The Use of Non-Destructive Tests for Characterization of Hydrogen in Advanced Alloys

8/10/2019 The Use of Non-Destructive Tests for Characterization of Hydrogen in Advanced Alloys

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C O R R O S I O N S O L U T I O N S C O N F E R E N C E 2 0 0 9 P R O C E E D I N G S

The Use of Non-DestructiveTools for Characterization of Hydrogen in Advanced Alloys

P A P E R 3 E 1

ANGELIQUE LASSEIGNECEO, METALLURGICAL AND

MATERIALS ENGINEER

Generation 2 Materials Technology, LLC10281 Foxfire Street Firestone, Colorado 80504USAT: 303-304-9785F: 720-836-4194E: [email protected]

Co-authors

J.E. JACKSONPRESIDENT

Generation 2 Materials Technology, LLC

K.E. KOENIGGRADUATE STUDENT

Colorado School of Mines

D.L. OLSONPROFESSOR OF METALLURGICAL AND

MATERIALS ENGINEERING

Colorado School of Mines

BIOGRAPHYDr. Lasseigne is a metallurgical andmaterials engineer at Generation 2Materials Technology, LLC focusingon the development of real-time in-situ non-destructive systems to givecomplete characterization of materials before significant damageoccurs. Angelique received herundergraduate degrees in Physicsand Metallurgical and MaterialsEngineering from Centenary Collegeof Louisiana and Colorado Schoolof Mines in Golden, Colorado. Shecontinued on at the ColoradoSchool of Mines for Masters andPh.D. degrees in Metallurgical andMaterials Engineering. Dr.Lasseigne completed a NationalResearch Council Post-Doctoral

Fellowship in the MaterialsReliability Division at the NationalInstitute of Standards and

Techn ol og y in Bo ul de r, C ol or ad owhere she worked on developmentof advanced sensors tocharacterize the state of materialsbefore the occurrence of defects orfailure. Angelique has also beenResearch Faculty and is currently

an Adjunct Faculty to the ColoradoSchool of Mines.

ABSTRACTMany advanced materials that areconsidered to have superiorcorrosion resistance experiencesevere problems in hydrogen-containing environments.Susceptible alloys can absorb largeamounts of hydrogen, especially athigher temperatures, resulting inhydrogen saturation and theformation of hydride phases. Thealloy composition and microstructureis directly related to the solubility of hydrogen, and therefore,susceptibility to hydrogen damage.Non-destructive electronic and

magnetic tools can be used toassess the electronic structure of analloy and are sensitive to anyperturbations in the structure.

Thermoelectr ic power and lowfrequency impedance sensors havesuccessfully been utilized to quicklyachieve the non-destructiveequivalent of the pressure-composition-temperature (activity)


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140 3E1 THE USE OF NON-DESTRUCTIVE TOOLS FOR CHARACTERIZATION OF HYDROGEN IN ADVANCED ALLOYS


diagram. Linking non-destructivesensors with the activity diagram forthe specific material allows for rapiddirect assessment of hydrogensolubility and phase. The use of thermoelectric power and low

frequency impedance to characterizehydrogen content in advanced alloysis presented.

KEYWORDS hydrogen content

determination non-destructive electronic tools materials characterization thermoelectric power low frequency impedance

INTRODUCTIONHydrogen can be both beneficialand detrimental to materialproperties and capabilitiesdependent upon the material.Hydrogen has many desirableproperties for use as an energysource, which requires materials thatcan safely and efficiently absorb anddesorb hydrogen. In other cases,hydrogen can potentially begin as abeneficial alloying element (interstitialhydrogen acts as interstitialstrengthener) until a specifichydrogen concentration is achieved.

A cr it ical hydrog en concentr at io nwould need to be determined at thepoint where degradation of materialproperties begin to preventsignificant damage or catastrophic

failure. As material capabilities arebeing pushed to extreme limits, thecritical hydrogen concentration iseven more important because evenvery small amounts of hydrogen canchange the properties of many

advanced materials. The abil ity of a meta l al loy to

absorb and desorb hydrogendepends on the interaction with themetals electronic bands. Whenhydrogen enters the crystal lattice itacts as either an electron acceptoror an electron donor as seen inFigure 1. The elements to the left of manganese on the periodic table areelectron acceptors; having a negativeheat of mixing with hydrogen, whichresults in the formation of hydrides.

