NASA Technical Memorandum 107043

AIAA-95-2398 A /¢

Rhenium Material Properties

James A. BiaglowLewis Research Center

Cleveland, Ohio

Prepared for the

31st Joint Propulsion Conference and Exhibition

cosponsored by AIAA, ASME, SAE, and ASEE

San Diego, California, July 10--12, 1995

(NASA-TM-107043)

PROPERTIES (NASA.

Center) 17 p

National Aeronautics and

Space Administration

RHENIUM MATERIAL

Le. is Research

N96-13042

Unclas

G3126 0065450

RHENIUM MATERIAL PROPERTIES

James A. BiaglowNational Aeronautics and Space Administration

Lewis Research CenterCleveland, Ohio 44135

Abstract

Tensile data were obtained from four

different types of rhenium at ambient andelevated temperatures. The four types ofrhenium included chemical vapordeposition (CVD) and three powdermetallurgy (PM) types, i.e., rolled sheet andpressed and sintered bars, with and withouthot isostatic pressure (HIP) treatment.Results revealed a wide range of valueswith ultimate strengths at ambienttemperatures varying from 663 MPa forCVD rhenium to 943 MPa for rolled sheet. Asimilar spread was also obtained formaterial tested at 1088 K and 1644 K. Thewide variance observed with the differentmaterials indicated that the rheniummanufacturing process, materialcomposition and prior handling stronglydictated its properties. In addition to tensileproperties, CVD, pressed and sinteredmaterial and HIP rhenium successfullycompleted 100 cycles of low cycle fatigue.Creep data were also obtained showingthat CVD and pressed and sintered rheniumcould sustain five hours of testing under atension of 27.5 MPa at 1922 K.

Introduction

The On-Board Propulsion Branch of NASALewis Research Center (LeRC) and theaerospace industry are currentlyinvestigating a series of 22 N to 890 Nthrust chambers (refs. 1, 2) made fromrhenium material coated with iridium foroxidation protection. The longest test timeon a single chamber so far has been 39hours at NASA LeRC with a oxide coatediridium/rhenium 22N chamber (ref. 3) and

6.3 hours with a flight type 440 N thrustchamber (ref. 4). The operating temperatureof these chambers were in excess of 2000

K yielding 8 percent improvement inperformance over conventional chambers.This excellent performance means less filmcooling, greater life, and increasedpayloads into orbit with space vehicles usingrhenium thrust chambers. However, the lackof reliable material properties data arehindering their full acceptance. Currentproperties data are very sparse andscattered throughout the literature.Furthermore, property data are oftenreported for forms of rhenium that are notused for chamber manufacture or where thematerial history is not reported. Propertydata for various forms of rhenium arereported in references 5 to 8. The data theyreport are within the scatter of the resultsobtained here.

This paper presents the material propertiesof rhenium in manufacturing forms that wereconsidered prime candidates for thrustchamber development. Reproducible data,obtained in controlled environments, arerequired before rhenium can be consideredas a viable candidate for thrust chamberdevelopment. In particular the tensilestrength, low cycle fatigue, and creepproperties were determined for up to fourdifferent types of manufactured rhenium.The four different types of rheniumincluded: chemical vapor deposition (CVD),and powder metallurgy (PM) in the forms ofrolled sheet, pressed and sintered bars, andhot isostatic pressure (HIP) treated material.Using these four material varieties, aprogram plan was developed to determinethe properties of 59 rhenium samples. This

large number of test samples was selectedto insure that any large variation fromestablished trends could easily be identifiedand further investigated for their deviation.

