CID-

DTHE DrIESIONAL STABILITY OF

SELECTED ALLOY SYSTBMS

HARD COPY ' $-__ ________ ,__ MIROI'CHE $.C.J

C.). Final Report

June 1, 1963 to August 31, 1964

Prepared under:

Contract No. N140(131)75098-Naval Applied Science Laboratory

New York Naval Shipyard

Development, Engineering, Bro-klyn 1, New York

and Manufacturinghigh and ultra high ALLQXD.QENERAL CORPORATIONvacuum equipment M,,N OfFICES: 37 CAMBRIDGE PKY. CAMBRIDGE. MLAS O 2142 P•I4ONE , USM AREA COE 61,

electron beamn euipmentadvanced materials

research ,

mH I31$emu=

THE DIbW ICKAL BABILXT Of8Elf-UCTM ALLM BMIWTa

byl

SI,?J. Weihrmaxch)&.J. Mordoft

?imal Rleport

June Is 1963 to August 31., 19644

Prep.m under&t

Contract no. 3lL4U(l31)75Q98MNaval. P'Ppled Sclience Lakoratory

3fie York Noval SbLipyarciXrooklyn 1., Nov York

a ubmitted by I

Alloya Gawwrl Corprortion,ý7 Caaobvidge Parkway

c~ia~tiridge 4&0. nasaachusetts

Pan

1. . UCT oB .... . ... ION . . .............. . . . 1

s MATRUAI.& AND .P.P.TIO.. ........ .............. .

3o RXP~Xh4ZNTL PROCEDURE, * .* ** * *. ** . *. .oa* . 5

4. MS ADOZCU8B.sS * AC .. .. .. .. .. . ..... 77

5. ]DISTORTION MEASURa4NK ýACIarTY **ov*ewe*4S40*o*S 77

6. M UM WORK. ........................ ........ .... a3

7. *~ ~ ~ ................... . 84

x. choical. composi~tion ot specimen materials 3

it H eat Troatiaig and I4CMachini Scbedules 4

111. A~pplied Cvwe) Stresse 1

IV. SlAsthc Unmits and 2lastic Koduli ot. Tkhr"Alloys at 75m, 1.5U and ~icuJW 4d

V. Crsep Constanto for Squation 14 66

V1. Creep Constanits for lquatioin 3 7

Zan

Figure I - OcLeastic view of capacitance gauge andSpOcLAn.. ......... .. .... .............* 6

FiguXe i - Capacitance gauge test specin.......... 7

Figure, - Constant temperature chamber tar elasticI Imit measurements . . .. .. .. . . . ., . . .* .* a* 11

Figure 4 - Coautant temedrture and constantatmosphere chamber for creep measures•nts. 14

Figure 5 - Storage specimen for dimensional stabilLtytestj ................ ....*.. .... *. ....*o . 18

Figure 6 - Stress-total strain And stress plasticstrain curves of free cut Invar "•6u at75, 150 and kC¥..F .... . ..... . 4

Figure 7 - Stream-total strain 8nd stress plasticstraLn cur•ves of 356-T6 aluminum at 75,150 and •,o,... . , . . . . ... . .

Figure 8 - Stress-total strain and stress-plasticstrain curves of 31Q stainless steel at75, 150 and i0VF. .... ..... ** *.*..*... . .. .. .

Figure 9 - Stress-total stxain and stress-plasticstrain curves of 6U61 aluminum at 75,150 and 2 . 5

Figu•re 1-8tress-total strain and stress-plasticstrain curves of PZ9dA magnrAsusm t 75,150 and 2 0 .*7 .. .• • * * * .. *.. . .. * * * * * ..... * 6

Figu"* U-Square root of plastic strain vs. stressfor five alloys tested at 7528....... ....

Figure le-?otal caeep curves of Xnvar 136" at 5*YF.. 30

Av

Latt 01 PLUrMeS .- ContOWiA9

uAM

FLgue 13 - Total ;:reep curves of Invar "36" at 150F. 31

71$4r@ 1.4 - Total creep curves of lnvar "36" at ýUQ:k. 3

tLguxOe 15 - Total creep curves of 356-T6 aluminum at85°*r 4, .a a . . .. . . .. . . . .. .. *......#a4 6 0aa4a a0a06 33

Fagure 16 - Total c"ep curves of 356-T6 aluminumat . ..... ........ .. 4.. . 34

Figure 17 - Total creep curves of 356-T6 aluminumat •UOF. ......... .. 35

Figure A• - Total creep curves of 31 stalinesssteel at 85•* ..................... ..... 36

FLOgM" 19 - Total creep cur-e' of 310 stainlesssteel at 15 o0 * . . . . .. .... . .* a 0 * 0 * * 4 * * & .* 37

rIgure 2U. - Total cxewp curvs of 3Lu stainlesssteel at 20u*... ....... ...4..4 ...... -3s

FLqure 21 - Total caeep curves of 6,.,6L-T6 alumi.nuaat 8 0 . .. . . . .. . . . . . .. . . .. 39

Fig•i• i• - Total creep curves of 606i-T6 aluminumat 4u.. . . . . . . . ... . .. . . . .•

Figwm 23 - Total czeep curves of 606l-v6 aluminumat 2uU*F.................... ..... ......... 41

?J~gIxr i; -Total creep curves of ?59eA mgnesiumat 65F ............. . ............. 4k.

Figure 25 - total creep curves of Azr9A wigneIuMat 45°..... * ......... .. 43

Aigume 26 - Total creep curves of A29"A •agnesiumat 4O04.......... ... .