The elements to the ri ght of manganese on the periodic table areelectron donors; having a positiveheat of mixing so that hydrogenstays in solution. There are materialsconsisting of elements thattranscend these extremities of theperiodic table, producing alloys thatcan have large ( (interstitialhydrogen) + (formed hydride))-region and offer large hydrogenstorage and rapid charging anddischarging characteristics. For thesafe and reliable use of advancedmaterials in hydrogen environments,it is essential to have a means of monitoring hydrogen concentrationsto determine whether the material of interest accepts hydrogeninterstitially or as a formed hydride,and then to determine the hydrogen

and hydride concentrations andlimits to achieve the desired materialproperties.

A pressure-composi ti on-temperature diagram can be used tocharacterize the phase of hydrogen

present at specific temperatures,pressures, and hydrogenconcentrations. Figure 2 is aschematic PCT diagram showingthree distinct regions. In the firstregion, hydrogen is in solid solutionand is known as the alpha phase ( ).

The reaction of hydrogen absorbedin this region is 1/2 H 2(g) H(M).

The second region is a two-phaseregion ( + ), which is the so-cal ledplateau region. In this second region,there is the coexistence of solidsolution and hydride phase. In thethird region, hydrogen is in the formof a metal hydride and is called betaphase ( ). The PCT diagram can beused to determine the phase of hydrogen present in a material andtherefore the materials susceptibilityto hydrogen damage.

A new genera tion of materialscharacterization is emerging throughthe use of electronic,electromagnetic, and elastic non-destructive tools. Electronic andelectromagnetic non-destructivetools can detect very small changesin the electronic structure of amaterial due to perturbations in theelectronic structure from alloyingadditions, interstitials (such ashydrogen), phase changes, residualstress, aging, service and

Figure 1. Electronic behavior of hydrogen in transition metal alloys.


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processing, etc. Non-destructivetools have been used to rapidlygenerate equivalent PCT diagramsfor materials to determine thehydrogen solubility and phase, andtherefore the materials susceptibility

to hydrogen damage. Thermoelectricpower and low frequency impedancesensors have successfully beendesigned to quickly generate andachieve equivalent PCT diagrams invarious materials. A brief backgroundis described for the use of thermoelectric power and lowfrequency impedance to characterizehydrogen in materials.

Thermoelectric Power The thermoelectric power coefficient(also referred to as the Seebeck coefficient) is a temperature-dependent electronic materialproperty that can be described asthe entropy of the free electrons inthe alloy. In metallic alloys, the valueand the sign of the thermoelectricpower coefficient are dependentupon factors including the electronicfeatures in the vicinity of the Fermienergy level, the effective masstensor, the density of electronicstates and the dominating scatteringmechanism [1] . In turn, the value of the Fermi energy (the Fermi energysurface in the k-space) changes withelectronic filling in the conductionband due to electron donation byhydrogen atoms. For example, withthe high degeneracy of free electrongas, the resulting thermoelectricpower coefficient, is related toelectronic theory through thefollowing expression:

where r is the scattering parameterdetermined by the dominatingscattering mechanism, and h isPlancks constant,

k is Boltzmanns

constant, n* is the electronconcentration, and me is the effectivemass. From the free electron model,the electron concentration is directly

related to the Fermi energy. Theelectronic effective mass defines therate of Fermi energy change withincreasing electron concentration [1] .

