The automotive Stirling engine, being investigated jointly by the Department of Energy and NASA Lewis as an alternate to the internal combustion engine, uses high-pressure hydrogen as the working fluid. The long-term effects of hydrogen on the high temperature strength properties of materials is relatively unknown. This is especially true for the newly developed low-cost iron base alloy NASAUT 4G-A1. This iron-base alloy when tested in air has creep-rupture strengths in the directionally solidified condition comparable to the cobalt base alloy HS-31. The equiaxed (investment cast) NASAUT 4G-A1 has superior creep-rupture to the equiaxed iron-base alloy XF-818 both in air and 15 MPa hydrogen

Scheuerman, C. M.

Stephens, J. R.

Titran, R. H.

English

NASA Technical Reports Server

: " DOE/NASA/51044-37%
NASA TM-87209
• t
, Creep Rupture Behavior of
_-,.._.• , Stirli_g Er:gine Materials
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R.H. Titran. C.M. Scheuerman, and J.R. Stephens
National Aeronautics and Space Administration
Lewis Research Center F
E-
•-._ [N&SA-T_-_720£) CE_E_ _g_UHE _P.HAVIOR 0_" N86-I-=380
S_IRLI_G ENGI_F. M).TEEIALS (NAEI) 10 p
"_ HC AO2/MF AO| CSCL I|Y
Unclas
G3/2b 05126
• Work performed for ,,
U.S. DEPARTMENT OF ENERGY _ _'i. :_ _ ,
" Conservation and Renewable Energy _,- _;_;_._ _ ,
_.,.o-,_._ ,_'.(.,'1,_L,_'
Office of Vehicle and Engine R&D _',_._-"_'.",,,,_7 J
",:,p_. ,)L%,T
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..i Prepared for
Advanced Technology Development Contractors' Coordination Meet;qg
• sponsored by U.S. Department of Energy
" Dearborn, Michigan, October 21-24, 1985
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1986005910
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DOE/NASA/51044-37
I NASA TM-87209
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' Creep Rupture Behavior of
_ Stirling Engine Materials
i
R.H. Titran. C.M. Scheuerman, and J.R. Stephens
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
J
t
Work performed for _.
U.S. DEPARTMENT OF ENERGY
Conservation and Renewable Energy
Office of Vehicle and Engine R&D
Washington, D.C. 20545
-i Under In'eragency Agreement DE-AI01-77CS51044
I i
:4 Prepared for
! Advanced Technology Development Contractors' Coordination Meeting
sponsored by U.S. Department of EnergyI
-t Dearborn, Michigan, October 21-24, 1985
i!
1
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] 9860059 ] 0-002
_ L,_Ii. l__ _ '.-: ,_ - ,,
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this paper, have been subjected to a simulated braze cycle heat treatment.
• This paper wlll summarize the creep-rupturetechnology of the prototype and
= the present candidate cast heater head alloys in various heat treated condi-
tions as well as casting techniques. As with all summarizatlonswe will com-f
ii pare the candidate alternate Iron-base alloys to the prototype alloy, HS-31
_ and recommend that a new design criteria for the cast heater head components
! be considered and adopted.
MATERIALS AND EXPERIMENTAL PROCEDURES
The nominal composition of the cast alloys evaluated in creep-rupture
:g tests Is given in table I. The two alloys NASAUT 4G-AI and NASACC-I were
'_ developed under contract to NASA Lewis by United Technologies (ref. 4) and
AiResearch Manufacturing Co (ref. 5).
Prior to creep-rupturetesting the alloys were given a simulated braze-
cycle heat treatment based upon "best effort" estimates of Joining practices
likely to be encounted. Table II shows the heat treatment each of the a11oys
had received prior to testing and represents a chronological change in the
braze Joining philosophy. HS-31 and XF-818 had a simulated braze cycle based
upon anticipated temperatures and times without regard to the properties of
the heater head tubes. The alloys NASAUT 4G-AI and NASACC-I which were
developed later in the technology program were tested in conditions which
reflect the manufacturer recommended heat treatment for the cast alloy. Also
a brazlng cycle and aging cycle were introduced, which reflects the present
recomm_Aded solutloning and aging treatment required for the heater head tube
materlal, CG-27. All heat treatments were conducted In vacuum, at pressures
generally in the 1.5 mPa regime.