V

LAst of V*ulr - Co!tlnumd

iLgure 27 Total cr"ep curves of f•ree cut Invar at7 5 O* °51

figure 48 - Creep curves of free cut Ynvar at I3UdW 52

tigure 29 - Creep curves o9 fret cut Invar at -Oue. 53

Vigure 3U - Creep cuirves of s56'-T6 alumainum at 75 • ,* 544

FPIure 31 - Creep curves of 356-T6 aluminum at 150Ci . 55

Figure 3ý -Creep curves of 356-'•6 alu•ai•um at 2•QF* . 56

Figure 33 - Creep Gurves of 310 stainless PtOeOat 75 . .* * . .................. .. ...... 57

Fiure a - Creep curves of 31( stainless steelat 151U,*P .. .. . .. . . •. .. .........*oo 56

Figure 35 - Creep curves of 310 ataLnules stoeelat idou~p ..... *.,. .. .. .. .. . . *. . . . .. ... ... . . 59

r gure 36 creep curves of 6u61 a.1wminum at 75el1.... 6Q

Figure 37 - Creep curves ox 6U6L aluminum at L507P ... 61

Figure 38 - Creep curves of 6u61 aluminu at 2uur *..6

Figure 39 - Cxep curves of1 AkZ9ii - T6 magmeiumat 75of .... . 4.e....*.. ...... . .......... 63

FAgure 4U - Creep curves of A29.\ a0gsesium •It 15u7, 64

FIgure 414 - Creep curves of ,-Z92A nagnesium at iuOJr . 65

rigure 42 - DiensiaAoal change of fow cut Irivar 36stored at 75, 150 and O&1a0 '• .... ,,..... 71

FIgure 43, - DiznaLouaL chn"es oi 356-Tu6 Aumiuumstomd at 75, 150 and 2OfW .*............ 7*

vi

Linat o liaxes - Cati.4

Figure 44 - Dimensional Changes of 3.v staLLeOssteel Otore( at 75, 15u and i"6......... "73

FIqvre 45 - Dimonsional changes of 6•6• Aluainumstored at 75, 150 and 74*.............. "

Figure 46 - Dimenslonal change of r;.9P. magnesiumstored at 75o, 150.. and •jt....,......, ,.. 75

L'gure 47 - Distortion specimen ............ ..... • 7•

FiwMe 46 - Scematic view oi distortion measur~ugfacility. ............. ... *6#609460's 6* a *

vii

Slastic limits, elastic moduli, strems-total

strain and stress-plastic *train curves were dtermined

for tfa cuttnvg Invar 36, 356-T6 sliumins 310 stainless

steel 6Q61 aluminum and ?,Z9k, nagmasium at 715,, L5 and d'o.

Tas creep behavior of these aolaj & was studiLd at the same

temperatures of interest at stresses above, below and at

the elastic limit.

In all cases It was found that the precision

elastic limit did not define the sinism stress to cause

creep, in fact creep took place at stresses below tha3

elastic limit at a much reduced rat&. The data was

analysed in the light of current creep theory and micro-

yield theory. A dislocatIon Model was Used to deriv4

analytic eAprsiLons for creep nar the 10"6 elastic limit

stress. below the elastic limit creep was found to

follow an exponential time depwduc, while above tke

elastic limit a ta tine dependence was followed wLth

values of a from 1/) to 1/2.

The dimwnsLonal Oangias taking place in these

alloys under storage conditions at the three texperatuma

of interest is also presented.

A facility fox noasariw~ dintortios as a fuwtictn

of beat tz~tuq an mach mcih*Jw oplaatlow was dooLqued

wkd coustmuited and is deacrLbo.d

The present report suuisrises the work under-

takcen by Jklloyd Geoneral. CorpozatAoz duzizag the period

jume is, 19b6i to August 31, 1964 unader the sponsotshl.p

of the Naval. Appl~ied Science Lab~oratory,, New York~ Saval

Shipyard& to investigate the dinenajommi. sta~i)lity at

several alloy systems.

In the course of this program dimeanionAl

staoitJlty evaluationse were madoe ot five alloys,, free

cut in2var 36, .356-T6 aluoinum, 31o st~ainless steel 6u6).

aluminum and A4SVA magn~esium. An osperimental, program

was developed for dete rmining the dimension&l distortion

of castlags acconpnying metal. fabricating operations.,

and the necessary equipment was deaIgned and constructed.

Masurements, of distortions acconpauying heat treating an~d

muchining operations were made tar cast~ins ot type

i. .& 0. 25UZ M..A& .ZMM

e alloys tasted were Fzve cut Inver 036',

.56-•6 a3luminum, 31u st.in•l is stoeel,6u61 aluwzaiurm and

A29d. magriessam. The Invar and 6&06l alum~nuu were

received in the form of I 4nr.h diaaeter coCLu drawn

unanarasled rod. The 356 aluminum and 3L. otaine.as

stock was received as 1 A 1 x 6 iz41h cast blanks. The

magaesium was roeav± d in te form of e5 pound cast

Aaiots. ?as ;h*m1.c&l compositions ot these alloys are

Siven in Table 1.

k 2 Beet =- atA- anad .achgiAM Sckedu1L

•The as-receivad materIals Were givon heat

tratmes reomnded for maximum disionsionaL wtsabiity. (i)

The heat treating and uacbining schedules -s well as the

final hardn as of eaec alloy Are prosented in Table It.

Chmi~ C~aa~in atMaciin M&Aerials

invar 31

maz 1.0 -. .24

9L. 0.3I5 2.070u.6 <2

cc 23.0 U.2 -4

N±+Co 36. L, .0 do .10

mi ft 19 u - -

ire ~ a. bal..-a

-- bal. bal. .

- m1.LI bal.

Cua u d .o

36 a. -

heat 9rati*a and iac_€xinip schidu~le

xnvar " 1. Is8t treat 1541Vr in hydrogen -V1r ho", water quanih.B. lough machine to over also diamisoms.

bardanesi . Neat treat 12uJ in hydrogen - airUockwell "&,, 85 cooL.

4. Final macaine5, sabi W'r - '48 house, air cool.

A1U asta.Lea 1. oueQnc. Aabaa• . 195,.'a Ln hydrogen - "steel A/• hour, water quench. -'

2. sough machine to oves iz.e 4iunowione.hardness 3. Stress reollev 750"r Ln a.r - 1 hour,

ockWale "so 83 aiAr cool.4. Pinal. Uabhine5. gtabILla 20047 - 2u hours, air cool.

356-26 1. solution ana"ml- I-U•U" Ln air - d bra.aLuminum i. uenck% in boiling water"arCdn 3s. 3* h wa miain to oversL" d4Jnions.' 14lLwlSl "Vo, T7 4. Temper 3.Q*P - 4 'hours, air cool.

