version of this article.)

pure P

d

Pd - Cu

as-ca

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rolle

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Co5

- T = 400oC

pure P

d

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30

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roge

n fl

ux (

ml /

cm

2 min

) V85

Al10

Co5 - T= 400oC

a b

Fig. 6. Hydrogen permeation properties at 400 �C for the V85Al10Co5 samples and comparison with pure Pd and PdeCu alloy tested in identical condition; a) hydrogen permeability,and b) hydrogen flux.

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e11381136

suggest that the fast cooling after annealing at high temperatureachieved by water quenching is favorable in terms of the hydrogenpermeability.

It is acknowledged that the microstructure plays a major role onthe hydrogen permeability of metallic alloys. The rolled androlled þ annealed samples are all composed of vanadium solidsolution. The EBSD analyses indicated that the major differences inthe structure of these annealed samples are the slightly smallergrain sizewith a narrower grain size distribution, the larger fractionof special grain boundaries and the lower misorientation anglebetween adjacent grains for the rolled þ WQ sample.

Though extensive experimental investigations on the diffusionof hydrogen have been carried out for various metals and alloys, theevidence of the dependency of the hydrogen diffusion on thecrystallographic orientation in bcc metals and particularly invanadium alloy is still lacking because of inherent experimentallimitations. Using first-principle calculation, Jiang and Carter [21]observed that the diffusion of H into Fe sub-surfaces is predictedto have a much lower barrier for (100) plane than (110) plane. Theyalso found that H diffuses through bcc Fe not via a straight linetrajectory, but rather hoppings from one tetrahedral-site toa neighboring tetrahedral-site by a curved path. For a vanadiumlattice, the favorable sites are also the tetrahedral sites [22]. Thusthe diffusion along particular crystallographic planes and directionscan be interpreted as a result of successive hopping through variousenergetically favorable paths. In vanadium alloys, though thehopping of hydrogen from tetrahedral-to-tetrahedral sites ispossible [23], it has been demonstrated for tantalum alloy that thediffusion takes advantage of the nearby octahedral sites, whichcould make the diffusion more complex [24]. In the dilute case, thehydrogen diffusion should thus be independent of the orientation,but under high hydrogen pressure and for a high concentration ofhydrogen, the orientation might play a more important role.However there is no experimental evidence that the hydrogendiffusion would be significantly affected by the crystallographicorientation particularly in the temperature range of thisinvestigation.

Beside the effect resulting from the atomic structure, it isexpected that the hydrogen diffusivity and solubility are dependenton the presence of defects such as vacancy, dislocations, grainboundaries, impurities, segregations and others obstacles that can

alter the diffusivity and solubility of hydrogen [11,25e27]. Althoughthe V3(Al,Co) phase might precipitate during annealing at hightemperature, the volume fraction of this minor phase is notexpected to be significantly different between rolled þ AC androlled þ WQ samples.

It has been demonstrated that the trapping of hydrogenenhances the solubility but decreases the diffusivity [13,14]. Earlierworks on bcc iron have shown that the change in the hydrogendiffusivity and solubility with the degree of cold deformationdepends on the concentration of lattice defects thus introduced andtheir interaction with hydrogen atoms [13]. Also the propertieswere found to be restored by application of an annealing treatmentthat removed the non-equilibrium defects [13,28]. More recently,Song et al. [15] have clearly demonstrated that the values of thehydrogen permeability for rolled V85Ni15 alloys were reduced incomparison to those of the as-cast sample of the same alloycomposition owing to the increase in the density of defects.According to Hagi et al. [29] the defects associated with the grainboundaries and dislocations can be treated as having similarproperties with respect to the hydrogen trapping effect. Byincreasing the grain size and reducing the dislocation density, theapplication of a post-annealing treatment at high temperature wasfound to obviate this adverse effect [15]. Similar effect was reportedin NbeTieNi permeable alloy with a duplex structure [19]. Suchmechanism could explain the increase in the value of the hydrogenpermeability of the V85Al10Co5 rolled samples however our resultssuggest that another mechanism responsible for the difference inthe hydrogen permeability for rolled þ AC and rolled þ WQsamples should also arise.

Three stages of structural changes are generally taking placeduring annealing of materials deformed at low temperature. Thefirst of these stages is termed the recovery stage and is dominatedby a reduction in the density of point defects. The second annealingstage corresponds to recrystallization and in the last stage the graingrowth occurs to reduce the total grain boundary area/energy [30].The first stage is assumed to be identical in both annealedV85Al10Co5 alloys, and the recrystallization process was found to behomogeneous. Our results indicated that the orientation of therecrystallization in this V alloy preserved the {002} texture in bothof water quenched and air cooled specimens. This would suggestthat, for such thermo-mechanical history, the recrystallization in

Table 1Fraction of grain per unit area with the corresponding level of orientation spread.