RESULTS AND DIICUSSION
Figure l shows the resultant creep-rupture data for the prototype HS-ll
alloys and its first alternate candidate alloy XF-BI8 tested at 760 °C in both
air and 15 MPa hydrogen (refs. 6 and 7). Statistically, there appears to be
no effect of test environment on the creep-rupture lives of HS-31 or XF-SIB.The note w rthy poi t Is that XF-SI8 ulth approximately two-thlrds of the Iong-
i time (3500 hr) rupture strength of HS-31 has been successfully tested in an
.I engine with no creep-rupture failures (ref. 8). Figure 2 shows the 3500 hr
design cr_teria curves for the HS-ll and XF-81B alloys. The present MOD-I
i criteria for rupture life is a stress level of ll9 MPa at 775 °C.
The recently developed alloys NASAUT 4G-AI and NASACC-I were creep-rupture
tested in air at NASA Lewis. Figure 3 shows the results of air creep-rupture
tests at 775 °C. The NASAUT 4G-AI well illustrates the superiority of the
dlrectlonally solidified (DS) casting technique over that of the conventional
equlaxed castings. The DS materlal has a projected s_ress level capability of
about 175 MPa at 3500 hr while the equlaxed material (HT-I) has a stress level
of about 135 MPa. The DS material, presently represents typical stress-rupture
properties attainable with the present composition. A change in the cylinder/
regenerator housing casting techniques may be warranted to utilize the approxi-
mate 25 percent strength improvement over the base heat treatment. The HT-2
curve which is the simulated braze cycle plus aging does indicate an approxi-
mate additional 20 percent loss In the projected 3500 hr stress-rupturestrength.
2
4
1986005910-003
; CREEP PUPTURE BEHAVIOR OF STIRLING ENGINE MATERIALS
R.H. Tttran, C.M. Scheuermann, and J.R. Stephens
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohlo 44135
-_ SUMMARY
The automotive Stlrllng engine, being investigatedJointly by the Depart-
ment of Energy and NASA Lewis as an alternate to the internal combustion
.; engine, uses hlgh-pressure hydrogen as the working fluid. The long-term ,
_ effects of _,ydrogenon _he hlgh temperature strength properties of materials
Is relatively unknown. Thls Is especially true for the newly developed low-
co cost iron base alloy NASAUT 4G-AI. This Iron-base alloy when tested in alr
c_J
, has creep-rupture strengths in the dlrectlonally solidified condition compar-
"' able to the cobalt base alloy HS-31. The equlaxed (investment cast) NASAUT
4G-AI has superior creep-ruptureto the equlaxed Iron-base alloy XF-BIB both
• In air and 15 MPa hydrogen.
w
: INTRODUCTION
_ A Joint program of the Department of Energy and NASA Lewis is under way
to develop the Stlrllng engine as an alternate to the internal combustion
engine for automotive applications. The Stlrllng engine Is an external combus-
._ tlon engine that offers the advantage of potential hlgh fuel economy, multiple '_
fuel capability, low emissions, low noise, and low vibrations compared to
present internal combustion automotive engines. The most critical engine com- i
ponent from a materials viewpoint Is the heater head consisting of the heater
T- tubes, cylinders and regenerator housings. A goal of the Automotive Stlrllng
Engine Program is to achieve a 30 percent increase in fuel economy over inter-
nal combustion engines of similar slze and vintage (refs. l and 2). To achieve
these operating characteristics,the Stlrllng engine wlll operate near 820 °C
and use hydrogen, at a pressure of 15 MPa, as the working fluid.
f
The long-term effects of high pressure hydrogen at high temperature on
the physical and mechanical properties of high temperature Iron-base alloys
are generally unknown. Candidate alloys for Stlrllng engine applications must
not only meet all the property requirements in alr as well as In hlgh-pressure
hydrogen, but must also be of low cost to be compatible wlth automotive appli-
cations (ref. 3). The prototype engine used a cast cobalt base alloy, HS-31,
for the cylinders and regenerator housings. Because of limited availability
of cobalt and its hlgh cost, cobalt free Iron-base alloys wlll be required for
the heater head materials.