5. ftnal machine

6(6i 1. Solution aanaL - 970F ia air - k bira.alumaum 2. Water quenchhardness 3. Roshs mchin to oversize d&hm•inmsiPockwlL "am, 55 4. Aje Iirden - 3% i, 6 bra.., aIs cool

5. rual maChLaw

AM. I. Solution anneal - 750OF in tOkMagis AtmostWre - 2V hes.berdnme* 2. Mr blast cool3otell o" , 86 3. •ugh madbLve to overaise dimasions

4. Age harfn - 5UO', 44 brs., eaLr cool- -- A.

3.1I Cawaacitanc StriMM& g eamiain

All creep Vbavior as well as the elastic liait

and stress-strain deterl•e tiona ot tbe alloys were made

with a capacIta•ce Otrain gauge. This gauge (Figure 1)

consists of a two piece precision machined Invar housing

which Is mounted on the houldexs of the speclmen (Figure 4.),

A quarts disc plated with platinum on one face is mounted

in the upper section and acts as tkm positive electrode

of a parallel plate capacitor. The face of the lower

housing Is highly polished and acts as tre ground electrodf

of the capauitor. The height of the housUng can be varied

with the adjustment screwn and the gauge sensitivity can

be varied within broad liits by changing the capacitor

spacing. with this device, changes in specimen leagth

result in a cnaage of capacitor spacing which. in torn,

is translated into a change in capacitance.

'The elastic limit at a material is defuled as

the lowest stress VWNqured to produce a mmessrsbl amamt

of -r~-t- ww-Pw ý. I- -040if-f -ste - e in these detecaSatiOss

was the lood-u-load technique of Stalr and Averbacb. (2)

-5-"

SPECIMEN 5QUARTZ PLATE HOLDER

INSULATOR-SPECIMEN

PLATE LEAD------. CLAMPING SCREW

AIR GAP ADJ.PLATE

_____LOCKING SCREY

QUARTZPLATE SPECIMEN

; SPECIMENHOLDER

USPECIMEN

FIGURE 1 SCHEMATIC VIEW OF CAPACITANCE GAUGE

AND SPECIMEN

o z

00

0 Li.

(D LU

CD 00 L

00 C3

0 z D

-1-

CD LU

LOU

4;olj C0 q

0 CnLL

IL -. Q

Tests %ere conducted In an ixstron gpet-driven testing

machine Of 1.0,0U pounds capacity. Th 50Jý and 1W(M

pound scales Were used and loads vex* road to the noarest

5 mad 10 poundA, rspectLvely. The test epecluen, shown

Ln Figure i, was gripped against Its 45 shoulders by

matechd split nuts wb.cb weve threaded Lnto grips. the

grpS woewe connected to the frams and cross-head ot the

amchine by mild steel rafd hangers through spherical rod-

end bearings. Load" were applied in increments ot 4M) pei

in the egion of the antsicpatod elastic l.mit. The load-

ajg rate was approiLmately 2UIO(Q psL per Anaute and tbe

specimen was immdiately unloaded on reaching the desired

stress. Repeatable Osevog stiress condition vwre achieved

by al41owig the specime to UMag freely udemr tAe weLght

of the lower grip and hamger for unloaded strain readings.

AlU the ComjpnQts of the gripping system we precision

machined to maintan a &ahILty of loading.

upon re&acIng tke elastic limit the 3.oad-Unlod

seqmeco swas continued until the msacroecopic yield point

was zoached. lbo change In capacitanco was read at the

msximm load and u unloadi6ng, Zn this way the Stres-

total strain and stress-plastic strain curves were gemerated.

-8-

The chubgO in gaug capScitauce was msaued wfth a

lobertsbaw and V'alton Frow~niaty "~tog, geg O&Luvate

os car~reLd out for each Specimen by Loading the specim

to stesses well DeLoW the elastic limit and notixq the

motor 4f1ctLon. There are sAz mot scale factors Which

allow strain xmasuxements -o be mId in a range £fro

I x I-7 to 8O&x i-6 ionches/1wh. "N caljbration was

found to be linear over this range as evidenced by

comparison with electrical resistance strain-Sauge

measurementm. The ma.m strain sensitivity achieved vLth

the capacitance gouge was I x lu' 7 bnches/ibh., howaver,

dii iiculties in teaerstux* control caused theural *m~axwom

and contraction durjing the loa4d-unload cycle which, An some

cases$ dwarfed length changes due to plastic strain, As

a result te s&train onsItLvity aused was 5 x LO.-7 I&eW

inch.

TestMW wAs carri out at tbree temperatureso

75, 150 an 2(JO?. Th Moo. t*NP'ture tests (75V)

wore carvied out in asi without texperature coatrol.

to tIMO lave: thermav asas of the spscimn-capscitaace gauge

contiguratio, te erature f1uctuations took place voye

slowly so that expansion ot contraction duriig a•y Load-

-i9-.

unload cycle was lose than 5 x 10`7 ichee/incch. 'At the

higher tapme'atum-e (150zoo 6=4 fto~r totag Was.. Car!"ou

in a temperature conatrlLed air cbhaber. The apparatus

(8ee Liguqeo 3) consi~ted Of an annular container. The

inner cyLinder of the container was a alchroe woamd

resistance furnace and served as a constant temperaturs

enclosure for the spec • ien and grips. The temperature

was controlled to withli t 1V by a thermocouple controller.

1-l temperature was read independently with an iron-

colatantan tkaeruocouplo mounted on the spt-imen.

3.3. tl~asti.c Mdu~un M)e~surmnta

Sineo the PoALmity Moter does not give

absolute values ot stjran aA4 muot be calibrated for each

spec"Wn, it is natessa•y to measure the elastic modulus

indepndently at each temperature. To acco•lplih this,

etched foil electrical rsst-nze strain gauges wexe bonded

to tho gauge section of the specim"n with MIQ( epo•y

cement. To gauges mounted on opposite sides o f the

specim and w£ietd in series Aare used to balance ony

effect due to noaaoxality Q" loading and to produce a

eaImy of aveegro Strain. 'The gouges W03* umoistua prooted

vith a coat of stycast i651 hiGh teRPeature ePoy.