The ef fect ive mass can bedescribed as:

where k is the wave number. Theeffective mass, me, describes theshape of the s , p, and d bands thatare in contact with the Fermi energylevel. The shape of the bands at thecontact position offers acharacteristic indication that can bemeasured with changes in the Fermienergy level due to electrondonation from the hydrogenaddition. To gauge the magnitudeof the thermoelectric power effect,the thermoelectric power coefficient, , is defined as the potentialdifference developed, dV, per unittemperature difference, dT:

Two copper probes maintained at aconstant temperature difference areplaced on the material, which thengives rise to a developed potential,V, between the copper probe andthe material being investigated. The

thermoelectric power coefficient of the a, is then calculated as:

where Cu is the thermoelectric powercoefficient of the reference copperprobe. A schematic thermoelectricpower sensor used for powdermaterials is shown in Figure 3, whereheating cartridges are inside eachprobe to maintain the temperaturedifference necessary to develop ameasurable potential difference.Figure 4 shows thermoelectric powerprobes designed for determination of nitrogen and hydrogen in stainlesssteel weldments.

Figure 2. Schematic pressure- composition-temperature (activity) diagram.

Figure 3. Schematic thermoelectric power probes for powder materials [2] .


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Low Frequency ImpedanceLow frequency impedancemeasurements offer an alternativeand complimentary technique tothermoelectric power because theyprovide a means to perform non-

destructive, non-contact hydrogencontent measurements as afunction of depth in materials.Previous research has found thatlow frequency impedancemeasurements are extremelysensitive to variations in hydrogencontent in high-strength steelspecimens [4] .

In eddy current testing forhydrogen determination inmaterials, a low frequencyelectromagnetic coil is used to

induce an electromagnetic field (byan alternating current) into amaterial. In response, the inducedelectromagnetic field produceseddy currents in the sampleopposing the generated

electromagnetic field. The inducedelectromagnetic field is comparedto the opposing electromagneticfield produced (d ue to Lenzs law)within the inspected material.

When an alternating current isapplied to the material beinginspected, the electromagnetic coilpossesses both resistance andreactance. Along with resistance,there is a changing flux in the coil,which exhibits inductance [5] . Theimpedance, , of the system can

be expressed:

where is angular freque ncy, L is

inductance, C is capacitance, and Ris resistance. Impedance is ameasurement of resistance, but withdepth capabilities provided by theangular frequency. At very lowfrequencies, impedance becomes aresistance measurement making iteasier to see the changes inresistivity with the addition of eachhydrogen atom. Resistancemeasurements bring into play newfactors that are not included inthermoelectric power measurements

Figure 4. Photograph of thermoelectric power surface probes designed for weldments [3] .


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because impedance is pushingcurrent, which means that anyscattering sites within the materiallattice will change the value of resistance. This means that lowfrequency impedance will require

more variable separation andcalibrations necessary for use, butit may be worth it t o have a meansof monitoring hydrogen in materialswithout having to touch the surfaceof the specimen. But for a resistancetype of measurement, it is essentialto have a mean of separating out theeffects of all scattering sites toachieve an accurate hydrogencontent measurement [4] . Furthertheoretical development of

thermoelectric power and lowfrequency impedance are discussedin multiples sources [4] .

A ph ot og ra ph of anelectromagnetic coil designed forlow frequency impedance hydrogen

content measurements on pipelinesteel weldments is shown in Figure5 [6] . The electromagnetic coil hasbeen designed in this manner tocreate a powerful magnetic fieldstrength to overcome any magneticremanence present in the pipelinefrom smart pigging and the weldingprocess. The electromagnetic coilsare designed for each applicationand material and can have a sizerange spanning from less than a

couple of centimeters to arrays of coils for inspecting very largesections of materials. Lowfrequency impedance hydrogencontent measurements have beensuccessfully performed in the

laboratory and in the field [6] .

EXAMPLES OF NON-DESTRUCTIVE CHARACTER-IZATION OF HYDROGEN IN

ADVANCED ALLOYS Th ermoelec tr ic po wer and lo wfrequency impedance have bothbeen developed to monitorhydrogen contents in many differentadvanced alloys such as MONEL

Figure 5. Photograph of electromagnetic coil designed for low frequency impedance hydrogen content measurements in pipelinsteel weldments [6] .

MONEL is a registered trademark of Special Metals Corp.