Background

Current on-board propulsion systems use ahigh temperature alloy C-103 with adisilicide oxide coating. These chambers arelimited by wall temperature to 1593 Koperation. In order to maintain walltemperature below this limit, 30 to 40percent of the fuel is usually required as afilm cooling barrier. This large film coolingrequirement extracts a penalty inperformance since operation of thechamber is kept below levels that wouldyield optimum specific impulse. A leadingcandidate to replace C-103 is rhenium withiridium used as an oxidation resistant

coating. Rhenium has a high meltingtemperature of 3453 K along with hightemperature strength and thermal shockresistance. Performance gains of up to 20seconds specific impulse are demonstratedwith rockets using earth storable fuel andrhenium chambers (ref. 9). These gains areachieved through designs which eliminatedfilm cooling and improved combustionefr¢iency. CVD and PM are two of theprime material preparation techniques forthis rhenium material. The successfulperformance of these materials generatesa need to know their physical properties inmore detail. These material data areespecially important in the design processfor determining the durability of thrustersduring launch vibration and repeated firingon-orbit.

In order to generate the needed information,LeRC conducted a rhenium materials

development program under the SpaceStorable Rocket Technology Program(SSRT) with TRW and a parallel effort in-house. The SSRT program investigated theproperties of 37 samples made by CVD andPM produced from pressed and sinteredmaterial. LeRC investigated 22 samples,including CVD, HIP, and rolled sheetrhenium.

CVD rhenium The CVD material used inthis investigation was obtained fromUltramet. The CVD process produces athick structural deposit by the chemicalreaction of a vapor at a surface on a heatedsubstrata. To form structures of 0.132 cm

thickness required in this study, thedeposition was done in several layers Thefirst layer formed at nucleation sites. Afterthe substrate is fully covered growthcontinued on the crystal faces of the deposituntil the desired thickness was reached.The process was then halted as many timesas needed to prevent large crystalformation. The surface was machinedsmooth and the process restarted until thefinal desired thickness was reached.

Powder _ All three types ofpowder metallurgy samples were madefrom a high green strength 200 meshpowder that was 99.99 percent pure.Rhenium Alloys Inc. provided all the PMsamples. The pressed and sintered barsmeasured 95 to 96.3 percent dense. Therolled sheet was obtained from an ingot thatwas rolled in the longitudinal direction toproduce a sheet that was nominally 8 cmwide by 38 cm long and 0.16 cm thick.Density of the rolled sheet was greater than99 percent. The HIP treated samples wereobtained from the outer perimeter of a largecylindrical ingot that was used tomanufacture a 440 N thrust chamber.Density of these samples was also greaterthan 99 percent.

Test Procedure

All sample bars, both those required in theSSRT program and LeRC in-house

investigations were sent for testing toEnergy Material Testing Laboratory (EMTL).This was done to assure consistency in testprocedures and measured results. The flatbars which measured approximately 2.2 cmwide by 10.1 cm long, were electrondischarged machined (EDM) using copperwire into the dog bone shape shown inF_ure 1. The dog bone samples were thenacid scrubbed to remove any melt or recrustarea formed by machining. The test pieceswere then acid washed several times to

removeany contaminates.Any test piecenotannealedby the manufacturewasthenannealed.Forthe LeRCin-housesamples,onlytheHIPmaterialhadto beannealedat1922K for 30 minutes.Data,fromrheniummaterial that has been annealed,areimportantas it simulates the condition of thethrust chamber after hot rocket acceptancetesting. After annealing, Rockwell hardnessmeasurements were made and wererecorded for the LeRC samples in Table I.All samples were then weighed,photographed and visually inspected beforetesting. Test samples were placed in achamber that was first purged with argonwhich was then out gassed until a oxygensensor dropped below 50 ppm. Samples tobe tested were heated at a rate of 13 K perminute until target temperature wasreached. Tensile testing of all samples wasthen conducted at a load rate cross headvelocity of 0.13 cm per minute until thesample failed. Upon the occurrence offailure all data were saved and the sampleredimensioned to determine any lengthchange due to plastic deformation. Thetesting facility, EMTL then prepared andsubmitted a detailed report to LeRC (ref.10).