Sa~ -- - -

I HEflmOCOUPLELEAD UPP~ER ROD

FLLU) 7 ROUGH

GAS

I OUTLET

LIMIT MSSURCIMET

-LI -T

Fox tests at &"Lbent temperature a simsilarly prepared

ustressed specimen wasn mounted AeAr the test aPeiA.~Me to

act mus a tamprature compenbator. At l5c#* and eit-O the

unstressed spec imen was mounted to an air furnace and

An~opedSently maintained at temperature. both the test

OPe41110 OW~ compOUsator spec Len %emperatures Were

monitored with Iron-constantan thermocouples. For room

texperature tests no temperatuare control was necessary

since the ambient did not vary more than I O.,eF during

tL~e short testing tiames. The stress values were read

anb the Instron Chart to an accuracy of ±t lwa pal, and the

$train values to t d l- L~ nches/inch with a Baldwin

type N &train Indicator.

A stress was applied below t~he elastic limit

and the strain was memaurod, rive independent measure-

*auts weze sade for esob specimesn at each temperature and

time modulus was calculated. Thu five values were then

averaged.

3.44 ui.aa

Creep tests we"e conducted In a bank of six

dead-load creap seichimes using ain Interrupted lcoading

tocdaique. Yhe test specimen was encloed An a &cistant

temperature and Constalt atmosphere chamber bLeh was

mounted an supports connected to the creep tram ("ee

Figure 4). Whe temperature was maIntaIned by a tibUlar

nichroue would resistance furnace and controlled by a

tharAstor element to & 4.10r. Nitrogen was contiauously

fed into the chamber after passimng throug a dryang and

heating column.

I, creep stress was applied for a period og time

and then removedu the stress was mesusred with a otaian

gage load cell and the residual strain was measured by

trA capacitance Btra.An 1age. The speciAmAn Was thea

reloaded for A JouV4er per, od o£ time. the PXcedure was

continued for increasing perio4s of time until a total

oi 5W0 hours of creep was accumulated.

The strain was measured using the capacitance

gauge and the PecLmen of tIgure 1.

m" changes in gage capacity WreW measured with

an llectro-6cAOntif ic XndustrAes 707A capacitance brl*ýe

of variable sensitivity. The meter was calibrated by

loading the specimen with knoun %ieights and f ECUthe stwes-

strain curve, equatisg the strain to the meter defgdcaton.

dPI34&

L EAD UPPER

ROD

GASBAFFEL

GAS

GROUNDLEAD

C APAS ITANC EGLASZ -- , eGUAGE

SPECIMEN

GAS

RUBE ELOSAOF5FE TTO

LOASRODE

KaOtmM strmas resoluttiton of 1 • 107 inches per inch is

The specimen was gripped against its shoulders

by matched split nuts wich woez threaded into grips.

The grips were connected by threade rous to the upper

and lower yokes. Te lower yoke, ft&ic also served as

a load cell for messurixg stress, was connected by a

spherical thrust bearing to the frame of the machine.

The upper yoke wae pinned to the lever arm. The lever

arm was pivoted on a pin in a support block and could be

arranged to give a wmchanIcal advantage of ten or twenty

to one. Stress was applied to the creep specimen by mons

of cast iron weights stacked on a hanger attached to tIe

lever arm. The lhad was removed by means of a hydraulic

jack. For wro readings, the lever arm was held an the

unloaded posation by a support arm ond pin.

The creep stress was Measured by Oman of a

load cell in the lower yoke of the czeep maeAine. The

cell consisted of a .J35v Inch daaeter section of the yoke

machined into a ; In.ch tensile bLr. The tensile bar wes

instrumented with two etched foil strain gages located on

opposite sides of tke gage section perpendicular to the

-l5 -

lover azm and wired Am seties. the strain gages were

molituxeoprooted with a coatLaq of Stycast 251 eposy

potting compound. P Similar dmW bar was buwg next to

the load coll as a temperature Cospeastor. A Maldvin

type 3 strain indicator was used for strain readings

ii1ch were converted to stzess by the atrea-stxraLn curve

of the mild steel rod.

Table IIZ Lists the creep stresses and tomper-

atures investigated for each material dutring this program.

3.5 CON""1AU~ ~hnIs it XU aem ADD1±c LRAdIS

In order to study the dimensional J;ngeo under

storage conditiona, specimens Of the four alloys were

macined to the dtmnsLoas of rigure 5 following t:le same

heat treating and machLnan schedule previously outlined.

After the final bat treatmeat the speci• ss were given

* hand polih with 3/u grLt emey paper tfl.olecl wdy a

careful. polish with a fine micropolJshoang paper.

Toe specimns were then placed in air furnaces

maintained at T5,.15U and ?.uUr and their lengths

periodically mnasured. Tkb turnace teerature was

maintained at t u,.5*r of the designated teaperatures.

j j ... j 16

I1ree Cut50vQI48,ujItwZavar 36 3 i,3sw4sW

356ft1354.K) 15QU

6,3Q691ou 5 9 Wh

31.0 stainleos 3s5Q3, w>,5ksteol 25O ~o4 -3 0

16,,70 16,luuu~i c4,O(

175 5 a5w~ 15 s OW

Magnesium 5 i8u 5SU4,78o.3,70U 3,,53U 3 p34(ý

-1.700

K

-4

-j

A

4

'.1)r2 U 5

'-4 -' 0* -4

,�j I-.�00 C'K)

r-1

*�1

42w*��1

C)

CLoC) U

-�

oo '-4

C)'4-4

�3)-I

UC)U4U)

(!)

��1

04)U)

�J (j I'-1

4-.

(;,)

�1 C)w wcILl *�-4

a,. -0 �

(n 41) -4.4 U"

0 -4 -�4--. 0) I J

4-)

(2CL 0

- L

D.naLonaal cisagos were determxved fgom

precision 1amsurwmsnts of the 0- *rall length oa the

specimen after each storage period. All aeasuremeate

were made using a abeffield aechanical optical com.rstor

with an accuracy oL 1 5 mLcroinchss/inch. The comparator

indicated the dLfferwae in length betweem the test

specimen and a gage block of known length.