A continuing supporting m_terlals research and technology program at NASA
Lewis has identified the cast alloys XF-BIB, NASAUT 4G-AI (ref. 4) and NASACC-I
(ref. _) as candidate replacements for the cobalt containing prototype alloy
. HS-3I. Generally, these Iron-b_se superalloys were studied, In alr and hlgh
.,,
pressure (15 MPa) hydrogen, In the recommended heat treated condition. However
•, common manufacturing practice indicated the heater head materials may be sub-
Jected to a brazlrg process to Joln heater head tubes to the cast cylinder
heads. The candidate cyllnder/regeneratorheater head materials described In i
1986005910-004
If it is assumed that an equivalent 20 percent loss would occur tn the DS
materlal follow!ng a braze cycle plus aging, Its 3500 hr stress-rupture
' strength would be approximately 140 MPa or about 17 percent above the present
design criteria. The NASACC-1alloy has an indicted 3500 _ Jtress-rupture
strength of 80 MPa. Presently It is belleved that _ ^" _ent deficit in
stress-rupture strength ts too great of a loss an-' Jlloy will be dropped
from thc automotive engine testing program.
• High pressure (15 MPa) hydrogen creep-rupture tests were conducted on the
NASAUT4G-A1 alloy (ref. 9) in the HT-2 heat treated condition. Figure 4 com-
pares the rupture llfe of NASAUT4G-A1 tested In 15 MPa hydrogen and In alr.
While the curves show that testing In hydrogen yield higher 3500 hr stress-
rupture strengths, 145 MPa compared to 115 MPa In air, thls improvement ls not
,_ believed to be significant due to the large amount of scatter tn the hydrogen
; data (ref. 9). The important point to be noted ts that the NASAUT4G-A1 did
not suffer a drastic or catlstrophlc loss of properties in hydrogen as was
._ feared because o, tts high (1.5 percent) carbon 1- el.
The 3500 hr rupture stress levels for the prototype HS-31 cobalt alloy
- and the presently uttllzed XF-818 alloys when compared to the NASAUT4G-A1
alloy, as shown in figure 5, indicate that the NASAUT4G-A1 would be a feaslble
alternate The DS material in its recommendedheat treated conditionalloy.
(no braze cycle) appears slightly stronger than the HS-31 in the braze cycle:. condition. Where s the equlaxed NASAUT 4G-Ai in the braze cycled plus aged
condition (considered a worst case condition) is comparable to tileXF-81B alloy
which itself has never exhibited a creep-rupture failure.
I Creep-ruptureas the design criteria for the cast cyllnder/regenerator
housings appears to be a very restrictive parameter especially when it Is
realized that a rupture failure has never occurred in a cylinder or regenerator
--, housing. It Is believed that a design criteria based upon some finite strain
, level, perhaps in the 0.5 to l.O percent range, would allow for a better
assessment of engine efficiency and performance and be relatable to othert
important failure modes. Figure 6 which shows the projected 3500 hr air stress i
levels to llmit creep strain to l percent indicates that what is considered
the worst case condition for the NASAUT 4G-AI alloy (HT-2, braze cycled plus
L
aged with an equlaxed grain structure) has approximately a 30 percent stress !_
advantage over XF-BIS.
CONCLUSIONS AND RECOMMENDATION
(1) The NASAUT 4G-AI, In the dlrectlonally solidified condition has
superior l percent creep strength which should be utilized In the design of
' the Automotive Stlrllng Engine.