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K-500, hydrogen storage materials,pipeline steels, zirconium, etc.Examples of the use of thermoelectric power and lowfrequency impedance are describedin the following section.

Characterization of Hydrogen in MONEL K-500 MONEL K-500 (UNS N05500) isan age-hardenable copper-nickelalloy with excellent corrosionresistance and high-strength and

hardness. Thermoelectric powercoefficient measurements wereperformed on MONEL K-500 toassess the effect of cathodiccharging from cathodic protection [1] .

The co rr el at io n be tw een

thermoelectric power coefficient andthe hydrogen content of hydrogencharged MONEL K-500 specimensis shown in Figure 6, whichillustrates the hydrogen content atthe advent of metal hydrideformation. Figure 6 is the non-destructive corollary to thepressure-composition-temperaturediagram shown in Figure 2 becauseit can be divided into distinctregions, the -region (diffusiblehydrogen) and the ( + )- regi on(diffusible hydrogen and formedhydrides). Determination andmonitoring of the onset andprogression of hydride phaseformation can prevent materialdegradation and failure.

Characterization of Hydrogen in LaNi 5 Hydrogen Battery Materi alsLaNi 5 is a reversible metal-hydridebattery material, which operates inthe two-phase, ( + )- regi on , asseen on the pressure-composition-temperature diagram (activitydiagram) for LaNi 5 shown in Figure7. For reversible metal-hydridebatteries, the two-phase region,consisting of both soluble (diffusible)hydrogen and formed hydrides, isthe most important region becauseas a battery is charged, the H/LaNi 5ratio is on the far right sid e of theactivity diagram where it is purehydride phase, then as the diffusible

hydrogen is released for energyusage, the hydrogen concentrationin the material goes back to the verybeginning of the ( + )- phaseformation. Theoretically, the rule-of-mixtures can be utilized in the two-phase region to determine thepercentage of hydride and diffusiblehydrogen at a given H/LaNi 5 value.Sieverts law holds true for hydrogenin the alpha-phase region because

Figure 6. TEP coefficient a function of charged hydrogen content in MONEL K-500 [1] .

Figure 7. Isotherms of hydrogen gas (pressure p atm) in equilibrium with absorbed hydrogen in LaNi5 (concentration: H atoms/LaNi5).7 Notice the alpha-region is where

hydrogen is in solid solution, the (alpha+beta)-region is made-up of both solid solution hydrogen and hydrides, and the beta-region is primarily formed hydride.


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hydrogen gas molecules becomedissociated into atoms while beingdissolved into metals in the regionwhere hydrogen can be regarded asan ideal gas. At higher pressuresand temperatures, the chemical

potential and solubility of hydrogendeviates from the ideal gas behavior,thus Sieverts law no longer applies.

The ab il it y to quan ti fy andcharacterize both the diffusiblehydrogen and hydride contents inthe two-phase region is critical tothe performance of the reversiblehydrogen storage materials.

Thermoelectr ic po wermeasurements can successfullygenerate an equivalent activitydiagram for LaNi 5 at roomtemperature and 190C (374F) asshown in Figure 8. Notice how eachregion in Figure 8 corresponds to theactivity diagram in Figure 7.

Thermoelectric power can thereforebe utilized as a hydrogen fuel gauge.

Characterization of Hydrogen in NaAlH 4NaAlH 4 is another hydrogen storagematerial similar to LaNi 5 discussedin Figures 7 and 8, however NaAlH 4has a dual two-phase region shownin Figure 9 indicating formation of different hydride phases at specifichydrogen concentrations. Theactivity (PCT) diagram for NaAlH 4(Figure 9) shows that primaryreaction occurs from approximately0 to 1.0 H/Al and a secondaryreaction occurs from approximately1.0 to 2.5 H/Al. Thermoelectricpower measurements wereperformed as a non-destructivemeans of generating an activity

diagram shown in Figure 10. Thermoelectric power as a functionof H/Al (Figure 10) exhibits the sametwo-reaction behavior as indicatedin Figure 9.