The nominal finished length oa the storage

spec imens was •4 inches but the length varied froem specieia

to specimen. Since the scale range of the comparator is

Sj.4 iwhes, a single gauge block (4.-ob inches in

length) was used. Whaen requirod, a small standard block

could be selected from a series of standards and placed

under the specimen so that the overall height of the

specimen plus block was within u. l Inches of 4.05U inches.

The storage specimse, upon removal from the

furnace, was placed on a large copper block for a period

in escess of 30 minutes. Because of its large thermal

mass$ tme copper block served as a comstane• temperature

plate. A reading of the specimen was taken on the

ft

The gage block to then road. rAsA procedure was epested

thasow tWwsa and aws&.gud forc w-ith spec 1n and gage

block. Tbe relatIve Leagth of the mpcAMn was caJlulated

£rom these values. The reoolation of tAe comparator was

5 A0 LO6 ±nhes. Voa a 4 iLwh peci•Ison ,ength, tLhs

reulted LA a smesitivity of 1.2 x 1- O inches per inch.

The speciamaw and gage blocks vex* handled wLth gloved

haads at a&L tims to reduce hesting and miasture changes

MaW handlung was kept to a ainisum.

-m;O0-

i • k3*IIW •tu DL___SJJ___JJttSU

4., -- atic 1lt mtaAgd aUX ctavild flhbvvhr

The stress-total strain and atresa-plastAc strain

curves for the five alloy systems are pesnted in Figuris

6 - 10. All determination* reported were made witu the

capacitanme strain gauge and the elastic limits are th

stresses at wich the first 5 x IU-7 strain was detected.

Th elastic limits and elastic nodulU are suarixed in

Table IV. The elastic •Lmits and the elastic moduli showed

a similar temperature diependene, but the elastic liAmLts

were somewhat move senuitiv to temperature. This has

been confirmed in other pure as( ad aluoys(4) aud

has Aeen explained by a thermally activated achaniza ot

,dislocation lultJ• L4plation and motion.

brown and iLakens( 5) and ?homss and Averbach( 6)

have oboesved and explained a parabolic relatiowsbip

between stress adn plastic stratn. Ine room temperstuwe

plastic strain curves of Figures 6-10 are replotted Ia

Figure 11 wit the stress plotted against the squave voot

of the plastic strakin A straight Line dopen4swue was

observed cOnfiusing the parabolic worX hardening law.

0

4-(0

wL 0 07U. 0 0

0 * rW I.- '

00 ~ 0

C- -4

4-)s, T,

0G4J

M

!--4

' ul

0 * 4J:000

CLU) U-i

00 000 qt

(Isdrl) s~i00

4.

0 r0

9-4a 02-1

U)- J,

L

U- U)

0r-4

00-41

-41

Ul f

ý4

(Isdol) s~u0

LL 0

0 10

UU)

000

, 14

044

(15dr~l SS.U)

0to

U..

0,00 0 o

0~-

-iCA.J

InJ

U)

0 i

--4

4-3

- I In.

NO 41

In

0 .j f

(4,- 0~)S 3 I

4'4~4-1

4J

14)

(jj)

4-1

0I

'Jc i

r14

21a"tic Limi~t~s and zlastic Modaul ofZhree allovz at 1%. I1%0 and aweV

Test slastic. Slastic

Inver 75 ýý6,4vUQ2150

356-'T6 75 8,iUU 11.3Alumi.num 150 7o3550 11.1

ko0 7slW1U.

310 stainl~ess 75 22,70i9.stool 15v 2(, 4u 9.J.

.. a:U ýýOUQU 8.7

6cl75 ie.40 o.8Pluminiam 150 1L,70Q 1045

AZ92A 75 5t280 6.5magnesium 15U 5,0u4u .

2W4j7& 6a.

4-4 ) -4

4 r-)

I ->

I I I - -q

.I4 4-1

U~"3-

F- 44'-

4..2 Crenfevol

The creep behavior uAftr load ot free cut lava:

6, 556-T6 alUminum, 3l1 stain'less .tIe1. 6061 a3msn"u

and AZ92F magneIAuSM at 85,15U and kuuOy is paesemted in

Figures The creep rate in all cases was Seen to

start at a hbgh value andi cdcgase continuouslLy until it

approached a steady state condition. The early creep

rate and creep strain are seen to increase witn te"perature

at ¢Omparable stresses.

At creep stresses Lalow the elastIc liSit the

.r-eep rate in all cases decreased continuously approachi•g

zero at the lower te"Ceratures in a swxt tim. %ear

the elastic limit stress the creep rate decreased

continuously approaching a steady state creep rate. At

still hiher temperatures the creep rate was hLghar and

decreasd more slowly.

In order to und"Stand the creep behavior ot

tbase alloys it is necessary to develop a dislocation

maecbanism of creep. Creerp at high load* generally consists

of tbree stages, the iArat of which is characterAsed by a

decreasing creep rate (transient creep). RventualLy the

i -'9-.

500

400

50,000 PSI'"

b3000

z4[

0

c. 200

--W

uo 34,000 PSIUa:

Jt-0

I--I00

22a,000 PSi

IIi100 200 300 400 500

TIME, HOURS

Figure 1.....Total Crccp Curves of fnvar " at;,-F.

-50-

500

400- 46,000 PSI

'"300

_z4 o

Ir

,00 22,000 PSI

too 200 300 400 500

TIME, HOURS

Figjure 1 - Total creep curve.; of inv'wr at 1.'--

. .. I I I I I

500

400

.O --- -- ....

C'300 - 35,000 PSI

'200-I.w 0C.,

-J 25,000 PSiI.-

1t 00

S. . ..... .... ... ... . .... . .. 15 ,0 0 0 P S I

100 200 300 400 500

TIME, HOURS

FLJurel. - Total Crccp curves of Invar "-" at F.