Test Results

The data for rhenium tensile samples arepresented in Table II and includes valuesfor unannealed and annealed bars. Test

data are presented for tensile yields of 0.2and 0.5 percent ,ultimate strength, elasticmodulus, and percent strain to failure ratio.Figure 2 plots ultimate strength and the 0.2percent yield data. Comparison of the datashows that rhenium tensile strength has awide range of values based on the anneal,the method of material preparation, and thetest temperature. For ease of comparison,powder metallurgy results are plottedseparately in Figure 3 and CVD results inFigure 4. In addition to tensile data, creepdata is presented in Table III for CVD andPM pressed and sintered rhenium while lowcycle fatigue data is presented for CVD, PMpressed and sintered and HIP rhenium inTable IV.

Rolled Sheet. From Figure 2 it is seen therolled sheet produced some of the highestas well as the most consistent data of all therhenium materials tested. Maximum yieldstrength at room temperature was 590.1MPa with a ultimate strength of 943.1 MPa,elastic modulus 434.4 GPa and a strain tofailure of 17.2 percent. When the testtemperature was raised to 1644 K, yieldwas reduced to 370.1 MPa, ultimate to443.3 MPa with a elastic modulus of 195.1GPa and a strain to failure ratio of 1.38percent. The rolled sheet was the only PMmaterial that showed the typicalcharacteristic of decreasing yield strengthwith increasing temperature.Electron microscope photographs in F=cjure5 further detail some of the uniquecharacteristics of rolled rhenium. Figure 5shows that failure was preceded byelongation or necking of the specimenfollowed by rupture. In several cases thisfailure is along a 45 degree angle with theload. This type of failure is characteristic ofductile materials and is a good indicationthat intergranular shear forces are primaryresponsible for failure. Scanning electronmicroscope (SEM) photographs taken attimes sixty magnification (Figure 6) indicatethat failure is due to intergranular ductilerupture at room temperature with somedimple rupture evident at the 1644 Ktemperature. Observations of the samplesafter testing showed that three of themexhibited signs of plastic deformation on thesample surface due to material yield. Thisbehavior was observed outside of therupture location No low cycle fatigue orcreep tests were conducted with the rolledsheet.

Pressed and sintered The pressed andsintered samples were investigated underthe SSRT program and are reported indetail in Reference 11. Results presentedhere are meant to summarize the materialsperformance and show how it compared tothe other forms of manufactured rheniumsamples. The pressed and sintered PMmaterial produced the lowest ultimatestrength levels of any PM sample tested.Figure 4 shows that yield strengths werebelow any other tested rhenium sample.

Theselowvalueswereattributedto the lowdensityof the material,95 to 96 percent.Table II shows that unannealedtestsampleshave lower ultimate strength thanannealed. This difference was opposite towhat was anticipated and was attributed torepressing of some of the samples altersintedng and annealing. This repressing orstraightening was done on samples thatshowed signs of being warped and as aresult added work hardening to the material.The sintered PM was one of three types ofrhenium that was tested for low cyclefatigue as shown in Table IV. Resultsindicated that in tension and compressionPM sintered rhenium had sufficient strengthto successfully sustain 100 low fatiguecycles based upon yield strengths. Anothersample of this same material completed afive hour creep test at 1922 K and 27.5MPa. The creep test temperature andpressure were values selected thatrepresent the worst case scenario for 440 to880 N thrust class rockets.

HIP The HIP treated PM rhenium sampleswere second only to the rolled sheet inultimate strength when evaluated at ambientand 1088 K. When the test temperaturereached 1644 K values of ultimate strengthas with sintered PM were below that of theCVD samples. Yield strengths at alltemperatures were the second lowest of alltested material. The HiP material alsoexh_ited the unique property of increasedyield strength as the test temperature wasraised from ambient to 1088 K (Figure 3).

Examination of the ruptured samples inFigure 5 shows that in all cases the breakproduced almost no reduction or necking ofthe sample. This lack of necking and thetransverse breaks are a good indicationthat HIP rhenium is more brittle in naturethan was seen in the previous samples.Fkjure 6 shows the HIP rhenium had a veryfine almost sand like structure rather than astringy or rock candy like texture. The sandlike structure indicates that failure was

through transgranular rupture rather thanintergranular that was characteristic of theother PM materials. PM HIP material thusbehaves more like a structure that fractures

across a fine grain surface. Observations ofthe samples after testing showed nonoticeable surface plastic deformation.Table IV shows that HIP rhenium

possesses the ability to withstand 100 lowfatigue cycles at both 1088 K and 1644 K.The one sample that failed to reach thisgoal was accidentally pretested to 400 MPaand inadditlon was warped across the widthdirection. This sample was warped due tostress relieving after annealing and wassufr¢ient to prevent correct alignment in thetest apparatus.