Characterization of Hydrogen in Pipeli ne Steel Pipeline operators are moving tohigher strength steels for thedevelopment of future pipelines.

Figure 8. Thermoelectric power coefficient as a function of H atoms/LaNi 5 for hydrogen charged LaNi 5 at room temperature (green) and 190C (374F) (blue) [8] .

Figure 9. Pressure-composition-temperature isotherms for NaAlH 4 and Na 4 AlH 6- [2,9] .


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Most steels have problems inhydrogen environments, but as thestrength of the steel increases thethreshold content leading to failure

due to hydrogen is lowered. Thermoelectr ic powermeasurements were performed inthe three examples discussed, but

for hydrogen content determinationin operating pipeline steels, lowfrequency impedance is essentialbecause surface contact is notalways possible. Induced current lowfrequency impedance analysis has

been developed to make non-contact determination of hydrogencontent in linepipe steel specimensin the laboratory and in the field.Laboratory low frequency impedanceexperiments show that impedanceis very sensitive to small changes inhydrogen content as seen in Figure11. The figure shows impedance asa function of hydrogen for hydrogencharged X80 linepipe steelspecimens at a frequency of 100 Hz(bulk of the specimen). Impedancemeasurements appear to be moresensitive than other analyticaltechniques to hydrogenconcentrations below less than onepart per million. For measurementsperformed in the field, separation of

Figure 10. Thermoelectric power coefficient as a function of H/Al for hydrogen charged NaAlH 4 [4] .

Figure 11. Frequency sweep of impedance with change in hydrogen content in tin coated hydrogen charged X80 steel specimens [4] .


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CONCLUSIONSKnowledge of the amount and typeof hydrogen present in a material iscrucial to the performance of criticalmaterials. Non-destructive electronicand electromagnetic tools can be

successfully developed to monitorhydrogen contents in advancedmaterials through the use of equivalent activity diagrams tomonitor the hydrogen content andextend materials lifeteime whilepreventing failures.

ACKNOWLEDGEMENTSGeneration 2 Materials Technologyappreciates the guidance andadvice of Steve Sparkowich of ATIWah Chang. a

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Kaydanov, and D .L. Olson,Thermoelectric Diagnosticsfor Non-Destructive Evaluationof Materials, 10th CF/DRDCMeeting on Naval Applicationsof Materials Technology,CRDC, Dartmouth, NS,Canada, pp 648666, May1315, 2003.

2. A.N. Lasseigne, B. Mishra, andD.L. Olson, Characterizationof Hydrogen StorageCapability in Advanced BatteryMaterials, Proc. ICAMMP2006, III Khanaspur, India,February 3-5, 2006.

3. A.N.Lasseigne, "Non-Destructive Determination of Interstitial Nitrogen Content in

Austenit ic Stainless Steel Weld

Metal Utilizing ThermoelectricPower," Masters Thesis, T-5899, May 2004.

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Advanced Materials, Ph.D. Thesis, Colorado School of Mines, 2006.

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Non-Destructive Evaluation: A Tool in Design,Manufacturing, and Service,Rev. Ed., CRC Press, Inc.,

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D.L. Olson, J.E. Jackson, B.Mishra, and J . McColskey,Real-Time Low FrequencyImpedance Measurements forDetermination of HydrogenContent in Pipeline Steel,QNDE 2008, AmericanInstitute of Physics, In press.

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and H.C.A.M. Bruning,Reversible Room Temperature

Absorption of Large Quantit iesof Hydrogen by Intermetallic

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Two-Phase Region of LaNi 5", Advanced Materials for EnergyConversion II, Eds. Chandra,Bautista, and Schlapbach,

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Figure 13a &13b. Impedance as a function of hydrogen content for hydrogen charged Zircaloy-4 at 200 Hertz in water [4] .


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127135, 2006.9. B. Bogdanovic and G.

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MRS Bulletin, pp 712719,September, 2002.

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The Use of Non-Destructive Tests for Characterization of Hydrogen in Advanced Alloys

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