500

400

300 13.000 PSI

Ch 200Q

C9 9600 PSI

6300 PSI

00

100 200 300 400 500

TIME, HOURS

F'igure l) Totz,1 Croup curves of '"--T,' luinum a

500

400

~'300

00

~'200

0~

100

00

100 200 300 400 500

TIME, HOURS

Fiuurc i,.-Toti-l creep-I curves of 7 KT.Aluminum ast L . P

00 12,000 PSI

0

400 -

6 300z

,

/

G. 200- /0w

U /Z.,J / 0

1- 00 0,'O0 C

/o . 5800 PSI

t00 200 300 400 S00

TIME, HOURS

•.v•jur i' - TotaI c-•• cur-ves or .... P'- Aluminulm lat F.

500 3,0 S

400

*:300 o e

CC0

200

100 t00 300 400 500

TIME, HOURS

F'Ii qure -Total cree'p curves of -*I(" stainless steel.a tt r>F

31, 000 PSI

500

400-

400 -1

2~00

10 0

a-t

-37

S00 30,000 PSI

400

22,000 PSI

0

- 300

7

t-

S200

j 14,500 PSI

I-O1- 00

0I- 100

100 200 300 400 800

TIME, HOURS

Figure 7 - Tota•l creep curves of KlQ stainless steel

at '•< .

-38-

Lps

timeo. noursz

I'Ljurc2 Zi Total crecl- curves of ><~1-T' aluminum at 5.

Time. Hours

Ficju~rc '2,2' Total1 creep curvcsq of aluminum atLj(.

.........

time. hours

ri,.urc *-rpota! creep curves of I-( le~uninuin at Ž000ýOF.

U0

Fiyurc: 24-ý Total creep curves Of PZ-,;.A magnesiun, at IF

-- 0

-ps

timeo. hours

Figure z- -'rotai creep curves of t\Z WA magnlesiumn at 1500F.

(.°

/,p

C

. I.

"." .....-. ;I-. .- . I -..

creep rate diecreases to a GM ntant or steady state

condition (mecO1.6 stage) wni" is faiu±oJ.l.owd bY ani

increasitg creep rate (tertiary creep) until failure

occurs.

To explain creep behavior in the first or

transient stage two mechanisms have Leon advanced.

Considering the rate determining swchanism at low tem-

peratures as the motion of dislocations through a torest

ot dislocations b, te crea4Ion oi jogs Leads to the well

known logarlthmic creep law(T) given bya

A t higher temperatures where the dislouations can

acquire enough therml energy to climb and tkereby

avoid obsetaces, analysis gLves the Pudrode relation-

ship. (8)

which is Ulnown as the i-creip law.

Both these macuaniass assume a Large degriee

of cold work prior to creep in order to create the forest

of dislocations. nowever, it has been recently denmostrated

that although well detinmd defornation occucs 4n the micro-

yield region, the dislocatLos are not extanenLve enough

.W45-

to form ectensive forests. ( 9) Thus, at stress below aad

si~ghtly above thte elastic 1LAit the i and logarithni•

creeps laws are not expected to be strictly valid.

It has been dmsnstrated that in the region

of the •-b or 1V"7 elastic limLt, permanent plastic

deaorwition tages place by the multiplication and motion

of pinned dislo%ationn and that this mechanism in

tersailly activated.(-' 4 ) With tie applicatlon of a

stress in the region of the elastic limit, dis•lo8ations

bow out creating 4ew dislocations Vftich move until

oistacl~es are mat. The dislocation Wualtipliaticn

ceases whers the back st"ess rom the blocked diiuslotions

stops the operation oz US source. ThIS is the itate

%ben mcr:ocroep beg .s.

ince the average sources active at the constant

stress level have been eohausted further deformatio can

only be accoalished by activating move dislocation

soCoes or by re-activating the daikausted sou0ces. It

Is aseuamd that this occurs uba a fluctuation of the

internal stress aided by thermal activation takes place.

?he creep rate fax this procees s ±: "1. "P-

dt

I I I I I I I I I I I I I I ' ' ' , i i

where N Ls tol number of dis1l.catLon loops per sqisre

contia-eter, A Las te area of active slip planes In the

specizan, b tne burger's vector, .a the rate of malti-

plication of disLocations, and n is the number of fluc-

tuations necessary to build up to the mLnisum stress

to activate a dislocatioa source. it we assume that

random stress tluctuations take place with a mean square

distribution around the applied stress -it, then:

.n (4)

From the stress-plastic strain curves of Figure 11, at

stress levels above the elastic Limit and stress

fluctuation Is given by&

V 1=• (5)

Bowever, sinwe the creep curves represent total creep

rather than the plastic cawonut of total croep, the

strams iluctuatiCna may not be defined by the plastic

strain curves but should fall nearer the stress-total

strain curves. Vr~ttlAq the stress fluctuation as

t" " tie •(6 )

0047-

,fte re O<: a ,..1.,P

dt 2

wkhich Integrates to

€2la t) + (8)

or

S• K (. t) i,=+].(

For the parabolic stresB dependence, m 14: and

Eq. (9) reduces to )y5,7( t) 3 /". The difftronce

AjtweeI the cuie root ties dependence o 1 -crmp and

the parabolic time dependence of equation ' a"ies

trom tie value of the stress fluctuations wbirch in

the -3-c p derivatLon were assumed to ke directly

proportional to the strain.