CVD Chemical vapor deposition results arepresented for tensile data obtained underthe SSRT program and the LERC in-houseeffort. The SSRT data are reported in detailin Reference 11. The SSRT and LERC

samples were obtained from the samemanufacturing run. Since both sets ofmaterial were from the same run and

identical procedures were used to obtaintensile data, they are treated in this reportas if coming from one source. Results oftensile tests indicate good agreement withyield strengths at ambient conditions but awide variation as the temperature wasraised to 1088 K and 1644 K. The CVD

samples also showed the unique property ofincreased yield strength, as noted with PMmaterial, when the temperature wasincreased from ambient to 1088 K. Ultimatestrengths showed good agreement atambient and 1088 K but a wide variation at

1644 K. Figure 5 and 6 reveal some of theunique characteristics of the CVD materialas far as rupture and grain structure. InFigure 5, in the majority of cases there is anoticeable elongation in the area of therupture followed by a very jagged andirregular tearing type break across thesample. This type of very coarse rupturereveals several layers of the CVD materialindicating that rupture points occurred indifferent planes. The elongation of thesamples and the ragged angular breaksidentified the CVD material as being ductilein nature. It is this elongation 0.4 percent forsample 6-CVD and 3.1 percent 5-CVD thatis responsible for the large spread in data at1644 K (Figure 4) . In addition to theelongation and jagged breaks, Figure 6

4

showsthat CVDmaterial had a differentgrainstructurethanwasseenwith anyofthe other manufactured rhenium samples.The grain structure consisted more of largecolumnar or rock candy surface and thatfailure was by intergranular fracture modes.As with the SSRT samples, there was noindication of laminar separation.Observations of the samples after testingshowed that all but one had numerous smallcracks on the edge of the test piece. Thesecracks extended only slightly into the gagesection. No noticeable plastic deformationwas observed with the CVD samples.

The CVD material was also tested for lowcycle fatigue and the ability to withstandcreep. CVD rhenium showed the ability tocomplete 100 cycles of 137.9 MPa tensionand 68.9 MPa compression but sufferedfrom plastic deformation. The CVD rheniumalso showed no creep failure at 1922 K and27.5 MPa.

Summary/C0nclusions

(1) Tensile tests of four different rheniummaterials revealed a wide range of valuesthat strongly suggest rhenium strength isprocess controlled and that selection of arhenium manufacturing process and priorhandling will strongly dictate its properties.(2) HIP rhenium demonstrated some of thehighest levels of strength along with theability to withstand 100 low fatigue cyclesbased upon yield strengths. Its failure wascharacterized by a sharp brittle like break.(3) Rolled sheet demonstrated the highestlevel of strength. Its failure was byintergranular and dimpled rupture indicativeof a ductile material.

(4) CVD material demonstrated a widerange of tensile strengths failing byintergranular shear forces. Tensile data waswithin the scatter of previously reportedresults.(5) Pressed and sintered rhenium showedthe lowest level of strength for PM samplestested but was sufficiently strong enough topass the low cycle fatigue and creep tests.

REFERENCES

1. Schneider, S. J., "High-Temperature Thruster Technology ForSpacecraft Propulsion', IAF-01-254, 42NDCongress of the International AstronauticalFederation, Montreal, Canada, October5,1991.

2. Schneider, S. J., "Low ThrustChamber Rocket Technology', IAF-92-0669, 43ND Congress of the InternationalAstronautical Federation, Washington, DC.,August 1992.