Gran orientation spread

0e1� 1e2� 2e3� 3e4� 4e5�

Rolled þ AC 0.845 0.073 0.061 0.021 0.0Rolled þ WQ 0.873 0.059 0.046 0.018 0.003

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e1138 1137

the annealed V85Al10Co5 alloys would obey the growth selectiontheory, which assumes that the recrystallization nuclei alreadyexist in the deformed grains with the specific orientation [31]. Therolled þ WQ sample shows a larger fraction of low angle misori-entation while the rolled þ AC specimen shows more similarrandom misorientation of cubic material (Fig. 5). It means that,because of the lower cooling rate, the rolled þ AC sample experi-ences longer time for the grain growth and rearrangement of grainboundary structure while the rolled þ WQ sample do not experi-ence enough annealing time for the further grain boundary struc-ture rearrangement. This result also confirmed the broader grainsize distribution in air cooled specimen (Fig. 3).

Assuming that the grain boundaries act as trapping sites andhinder the diffusion of hydrogen atoms, the value of the hydrogenpermeability is expected to be larger for the sample with largegrain, i.e., the rolled þ AC sample. However the interaction force ofgrain boundary on the hydrogen atoms is directly correlated to theenergy level of the grain boundary. The high angle grain boundarywill have higher grain boundary energy and will show higherinteraction force than the low angle grain boundary. The EBSDanalyses (Figs. 2 and 5) indicated that, though the grains are slightlysmaller, the fast quenching leads to low angle misorientationbetween adjacent grains in the rolled þ WQ sample. It has beendemonstrated that the grain boundary energy of alloy with cubicsymmetry increases continuously up to about 15� and then satu-rated beyond that angle [32]. Considering that the grain boundaryenergy in vanadium alloy follows a similar variation with themisorientation, i.e., a linear increase up to 15� and a constant valuebeyond that value [33], the total energy levels of the grainboundaries for both rolledþ AC and rolledþ QC samples have beencalculated based on the misorientation distribution. When theenergy level of one pixel boundary of high angle boundary isconsidered as the reference energy level, the total grain boundary

Fig. 7. Maps showing the grain orientation spread for; a) rolled þ AC, b) rolled þ WQ.

energy per unit area of the rolledþWQ sample is 124,835 times thereference energy level and that of the rolledþ AC sample is 128,164times the reference energy level. Even though the rolled þ ACsample has a shorter grain boundary length, it has an energy level3% larger than the rolled þ WQ sample because of the larger frac-tion of grain boundaries with high energy. The large fraction of lowangle boundary (below 15�) of the rolled þ WQ sample suggeststhat the trapping force of the sample will be smaller than that ofrolled þ AC sample.

Not only the grain boundary but also the presence of defectssuch as dislocations inside the grain can affect the hydrogenpermeability. The stored energy level of the samples can be quan-tified based on the concept of ‘grain orientation spread’ [17]. Thegrain orientation spread is an average value of misorientation of allthe pixels in one grain. A large value of the orientation spread fromthe average orientation of grain means a large fraction of defectsinside the grains. The Fig. 7a and b shows the statistical misorien-tation spread of grains in rolled þ WQ and rolled þ AC samples,respectively. In the rolled þ WQ sample, 87.3% of the grains haveamisorientation between 0 and 1�, while the fraction of grains withthe lowest level of orientation spread is found for 84.5% of thegrains in the rolled þ AC sample (Table 1). Also the rolled þ ACsample showed a higher fraction of high grain orientation spreadlevel per unit area. A simple arithmetic calculation of the total grainorientation spread by taking for each level the mean value andmultiplied it by the fraction of each level showed that the grainorientation spread in the rolledþ AC sample is 5.8% larger than thatof the rolledþWQ sample. This result is in agreement with the roleof defects on the hydrogen permeability discussed by Song et al. forthe rolled binary V85Ni15 alloy [15].

Both quantitative evaluations give larger values of the energy atthe grain boundary as well as the intra-grain misorientation forrolled þ AC sample in comparison to that for rolled þ WQ sample.The larger value of the hydrogen permeability for the rolled þ WQsample in comparison to the rolled þ AC sample can thus beattributed to the presence of the low angle grain boundaries andlow level of misorientation within the grains.

5. Conclusion

The effect of the annealing treatment on the hydrogen perme-ation property has been investigated for rolled V85Al10Co5 alloys.The deformation by cold rolling reduced the hydrogen permeabilityhowever this work shows that a short post-annealing treatmentrestored almost entirely the hydrogen permeation properties, andthat a high value of the hydrogen flux of about 45 ml/cm2.min wasachieved for the water quenched sample tested at 400 �C undera hydrogen pressure of 2 bars. The EBSD analyses indicated that theannealing induced the recrystallization of the grains and thetexture after annealing was preserved during annealing particu-larly for the water quenched sample displaying a more perfectorientation in comparison to the air-cooled sample. The discrep-ancy in the hydrogen permeability properties at 400 �C was inter-preted by the character of the grain boundaries and the grainorientation spread formed during annealing and quenching treat-ment owing to the difference in the cooling rates.

E. Fleury et al. / Current Applied Physics 12 (2012) 1131e11381138

Acknowledgments

The authors thank Mr. Dong-Hyeon Kim and Mr. Ju-Heon Kimfor their experimental assistance to sample preparation and char-acterization. This work was supported by the Energy & ResourceR&D program (2008-C-CD11-P-09-0-0000) under the Ministry ofKnowledge Economy, Republic of Korea.

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