In the theory of P-creep the rate of dis-

location multiplIcation is replaced by the rate of

dislocation climb. To evaLuate w is *iauat

tko probabilit~y of creatLsAg a mobile &tislocotion. Xt hasn

ba~t eauutated t1A~t th.Le process tAkal Place mhGRe an

unpinped length of dislOcatiob bOws Out to &A Unstable

mie v~eier its radius ot curvatura reacbem hail tbe

orig inal pinned dislocat~ion length. FurtherInOte, this

lpra:.ss Ls tbermAlly activa ted sad aided by tAe initernal

&tress. Denoting the activoti4c energy as 0, the

activastion proba ility tor dialacatIon .ultipLicatiosi

Ina the lorward dixection is given bys

%dam"* 0a is the critical Strsas necessary to octivate

tb* avexage dislocation source. Xn the reve-rse direction,

the SAPteSUa is$±5

Biwae the rate of dAslocation saltpl.ctiosa

As given by' ttie product 99 the number og attempts to

climb tUs energy barter and the probabiLity at Over-

caim4A the barrier,, adding equations 10 and 11 Sivems

the ase% rate of dislooation multiplieation ase

kT

whore n is the number of sources and v the vibration

frequency of the dislocation lirne. Combining equations

9 and 1 Fields a tinal expression tor the ceep strain

asove the 1U"6 elastic limit stress of

is ( +l exp- (enal)k? (3)lkT -

or

L* J-2 ' j t siub 33.*i (314)

In FVi~ure a4-A41 the creep curves are

replotted on a logaritbmic. scale. The constants of

equation 1~4 were calcuLated from the curves at striasses

above the elastic Limuit and are tabulated in Tdable V.

the values of 09e rnn to vary betwen 1/.3 and 11W.

The value of Ilk results fron a stxess fluctuation

defined by the stress-plastic strain curve and equation5

whihle the 1/3 value wouald come from equation 6 with a -,- 1.

-504

ý4)u1

0

-4J

ol -1E

4J

'44

141

UUl

*.-

"-44

,4)(U

Ci)

$14

UTL~,4s IODC

00

.4-

,)

I[ d aU

,.-.

(r~.. T UL?..X~3 ~zuz

3

F *14

4

.1

1

'-4 -4

4J'U

IC

0 0

0 (1)* -4;4�) H

I'410 -

(.1)

-4 (1)

r) I�I4 -

ci)

U

1-4

ci))

*1-4

1-4 4 1-4

-_ 1 UTc214� d�o.t� I

IL

"44

-,4

1-44

'U

""5

*-4)

-2.2-

~~4-1

4-3I

ý4.

u~~~ -I1,7 4s o .[Z

CLn

-4

-4 1(1

QH(U::3

U-um-4 (()I

01

ý4

ý4

U)l

u-, a Da

:1i

41

cicmj

F--4

-i'

04.

44 ;

u-rea4s dz~jZ

ILI

44

1ý4

$13

* -S4

FT I I

II

qI

GJ

'U fV

~I-4

U.) IU . ,>•••

'. . ' ' 'I I I I

04

'u

uluaqo

K L

.. 7

H

0 'U

o

-I..

-N-

l , 0. • ,.) ,Cl)

.~

_' |.H

t.., ...

nv 310 356-T6 6u61 AZ92A

n .3 -3 u.J45 0.5

k cn3/mole U-3 Q~i1.5 U.2

A hrl 1.6xl1,0* 5 Ixloo*4 2.5xl106 3.Lxlci"'7

Q cal/mol. ~48,oou 62,,000 21,IUOO 24,(XJ0

A.nalysis of the activation 5nlty, , Yields

reaults very close to reported values for the activat~ion

energy or selt d•i£union. DOtLusionaOI type Orep, howIvOr,

was not observed gor the ;A49,A mmgnesium *=Opt at the higher

teaperatures. This may be duo to the low toutiAg stresses

at •hich i•Ltualonal cJOOp may not predominate.

At satressas below th] elastic lit small stress

fluctuetLonA will not result in instantaneous creep defor-

mation since the stress-plastic strain curves have LnfinLto

sloyes in this regIon. aweosr, many dislocation sources

are active at stress*s below the elastic limit and ýbese

Will. *"Cate,, contribuating to tke creep stjrain untIl

exhausted. As these sources are exacusted the creep rate

uhouid dimJnih eventuaally going to sero when no more active

sotarces exist.

fOoloing Seneral reacti& rate theory and

Oasvse• w tha rate of Cuslocation geneaition is of first

order, the rate of exhaustion of active sources would be

proportLoaal to the concentration of active sources

dt

-67II

which upon integration yields

N - 104t (06)

Since the creep rate is given by

~L~ t ~(17)dt

where b is the urugers nector, p the rate at which the

dislocation sources operate and X the number of active

sources, the creep strain is given bys

SX02 (l -••)(8

wbere A is the limiting strain after infinite tim.pIt to expected that the linitiAq strain should be daxetly

proportional to the stress and the te erature, that Is

with increased temperature and at higher stresses the

'imiting strain increases. Analysis of the curves of

Fgwmes 27-41 at stremses below the elastic limit indicatoa

that the limiting trxain can be expremsed as

WhOre 'a4 Ls the applied stress sad I the absolute tempersatre.

-68-

CcmbLng equations 18 &ad 19 gives a final emp• esrion-v- balr• •...x jj6 ifm-jo.- .m!t Og

%F 40 r WW %.F

r A (1-.0"t) "'? (

te constants calculatad from figures ••4mr•l are tab-

ultated ln ealie V1.

In su:my, the reaults soWW that .isrocreep

can be expressed by two relationships depending on

%tither the applied stress Ls larger or smaller than the

1(i-"6 *mtjC limLt stress, co"

pirther analyst. will Sim at resoxving the

an5maous behavior of A292A aagniuim. afforts will be

mtds to evaluate the constants from a theoretical aodll.

2be fcti•onsl dependence o* te creep strain on

temperatuare and applied steos will be analyzed from

theoretical considerations.

4. n Diim% Uses Chn ma deg 21orUNA Cga itioaa

The results of tve sealuatLons of 1009;h

changes in the five alloys under storage conditions at

75j! 50) &ad 2(.w4 F are shown in figures 4~.Z-16. fegati ye

lenath changea were observed itn al.l the alloy after

50 hours With the e 0ptLon oi the 6U61 aluauinm.

-69-

3'

�

.46.4

.794I

4�% Qii'.4- I0.43 I

EQ ;.) 3.4

14'0 4� I

.4I

6.4

I94I

.4

I4.

U)

'44

'44I

'4tj

0

U)

.- 4.-

(1-4

WNi

01"J

E-4

fa C:

C I u

0

to)

"144

U4.

01' 7ouq le-~UD

*-72-

24 4J

ILI) 0 L

(D

00

"r-4

1440

00

r- ".