3. Reed B.Do, "Long Life Testing ofOxide Coated Indium/Rhenium Rockets",AIAA 95-2401, San Diego, CA., July 1995.

4. Jassowski D. M. "Advanced SmallRocket Chambers, Option 3", NASA CR195455, 1993.

5. Southern Research Institute "HighTemperature Tensile Evaluation of Pressedand Sintered Rhenium', February 1994.

6. Svedberg, R. C. and Bowen, W.W., "High Temperature Creep and TensileProperties of Chemically Vapor-DepositedRhenium', Report No. HEDL-SA-2695-FD,Metallurgical Coatings and ProcessTechnology Conference, San Diego, CA,April 1982.

7. Horak, J. A., and Kangilaski M.,"Effects of Irradiation on the TensileProperties of Rhenium", ORNL/TM-12360,U.S.Department OF Energy, April 1993.

8. Bryskin, B. D., "Evaluation ofProperties and Special Features for High-Temperature Application of Rhenium', 278-291, Ninth Symposium, Space NuclearPower Systems, Albuquerque, NM, 1992.

9. Chazen, M.L., Mueller, T. and Rust,T., "Space Storable Rocket TechnologyProgram', Option 1 Final Report, NASALero, CR-191171, August 1993.

10. Energy Materials TestingLaboratory, "Mechanical Property

Evaluations,TensileandLowCycleFatigueTestingof Rheniumat RoomandElevatedTemperatures',FinalReport1705,NASA-LeRCC-79086-C,March,1995.

11. Chazen,M. L., "Materials PropertyTest Results of Rhenium', AIAA 95-2938,San Diego, CA., July 1995.

6

TABLEI. RHENIUM HARDNESS RESULTS

MA_

PM ROLLED SHEET

CHEMICAL VAPOR

DEPOSITION

PM HOT ISOSTATIC

PRESSURE

SAMPLE ROCKWELL "B"HARDNESS

RS-I

RS-2

RS-3

RS-4

RS-5

RS-6

1-CVD2-CVD3-CVD4-CVD5-CVD6-CVD

Hiped-IBiped-2H_ped-3Hiped-4roped-5Hiped-6Hiped-'7I_ped-8Iaped-9Hiped-lO

105105103104

105102

99

99102

103

103102

8887878887898989

8788

7

;zp.

---.

+,14'

itt,3,=

III

i

+_,

|

i

!;

++Sl

eL

AX

8

TABLE III. RHENIUM CREEP DATA

SAMPLE TEMPERAll,JRE (K)

CHEMICAL VAPOR

OEPOSITION

CVD-15 1922

CVD-16

PM PRESSED AND

SINTERED

1922

STRESS MPa % STRNN

TENSION/COMPRESSION

27.5

27.5

0.22

0.24

PM-16 1922 27.5 3.60

PM-17 1922 27.5 1.7S

PM-18 1922 27.5 1.17

PM-19 1922 27.5 1.80

TABLE- IV. LOW CYCLE FATIGUE FOR RHENIUM

SAMPLE #

Chemical Vapor Deposition

CYD-10

CV1D-11

CYD-12

CVD-13

CVD-14

CYD-l$

CVD-14

PM Pnmud and Slntemd

PM4

Plkl0

PM-11

PM-12

PM-13

PIk14

PlklS

PM _ Isostati¢ Pmmre

HIPED-7

HIPED4

HmED-g

HiPED-10

TEMPERATURE (K) STRESS MPaTENSION/COMPRESSION

RT 151.7/151.7

FIT 151,7/151.7

1088 275.8/1793

1088 275.8/137.9

1088 275.8/137.9

1068 275.8/137.9

1644 137.9/68.9

1644 137.9/68.9

CYCLESCOMPLETED

100

100

FAILED ON IST CYCLE

100

11

12

85

37

RT 206.9z'206.9 100

RT 189.6/189.6 100

1088 193.0/193.0 100

1088 206.8/206.8 100

1644 137.9/137.9 23

1644 103.4/103.4 100

1644 103.4/103.4 100

I088 137.9/68.9 103

1088 127.8/62.1 20"

1644 131.0A52.1 100

1644 137.9/68.9 100

"Sample was accidentally loaded to 248.2 MPa in a pretest run and exhibited a plastic deforma_on of 1.2 percent when removqKI. TIw

sample was =dso warped in the width direc_on due to s_.l relieving during the anneal'rag cycle.