(2) The NASAUT 4G-AI alloy in the investment cast (equlaxed), simulated
braze cycled plus aged condition has a comparable rupture strength to the
present cast cyllnder/regeneratoralloy XF-818 at 775 °C.
(3) The NASAUT 4G-A1 alloy in the investment cast (equlaxed), slmulated
' braze cycled plus aged condition has superior 1 percent creep strength to the4
present cast cylinder/regeneratoralloy XF-BI8 at 775 °C.
i
3
I_m
1986005910-005
(4) Based on the materials research programs In support of the automotive
Sttrltng engine tt Is concluded that manufacture of the engine Is feasible from
the low-cost iron-base NASAUT4G-A1 alloy
REFERENCES
I. N.P. Nightingale, "Automotive Stlrllng Engine Development Program-Overvlew
and Status Report." Proceedings of the Twentieth Automotive Technology
Development Contractors' Coordination Meeting, Warrendale, PA, SAE, IgB2,
pp. 53-62.
2. ,].3.Brogan, "Highway Vehicle Systems Program Overview." Highway Vehicle
Systems, CONF-771037, 197B, pp. 3-5.
3. R.14.Tltran and 3.R. Stephens," Advanced Hlgh Temperature Materials for
the Energy Efficient Automotive Stlrllng Engine." 3ournal of Materials
for Energy Systems, Vol. 6, No. 2, Sept. 1984, pp. ll4-121.
4. Identificationof a Cast Iron Alloy Containing Nonstrateglc Elements,
NASA Contract No. DEN3-282.
5. Cast Fe-Base Cyllnder/RegeneratorHousing Alloy, NASA Contract No.
DEN3-234.
E. S.Bhattachayyra,"Creep-RuptureBehavior of SIx Candidate Stlrllng Engine
Iron-Base Superalloys In High Pressure Hydrogen, Vol. I-Alr Creep-Rupture
Behavior," NASA CR-163701, Dec. 19B2.
7. S. Bhattachayyra,W. Petermann,and C. Hales, "Creep-RuptureBehavior of ,_
Candidate Stlrllng Engine Iron Superalloys In Hlgh-Pressure Hydrogen,
Vol. II-HydrogenCreep-Rupture Behavior," NASA CR-174705, June 1984. 4
B. Erlk Skog, Michael Cronln, and Joseph Stephens, "Engine Evaluation of
Materials for Stlrllng Engine Hlgh Temperature Components." Proceedings
of the Twenty-Second Automotive Technology Development Contractors _;
CoordinationMeeting, Dearborn, MI, SAE, IgB4, pp. 175-1BO. '_
9. S. Bhattachayyraand W. Peterman, "Creep-RuptureBehavior of Iron-
Supe,alloys in Hlgh Pressure Hydrogen," NASA CR-175027, in print.
I r
1986005910-006
VAC.ANN.1hr-ll50°C
400-
_- -- HS-31
AIR
200- __._ H2
_-cc XF-818 __
_AIR
I I I I I I Ill I I _212o_" 2oo 4oo60olooo 200o 4_
RUPTURETIME,hr
Figure 1.- Air and15MPahydrogen/60 °C rupture livesfor HS-3i
andXF-818.
TEMPERATURE,°C
85n 825 775 75o
I I I20O- I
m- 120 ....
_ 10O-- _
80
6o 1 I II I
8.9 9.1 9.3 9.5 9.7xi0"4
l/T, K-1
Figure2.- 3500hr Air and15MPaH2 rupture
stressversustemperaturedesigncriteria
curvesfor HS-31andXF-811.
1986005910-007
400-
DS
-_ _. NASAUT4G-AI
=E 200
_HT-I
........ EOUIAXED
• _ __-- _NASAUTHT-2 -'--- _-
100 -- NASACC_I_'_,._._ 4G-A1
8O
60, I i I J I i Ill I I I
I00 200 400 600 I000 2000 4000
RUPTURETIME,hr
Figure3.-If5°CRupturelivesforNASAUT4G-AIandNASACC-I
testedinair.
i
H.T. 2, BRAZECYCLEDANDAGED
200-
H2
_4
100-- _.