-4 t

0i

'44

OT IbeoTUTUUT

I 4-

--

u 'X

r44

-tio~ Teoiszult

'D3

C))

- 0

w

r0

C-

t;I 0

rI rq

a~ueo Teo~sutul

2The 356-6 aImWinm and 310 etalUiess steel heoved a

slight increase in length followed by a decr*seo In 1ength.

The 6061 Aluamium showed an initial negative change which

slowly increased to an overall positive length change.

Tho 356-T6 Pluminum showed the greatest diuensional

lintawility. In all cases the magnitude of the divlnsional

changes were insignificant in comparison to the creep

changes under load.

The measurements, although not complete, show

dimensional changes similar to that reported by lUment

and Averb.ach.(1o)

4, -76-

A facility fox the Getexr• Ation ot distortioM

LA CastIsAs and Welded St~rtntUreS after heat treOatin

and machining operations was designed a*4 trio vecessary

*qtpment was pusrchoed and coustrited. fte fa#•lltty

Coisists of the foLlowing Items.

1. silger-watts TA-. autocollimator

k. RiLge.-wattes goo prism

3. e optically flat silvred mirrors

4. flat PYWOA platO Ld Ac li A 1/Se inC11

5. i standarw blacks

6. precision 44MUC stainless steel balls k,.375

inch ia diameter in several sise ranges.

2%e complete asawbl~y is momtmad on a granite

surf•a* plate f•.i±c is IsoIated from the floor by shock

alweormer to adaJlmie building vibrtion and ambLguJity

Ln tS es•ureMents.

""M distortion spacimen was sough MachLned to

the dimmimoas of figure 47 on a maiinLg sactine . On

the eternal faces eb oles were xoagh drilled with a

tap dxLU at the L•ic;atod points.

-77-

Following ageing a slot was cut as shown Ln

Figure 47 with an Ilox electrical discharge machining

unit with a brass electrode. The surtaceswere then

milled with all faces parallel to within v.001 inches.

The conical holes were then finish machined in a Moore

No. 3 jig-borer to a depth Of Q.233 inch using an

electronic depth stop. Carbide toolinj was used to

minimize tool wear. The hole dimension allows a u.375

inch steel ball to rest at a depth of U.100 Inch in the

distortion specimen.

The testing configuration is shown in Figurs 48.

The specimen rests on balls on the pyrex plate. The

standard block is placed against the distortion block.

For mesurements in the horizontal position the standard

block is fitted with a single steel ball. The mirror

rests on two balls on the specimen and one on the standard.

In this coufiguration a measuremant in the change of

height can Le made, and by turning the autocollimmtor

cross-haLis 90 the change In pitch of the specimen

surface can be masured.

-79-

.>-4

14J--r4

(i

-4

S--4

I 1-4-)

00

.,- 0

• 4 '•3 U.-4 £ () U---4 ,L -4 .,4(')

4 J CU (I)n

C) (U-A-ir

, .o

JA"I ""L

In the vertical position the standard bloch is

fitted with two balls. fTe sirror rests on these two

balls and one in the specimen. Rwasurewze s of the

distortion across the slot are made by resting the mirror

on three balls placed in holes on both sides of th6 *lot.

A boam of light from the autocolllmator passes through

the prism and is reflected by the mirror back through

the prism and into the autocollinator. The angular

divergence of the light beam in its passage appears as

a shadow displaced from the cross-hairs of the izitnimant.

This displacemnt can be read and from simple geometry

converted to the angle @ that the mirror makes with the

distortion block. By measuring this angle 0 before and

after a machining and/or beat treating operation, it Is

possible to measure the distortion due to these operation*.

By rearranging the speclamw, linar distortion of the

specimen can be aeasred in all directions.

Zn the event that distortion causes cetlain of

tte measurements to fall outside the field of the auto-

collimator, balls of difterent *Laos can be calibrated

and used.

Wg.ininaxy -wasureatim of dLetortLoa in i56-"6

S LUm"UNm riAV* 96 Sadie **ach bave desmaotirated the

tebqa high resolution a•s umisfuJleu. DiLstortion

vwil be det*±U as a functLoR of mbchhnLat operation.,

age hiddULng and BtseZss relief beat tmatmests for each

of th give alloys evaluated Ln th•s pogram and for the

thre alloys to b ev wamited Ln the coming year.

-a1a-

6. .. in

This work will continue in the next year under

a reeWS1 contract. Dimensional stability evaluations

will be conducted for H).A-T6 magnesium-thorLum,

beryllium-copper and H-i1 ausforamng tool &tool.

The analysis of microyield and microcreep data

will continue in order to understand the maechanisms for

these phenomena.

The measurements of dimensional changes under

storage conitLons will be carried out using auto-

collimation techniques. This technique will eliminate

errors due to slight temperature variations and wear on

the ends of the specimens from the comparator probe

A testing program to evaluate distortion as a

function of beat treating and machining operations will

be LuntLated as outlined in section 5. The five alloys of

the previo•s program as well as those mtiood a8boeo

will be tested after fabrication procodureo sLmLlar to

those comonly used in structural appliati.oms of each

alloy.

-8)-

7. Wa

kJ1Xi1 JanuarY 1957.

ýk Mwip Hop Avexbaf..bs m.LO and CCoenp stop Trans@ )'N5MP

3. loaiemtialdp 2.1k.. and Avexbacbp N.L,, Acta. Not., .

4., ift~bx*UCAh P.P. and Averbaech, B.L., M.X.T. MastorsTbOeLS4, J~anuary (1964).

5. broim, No and Luk~ens, X,]?. Jr., Act&. Ket., 2 (1961)p. 106.

6. 2thoii, D.A. and Averbach, B.L.p Acta. Mt., Z (1959)p. 69.

7. r@lthow, P., Proc. Phiys. Soc., j~k (1956) y. 1173.

8. relthanj P. and iibkakt J.D., Acts. met., 2 (L959)p. 614.

9. suits, J.C. and Chalmas a, ., Act&. net., (1961)p. ilj6.

1.0. Leanto 3.5. and Averimcbp S.L.,, M.I.T. LaatximamstatIonLab.,, Report 2-95p December 1955.