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TESTTEMPERATURE(K)

Figure2-e. RHENIUMULTIMATESTRENGTHVS TEMPERATURE(K)

700

100

2O0

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0 CVO-SSmO CVO_SF_ _• CVO-bmRC

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400 600 800 1000 1200 1400 1600 1800

TESTTEMPERATURE(k")FIGURE2-b.RHENIUMYIELDSTRENGTHVS TEMPERATURE(10

FIGURE 2. ULTIMATE AND YIELD STRENGTH VS TEMPERATURE (K)

11

1000

900

80O

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i oo

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200 400 600 800 1000 1200 14430 1600 1800

_ _'I1JP, E (K)

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200 400 600 800 1000 1200 1400. 1600 1800

TESTI"I_PERATURE(K)

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FIGURE 3. PM ULTIMATE AND YIELD STRENGTH VS TEMPERATURE (K)

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8OO

700

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400¢3

300

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is= cvo- ssm"

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200 400 600 800 1000 1200 1400 1600 1800

TEST'I"_PB_J_TUI_ (K)

4.4. CYD ULllMATE STRENGTH YS TEHSERATURE (K)

450

400 -

Z

._ 350 -

"_ 300 --JW

I,-

o 250 -n,-IllQ,.

o

BBA

200 -

150

AA

@

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A CVD-I.=RC

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200 400 600 800 1000 1200 1400 1600 1800

TEST TEMPERATURE (K)

FIGURE 4-b. CVD YIELD STRENGTH VS TEMPERATURE {K)

FIGURE 4. CVD ULTIMATE AND YIELD STRENGTH VS TEMPERATURE (K)

]3

PM rolled sheet

PM HIP rhenium

CVD rhenium

Figure 5. Typical tensile breaks for tested materials

14

RoomTemperature HIP Material 1644 K HIP Matedal

Room Temperature Rolled Sheet 1644 K Rolled Sheet

Room Temperature CVD 1644 K CVD

Figure 6,- Comparison of 60x electron microscope photographs of PM HIP, PM

rolled sheet and CVD rhenium at room temperature and 1644 K.

]5

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1. AGENCY USE ONLY (Leave blank)

4. TITLE AND SUB_

Rhenium Material Properties

2. REPORT DATE

September 1995

s. AUTt_RKS)

James A. Biaglow

7. PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES)

National Aeronautics and Space AdministrationLewis Research Center

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

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Technical Memorandum

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WU-232--02--03

8. PERFORMING ORGANIZATIONREPORT NUMBER

E-9878

10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

NASATM-107043

AIAA-95-2398

11. SUPPLEMENTARYNOTES

Responsible person, James A. Biaglow, organization code 5330, (216) 977-7480.

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13. ABSTRACT (Maximum200 words)

Tensile data were obtained from four different types of rhenium at ambient and elevated tempea'atures. The four types ofrhenium included chemical vapordeposition (CVD) and three powder metallurgy (PM) types, i.e., rolled sheet and

pressed and sintered bars, with and without hot isostatic pressure (HIP) treatment. Results revealed a wide range of valueswith ultimate strengths at ambient temperatures varying from 663 MPa for CVD rhenium to 943 MPa for rolled sheet. A

similar spread was also obtained for material tested at 1088 K and 1644 K. The wide variance observed with the different

materials indicated that the rhenium manufacturing process, material composition and prior handling strongly dictated its

properties. In addition to tensile properties, CVD, pressed and sintered material and HIP rhenium successfully completed100 cycles of low cycle fatigue. Creep data were also obtained showing that CVD and pressed and sintered rhenium

could sustain five hours of testing under a tension of 27.5 MPa at 1922 K.

14. SUBJECT TERMS

Rhenium material; Material propeaties

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