-
"_ 80--
6n, i I , I, I_1 1 J I
-ZOO 400 600 1000 2000 4000
RUPTURETIME.hr
Figure4.- ll5 °CRupturelifecurvesofNASAUT4G-A1in
in air and15MPahydrogenfor the condition.
1986005910-008
_wa./
TEMPERATURE,°C
850 8z5 775 760
zoo- I I lj "
NASAUT _
4G-AI(DS)._./_ _" 15MPaH2
:E 100 _.._-_
/
.-.--NASACC-18o /,," II/
- z.NASAUT4G-A1
60- EQUIAXED,HT'2
I
4o i I I
8.9 9.1 9.3 9.5 9.7x10"4
I/T,K-I
Figure5.-3.500hrRupturestressversustemperature
designcriteriacurvesforcandidateStirling engine
alloyscomparedto MOD-1designcriteria (3500hr
lifeat/?5 °Clll9 MPa).
i
J
I
f
!
i
TEMPERATURE,°C
85rl 825 775 76n
2oo!- I i !
_ _NASAUT
---- _, 4G'AI ''-j,
N 80-(EOUIAXEDL_- /
_, - HT-2J _ HS-3_..../
6n'- / XF-Sl8 )
I I I i
488.9 9.1 9.3 9.5 9./xlO"4
liT,K-I
Figure6,-3500hrstressforonepercentstrainversus
temperatureforcandidateStirlingenginesalloys
testedinair.
• - _ /'_
1986005910-009
• /
1 ReportNo 2 GovernmentAccession No 3 Recip=enrsCatalog No
NASA TM-87209
4. Title ar,d Subtitle 5. Report Date
Creep Rupture Behavior of Stlrllng Engine Materials
6. Performing Orgahization Code
778-35-13
7 Author(s) 8. Performing Organization Report No.
R.H. Tltran, C.M. Scheuerman, and 3.R. Stephens E-2846
10 Work Unit No
9 PerformingOrgamz_tion Name and Address 11 Contractor Grant No
National Aeronautics and Space Administration
, Lewis Research Center
: Cleveland, 0hlo 44135 13.TypeofReportandPerlodCovered
12 SponsoringAgency Nameand Address Technl cal Memorandum
U S Department of Energy 14SponsoringAgency,Co--Report NO.Office of Vehicle and Engine R&D
Washington, D.C. 20545 DOE/NASA/51044-37
i5 Supplementary Notes
Prepared under Interagency Agreement DE-AI01-77CS51044 Prepared for Advanced
Technology Development Contractors' Coordination Meeting sponsored by U S
Department of Energy, Dearborn, Michigan, October 21-24, 1985
!
i -
! 16 AbstractI
The automotive Stlrllng engine, being investigatedJointly by the Department of
Energy and NASA Lewis as an alternate to the internal combustion engine, uses
hlgh-pressurehydrogen as the working fluid. The long-term effects of hydrogen
on the hlgh temperature strength properties of materials Is relatively unknown.
Thls Is especially true for the newly developed low-cost Iron base alloy NASAUT
4G-AI. Thls Iron-base alloy when tested In alr has creep-rupture strengths In
the dlrectlonally solidified condition comparable to the cobalt base alloy HS-31.
The equlaxed (investment cast) NASAUT 4G-A1 has superior creep-rupture to the i
equlaxed Iron-base alloy XF-818 both in alr and 15 MPa hydrogen.
17, Key Words (Sugcesteclby Author(s)) 18. Distribution Statement
Stlrllng engine; Creep rupture; Unclassified - unlimited
Hydrogen; Iron superalloys STAR Category 26
DOE Category UC-25
19 Security Clesslf (of this report) 20 Security Classlf (of this plOe) 21 No of Ngos 22 Price" ,f
Unclassified Unclassified A02 _.
"For sale by the National Techmcal InformaUon Service Springfield Virginia 22161
1986005910-010


Creep rupture behavior of Stirling engine materials

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